Transport Layer Security Working Group Alan O. Freier
INTERNET-DRAFT Netscape Communications
Expire in six months Philip Karlton
Netscape Communications
Paul C. Kocher
Independent Consultant
November 18, 1996
The SSL Protocol
Version 3.0
<draft-freier-ssl-version3-02.txt>
Status of this memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet- Drafts.
Internet-Drafts are draft documents valid for a maximum of six
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as reference material or to cite them other than as work in
progress.
To learn the current status of any Internet-Draft, please check the
1id-abstracts.txt listing contained in the Internet Drafts Shadow
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(Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
Rim).
Abstract
This document specifies Version 3.0 of the Secure Sockets Layer
(SSL V3.0) protocol, a security protocol that provides
communications privacy over the Internet. The protocol allows
client/server applications to communicate in a way that is designed
to prevent eavesdropping, tampering, or message forgery.
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Table of Contents
Status of this memo 1
Abstract 1
Table of Contents 2
1. Introduction 4
2. Goals 4
3. Goals of this document 5
4. Presentation language 5
4.1 Basic block size 5
4.2 Miscellaneous 6
4.3 Vectors 6
4.4 Numbers 7
4.5 Enumerateds 7
4.6 Constructed types 8
4.6.1 Variants 8
4.7 Cryptographic attributes 9
4.8 Constants 10
5. SSL protocol 10
5.1 Session and connection states 10
5.2 Record layer 12
5.2.1 Fragmentation 12
5.2.2 Record compression and decompression 13
5.2.3 Record payload protection and the CipherSpec 13
5.2.3.1 Null or standard stream cipher 14
5.2.3.2 CBC block cipher 15
5.3 Change cipher spec protocol 16
5.4 Alert protocol 16
5.4.1 Closure alerts 17
5.4.2 Error alerts 17
5.5 Handshake protocol overview 18
5.6 Handshake protocol 20
5.6.1 Hello messages 21
5.6.1.1 Hello request 21
5.6.1.2 Client hello 21
5.6.1.3 Server hello 24
5.6.2 Server certificate 25
5.6.3 Server key exchange message 25
5.6.4 Certificate request 27
5.6.5 Server hello done 27
5.6.6 Client certificate 28
5.6.7 Client key exchange message 28
5.6.7.1 RSA encrypted premaster secret message 28
5.6.7.2 FORTEZZA key exchange message 29
5.6.7.3 Client Diffie-Hellman public value 30
5.6.8 Certificate verify 30
5.6.9 Finished 31
5.7 Application data protocol 32
6. Cryptographic computations 32
6.1 Asymmetric cryptographic computations 32
6.1.1 RSA 32
6.1.2 Diffie-Hellman 33
6.1.3 FORTEZZA 33
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6.2 Symmetric cryptographic calculations and the CipherSpec 33
6.2.1 The master secret 33
6.2.2 Converting the master secret into keys and MAC 33
6.2.2.1 Export key generation example 35
A. Protocol constant values 36
A.1 Reserved port assignments 36
A.1.1 Record layer 36
A.2 Change cipher specs message 37
A.3 Alert messages 37
A.4 Handshake protocol 37
A.4.1 Hello messages 38
A.4.2 Server authentication and key exchange messages 39
A.5 Client authentication and key exchange messages 40
A.5.1 Handshake finalization message 41
A.6 The CipherSuite 41
A.7 The CipherSpec 42
B. Glossary 44
C. CipherSuite definitions 47
D. Implementation Notes 49
D.1 Temporary RSA keys 49
D.2 Random Number Generation and Seeding 49
D.3 Certificates and authentication 50
D.4 CipherSuites 50
D.5 FORTEZZA 50
D.5.1 Notes on use of FORTEZZA hardware 50
D.5.2 FORTEZZA Ciphersuites 51
D.5.3 FORTEZZA Session resumption 51
E. Version 2.0 Backward Compatibility 52
E.1 Version 2 client hello 52
E.2 Avoiding man-in-the-middle version rollback 53
F. Security analysis 55
F.1 Handshake protocol 55
F.1.1 Authentication and key exchange 55
F.1.1.1 Anonymous key exchange 55
F.1.1.2 RSA key exchange and authentication 56
F.1.1.3 Diffie-Hellman key exchange with authentication 57
F.1.1.4 FORTEZZA 57
F.1.2 Version rollback attacks 57
F.1.3 Detecting attacks against the handshake protocol 58
F.1.4 Resuming sessions 58
F.1.5 MD5 and SHA 58
F.2 Protecting application data 59
F.3 Final notes 59
G. Patent Statement 60
References 61
Authors 62
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1. Introduction
The primary goal of the SSL Protocol is to provide privacy and
reliability between two communicating applications. The protocol
is composed of two layers. At the lowest level, layered on top of
some reliable transport protocol (e.g., TCP[TCP]), is the SSL
Record Protocol. The SSL Record Protocol is used for encapsulation
of various higher level protocols. One such encapsulated protocol,
the SSL Handshake Protocol, allows the server and client to
authenticate each other and to negotiate an encryption algorithm
and cryptographic keys before the application protocol transmits or
receives its first byte of data. One advantage of SSL is that it
is application protocol independent. A higher level protocol can
layer on top of the SSL Protocol transparently. The SSL protocol
provides connection security that has three basic properties:
- The connection is private. Encryption is used after an
initial handshake to define a secret key. Symmetric
cryptography is used for data encryption (e.g., DES[DES],
RC4[RC4], etc.)
- The peer's identity can be authenticated using asymmetric, or
public key, cryptography (e.g., RSA[RSA], DSS[DSS], etc.).
- The connection is reliable. Message transport includes a
message integrity check using a keyed MAC. Secure hash
functions (e.g., SHA, MD5, etc.) are used for MAC
computations.
2. Goals
The goals of SSL Protocol v3.0, in order of their priority,
are:
1. Cryptographic security
SSL should be used to establish a secure
connection between two parties.
2. Interoperability
Independent programmers should be able to
develop applications utilizing SSL 3.0 that
will then be able to successfully exchange
cryptographic parameters without knowledge of
one another's code.
Note: It is not the case that all instances of SSL (even
in the same application domain) will be able to
successfully connect. For instance, if the server
supports a particular hardware token, and the client
does not have access to such a token, then the
connection will not succeed.
3. Extensibility SSL seeks to provide a framework into which new
public key and bulk encryption methods can be
incorporated as necessary. This will also
accomplish two sub-goals: to prevent the need
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to create a new protocol (and risking the
introduction of possible new weaknesses) and to
avoid the need to implement an entire new
security library.
4. Relative efficiency
Cryptographic operations tend to be highly CPU
intensive, particularly public key operations.
For this reason, the SSL protocol has
incorporated an optional session caching scheme
to reduce the number of connections that need
to be established from scratch. Additionally,
care has been taken to reduce network activity.
3. Goals of this document
The SSL Protocol Version 3.0 Specification is intended primarily
for readers who will be implementing the protocol and those doing
cryptographic analysis of it. The spec has been written with this
in mind, and it is intended to reflect the needs of those two
groups. For that reason, many of the algorithm-dependent data
structures and rules are included in the body of the text (as
opposed to in an Appendix), providing easier access to them.
This document is not intended to supply any details of service
definition nor interface definition, although it does cover select
areas of policy as they are required for the maintenance of solid
security.
4. Presentation language
This document deals with the formatting of data in an external
representation. The following very basic and somewhat casually
defined presentation syntax will be used. The syntax draws from
several sources in its structure. Although it resembles the
programming language "C" in its syntax and XDR [XDR] in both its
syntax and intent, it would be risky to draw too many parallels.
The purpose of this presentation language is to document SSL only,
not to have general application beyond that particular goal.
4.1 Basic block size
The representation of all data items is explicitly specified. The
basic data block size is one byte (i.e. 8 bits). Multiple byte
data items are concatenations of bytes, from left to right, from
top to bottom. From the bytestream a multi-byte item (a numeric in
the example) is formed (using C notation) by:
value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) | ...
| byte[n-1];
This byte ordering for multi-byte values is the commonplace network
byte order or big endian format.
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4.2 Miscellaneous
Comments begin with "/*" and end with "*/".
Optional components are denoted by enclosing them in "[[ ]]" double
brackets.
Single byte entities containing uninterpreted data are of type
opaque.
4.3 Vectors
A vector (single dimensioned array) is a stream of homogeneous data
elements. The size of the vector may be specified at documentation
time or left unspecified until runtime. In either case the length
declares the number of bytes, not the number of elements, in the
vector. The syntax for specifying a new type T' that is a fixed
length vector of type T is
T T'[n];
Here T' occupies n bytes in the data stream, where n is a multiple
of the size of T. The length of the vector is not included in the
encoded stream.
In the following example, Datum is defined to be three consecutive
bytes that the protocol does not interpret, while Data is three
consecutive Datum, consuming a total of nine bytes.
opaque Datum[3]; /* three uninterpreted bytes */
Datum Data[9]; /* 3 consecutive 3 byte vectors */
Variable length vectors are defined by specifying a subrange of
legal lengths, inclusively, using the notation <floor..ceiling>.
When encoded, the actual length precedes the vector's contents in
the byte stream. The length will be in the form of a number
consuming as many bytes as required to hold the vector's specified
maximum (ceiling) length. A variable length vector with an actual
length field of zero is referred to as an empty vector.
T T'<floor..ceiling>;
In the following example, mandatory is a vector that must contain
between 300 and 400 bytes of type opaque. It can never be empty.
The actual length field consumes two bytes, a uint16, sufficient to
represent the value 400 (see Section 4.4). On the other hand,
longer can represent up to 800 bytes of data, or 400 uint16
elements, and it may be empty. Its encoding will include a two
byte actual length field prepended to the vector.
opaque mandatory<300..400>;
/* length field is 2 bytes, cannot be empty */
uint16 longer<0..800>;
/* zero to 400 16-bit unsigned integers */
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4.4 Numbers
The basic numeric data type is an unsigned byte (uint8). All
larger numeric data types are formed from fixed length series of
bytes concatenated as described in Section 4.1 and are also
unsigned. The following numeric types are predefined.
uint8 uint16[2];
uint8 uint24[3];
uint8 uint32[4];
uint8 uint64[8];
4.5 Enumerateds
An additional sparse data type is available called enum. A field
of type enum can only assume the values declared in the definition.
Each definition is a different type. Only enumerateds of the same
type may be assigned or compared. Every element of an enumerated
must be assigned a value, as demonstrated in the following example.
Since the elements of the enumerated are not ordered, they can be
assigned any unique value, in any order.
enum { e1(v1), e2(v2), ... , en(vn), [[(n)]] } Te;
Enumerateds occupy as much space in the byte stream as would its
maximal defined ordinal value. The following definition would
cause one byte to be used to carry fields of type Color.
enum { red(3), blue(5), white(7) } Color;
One may optionally specify a value without its associated tag to
force the width definition without defining a superfluous element.
In the following example, Taste will consume two bytes in the data
stream but can only assume the values 1, 2 or 4.
enum { sweet(1), sour(2), bitter(4), (32000) } Taste;
The names of the elements of an enumeration are scoped within the
defined type. In the first example, a fully qualified reference to
the second element of the enumeration would be Color.blue. Such
qualification is not required if the target of the assignment is
well specified.
Color color = Color.blue; /* overspecified, legal */
Color color = blue; /* correct, type implicit */
For enumerateds that are never converted to external
representation, the numerical information may be omitted.
enum { low, medium, high } Amount;
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4.6 Constructed types
Structure types may be constructed from primitive types for
convenience. Each specification declares a new, unique type. The
syntax for definition is much like that of C.
struct {
T1 f1;
T2 f2;
...
Tn fn;
} [[T]];
The fields within a structure may be qualified using the type's
name using a syntax much like that available for enumerateds. For
example, T.f2 refers to the second field of the previous
declaration. Structure definitions may be embedded.
4.6.1 Variants
Defined structures may have variants based on some knowledge that
is available within the environment. The selector must be an
enumerated type that defines the possible variants the structure
defines. There must be a case arm for every element of the
enumeration declared in the select. The body of the variant
structure may be given a label for reference. The mechanism by
which the variant is selected at runtime is not prescribed by the
presentation language.
struct {
T1 f1;
T2 f2;
....
Tn fn;
select (E) {
case e1: Te1;
case e2: Te2;
....
case en: Ten;
} [[fv]];
} [[Tv]];
For example
enum { apple, orange } VariantTag;
struct {
uint16 number;
opaque string<0..10>; /* variable length */
} V1;
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struct {
uint32 number;
opaque string[10]; /* fixed length */
} V2;
struct {
select (VariantTag) { /* value of selector is implicit */
case apple: V1; /* VariantBody, tag = apple */
case orange: V2; /* VariantBody, tag = orange */
} variant_body; /* optional label on variant */
} VariantRecord;
Variant structures may be qualified (narrowed) by specifying a
value for the selector prior to the type. For example, a
orange VariantRecord
is a narrowed type of a VariantRecord containing a variant_body of
type V2.
4.7 Cryptographic attributes
The four cryptographic operations digital signing, stream cipher
encryption, block cipher encryption, and public key encryption are
designated digitally-signed, stream-ciphered, block-ciphered, and
public-key-encrypted, respectively. A field's cryptographic
processing is specified by prepending an appropriate key word
designation before the field's type specification. Cryptographic
keys are implied by the current session state (see Section 5.1).
In digital signing, one-way hash functions are used as input for a
signing algorithm. In RSA signing, a 36-byte structure of two
hashes (one SHA and one MD5) is signed (encrypted with the private
key). In DSS, the 20 bytes of the SHA hash are run directly
through the Digital Signing Algorithm with no additional hashing.
In stream cipher encryption, the plaintext is exclusive-ORed with
an identical amount of output generated from a
cryptographically-secure keyed pseudorandom number generator.
In block cipher encryption, every block of plaintext encrypts to a
block of ciphertext. Because it is unlikely that the plaintext
(whatever data is to be sent) will break neatly into the necessary
block size (usually 64 bits), it is necessary to pad out the end of
short blocks with some regular pattern, usually all zeroes.
In public key encryption, one-way functions with secret "trapdoors"
are used to encrypt the outgoing data. Data encrypted with the
public key of a given key pair can only be decrypted with the
private key, and vice-versa. In the following example:
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stream-ciphered struct {
uint8 field1;
uint8 field2;
digitally-signed opaque hash[20];
} UserType;
The contents of hash are used as input for the signing algorithm,
then the entire structure is encrypted with a stream cipher.
4.8 Constants
Typed constants can be defined for purposes of specification by
declaring a symbol of the desired type and assigning values to it.
Under-specified types (opaque, variable length vectors, and
structures that contain opaque) cannot be assigned values. No
fields of a multi-element structure or vector may be elided.
For example,
struct {
uint8 f1;
uint8 f2;
} Example1;
Example1 ex1 = {1, 4};/* assigns f1 = 1, f2 = 4 */
5. SSL protocol
SSL is a layered protocol. At each layer, messages may include
fields for length, description, and content. SSL takes messages to
be transmitted, fragments the data into manageable blocks,
optionally compresses the data, applies a MAC, encrypts, and
transmits the result. Received data is decrypted, verified,
decompressed, and reassembled, then delivered to higher level
clients.
5.1 Session and connection states
An SSL session is stateful. It is the responsibility of the SSL
Handshake protocol to coordinate the states of the client and
server, thereby allowing the protocol state machines of each to
operate consistently, despite the fact that the state is not
exactly parallel. Logically the state is represented twice, once
as the current operating state, and (during the handshake protocol)
again as the pending state. Additionally, separate read and write
states are maintained. When the client or server receives a change
cipher spec message, it copies the pending read state into the
current read state. When the client or server sends a change
cipher spec message, it copies the pending write state into the
current write state. When the handshake negotiation is complete,
the client and server exchange change cipher spec messages (see
Section 5.3), and they then communicate using the newly agreed-upon
cipher spec.
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An SSL session may include multiple secure connections; in
addition, parties may have multiple simultaneous sessions.
The session state includes the following elements:
session identifier
An arbitrary byte sequence chosen by the server
to identify an active or resumable session
state.
peer certificate X509.v3[X509] certificate of the peer. This
element of the state may be null.
compression method
The algorithm used to compress data prior to
encryption.
cipher spec Specifies the bulk data encryption algorithm
(such as null, DES, etc.) and a MAC algorithm
(such as MD5 or SHA). It also defines
cryptographic attributes such as the hash_size.
(See Appendix A.7 for formal definition)
master secret 48-byte secret shared between the client and
server.
is resumable A flag indicating whether the session can be
used to initiate new connections.
The connection state includes the following elements:
server and client random
Byte sequences that are chosen by the server
and client for each connection.
server write MAC secret
The secret used in MAC operations on data
written by the server
client write MAC secret
The secret used in MAC operations on data
written by the client.
server write key The bulk cipher key for data encrypted by the
server and decrypted by the client.
client write key The bulk cipher key for data encrypted by the
client and decrypted by the server.
initialization vectors
When a block cipher in CBC mode is used, an
initialization vector (IV) is maintained for
each key. This field is first initialized by
the SSL handshake protocol. Thereafter the
final ciphertext block from each record is
preserved for use with the following record.
sequence numbers Each party maintains separate sequence numbers
for transmitted and received messages for each
connection. When a party sends or receives a
change cipher spec message, the appropriate
sequence number is set to zero. Sequence
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numbers are of type uint64 and may not exceed
2^64-1.
5.2 Record layer
The SSL Record Layer receives uninterpreted data from higher layers
in non-empty blocks of arbitrary size.
5.2.1 Fragmentation
The record layer fragments information blocks into SSLPlaintext
records of 2^14 bytes or less. Client message boundaries are not
preserved in the record layer (i.e., multiple client messages of
the same ContentType may be coalesced into a single SSLPlaintext
record).
struct {
uint8 major, minor;
} ProtocolVersion;
enum {
change_cipher_spec(20), alert(21), handshake(22),
application_data(23), (255)
} ContentType;
struct {
ContentType type;
ProtocolVersion version;
uint16 length;
opaque fragment[SSLPlaintext.length];
} SSLPlaintext;
type The higher level protocol used to process the
enclosed fragment.
version The version of protocol being employed. This
document describes SSL Version 3.0 (See
Appendix A.1.1).
length The length (in bytes) of the following
SSLPlaintext.fragment. The length should not
exceed 2^14.
fragment The application data. This data is transparent
and treated as an independent block to be dealt
with by the higher level protocol specified by
the type field.
Note: Data of different SSL Record layer content types may
be interleaved. Application data is generally of
lower precedence for transmission than other content
types.
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5.2.2 Record compression and decompression
All records are compressed using the compression algorithm defined
in the current session state. There is always an active
compression algorithm, however initially it is defined as
CompressionMethod.null. The compression algorithm translates an
SSLPlaintext structure into an SSLCompressed structure.
Compression functions erase their state information whenever the
CipherSpec is replaced.
Note: The CipherSpec is part of the session state
described in Section 5.1. References to fields of
the CipherSpec are made throughout this document
using presentation syntax. A more complete
description of the CipherSpec is shown in Appendix
A.7.
Compression must be lossless and may not increase the content
length by more than 1024 bytes. If the decompression function
encounters an SSLCompressed.fragment that would decompress to a
length in excess of 2^14 bytes, it should issue a fatal
decompression_failure alert (Section 5.4.2).
struct {
ContentType type; /* same as SSLPlaintext.type */
ProtocolVersion version;/* same as SSLPlaintext.version */
uint16 length;
opaque fragment[SSLCompressed.length];
} SSLCompressed;
length The length (in bytes) of the following
SSLCompressed.fragment. The length
should not exceed 2^14 + 1024.
fragment The compressed form of
SSLPlaintext.fragment.
Note: A CompressionMethod.null operation is an identity
operation; no fields are altered.
(See Appendix A.4.1)
Implementation note:
Decompression functions are responsible for
ensuring that messages cannot cause internal buffer
overflows.
5.2.3 Record payload protection and the CipherSpec
All records are protected using the encryption and MAC algorithms
defined in the current CipherSpec. There is always an active
CipherSpec, however initially it is SSL_NULL_WITH_NULL_NULL, which
does not provide any security.
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Once the handshake is complete, the two parties have shared secrets
which are used to encrypt records and compute keyed message
authentication codes (MACs) on their contents. The techniques used
to perform the encryption and MAC operations are defined by the
CipherSpec and constrained by CipherSpec.cipher_type. The
encryption and MAC functions translate an SSLCompressed structure
into an SSLCiphertext. The decryption functions reverse the
process. Transmissions also include a sequence number so that
missing, altered, or extra messages are detectable.
struct {
ContentType type;
ProtocolVersion version;
uint16 length;
select (CipherSpec.cipher_type) {
case stream: GenericStreamCipher;
case block: GenericBlockCipher;
} fragment;
} SSLCiphertext;
type The type field is identical to
SSLCompressed.type.
version The version field is identical to
SSLCompressed.version.
length The length (in bytes) of the following
SSLCiphertext.fragment. The length may
not exceed 2^14 + 2048.
fragment The encrypted form of
SSLCompressed.fragment, including the
MAC.
5.2.3.1 Null or standard stream cipher
Stream ciphers (including BulkCipherAlgorithm.null - see Appendix
A.7) convert SSLCompressed.fragment structures to and from stream
SSLCiphertext.fragment structures.
stream-ciphered struct {
opaque content[SSLCompressed.length];
opaque MAC[CipherSpec.hash_size];
} GenericStreamCipher;
The MAC is generated as:
hash(MAC_write_secret + pad_2 +
hash(MAC_write_secret + pad_1 + seq_num +
SSLCompressed.type + SSLCompressed.length +
SSLCompressed.fragment));
where "+" denotes concatenation.
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pad_1 The character 0x36 repeated 48 times for MD5
or 40 times for SHA.
pad_2 The character 0x5c repeated 48 times for MD5
or 40 times for SHA.
seq_num The sequence number for this message.
hash Hashing algorithm derived from the cipher
suite.
Note that the MAC is computed before encryption. The stream cipher
encrypts the entire block, including the MAC. For stream ciphers
that do not use a synchronization vector (such as RC4), the stream
cipher state from the end of one record is simply used on the
subsequent packet. If the CipherSuite is SSL_NULL_WITH_NULL_NULL,
encryption consists of the identity operation (i.e., the data is
not encrypted and the MAC size is zero implying that no MAC is
used). SSLCiphertext.length is SSLCompressed.length plus
CipherSpec.hash_size.
5.2.3.2 CBC block cipher
For block ciphers (such as RC2 or DES), the encryption and MAC
functions convert SSLCompressed.fragment structures to and from
block SSLCiphertext.fragment structures.
block-ciphered struct {
opaque content[SSLCompressed.length];
opaque MAC[CipherSpec.hash_size];
uint8 padding[GenericBlockCipher.padding_length];
uint8 padding_length;
} GenericBlockCipher;
The MAC is generated as described in Section 5.2.3.1.
padding Padding that is added to force the length of
the plaintext to be a multiple of the block
cipher's block length.
padding_length The length of the padding must be less than the
cipher's block length and may be zero. The
padding length should be such that the total
size of the GenericBlockCipher structure is a
multiple of the cipher's block length.
The encrypted data length (SSLCiphertext.length) is one more than
the sum of SSLCompressed.length, CipherSpec.hash_size, and
padding_length.
Note: With CBC block chaining the initialization vector
(IV) for the first record is provided by the
handshake protocol. The IV for subsequent records
is the last ciphertext block from the previous
record.
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5.3 Change cipher spec protocol
The change cipher spec protocol exists to signal transitions in
ciphering strategies. The protocol consists of a single message,
which is encrypted and compressed under the current (not the
pending) CipherSpec. The message consists of a single byte of
value 1.
struct {
enum { change_cipher_spec(1), (255) } type;
} ChangeCipherSpec;
The change cipher spec message is sent by both the client and
server to notify the receiving party that subsequent records will
be protected under the just-negotiated CipherSpec and keys.
Reception of this message causes the receiver to copy the read
pending state into the read current state. The client sends a
change cipher spec message following handshake key exchange and
certificate verify messages (if any), and the server sends one
after successfully processing the key exchange message it received
from the client. An unexpected change cipher spec message should
generate an unexpected_message alert (Section 5.4.2). When
resuming a previous session, the change cipher spec message is sent
after the hello messages.
5.4 Alert protocol
One of the content types supported by the SSL Record layer is the
alert type. Alert messages convey the severity of the message and
a description of the alert. Alert messages with a level of fatal
result in the immediate termination of the connection. In this
case, other connections corresponding to the session may continue,
but the session identifier must be invalidated, preventing the
failed session from being used to establish new connections. Like
other messages, alert messages are encrypted and compressed, as
specified by the current connection state.
enum { warning(1), fatal(2), (255) } AlertLevel;
enum {
close_notify(0),
unexpected_message(10),
bad_record_mac(20),
decompression_failure(30),
handshake_failure(40),
no_certificate(41),
bad_certificate(42),
unsupported_certificate(43),
certificate_revoked(44),
certificate_expired(45),
certificate_unknown(46),
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illegal_parameter (47)
(255)
} AlertDescription;
struct {
AlertLevel level;
AlertDescription description;
} Alert;
5.4.1 Closure alerts
The client and the server must share knowledge that the connection
is ending in order to avoid a truncation attack. Either party may
initiate the exchange of closing messages.
close_notify This message notifies the recipient that the
sender will not send any more messages on this
connection. The session becomes unresumable if
any connection is terminated without proper
close_notify messages with level equal to
warning.
Either party may initiate a close by sending a close_notify alert.
Any data received after a closure alert is ignored.
Each party is required to send a close_notify alert before closing
the write side of the connection. It is required that the other
party respond with a close_notify alert of its own and close down
the connection immediately, discarding any pending writes. It is
not required for the initiator of the close to wait for the
responding close_notify alert before closing the read side of the
connection.
NB: It is assumed that closing a connection reliably delivers
pending data before destroying the transport.
5.4.2 Error alerts
Error handling in the SSL Handshake protocol is very simple. When
an error is detected, the detecting party sends a message to the
other party. Upon transmission or receipt of an fatal alert
message, both parties immediately close the connection. Servers
and clients are required to forget any session-identifiers, keys,
and secrets associated with a failed connection. The following
error alerts are defined:
unexpected_message
An inappropriate message was received. This
alert is always fatal and should never be
observed in communication between proper
implementations.
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bad_record_mac This alert is returned if a record is received
with an incorrect MAC. This message is always
fatal.
decompression_failure
The decompression function received improper
input (e.g. data that would expand to excessive
length). This message is always fatal.
handshake_failure Reception of a handshake_failure alert message
indicates that the sender was unable to
negotiate an acceptable set of security
parameters given the options available. This
is a fatal error.
no_certificate A no_certificate alert message may be sent in
response to a certification request if no
appropriate certificate is available.
bad_certificate A certificate was corrupt, contained signatures
that did not verify correctly, etc.
unsupported_certificate
A certificate was of an unsupported type.
certificate_revoked
A certificate was revoked by its signer.
certificate_expired
A certificate has expired or is not currently
valid.
certificate_unknown
Some other (unspecified) issue arose in
processing the certificate, rendering it
unacceptable.
illegal_parameter A field in the handshake was out of range or
inconsistent with other fields. This is always
fatal.
5.5 Handshake protocol overview
The cryptographic parameters of the session state are produced by
the SSL Handshake Protocol, which operates on top of the SSL Record
Layer. When a SSL client and server first start communicating,
they agree on a protocol version, select cryptographic algorithms,
optionally authenticate each other, and use public-key encryption
techniques to generate shared secrets. These processes are
performed in the handshake protocol, which can be summarized as
follows: The client sends a client hello message to which the
server must respond with a server hello message, or else a fatal
error will occur and the connection will fail. The client hello
and server hello are used to establish security enhancement
capabilities between client and server. The client hello and
server hello establish the following attributes: Protocol Version,
Session ID, Cipher Suite, and Compression Method. Additionally,
two random values are generated and exchanged: ClientHello.random
and ServerHello.random.
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Following the hello messages, the server will send its certificate,
if it is to be authenticated. Additionally, a server key exchange
message may be sent, if it is required (e.g. if their server has no
certificate, or if its certificate is for signing only). If the
server is authenticated, it may request a certificate from the
client, if that is appropriate to the cipher suite selected. Now
the server will send the server hello done message, indicating that
the hello-message phase of the handshake is complete. The server
will then wait for a client response. If the server has sent a
certificate request Message, the client must send either the
certificate message or a no_certificate alert. The client key
exchange message is now sent, and the content of that message will
depend on the public key algorithm selected between the client
hello and the server hello. If the client has sent a certificate
with signing ability, a digitally-signed certificate verify message
is sent to explicitly verify the certificate.
At this point, a change cipher spec message is sent by the client,
and the client copies the pending Cipher Spec into the current
Cipher Spec. The client then immediately sends the finished
message under the new algorithms, keys, and secrets. In response,
the server will send its own change cipher spec message, transfer
the pending to the current Cipher Spec, and send its finished
message under the new Cipher Spec. At this point, the handshake is
complete and the client and server may begin to exchange
application layer data. (See flow chart below.)
Client Server
ClientHello -------->
ServerHello
Certificate*
ServerKeyExchange*
CertificateRequest*
<-------- ServerHelloDone
Certificate*
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished -------->
[ChangeCipherSpec]
<-------- Finished
Application Data <-------> Application Data
* Indicates optional or situation-dependent messages that are not
always sent.
Note: To help avoid pipeline stalls, ChangeCipherSpec is
an independent SSL Protocol content type, and is not
actually an SSL handshake message.
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When the client and server decide to resume a previous session or
duplicate an existing session (instead of negotiating new security
parameters) the message flow is as follows:
The client sends a ClientHello using the Session ID of the session
to be resumed. The server then checks its session cache for a
match. If a match is found, and the server is willing to
re-establish the connection under the specified session state, it
will send a ServerHello with the same Session ID value. At this
point, both client and server must send change cipher spec messages
and proceed directly to finished messages. Once the
re-establishment is complete, the client and server may begin to
exchange application layer data. (See flow chart below.) If a
Session ID match is not found, the server generates a new session
ID and the SSL client and server perform a full handshake.
Client Server
ClientHello -------->
ServerHello
[change cipher spec]
<-------- Finished
change cipher spec
Finished -------->
Application Data <-------> Application Data
The contents and significance of each message will be presented in
detail in the following sections.
5.6 Handshake protocol
The SSL Handshake Protocol is one of the defined higher level
clients of the SSL Record Protocol. This protocol is used to
negotiate the secure attributes of a session. Handshake messages
are supplied to the SSL Record Layer, where they are encapsulated
within one or more SSLPlaintext structures, which are processed and
transmitted as specified by the current active session state.
enum {
hello_request(0), client_hello(1), server_hello(2),
certificate(11), server_key_exchange (12),
certificate_request(13), server_hello_done(14),
certificate_verify(15), client_key_exchange(16),
finished(20), (255)
} HandshakeType;
struct {
HandshakeType msg_type; /* handshake type */
uint24 length; /* bytes in message */
select (HandshakeType) {
case hello_request: HelloRequest;
case client_hello: ClientHello;
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case server_hello: ServerHello;
case certificate: Certificate;
case server_key_exchange: ServerKeyExchange;
case certificate_request: CertificateRequest;
case server_hello_done: ServerHelloDone;
case certificate_verify: CertificateVerify;
case client_key_exchange: ClientKeyExchange;
case finished: Finished;
} body;
} Handshake;
The handshake protocol messages are presented in the order they
must be sent; sending handshake messages in an unexpected order
results in a fatal error.
5.6.1 Hello messages
The hello phase messages are used to exchange security enhancement
capabilities between the client and server. When a new session
begins, the CipherSpec encryption, hash, and compression algorithms
are initialized to null. The current CipherSpec is used for
renegotiation messages.
5.6.1.1 Hello request
The hello request message may be sent by the server at any time,
but will be ignored by the client if the handshake protocol is
already underway. It is a simple notification that the client
should begin the negotiation process anew by sending a client hello
message when convenient.
Note: Since handshake messages are intended to have
transmission precedence over application data, it is
expected that the negotiation begin in no more than
one or two times the transmission time of a maximum
length application data message.
After sending a hello request, servers should not repeat the
request until the subsequent handshake negotiation is complete. A
client that receives a hello request while in a handshake
negotiation state should simply ignore the message.
The structure of a hello request message is as follows:
struct { } HelloRequest;
5.6.1.2 Client hello
When a client first connects to a server it is required to send the
client hello as its first message. The client can also send a
client hello in response to a hello request or on its own
initiative in order to renegotiate the security parameters in an
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existing connection. The client hello message includes a random
structure, which is used later in the protocol.
struct {
uint32 gmt_unix_time;
opaque random_bytes[28];
} Random;
gmt_unix_time The current time and date in standard UNIX
32-bit format according to the sender's
internal clock. Clocks are not required to be
set correctly by the basic SSL Protocol; higher
level or application protocols may define
additional requirements.
random_bytes 28 bytes generated by a secure random number
generator.
The client hello message includes a variable length session
identifier. If not empty, the value identifies a session between
the same client and server whose security parameters the client
wishes to reuse. The session identifier may be from an earlier
connection, this connection, or another currently active
connection. The second option is useful if the client only wishes
to update the random structures and derived values of a connection,
while the third option makes it possible to establish several
simultaneous independent secure connections without repeating the
full handshake protocol. The actual contents of the SessionID are
defined by the server.
opaque SessionID<0..32>;
Warning: Servers must not place confidential information in
session identifiers or let the contents of fake
session identifiers cause any breach of security.
The CipherSuite list, passed from the client to the server in the
client hello message, contains the combinations of cryptographic
algorithms supported by the client in order of the client's
preference (first choice first). Each CipherSuite defines both a
key exchange algorithm and a CipherSpec. The server will select a
cipher suite or, if no acceptable choices are presented, return a
handshake failure alert and close the connection.
uint8 CipherSuite[2]; /* Cryptographic suite selector */
The client hello includes a list of compression algorithms
supported by the client, ordered according to the client's
preference. If the server supports none of those specified by the
client, the session must fail.
enum { null(0), (255) } CompressionMethod;
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Issue: Which compression methods to support is under
investigation.
The structure of the client hello is as follows.
struct {
ProtocolVersion client_version;
Random random;
SessionID session_id;
CipherSuite cipher_suites<2..2^16-1>;
CompressionMethod compression_methods<1..2^8-1>;
} ClientHello;
client_version The version of the SSL protocol by which the
client wishes to communicate during this
session. This should be the most recent
(highest valued) version supported by the
client. For this version of the specification,
the version will be 3.0 (See Appendix E for
details about backward compatibility).
random A client-generated random structure.
session_id The ID of a session the client wishes to use
for this connection. This field should be
empty if no session_id is available or the
client wishes to generate new security
parameters.
cipher_suites This is a list of the cryptographic options
supported by the client, sorted with the
client's first preference first. If the
session_id field is not empty (implying a
session resumption request) this vector must
include at least the cipher_suite from that
session. Values are defined in Appendix A.6.
compression_methods
This is a list of the compression methods
supported by the client, sorted by client
preference. If the session_id field is not
empty (implying a session resumption request)
this vector must include at least the
compression_method from that session. All
implementations must support
CompressionMethod.null.
After sending the client hello message, the client waits for a
server hello message. Any other handshake message returned by the
server except for a hello request is treated as a fatal error.
Implementation note:
Application data may not be sent before a finished
message has been sent. Transmitted application data
is known to be insecure until a valid finished
message has been received. This absolute
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restriction is relaxed if there is a current,
non-null encryption on this connection.
Forward compatibility note:
In the interests of forward compatibility, it is
permitted for a client hello message to include
extra data after the compression methods. This data
must be included in the handshake hashes, but must
otherwise be ignored.
5.6.1.3 Server hello
The server processes the client hello message and responds with
either a handshake_failure alert or server hello message.
struct {
ProtocolVersion server_version;
Random random;
SessionID session_id;
CipherSuite cipher_suite;
CompressionMethod compression_method;
} ServerHello;
server_version This field will contain the lower of that
suggested by the client in the client hello and
the highest supported by the server. For this
version of the specification, the version will
be 3.0 (See Appendix E for details about
backward compatibility).
random This structure is generated by the server and
must be different from (and independent of)
ClientHello.random.
session_id This is the identity of the session
corresponding to this connection. If the
ClientHello.session_id was non-empty, the
server will look in its session cache for a
match. If a match is found and the server is
willing to establish the new connection using
the specified session state, the server will
respond with the same value as was supplied by
the client. This indicates a resumed session
and dictates that the parties must proceed
directly to the finished messages. Otherwise
this field will contain a different value
identifying the new session. The server may
return an empty session_id to indicate that the
session will not be cached and therefore cannot
be resumed.
cipher_suite The single cipher suite selected by the server
from the list in ClientHello.cipher_suites.
For resumed sessions this field is the value
from the state of the session being resumed.
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compression_method
The single compression algorithm selected by
the server from the list in
ClientHello.compression_methods. For resumed
sessions this field is the value from the
resumed session state.
5.6.2 Server certificate
If the server is to be authenticated (which is generally the case),
the server sends its certificate immediately following the server
hello message. The certificate type must be appropriate for the
selected cipher suite's key exchange algorithm, and is generally an
X.509.v3 certificate (or a modified X.509 certificate in the case
of FORTEZZA(tm) [FOR]). The same message type will be used for the
client's response to a certificate request message.
opaque ASN.1Cert<1..2^24-1>;
struct {
ASN.1Cert certificate_list<1..2^24-1>;
} Certificate;
certificate_list This is a sequence (chain) of X.509.v3
certificates, ordered with the sender's
certificate first followed by any certificate
authority certificates proceeding sequentially
upward.
Note: PKCS #7 [PKCS7] is not used as the format for the
certificate vector because PKCS #6 [PKCS6] extended
certificates are not used. Also PKCS #7 defines a
SET rather than a SEQUENCE, making the task of
parsing the list more difficult.
5.6.3 Server key exchange message
The server key exchange message is sent by the server if it has no
certificate, has a certificate only used for signing (e.g., DSS
[DSS] certificates, signing-only RSA [RSA] certificates), or
FORTEZZA KEA key exchange is used. This message is not used if the
server certificate contains Diffie-Hellman [DH1] parameters.
Note: According to current US export law, RSA moduli
larger than 512 bits may not be used for key
exchange in software exported from the US. With
this message, larger RSA keys may be used as
signature-only certificates to sign temporary
shorter RSA keys for key exchange.
enum { rsa, diffie_hellman, fortezza_kea }
KeyExchangeAlgorithm;
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struct {
opaque rsa_modulus<1..2^16-1>;
opaque rsa_exponent<1..2^16-1>;
} ServerRSAParams;
rsa_modulus The modulus of the server's temporary RSA key.
rsa_exponent The public exponent of the server's temporary
RSA key.
struct {
opaque dh_p<1..2^16-1>;
opaque dh_g<1..2^16-1>;
opaque dh_Ys<1..2^16-1>;
} ServerDHParams; /* Ephemeral DH parameters */
dh_p The prime modulus used for the Diffie-Hellman
operation.
dh_g The generator used for the Diffie-Hellman
operation.
dh_Ys The server's Diffie-Hellman public value
(gX mod p).
struct {
opaque r_s [128];
} ServerFortezzaParams;
r_s Server random number for FORTEZZA KEA (Key
Exchange Algorithm).
struct {
select (KeyExchangeAlgorithm) {
case diffie_hellman:
ServerDHParams params;
Signature signed_params;
case rsa:
ServerRSAParams params;
Signature signed_params;
case fortezza_kea:
ServerFortezzaParams params;
};
} ServerKeyExchange;
params The server's key exchange parameters.
signed_params A hash of the corresponding params value, with
the signature appropriate to that hash applied.
md5_hash MD5(ClientHello.random + ServerHello.random +
ServerParams);
sha_hash SHA(ClientHello.random + ServerHello.random +
ServerParams);
enum { anonymous, rsa, dsa } SignatureAlgorithm;
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digitally-signed struct {
select(SignatureAlgorithm) {
case anonymous: struct { };
case rsa:
opaque md5_hash[16];
opaque sha_hash[20];
case dsa:
opaque sha_hash[20];
};
} Signature;
5.6.4 Certificate request
A non-anonymous server can optionally request a certificate from
the client, if appropriate for the selected cipher suite.
enum {
rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4),
rsa_ephemeral_dh(5), dss_ephemeral_dh(6), fortezza_kea(20),
(255)
} ClientCertificateType;
opaque DistinguishedName<1..2^16-1>;
struct {
ClientCertificateType certificate_types<1..2^8-1>;
DistinguishedName certificate_authorities<3..2^16-1>;
} CertificateRequest;
certificate_types This field is a list of the types of
certificates requested, sorted in order of the
server's preference.
certificate_authorities
A list of the distinguished names of acceptable
certificate authorities.
Note: DistinguishedName is derived from [X509].
Note: It is a fatal handshake_failure alert for an
anonymous server to request client identification.
5.6.5 Server hello done
The server hello done message is sent by the server to indicate the
end of the server hello and associated messages. After sending
this message the server will wait for a client response.
struct { } ServerHelloDone;
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Upon receipt of the server hello done message the client should
verify that the server provided a valid certificate if required and
check that the server hello parameters are acceptable.
5.6.6 Client certificate
This is the first message the client can send after receiving a
server hello done message. This message is only sent if the server
requests a certificate. If no suitable certificate is available,
the client should send a no_certificate alert instead. This alert
is only a warning, however the server may respond with a fatal
handshake failure alert if client authentication is required.
Client certificates are sent using the Certificate defined in
Section 5.6.2.
Note: Client Diffie-Hellman certificates must match the
server specified Diffie-Hellman parameters.
5.6.7 Client key exchange message
The choice of messages depends on which public key algorithm(s) has
(have) been selected. See Section 5.6.3 for the
KeyExchangeAlgorithm definition.
struct {
select (KeyExchangeAlgorithm) {
case rsa: EncryptedPreMasterSecret;
case diffie_hellman: ClientDiffieHellmanPublic;
case fortezza_kea: FortezzaKeys;
} exchange_keys;
} ClientKeyExchange;
The information to select the appropriate record structure is in
the pending session state (see Section 5.1).
5.6.7.1 RSA encrypted premaster secret message
If RSA is being used for key agreement and authentication, the
client generates a 48-byte pre-master secret, encrypts it under the
public key from the server's certificate or temporary RSA key from
a server key exchange message, and sends the result in an encrypted
premaster secret message.
struct {
ProtocolVersion client_version;
opaque random[46];
} PreMasterSecret;
client_version The latest (newest) version supported by the
client. This is used to detect version
roll-back attacks.
random 46 securely-generated random bytes.
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struct {
public-key-encrypted PreMasterSecret pre_master_secret;
} EncryptedPreMasterSecret;
pre_master_secret This random value is generated by the client
and is used to generate the master secret, as
specified in Section 6.1.
5.6.7.2 FORTEZZA key exchange message
Under FORTEZZA, the client derives a Token Encryption Key (TEK)
using the FORTEZZA Key Exchange Algorithm (KEA). The client's KEA
calculation uses the public key in the server's certificate along
with private parameters in the client's token. The client sends
public parameters needed for the server to generate the TEK, using
its own private parameters. The client generates session keys,
wraps them using the TEK, and sends the results to the server. The
client generates IV's for the session keys and TEK and sends them
also. The client generates a random 48-byte premaster secret,
encrypts it using the TEK, and sends the result:
struct {
opaque y_c<0..128>;
opaque r_c[128];
opaque y_signature[40];
opaque wrapped_client_write_key[12];
opaque wrapped_server_write_key[12];
opaque client_write_iv[24];
opaque server_write_iv[24];
opaque master_secret_iv[24];
block-ciphered opaque encrypted_pre_master_secret[48];
} FortezzaKeys;
y_signature y_signature is the signature of the KEA public
key, signed with the client's DSS private key.
y_c The client's Yc value (public key) for the KEA
calculation. If the client has sent a
certificate, and its KEA public key is
suitable, this value must be empty since the
certificate already contains this value. If
the client sent a certificate without a
suitable public key, y_c is used and
y_signature is the KEA public key signed with
the client's DSS private key. For this value
to be used, it must be between 64 and 128
bytes.
r_c The client's Rc value for the KEA calculation.
wrapped_client_write_key
This is the client's write key, wrapped by the
TEK.
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wrapped_server_write_key
This is the server's write key, wrapped by the
TEK.
client_write_iv The IV for the client write key.
server_write_iv The IV for the server write key.
master_secret_iv This is the IV for the TEK used to encrypt the
pre-master secret.
pre_master_secret A random value, generated by the client and
used to generate the master secret, as
specified in Section 6.1. In the the above
structure, it is encrypted using the TEK.
5.6.7.3 Client Diffie-Hellman public value
This structure conveys the client's Diffie-Hellman public value
(Yc) if it was not already included in the client's certificate.
The encoding used for Yc is determined by the enumerated
PublicValueEncoding.
enum { implicit, explicit } PublicValueEncoding;
implicit If the client certificate already contains the
public value, then it is implicit and Yc does
not need to be sent again.
explicit Yc needs to be sent.
struct {
select (PublicValueEncoding) {
case implicit: struct { };
case explicit: opaque dh_Yc<1..2^16-1>;
} dh_public;
} ClientDiffieHellmanPublic;
dh_Yc The client's Diffie-Hellman public value (Yc).
5.6.8 Certificate verify
This message is used to provide explicit verification of a client
certificate. This message is only sent following any client
certificate that has signing capability (i.e. all certificates
except those containing fixed Diffie-Hellman parameters).
struct {
Signature signature;
} CertificateVerify;
CertificateVerify.signature.md5_hash
MD5(master_secret + pad_2 +
MD5(handshake_messages + master_secret + pad_1));
Certificate.signature.sha_hash
SHA(master_secret + pad_2 +
SHA(handshake_messages + master_secret + pad_1));
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pad_1 This is identical to the pad_1 defined in
section 5.2.3.1.
pad_2 This is identical to the pad_2 defined in
section 5.2.3.1.
Here handshake_messages refers to all handshake messages starting
at client hello up to but not including this message.
5.6.9 Finished
A finished message is always sent immediately after a change cipher
specs message to verify that the key exchange and authentication
processes were successful. The finished message is the first
protected with the just-negotiated algorithms, keys, and secrets.
No acknowledgment of the finished message is required; parties may
begin sending encrypted data immediately after sending the finished
message. Recipients of finished messages must verify that the
contents are correct.
enum { client(0x434C4E54), server(0x53525652) } Sender;
struct {
opaque md5_hash[16];
opaque sha_hash[20];
} Finished;
md5_hash MD5(master_secret + pad2 +
MD5(handshake_messages + Sender +
master_secret + pad1));
sha_hash SHA(master_secret + pad2 +
SHA(handshake_messages + Sender +
master_secret + pad1));
handshake_messages All of the data from all handshake messages
up to but not including this message. This
is only data visible at the handshake layer
and does not include record layer headers.
It is a fatal error if a finished message is not preceeded by a
change cipher spec message at the appropriate point in the
handshake.
The hash contained in finished messages sent by the server
incorporate Sender.server; those sent by the client incorporate
Sender.client. The value handshake_messages includes all handshake
messages starting at client hello up to, but not including, this
finished message. This may be different from handshake_messages in
Section 5.6.8 because it would include the certificate verify
message (if sent).
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Note: Change cipher spec messages are not handshake
messages and are not included in the hash
computations.
5.7 Application data protocol
Application data messages are carried by the Record Layer and are
fragmented, compressed and encrypted based on the current
connection state. The messages are treated as transparent data to
the record layer.
6. Cryptographic computations
The key exchange, authentication, encryption, and MAC algorithms
are determined by the cipher_suite selected by the server and
revealed in the server hello message.
6.1 Asymmetric cryptographic computations
The asymmetric algorithms are used in the handshake protocol to
authenticate parties and to generate shared keys and secrets.
For Diffie-Hellman, RSA, and FORTEZZA, the same algorithm is used
to convert the pre_master_secret into the master_secret. The
pre_master_secret should be deleted from memory once the
master_secret has been computed.
master_secret =
MD5(pre_master_secret + SHA('A' + pre_master_secret +
ClientHello.random + ServerHello.random)) +
MD5(pre_master_secret + SHA('BB' + pre_master_secret +
ClientHello.random + ServerHello.random)) +
MD5(pre_master_secret + SHA('CCC' + pre_master_secret +
ClientHello.random + ServerHello.random));
6.1.1 RSA
When RSA is used for server authentication and key exchange, a
48-byte pre_master_secret is generated by the client, encrypted
under the server's public key, and sent to the server. The server
uses its private key to decrypt the pre_master_secret. Both
parties then convert the pre_master_secret into the master_secret,
as specified above.
RSA digital signatures are performed using PKCS #1 [PKCS1] block
type 1. RSA public key encryption is performed using PKCS #1 block
type 2.
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6.1.2 Diffie-Hellman
A conventional Diffie-Hellman computation is performed. The
negotiated key (Z) is used as the pre_master_secret, and is
converted into the master_secret, as specified above.
Note: Diffie-Hellman parameters are specified by the
server, and may be either ephemeral or contained
within the server's certificate.
6.1.3 FORTEZZA
A random 48-byte pre_master_secret is sent encrypted under the TEK
and its IV. The server decrypts the pre_master_secret and converts
it into a master_secret, as specified above. Bulk cipher keys and
IVs for encryption are generated by the client's token and
exchanged in the key exchange message; the master_secret is only
used for MAC computations.
6.2 Symmetric cryptographic calculations and the CipherSpec
The technique used to encrypt and verify the integrity of SSL
records is specified by the currently active CipherSpec. A typical
example would be to encrypt data using DES and generate
authentication codes using MD5. The encryption and MAC algorithms
are set to SSL_NULL_WITH_NULL_NULL at the beginning of the SSL
Handshake Protocol, indicating that no message authentication or
encryption is performed. The handshake protocol is used to
negotiate a more secure CipherSpec and to generate cryptographic
keys.
6.2.1 The master secret
Before secure encryption or integrity verification can be performed
on records, the client and server need to generate shared secret
information known only to themselves. This value is a 48-byte
quantity called the master secret. The master secret is used to
generate keys and secrets for encryption and MAC computations.
Some algorithms, such as FORTEZZA, may have their own procedure for
generating encryption keys (the master secret is used only for MAC
computations in FORTEZZA).
6.2.2 Converting the master secret into keys and MAC secrets
The master secret is hashed into a sequence of secure bytes, which
are assigned to the MAC secrets, keys, and non-export IVs required
by the current CipherSpec (see Appendix A.7). CipherSpecs require
a client write MAC secret, a server write MAC secret, a client
write key, a server write key, a client write IV, and a server
write IV, which are generated from the master secret in that order.
Unused values, such as FORTEZZA keys communicated in the
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KeyExchange message, are empty. The following inputs are available
to the key definition process:
opaque MasterSecret[48]
ClientHello.random
ServerHello.random
When generating keys and MAC secrets, the master secret is used as
an entropy source, and the random values provide unencrypted salt
material and IVs for exportable ciphers.
To generate the key material, compute
key_block =
MD5(master_secret + SHA(`A' + master_secret +
ServerHello.random +
ClientHello.random)) +
MD5(master_secret + SHA(`BB' + master_secret +
ServerHello.random +
ClientHello.random)) +
MD5(master_secret + SHA(`CCC' + master_secret +
ServerHello.random +
ClientHello.random)) + [...];
until enough output has been generated. Then the key_block is
partitioned as follows.
client_write_MAC_secret[CipherSpec.hash_size]
server_write_MAC_secret[CipherSpec.hash_size]
client_write_key[CipherSpec.key_material]
server_write_key[CipherSpec.key_material]
client_write_IV[CipherSpec.IV_size] /* non-export ciphers */
server_write_IV[CipherSpec.IV_size] /* non-export ciphers */
Any extra key_block material is discarded.
Exportable encryption algorithms (for which
CipherSpec.is_exportable is true) require additional processing as
follows to derive their final write keys:
final_client_write_key = MD5(client_write_key +
ClientHello.random +
ServerHello.random);
final_server_write_key = MD5(server_write_key +
ServerHello.random +
ClientHello.random);
Exportable encryption algorithms derive their IVs from the random
messages:
client_write_IV = MD5(ClientHello.random + ServerHello.random);
server_write_IV = MD5(ServerHello.random + ClientHello.random);
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MD5 outputs are trimmed to the appropriate size by discarding the
least-significant bytes.
6.2.2.1 Export key generation example
SSL_RSA_EXPORT_WITH_RC2_CBC_40_MD5 requires five random bytes for
each of the two encryption keys and 16 bytes for each of the MAC
keys, for a total of 42 bytes of key material. MD5 produces 16
bytes of output per call, so three calls to MD5 are required. The
MD5 outputs are concatenated into a 48-byte key_block with the
first MD5 call providing bytes zero through 15, the second
providing bytes 16 through 31, etc. The key_block is partitioned,
and the write keys are salted because this is an exportable
encryption algorithm.
client_write_MAC_secret = key_block[0..15]
server_write_MAC_secret = key_block[16..31]
client_write_key = key_block[32..36]
server_write_key = key_block[37..41]
final_client_write_key = MD5(client_write_key +
ClientHello.random +
ServerHello.random)[0..15];
final_server_write_key = MD5(server_write_key +
ServerHello.random +
ClientHello.random)[0..15];
client_write_IV = MD5(ClientHello.random +
ServerHello.random)[0..7];
server_write_IV = MD5(ServerHello.random +
ClientHello.random)[0..7];
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Appendix A
A. Protocol constant values
This section describes protocol types and constants.
A.1 Reserved port assignments
At the present time SSL is implemented using TCP/IP as the base
networking technology. The IANA reserved the following Internet
Protocol [IP] port numbers for use in conjunction with SSL.
443 Reserved for use by Hypertext Transfer Protocol with
SSL (https).
465 Reserved (pending) for use by Simple Mail Transfer Protocol
with SSL (ssmtp).
563 Reserved (pending) for use by Network News Transfer
Protocol (snntp).
A.1.1 Record layer
struct {
uint8 major, minor;
} ProtocolVersion;
ProtocolVersion version = { 3,0 };
enum {
change_cipher_spec(20), alert(21), handshake(22),
application_data(23), (255)
} ContentType;
struct {
ContentType type;
ProtocolVersion version;
uint16 length;
opaque fragment[SSLPlaintext.length];
} SSLPlaintext;
struct {
ContentType type;
ProtocolVersion version;
uint16 length;
opaque fragment[SSLCompressed.length];
} SSLCompressed;
struct {
ContentType type;
ProtocolVersion version;
uint16 length;
select (CipherSpec.cipher_type) {
case stream: GenericStreamCipher;
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case block: GenericBlockCipher;
} fragment;
} SSLCiphertext;
stream-ciphered struct {
opaque content[SSLCompressed.length];
opaque MAC[CipherSpec.hash_size];
} GenericStreamCipher;
block-ciphered struct {
opaque content[SSLCompressed.length];
opaque MAC[CipherSpec.hash_size];
uint8 padding[GenericBlockCipher.padding_length];
uint8 padding_length;
} GenericBlockCipher;
A.2 Change cipher specs message
struct {
enum { change_cipher_spec(1), (255) } type;
} ChangeCipherSpec;
A.3 Alert messages
enum { warning(1), fatal(2), (255) } AlertLevel;
enum {
close_notify(0),
unexpected_message(10),
bad_record_mac(20),
decompression_failure(30),
handshake_failure(40),
no_certificate(41),
bad_certificate(42),
unsupported_certificate(43),
certificate_revoked(44),
certificate_expired(45),
certificate_unknown(46),
illegal_parameter (47),
(255)
} AlertDescription;
struct {
AlertLevel level;
AlertDescription description;
} Alert;
A.4 Handshake protocol
enum {
hello_request(0), client_hello(1), server_hello(2),
certificate(11), server_key_exchange (12),
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certificate_request(13), server_done(14),
certificate_verify(15), client_key_exchange(16),
finished(20), (255)
} HandshakeType;
struct {
HandshakeType msg_type;
uint24 length;
select (HandshakeType) {
case hello_request: HelloRequest;
case client_hello: ClientHello;
case server_hello: ServerHello;
case certificate: Certificate;
case server_key_exchange: ServerKeyExchange;
case certificate_request: CertificateRequest;
case server_done: ServerHelloDone;
case certificate_verify: CertificateVerify;
case client_key_exchange: ClientKeyExchange;
case finished: Finished;
} body;
} Handshake;
A.4.1 Hello messages
struct { } HelloRequest;
struct {
uint32 gmt_unix_time;
opaque random_bytes[28];
} Random;
opaque SessionID<0..32>;
uint8 CipherSuite[2];
enum { null(0), (255) } CompressionMethod;
struct {
ProtocolVersion client_version;
Random random;
SessionID session_id;
CipherSuite cipher_suites<0..2^16-1>;
CompressionMethod compression_methods<0..2^8-1>;
} ClientHello;
struct {
ProtocolVersion server_version;
Random random;
SessionID session_id;
CipherSuite cipher_suite;
CompressionMethod compression_method;
} ServerHello;
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A.4.2 Server authentication and key exchange messages
opaque ASN.1Cert<2^24-1>;
struct {
ASN.1Cert certificate_list<1..2^24-1>;
} Certificate;
enum { rsa, diffie_hellman, fortezza_kea } KeyExchangeAlgorithm;
struct {
opaque RSA_modulus<1..2^16-1>;
opaque RSA_exponent<1..2^16-1>;
} ServerRSAParams;
struct {
opaque DH_p<1..2^16-1>;
opaque DH_g<1..2^16-1>;
opaque DH_Ys<1..2^16-1>;
} ServerDHParams;
struct {
opaque r_s [128]
} ServerFortezzaParams
struct {
select (KeyExchangeAlgorithm) {
case diffie_hellman:
ServerDHParams params;
Signature signed_params;
case rsa:
ServerRSAParams params;
Signature signed_params;
case fortezza_kea:
ServerFortezzaParams params;
};
} ServerKeyExchange;
enum { anonymous, rsa, dsa } SignatureAlgorithm;
digitally-signed struct {
select(SignatureAlgorithm) {
case anonymous: struct { };
case rsa:
opaque md5_hash[16];
opaque sha_hash[20];
case dsa:
opaque sha_hash[20];
};
} Signature;
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enum {
RSA_sign(1), DSS_sign(2), RSA_fixed_DH(3),
DSS_fixed_DH(4), RSA_ephemeral_DH(5), DSS_ephemeral_DH(6),
FORTEZZA_MISSI(20), (255)
} CertificateType;
opaque DistinguishedName<1..2^16-1>;
struct {
CertificateType certificate_types<1..2^8-1>;
DistinguishedName certificate_authorities<3..2^16-1>;
} CertificateRequest;
struct { } ServerHelloDone;
A.5 Client authentication and key exchange messages
struct {
select (KeyExchangeAlgorithm) {
case rsa: EncryptedPreMasterSecret;
case diffie_hellman: DiffieHellmanClientPublicValue;
case fortezza_kea: FortezzaKeys;
} exchange_keys;
} ClientKeyExchange;
struct {
ProtocolVersion client_version;
opaque random[46];
} PreMasterSecret;
struct {
public-key-encrypted PreMasterSecret pre_master_secret;
} EncryptedPreMasterSecret;
struct {
opaque y_c<0..128>;
opaque r_c[128];
opaque y_signature[40];
opaque wrapped_client_write_key[12];
opaque wrapped_server_write_key[12];
opaque client_write_iv[24];
opaque server_write_iv[24];
opaque master_secret_iv[24];
opaque encrypted_preMasterSecret[48];
} FortezzaKeys;
enum { implicit, explicit } PublicValueEncoding;
struct {
select (PublicValueEncoding) {
case implicit: struct {};
case explicit: opaque DH_Yc<1..2^16-1>;
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} dh_public;
} ClientDiffieHellmanPublic;
struct {
Signature signature;
} CertificateVerify;
A.5.1 Handshake finalization message
struct {
opaque md5_hash[16];
opaque sha_hash[20];
} Finished;
A.6 The CipherSuite
The following values define the CipherSuite codes used in the
client hello and server hello messages.
A CipherSuite defines a cipher specifications supported in SSL
Version 3.0.
CipherSuite SSL_NULL_WITH_NULL_NULL = { 0x00,0x00 };
The following CipherSuite definitions require that the server
provide an RSA certificate that can be used for key exchange. The
server may request either an RSA or a DSS signature-capable
certificate in the certificate request message.
CipherSuite SSL_RSA_WITH_NULL_MD5 = { 0x00,0x01 };
CipherSuite SSL_RSA_WITH_NULL_SHA = { 0x00,0x02 };
CipherSuite SSL_RSA_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x03 };
CipherSuite SSL_RSA_WITH_RC4_128_MD5 = { 0x00,0x04 };
CipherSuite SSL_RSA_WITH_RC4_128_SHA = { 0x00,0x05 };
CipherSuite SSL_RSA_EXPORT_WITH_RC2_CBC_40_MD5 = { 0x00,0x06 };
CipherSuite SSL_RSA_WITH_IDEA_CBC_SHA = { 0x00,0x07 };
CipherSuite SSL_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x08 };
CipherSuite SSL_RSA_WITH_DES_CBC_SHA = { 0x00,0x09 };
CipherSuite SSL_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0A };
The following CipherSuite definitions are used for
server-authenticated (and optionally client-authenticated)
Diffie-Hellman. DH denotes cipher suites in which the server's
certificate contains the Diffie-Hellman parameters signed by the
certificate authority (CA). DHE denotes ephemeral Diffie-Hellman,
where the Diffie-Hellman parameters are signed by a DSS or RSA
certificate, which has been signed by the CA. The signing
algorithm used is specified after the DH or DHE parameter. In all
cases, the client must have the same type of certificate, and must
use the Diffie-Hellman parameters chosen by the server.
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CipherSuite SSL_DH_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0B };
CipherSuite SSL_DH_DSS_WITH_DES_CBC_SHA = { 0x00,0x0C };
CipherSuite SSL_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D };
CipherSuite SSL_DH_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0E };
CipherSuite SSL_DH_RSA_WITH_DES_CBC_SHA = { 0x00,0x0F };
CipherSuite SSL_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 };
CipherSuite SSL_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x11 };
CipherSuite SSL_DHE_DSS_WITH_DES_CBC_SHA = { 0x00,0x12 };
CipherSuite SSL_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 };
CipherSuite SSL_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x14 };
CipherSuite SSL_DHE_RSA_WITH_DES_CBC_SHA = { 0x00,0x15 };
CipherSuite SSL_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x16 };
The following cipher suites are used for completely anonymous
Diffie-Hellman communications in which neither party is
authenticated. Note that this mode is vulnerable to
man-in-the-middle attacks and is therefore strongly discouraged.
CipherSuite SSL_DH_anon_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x17 };
CipherSuite SSL_DH_anon_WITH_RC4_128_MD5 = { 0x00,0x18 };
CipherSuite SSL_DH_anon_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x19 };
CipherSuite SSL_DH_anon_WITH_DES_CBC_SHA = { 0x00,0x1A };
CipherSuite SSL_DH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1B };
The final cipher suites are for the FORTEZZA token.
CipherSuite SSL_FORTEZZA_KEA_WITH_NULL_SHA = { 0X00,0X1C };
CipherSuite SSL_FORTEZZA_KEA_WITH_FORTEZZA_CBC_SHA = { 0x00,0x1D };
CipherSuite SSL_FORTEZZA_KEA_WITH_RC4_128_SHA = { 0x00,0x1E };
Note: All cipher suites whose first byte is 0xFF are
considered private and can be used for defining
local/experimental algorithms. Interoperability of
such types is a local matter.
Note: Additional cipher suites will be considered for
implementation only with submission of notarized
letters from two independent entities. Netscape
Communications Corp. will act as an interim
registration office, until a public standards body
assumes control of SSL.
A.7 The CipherSpec
A cipher suite identifies a CipherSpec. These structures are part
of the SSL session state. The CipherSpec includes:
enum { stream, block } CipherType;
enum { true, false } IsExportable;
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enum { null, rc4, rc2, des, 3des, des40, fortezza }
BulkCipherAlgorithm;
enum { null, md5, sha } MACAlgorithm;
struct {
BulkCipherAlgorithm bulk_cipher_algorithm;
MACAlgorithm mac_algorithm;
CipherType cipher_type;
IsExportable is_exportable
uint8 hash_size;
uint8 key_material;
uint8 IV_size;
} CipherSpec;
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Appendix B
B. Glossary
application protocol An application protocol is a protocol that
normally layers directly on top of the
transport layer (e.g., TCP/IP). Examples
include HTTP, TELNET, FTP, and SMTP.
asymmetric cipher See public key cryptography.
authentication Authentication is the ability of one entity
to determine the identity of another entity.
block cipher A block cipher is an algorithm that operates
on plaintext in groups of bits, called
blocks. 64 bits is a typical block size.
bulk cipher A symmetric encryption algorithm used to
encrypt large quantities of data.
cipher block chaining
Mode (CBC) CBC is a mode in which every
plaintext block encrypted with the block
cipher is first exclusive-ORed with the
previous ciphertext block (or, in the case
of the first block, with the initialization
vector).
certificate As part of the X.509 protocol (a.k.a. ISO
Authentication framework), certificates are
assigned by a trusted Certificate Authority
and provide verification of a party's
identity and may also supply its public key.
client The application entity that initiates a
connection to a server.
client write key The key used to encrypt data written by the
client.
client write MAC secret
The secret data used to authenticate data
written by the client.
connection A connection is a transport (in the OSI
layering model definition) that provides a
suitable type of service. For SSL, such
connections are peer to peer relationships.
The connections are transient. Every
connection is associated with one session.
Data Encryption Standard
(DES) DES is a very widely used symmetric
encryption algorithm. DES is a block
cipher.
Digital Signature Standard
(DSS) A standard for digital signing,
including the Digital Signing Algorithm,
approved by the National Institute of
Standards and Technology, defined in NIST
FIPS PUB 186, "Digital Signature Standard,"
published May, 1994 by the U.S. Dept. of
Commerce.
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digital signatures Digital signatures utilize public key
cryptography and one-way hash functions to
produce a signature of the data that can be
authenticated, and is difficult to forge or
repudiate.
FORTEZZA A PCMCIA card that provides both encryption
and digital signing.
handshake An initial negotiation between client and
server that establishes the parameters of
their transactions.
Initialization Vector
(IV) When a block cipher is used in CBC
mode, the initialization vector is
exclusive-ORed with the first plaintext
block prior to encryption.
IDEA A 64-bit block cipher designed by Xuejia Lai
and James Massey.
Message Authentication Code
(MAC) A Message Authentication Code is a
one-way hash computed from a message and
some secret data. Its purpose is to detect
if the message has been altered.
master secret Secure secret data used for generating
encryption keys, MAC secrets, and IVs.
MD5 MD5 [7] is a secure hashing function that
converts an arbitrarily long data stream
into a digest of fixed size.
public key cryptography
A class of cryptographic techniques
employing two-key ciphers. Messages
encrypted with the public key can only be
decrypted with the associated private key.
Conversely, messages signed with the private
key can be verified with the public key.
one-way hash function
A one-way transformation that converts an
arbitrary amount of data into a fixed-length
hash. It is computation- ally hard to
reverse the transformation or to find
collisions. MD5 and SHA are examples of
one-way hash functions.
RC2, RC4 Proprietary bulk ciphers from RSA Data
Security, Inc. (There is no good reference
to these as they are unpublished works;
however, see [RSADSI]). RC2 is block cipher
and RC4 is a stream cipher.
RSA A very widely used public-key algorithm that
can be used for either encryption or digital
signing.
salt Non-secret random data used to make export
encryption keys resist precomputation
attacks.
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server The server is the application entity that
responds to requests for connections from
clients. The server is passive, waiting for
requests from clients.
session A SSL session is an association between a
client and a server. Sessions are created
by the handshake protocol. Sessions define
a set of cryptographic security parameters,
which can be shared among multiple
connections. Sessions are used to avoid the
expensive negotiation of new security
parameters for each connection.
session identifier A session identifier is a value generated by
a server that identifies a particular
session.
server write key The key used to encrypt data written by the
server.
server write MAC secret
The secret data used to authenticate data
written by the server.
SHA The Secure Hash Algorithm is defined in FIPS
PUB 180-1. It produces a 20-byte output
[SHA].
stream cipher An encryption algorithm that converts a key
into a cryptographically-strong keystream,
which is then exclusive-ORed with the
plaintext.
symmetric cipher See bulk cipher.
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Appendix C
C. CipherSuite definitions
CipherSuite Is Key Cipher Hash
Exportable Exchange
SSL_NULL_WITH_NULL_NULL * NULL NULL NULL
SSL_RSA_WITH_NULL_MD5 * RSA NULL MD5
SSL_RSA_WITH_NULL_SHA * RSA NULL SHA
SSL_RSA_EXPORT_WITH_RC4_40_MD5 * RSA_EXPORT RC4_40 MD5
SSL_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5
SSL_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA
SSL_RSA_EXPORT_WITH_RC2_CBC_40_MD5 * RSA_EXPORT RC2_CBC_40 MD5
SSL_RSA_WITH_IDEA_CBC_SHA RSA IDEA_CBC SHA
SSL_RSA_EXPORT_WITH_DES40_CBC_SHA * RSA_EXPORT DES40_CBC SHA
SSL_RSA_WITH_DES_CBC_SHA RSA DES_CBC SHA
SSL_RSA_WITH_3DES_EDE_CBC_SHA RSA 3DES_EDE_CBC SHA
SSL_DH_DSS_EXPORT_WITH_DES40_CBC_SHA * DH_DSS_EXPORT DES40_CBC SHA
SSL_DH_DSS_WITH_DES_CBC_SHA DH_DSS DES_CBC SHA
SSL_DH_DSS_WITH_3DES_EDE_CBC_SHA DH_DSS 3DES_EDE_CBC SHA
SSL_DH_RSA_EXPORT_WITH_DES40_CBC_SHA * DH_RSA_EXPORT DES40_CBC SHA
SSL_DH_RSA_WITH_DES_CBC_SHA DH_RSA DES_CBC SHA
SSL_DH_RSA_WITH_3DES_EDE_CBC_SHA DH_RSA 3DES_EDE_CBC SHA
SSL_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA * DHE_DSS_EXPORT DES40_CBC SHA
SSL_DHE_DSS_WITH_DES_CBC_SHA DHE_DSS DES_CBC SHA
SSL_DHE_DSS_WITH_3DES_EDE_CBC_SHA DHE_DSS 3DES_EDE_CBC SHA
SSL_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA * DHE_RSA_EXPORT DES40_CBC SHA
SSL_DHE_RSA_WITH_DES_CBC_SHA DHE_RSA DES_CBC SHA
SSL_DHE_RSA_WITH_3DES_EDE_CBC_SHA DHE_RSA 3DES_EDE_CBC SHA
SSL_DH_anon_EXPORT_WITH_RC4_40_MD5 * DH_anon_EXPORT RC4_40 MD5
SSL_DH_anon_WITH_RC4_128_MD5 DH_anon RC4_128 MD5
SSL_DH_anon_EXPORT_WITH_DES40_CBC_SHA DH_anon DES40_CBC SHA
SSL_DH_anon_WITH_DES_CBC_SHA DH_anon DES_CBC SHA
SSL_DH_anon_WITH_3DES_EDE_CBC_SHA DH_anon 3DES_EDE_CBC SHA
SSL_FORTEZZA_KEA_WITH_NULL_SHA FORTEZZA_KEA NULL SHA
SSL_FORTEZZA_KEA_WITH_FORTEZZA_CBC_SHA FORTEZZA_KEA FORTEZZA_CBC SHA
SSL_FORTEZZA_KEA_WITH_RC4_128_SHA FORTEZZA_KEA RC4_128 SHA
* Indicates IsExportable is True
Key Description Key size limit
Exchange
Algorithm
DHE_DSS Ephemeral DH with DSS signatures None
DHE_DSS_EXPORT Ephemeral DH with DSS signatures DH = 512 bits
DHE_RSA Ephemeral DH with RSA signatures None
DHE_RSA_EXPORT Ephemeral DH with RSA signatures DH = 512 bits,
RSA = none
DH_anon Anonymous DH, no signatures None
DH_anon_EXPORT Anonymous DH, no signatures DH = 512 bits
DH_DSS DH with DSS-based certificates None
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DH_DSS_EXPORT DH with DSS-based certificates DH = 512 bits
DH_RSA DH with RSA-based certificates None
DH_RSA_EXPORT DH with RSA-based certificates DH = 512 bits,
RSA = none
FORTEZZA_KEA FORTEZZA KEA. Details unpublished N/A
NULL No key exchange N/A
RSA RSA key exchange None
RSA_EXPORT RSA key exchange RSA = 512 bits
Key size limit The key size limit gives the size of the
largest public key that can be legally
used for encryption in cipher suites that
are exportable.
Cipher Cipher IsExpo Key Exp. Effect IV Block
Type rtable Material Key Mat ive Key Size Size
erial Bits
NULL Stream * 0 0 0 0 N/A
FORTEZZA_CBC Block NA(**) 12(**) 96(**) 20(**) 8
IDEA_CBC Block 16 16 128 8 8
RC2_CBC_40 Block * 5 16 40 8 8
RC4_40 Stream * 5 16 40 0 N/A
RC4_128 Stream 16 16 128 0 N/A
DES40_CBC Block * 5 8 40 8 8
DES_CBC Block 8 8 56 8 8
3DES_EDE_CBC Block 24 24 168 8 8
* Indicates IsExportable is true.
** FORTEZZA uses its own key and IV generation algorithms.
Key Material The number of bytes from the key_block that are
used for generating the write keys.
Expanded Key Material
The number of bytes actually fed into the
encryption algorithm.
Effective Key Bits
How much entropy material is in the key
material being fed into the encryption
routines.
Hash Hash Size Padding
function Size
NULL 0 0
MD5 16 48
SHA 20 40
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Appendix D
D. Implementation Notes
The SSL protocol cannot prevent many common security mistakes.
This section provides several recommendations to assist
implementers.
D.1 Temporary RSA keys
US Export restrictions limit RSA keys used for encryption to 512
bits, but do not place any limit on lengths of RSA keys used for
signing operations. Certificates often need to be larger than 512
bits, since 512-bit RSA keys are not secure enough for high-value
transactions or for applications requiring long-term security.
Some certificates are also designated signing-only, in which case
they cannot be used for key exchange.
When the public key in the certificate cannot be used for
encryption, the server signs a temporary RSA key, which is then
exchanged. In exportable applications, the temporary RSA key
should be the maximum allowable length (i.e., 512 bits). Because
512-bit RSA keys are relatively insecure, they should be changed
often. For typical electronic commerce applications, it is
suggested that keys be changed daily or every 500 transactions, and
more often if possible. Note that while it is acceptable to use
the same temporary key for multiple transactions, it must be signed
each time it is used.
RSA key generation is a time-consuming process. In many cases, a
low-priority process can be assigned the task of key generation.
Whenever a new key is completed, the existing temporary key can be
replaced with the new one.
D.2 Random Number Generation and Seeding
SSL requires a cryptographically-secure pseudorandom number
generator (PRNG). Care must be taken in designing and seeding
PRNGs. PRNGs based on secure hash operations, most notably MD5
and/or SHA, are acceptable, but cannot provide more security than
the size of the random number generator state. (For example,
MD5-based PRNGs usually provide 128 bits of state.)
To estimate the amount of seed material being produced, add the
number of bits of unpredictable information in each seed byte. For
example, keystroke timing values taken from a PC- compatible's 18.2
Hz timer provide 1 or 2 secure bits each, even though the total
size of the counter value is 16 bits or more. To seed a 128-bit
PRNG, one would thus require approximately 100 such timer values.
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Note: The seeding functions in RSAREF and versions of
BSAFE prior to 3.0 are order-independent. For
example, if 1000 seed bits are supplied, one at a
time, in 1000 separate calls to the seed function,
the PRNG will end up in a state which depends only
on the number of 0 or 1 seed bits in the seed data
(i.e., there are 1001 possible final states).
Applications using BSAFE or RSAREF must take extra
care to ensure proper seeding.
D.3 Certificates and authentication
Implementations are responsible for verifying the integrity of
certificates and should generally support certificate revocation
messages. Certificates should always be verified to ensure proper
signing by a trusted Certificate Authority (CA). The selection and
addition of trusted CAs should be done very carefully. Users
should be able to view information about the certificate and root
CA.
D.4 CipherSuites
SSL supports a range of key sizes and security levels, including
some which provide no or minimal security. A proper implementation
will probably not support many cipher suites. For example, 40-bit
encryption is easily broken, so implementations requiring strong
security should not allow 40-bit keys. Similarly, anonymous
Diffie-Hellman is strongly discouraged because it cannot prevent
man-in-the- middle attacks. Applications should also enforce
minimum and maximum key sizes. For example, certificate chains
containing 512-bit RSA keys or signatures are not appropriate for
high-security applications.
D.5 FORTEZZA
This section describes implementation details for ciphersuites that
make use of the FORTEZZA hardware encryption system.
D.5.1 Notes on use of FORTEZZA hardware
A complete explanation of all issues regarding the use of FORTEZZA
hardware is outside the scope of this document. However, there are
a few special requirements of SSL that deserve mention.
Because SSL is a full duplex protocol, two crypto states must be
maintained, one for reading and one for writing. There are also a
number of circumstances which can result in the crypto state in the
FORTEZZA card being lost. For these reasons, it's recommended that
the current crypto state be saved after processing a record, and
loaded before processing the next.
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After the client generates the TEK, it also generates two MEKs,
for one for reading and one for writing. After generating each of
these keys, the client must generate a corresponding IV and then
save the crypto state. The client also uses the TEK to generate an
IV and encrypt the premaster secret. All three IVs are sent to the
server, along with the wrapped keys and the encrypted premaster
secret in the client key exchange message. At this point, the TEK
is no longer needed, and may be discarded.
On the server side, the server uses the master IV and the TEK to
decrypt the premaster secret. It also loads the wrapped MEKs into
the card. The server loads both IVs to verify that the IVs match
the keys. However, since the card is unable to encrypt after
loading an IV, the server must generate a new IV for the server
write key. This IV is discarded.
When encrypting the first encrypted record (and only that record),
the server adds 8 bytes of random data to the beginning of the
fragment. These 8 bytes are discarded by the client after
decryption. The purpose of this is to synchronize the state on the
client and server resulting from the different IVs.
D.5.2 FORTEZZA Ciphersuites
5) FORTEZZA_NULL_WITH_NULL_SHA:
Uses the full FORTEZZA key exchange, including sending server and
client write keys and iv's.
D.5.3 FORTEZZA Session resumption
There are two possibilities for FORTEZZA session restart:
1) Never restart a FORTEZZA session.
2) Restart a session with the previously negotiated keys and iv's.
Never restarting a FORTEZZA session:
Clients who never restart FORTEZZA sessions should never send
Session ID's which were previously used in a FORTEZZA session as
part of the ClientHello. Servers who never restart FORTEZZA
sessions should never send a previous session id on the
ServerHello if the negotiated session is FORTEZZA.
Restart a session:
You cannot restart FORTEZZA on a session which has never done a
complete FORTEZZA key exchange (That is you cannot restart FORTEZZA
if the session was an RSA/RC4 session renegotiated for FORTEZZA).
If you wish to restart a FORTEZZA session, you must save the MEKs
and IVs from the initial key exchange for this session and reuse
them for any new connections on that session. This is not
recommended, but it is possible.
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Appendix E
E. Version 2.0 Backward Compatibility
Version 3.0 clients that support Version 2.0 servers must send
Version 2.0 client hello messages [SSL-2]. Version 3.0 servers
should accept either client hello format. The only deviations from
the Version 2.0 specification are the ability to specify a version
with a value of three and the support for more ciphering types in
the CipherSpec.
Warning: The ability to send Version 2.0 client hello
messages will be phased out with all due haste.
Implementers should make every effort to move
forward as quickly as possible. Version 3.0
provides better mechanisms for transitioning to
newer versions.
The following cipher specifications are carryovers from SSL Version
2.0. These are assumed to use RSA for key exchange and
authentication.
V2CipherSpec SSL_RC4_128_WITH_MD5 = { 0x01,0x00,0x80 };
V2CipherSpec SSL_RC4_128_EXPORT40_WITH_MD5 = { 0x02,0x00,0x80 };
V2CipherSpec SSL_RC2_CBC_128_CBC_WITH_MD5 = { 0x03,0x00,0x80 };
V2CipherSpec SSL_RC2_CBC_128_CBC_EXPORT40_WITH_MD5
= { 0x04,0x00,0x80 };
V2CipherSpec SSL_IDEA_128_CBC_WITH_MD5 = { 0x05,0x00,0x80 };
V2CipherSpec SSL_DES_64_CBC_WITH_MD5 = { 0x06,0x00,0x40 };
V2CipherSpec SSL_DES_192_EDE3_CBC_WITH_MD5 = { 0x07,0x00,0xC0 };
Cipher specifications introduced in Version 3.0 can be included in
Version 2.0 client hello messages using the syntax below. Any
V2CipherSpec element with its first byte equal to zero will be
ignored by Version 2.0 servers. Clients sending any of the above
V2CipherSpecs should also include the Version 3.0 equivalent (see
Appendix A.6):
V2CipherSpec (see Version 3.0 name) = { 0x00, CipherSuite };
E.1 Version 2 client hello
The Version 2.0 client hello message is presented below using this
document's presentation model. The true definition is still
assumed to be the SSL Version 2.0 specification.
uint8 V2CipherSpec[3];
struct {
unit8 msg_type;
Version version;
uint16 cipher_spec_length;
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uint16 session_id_length;
uint16 challenge_length;
V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length];
opaque session_id[V2ClientHello.session_id_length];
Random challenge;
} V2ClientHello;
msg_type This field, in conjunction with the version
field, identifies a version 2 client hello
message. The value should equal one (1).
version The highest version of the protocol supported
by the client (equals ProtocolVersion.version,
see Appendix A.1.1).
cipher_spec_length
This field is the total length of the field
cipher_specs. It cannot be zero and must be a
multiple of the V2CipherSpec length (3).
session_id_length This field must have a value of either zero or
16. If zero, the client is creating a new
session. If 16, the session_id field will
contain the 16 bytes of session identification.
challenge_length The length in bytes of the client's challenge
to the server to authenticate itself. This
value must be 32.
cipher_specs This is a list of all CipherSpecs the client is
willing and able to use. There must be at
least one CipherSpec acceptable to the server.
session_id If this field's length is not zero, it will
contain the identification for a session that
the client wishes to resume.
challenge The client's challenge to the server for the
server to identify itself is a (nearly)
arbitrary length random. The Version 3.0
server will right justify the challenge data to
become the ClientHello.random data (padded with
leading zeroes, if necessary), as specified in
this Version 3.0 protocol. If the length of
the challenge is greater than 32 bytes, then
only the last 32 bytes are used. It is
legitimate (but not necessary) for a V3 server
to reject a V2 ClientHello that has fewer than
16 bytes of challenge data.
Note: Requests to resume an SSL 3.0 session should use an
SSL 3.0 client hello.
E.2 Avoiding man-in-the-middle version rollback
When SSL Version 3.0 clients fall back to Version 2.0 compatibility
mode, they use special PKCS #1 block formatting. This is done so
that Version 3.0 servers will reject Version 2.0 sessions with
Version 3.0-capable clients.
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When Version 3.0 clients are in Version 2.0 compatibility mode,
they set the right-hand (least-significant) 8 random bytes of the
PKCS padding (not including the terminal null of the padding) for
the RSA encryption of the ENCRYPTED-KEY- DATA field of the
CLIENT-MASTER-KEY to 0x03 (the other padding bytes are random).
After decrypting the ENCRYPTED- KEY-DATA field, servers that
support SSL 3.0 should issue an error if these eight padding bytes
are 0x03. Version 2.0 servers receiving blocks padded in this
manner will proceed normally.
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Appendix F
F. Security analysis
The SSL protocol is designed to establish a secure connection
between a client and a server communicating over an insecure
channel. This document makes several traditional assumptions,
including that attackers have substantial computational resources
and cannot obtain secret information from sources outside the
protocol. Attackers are assumed to have the ability to capture,
modify, delete, replay, and otherwise tamper with messages sent
over the communication channel. This appendix outlines how SSL has
been designed to resist a variety of attacks.
F.1 Handshake protocol
The handshake protocol is responsible for selecting a CipherSpec
and generating a MasterSecret, which together comprise the primary
cryptographic parameters associated with a secure session. The
handshake protocol can also optionally authenticate parties who
have certificates signed by a trusted certificate authority.
F.1.1 Authentication and key exchange
SSL supports three authentication modes: authentication of both
parties, server authentication with an unauthenticated client, and
total anonymity. Whenever the server is authenticated, the channel
should be secure against man-in- the-middle attacks, but completely
anonymous sessions are inherently vulnerable to such attacks.
Anonymous servers cannot authenticate clients, since the client
signature in the certificate verify message may require a server
certificate to bind the signature to a particular server. If the
server is authenticated, its certificate message must provide a
valid certificate chain leading to an acceptable certificate
authority. Similarly, authenticated clients must supply an
acceptable certificate to the server. Each party is responsible
for verifying that the other's certificate is valid and has not
expired or been revoked.
The general goal of the key exchange process is to create a
pre_master_secret known to the communicating parties and not to
attackers. The pre_master_secret will be used to generate the
master_secret (see Section 6.1). The master_secret is required to
generate the finished messages, encryption keys, and MAC secrets
(see Sections 5.6.9 and 6.2.2). By sending a correct finished
message, parties thus prove that they know the correct
pre_master_secret.
F.1.1.1 Anonymous key exchange
Completely anonymous sessions can be established using RSA,
Diffie-Hellman, or FORTEZZA for key exchange. With anonymous RSA,
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the client encrypts a pre_master_secret with the server's
uncertified public key extracted from the server key exchange
message. The result is sent in a client key exchange message.
Since eavesdroppers do not know the server's private key, it will
be infeasible for them to decode the pre_master_secret.
With Diffie-Hellman or FORTEZZA, the server's public parameters are
contained in the server key exchange message and the client's are
sent in the client key exchange message. Eavesdroppers who do not
know the private values should not be able to find the
Diffie-Hellman result (i.e. the pre_master_secret) or the FORTEZZA
token encryption key (TEK).
Warning: Completely anonymous connections only provide
protection against passive eavesdropping. Unless an
independent tamper-proof channel is used to verify
that the finished messages were not replaced by an
attacker, server authentication is required in
environments where active man-in-the-middle attacks
are a concern.
F.1.1.2 RSA key exchange and authentication
With RSA, key exchange and server authentication are combined. The
public key may be either contained in the server's certificate or
may be a temporary RSA key sent in a server key exchange message.
When temporary RSA keys are used, they are signed by the server's
RSA or DSS certificate. The signature includes the current
ClientHello.random, so old signatures and temporary keys cannot be
replayed. Servers may use a single temporary RSA key for multiple
negotiation sessions.
Note: The temporary RSA key option is useful if servers
need large certificates but must comply with
government-imposed size limits on keys used for key
exchange.
After verifying the server's certificate, the client encrypts a
pre_master_secret with the server's public key. By successfully
decoding the pre_master_secret and producing a correct finished
message, the server demonstrates that it knows the private key
corresponding to the server certificate.
When RSA is used for key exchange, clients are authenticated using
the certificate verify message (see Section 5.6.8). The client
signs a value derived from the master_secret and all preceding
handshake messages. These handshake messages include the server
certificate, which binds the signature to the server, and
ServerHello.random, which binds the signature to the current
handshake process.
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F.1.1.3 Diffie-Hellman key exchange with authentication
When Diffie-Hellman key exchange is used, the server can either
supply a certificate containing fixed Diffie-Hellman parameters or
can use the server key exchange message to send a set of temporary
Diffie-Hellman parameters signed with a DSS or RSA certificate.
Temporary parameters are hashed with the hello.random values before
signing to ensure that attackers do not replay old parameters. In
either case, the client can verify the certificate or signature to
ensure that the parameters belong to the server.
If the client has a certificate containing fixed Diffie- Hellman
parameters, its certificate contains the information required to
complete the key exchange. Note that in this case the client and
server will generate the same Diffie- Hellman result (i.e.,
pre_master_secret) every time they communicate. To prevent the
pre_master_secret from staying in memory any longer than necessary,
it should be converted into the master_secret as soon as possible.
Client Diffie- Hellman parameters must be compatible with those
supplied by the server for the key exchange to work.
If the client has a standard DSS or RSA certificate or is
unauthenticated, it sends a set of temporary parameters to the
server in the client key exchange message, then optionally uses a
certificate verify message to authenticate itself.
F.1.1.4 FORTEZZA
FORTEZZA's design is classified, but at the protocol level it is
similar to Diffie-Hellman with fixed public values contained in
certificates. The result of the key exchange process is the token
encryption key (TEK), which is used to wrap data encryption keys,
client write key, server write key, and master secret encryption
key. The data encryption keys are not derived from the
pre_master_secret because unwrapped keys are not accessible outside
the token. The encrypted pre_master_secret is sent to the server
in a client key exchange message.
F.1.2 Version rollback attacks
Because SSL Version 3.0 includes substantial improvements over SSL
Version 2.0, attackers may try to make Version 3.0- capable clients
and servers fall back to Version 2.0. This attack is occurring if
(and only if) two Version 3.0-capable parties use an SSL 2.0
handshake.
Although the solution using non-random PKCS #1 block type 2 message
padding is inelegant, it provides a reasonably secure way for
Version 3.0 servers to detect the attack. This solution is not
secure against attackers who can brute force the key and substitute
a new ENCRYPTED-KEY-DATA message containing the same key (but with
normal padding) before the application specified wait threshold has
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expired. Parties concerned about attacks of this scale should not
be using 40-bit encryption keys anyway. Altering the padding of
the least-significant 8 bytes of the PKCS padding does not impact
security, since this is essentially equivalent to increasing the
input block size by 8 bytes.
F.1.3 Detecting attacks against the handshake protocol
An attacker might try to influence the handshake exchange to make
the parties select different encryption algorithms than they would
normally choose. Because many implementations will support 40-bit
exportable encryption and some may even support null encryption or
MAC algorithms, this attack is of particular concern.
For this attack, an attacker must actively change one or more
handshake messages. If this occurs, the client and server will
compute different values for the handshake message hashes. As a
result, the parties will not accept each others' finished messages.
Without the master_secret, the attacker cannot repair the finished
messages, so the attack will be discovered.
F.1.4 Resuming sessions
When a connection is established by resuming a session, new
ClientHello.random and ServerHello.random values are hashed with
the session's master_secret. Provided that the master_secret has
not been compromised and that the secure hash operations used to
produce the encryption keys and MAC secrets are secure, the
connection should be secure and effectively independent from
previous connections. Attackers cannot use known encryption keys
or MAC secrets to compromise the master_secret without breaking the
secure hash operations (which use both SHA and MD5).
Sessions cannot be resumed unless both the client and server agree.
If either party suspects that the session may have been
compromised, or that certificates may have expired or been revoked,
it should force a full handshake. An upper limit of 24 hours is
suggested for session ID lifetimes, since an attacker who obtains a
master_secret may be able to impersonate the compromised party
until the corresponding session ID is retired. Applications that
may be run in relatively insecure environments should not write
session IDs to stable storage.
F.1.5 MD5 and SHA
SSL uses hash functions very conservatively. Where possible, both
MD5 and SHA are used in tandem to ensure that non- catastrophic
flaws in one algorithm will not break the overall protocol.
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F.2 Protecting application data
The master_secret is hashed with the ClientHello.random and
ServerHello.random to produce unique data encryption keys and MAC
secrets for each connection. FORTEZZA encryption keys are
generated by the token, and are not derived from the master_secret.
Outgoing data is protected with a MAC before transmission. To
prevent message replay or modification attacks, the MAC is computed
from the MAC secret, the sequence number, the message length, the
message contents, and two fixed character strings. The message
type field is necessary to ensure that messages intended for one
SSL Record Layer client are not redirected to another. The
sequence number ensures that attempts to delete or reorder messages
will be detected. Since sequence numbers are 64-bits long, they
should never overflow. Messages from one party cannot be inserted
into the other's output, since they use independent MAC secrets.
Similarly, the server-write and client-write keys are independent
so stream cipher keys are used only once.
If an attacker does break an encryption key, all messages encrypted
with it can be read. Similarly, compromise of a MAC key can make
message modification attacks possible. Because MACs are also
encrypted, message-alteration attacks generally require breaking
the encryption algorithm as well as the MAC.
Note: MAC secrets may be larger than encryption keys, so
messages can remain tamper resistant even if
encryption keys are broken.
F.3 Final notes
For SSL to be able to provide a secure connection, both the client
and server systems, keys, and applications must be secure. In
addition, the implementation must be free of security errors.
The system is only as strong as the weakest key exchange and
authentication algorithm supported, and only trustworthy
cryptographic functions should be used. Short public keys, 40-bit
bulk encryption keys, and anonymous servers should be used with
great caution. Implementations and users must be careful when
deciding which certificates and certificate authorities are
acceptable; a dishonest certificate authority can do tremendous
damage.
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Appendix G
G. Patent Statement
This version of the SSL protocol relies on the use of patented
public key encryption technology for authentication and encryption.
The Internet Standards Process as defined in RFC 1310 requires a
written statement from the Patent holder that a license will be
made available to applicants under reasonable terms and conditions
prior to approving a specification as a Proposed, Draft or Internet
Standard. The Massachusetts Institute of Technology has granted
RSA Data Security, Inc., exclusive sub-licensing rights to the
following patent issued in the United States:
Cryptographic Communications System and Method ("RSA"),
No. 4,405,829
The Board of Trustees of the Leland Stanford Junior University have
granted Caro-Kann Corporation, a wholly owned subsidiary
corporation, exclusive sub-licensing rights to the following
patents issued in the United States, and all of their corresponding
foreign patents:
Cryptographic Apparatus and Method ("Diffie-Hellman"),
No. 4,200,770
Public Key Cryptographic Apparatus and Method ("Hellman-
Merkle"), No. 4,218,582
The Internet Society, Internet Architecture Board, Internet
Engineering Steering Group and the Corporation for National
Research Initiatives take no position on the validity or scope of
the patents and patent applications, nor on the appropriateness of
the terms of the assurance. The Internet Society and other groups
mentioned above have not made any determination as to any other
intellectual property rights which may apply to the practice of
this standard. Any further consideration of these matters is the
user's own responsibility.
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References
[DH1] W. Diffie and M. E. Hellman, "New Directions in
Cryptography," IEEE Transactions on Information Theory, V.
IT-22, n. 6, Jun 1977, pp. 74-84.
[3DES] W. Tuchman, "Hellman Presents No Shortcut Solutions
To DES," IEEE Spectrum, v. 16, n. 7, July 1979, pp40-41.
[DES] ANSI X3.106, "American National Standard for
Information Systems-Data Link Encryption," American National
Standards Institute, 1983.
[DSS] NIST FIPS PUB 186, "Digital Signature Standard,"
National Institute of Standards and Technology, U.S.
Department of Commerce, 18 May 1994.
[FOR] NSA X22, Document # PD4002103-1.01, "FORTEZZA:
Application Implementers Guide," April 6, 1995.
[FTP] J. Postel and J. Reynolds, RFC 959: File Transfer
Protocol, October 1985.
[HTTP] T. Berners-Lee, R. Fielding, H. Frystyk, Hypertext
Transfer Protocol -- HTTP/1.0, October, 1995.
[IDEA] X. Lai, "On the Design and Security of Block
Ciphers," ETH Series in Information Processing, v. 1,
Konstanz: Hartung-Gorre Verlag, 1992.
[KRAW] H. Krawczyk, IETF Draft: Keyed-MD5 for Message
Authentication, November 1995.
[MD2] R. Rivest. RFC 1319: The MD2 Message Digest Algorithm.
April 1992.
[MD5] R. Rivest. RFC 1321: The MD5 Message Digest Algorithm.
April 1992.
[PKCS1] RSA Laboratories, "PKCS #1: RSA Encryption
Standard," version 1.5, November 1993.
[PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate
Syntax Standard," version 1.5, November 1993.
[PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic
Message Syntax Standard," version 1.5, November 1993.
[RSA] R. Rivest, A. Shamir, and L. M. Adleman, "A Method for
Obtaining Digital Signatures and Public-Key Cryptosystems,"
Communications of the ACM, v. 21, n. 2, Feb 1978, pp. 120-
126.
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[RSADSI] Contact RSA Data Security, Inc., Tel: 415-595-8782
[SCH] B. Schneier. Applied Cryptography: Protocols,
Algorithms, and Source Code in C, Published by John Wiley &
Sons, Inc. 1994.
[SHA] NIST FIPS PUB 180-1, "Secure Hash Standard," National
Institute of Standards and Technology, U.S. Department of
Commerce, DRAFT, 31 May 1994.
[TCP] ISI for DARPA, RFC 793: Transport Control Protocol,
September 1981.
[TEL] J. Postel and J. Reynolds, RFC 854/5, May, 1993.
[X509] CCITT. Recommendation X.509: "The Directory -
Authentication Framework". 1988.
[XDR] R. Srinivansan, Sun Microsystems, RFC-1832: XDR:
External Data Representation Standard, August 1995.
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Authors
Alan O. Freier Paul C. Kocher
Netscape Communications Independent Consultant
freier@netscape.com pck@netcom.com
Philip L. Karlton
Netscape Communications
karlton@netscape.com
Other contributors
Martin Abadi Robert Relyea
Digital Equipment Corporation Netscape Communications
ma@pa.dec.com relyea@netscape.com
Taher Elgamal Jim Roskind
Netscape Communications Netscape Communications
elgamal@netscape.com jar@netscape.com
Anil Gangolli Micheal J. Sabin, Ph. D.
Netscape Communications Consulting Engineer
gangolli@netscape.com msabin@netcom.com
Kipp E.B. Hickman Tom Weinstein
Netscape Communications Netscape Communications
kipp@netscape.com tomw@netscape.com
Early reviewers
Robert Baldwin Clyde Monma
RSA Data Security, Inc. Bellcore
baldwin@rsa.com clyde@bellcore.com
George Cox Eric Murray
Intel Corporation ericm@lne.com
cox@ibeam.jf.intel.com
Cheri Dowell Avi Rubin
Sun Microsystems Bellcore
cheri@eng.sun.com rubin@bellcore.com
Stuart Haber Don Stephenson
Bellcore Sun Microsystems
stuart@bellcore.com don.stephenson@eng.sun.com
Burt Kaliski Joe Tardo
RSA Data Security, Inc. General Magic
burt@rsa.com tardo@genmagic.com
Freier, Karlton, Kocher [Page 63]
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INTERNET-DRAFT SSL 3.0 November 18, 1996
Send all written communication about this document to:
Netscape Communications
466 Ellis Street
Mountain View, CA 94043-4042
Attn: Alan Freier
Freier, Karlton, Kocher [Page 63]
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