draft-ietf-tls-psk-00.txt   draft-ietf-tls-psk-01.txt 
TLS Working Group P. Eronen TLS Working Group P. Eronen
Internet-Draft Nokia Internet-Draft Nokia
Expires: November 22, 2004 H. Tschofenig Expires: February 16, 2005 H. Tschofenig
Siemens Siemens
May 24, 2004 August 18, 2004
Pre-Shared Key Ciphersuites for Transport Layer Security (TLS) Pre-Shared Key Ciphersuites for Transport Layer Security (TLS)
draft-ietf-tls-psk-00.txt draft-ietf-tls-psk-01.txt
Status of this Memo Status of this Memo
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and any of which I become aware will be disclosed, in accordance with and any of which I become aware will be disclosed, in accordance with
RFC 3668. RFC 3668.
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
This document specifies new ciphersuites for the Transport Layer This document specifies three sets of new ciphersuites for the
Security (TLS) protocol to support authentication based on pre-shared Transport Layer Security (TLS) protocol to support authentication
keys. These pre-shared keys are symmetric keys, shared in advance based on pre-shared keys. These pre-shared keys are symmetric keys,
among the communicating parties, and do not require any public key shared in advance among the communicating parties. The first set of
operations. ciphersuites uses only symmetric key operations for authentication.
The second set uses a Diffie-Hellman exchange authenticated with a
pre-shared key; and the third set combines public key authentication
of the server with pre-shared key authentication of the client.
1. Introduction 1. Introduction
Usually TLS uses public key certificates [TLS] or Kerberos [TLS-KRB] Usually TLS uses public key certificates [3] or Kerberos [11] for
for authentication. This document describes how to use symmetric authentication. This document describes how to use symmetric keys
keys (later called pre-shared keys or PSKs), shared in advance among (later called pre-shared keys or PSKs), shared in advance among the
the communicating parties, to establish a TLS connection. communicating parties, to establish a TLS connection.
There are basically two reasons why one might want to do this: There are basically two reasons why one might want to do this:
o First, TLS may be used in performance-constrained environments o First, TLS may be used in performance-constrained environments
where the CPU power needed for public key operations is not where the CPU power needed for public key operations is not
available. available.
o Second, pre-shared keys may be more convenient from a key o Second, pre-shared keys may be more convenient from a key
management point of view. For instance, in closed environments management point of view. For instance, in closed environments
where the connections are mostly configured manually in advance, where the connections are mostly configured manually in advance,
it may be easier to configure a PSK than to use certificates. it may be easier to configure a PSK than to use certificates.
Another case is when the parties already have a mechanism for Another case is when the parties already have a mechanism for
setting up a shared secret key, and that mechanism could be used setting up a shared secret key, and that mechanism could be used
to "bootstrap" a key for authenticating a TLS connection. to "bootstrap" a key for authenticating a TLS connection.
This document specifies a number of new ciphersuites for TLS. These This document specifies three sets of new ciphersuites for TLS.
ciphersuites use a new authentication and key exchange algorithm for These ciphersuites use new key exchange algorithms, and re-use
PSKs, and re-use existing cipher and MAC algorithms from [TLS] and existing cipher and MAC algorithms from [3] and [2]. A summary of
[TLS-AES]. these ciphersuites is shown below.
CipherSuite Key Exchange Cipher Hash
TLS_PSK_WITH_RC4_128_SHA PSK RC4_128 SHA
TLS_PSK_WITH_3DES_EDE_CBC_SHA PSK 3DES_EDE_CBC SHA
TLS_PSK_WITH_AES_128_CBC_SHA PSK AES_128_CBC SHA
TLS_PSK_WITH_AES_256_CBC_SHA PSK AES_256_CBC SHA
TLS_DHE_PSK_WITH_RC4_128_SHA DHE_PSK RC4_128 SHA
TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA DHE_PSK 3DES_EDE_CBC SHA
TLS_DHE_PSK_WITH_AES_128_CBC_SHA DHE_PSK AES_128_CBC SHA
TLS_DHE_PSK_WITH_AES_256_CBC_SHA DHE_PSK AES_256_CBC SHA
TLS_RSA_PSK_WITH_RC4_128_SHA RSA_PSK RC4_128 SHA
TLS_RSA_PSK_WITH_3DES_EDE_CBC_SHA RSA_PSK 3DES_EDE_CBC SHA
TLS_RSA_PSK_WITH_AES_128_CBC_SHA RSA_PSK AES_128_CBC SHA
TLS_RSA_PSK_WITH_AES_256_CBC_SHA RSA_PSK AES_256_CBC SHA
The first set of ciphersuites (with PSK key exchange algorithm),
defined in Section 2 use only symmetric key algorithms, and are thus
especially suitable for performance-constrained environments.
The ciphersuites in Section 3 (with DHE_PSK key exchange algorithm)
use a PSK to authenticate a Diffie-Hellman exchange. These
ciphersuites give some additional protection against dictionary
attacks, and also provide Perfect Forward Secrecy (PFS).
The third set of ciphersuites (with RSA_PSK key exchange algorithm),
defined in Section 4, combine public key based authentication of the
server (using RSA and certificates) with mutual authentication using
a PSK.
1.1 Applicability statement 1.1 Applicability statement
The ciphersuites defined in this document are intended for a rather The ciphersuites defined in this document are intended for a rather
limited set of applications, usually involving only a very small limited set of applications, usually involving only a very small
number of clients and servers. Even in such environments, other number of clients and servers. Even in such environments, other
alternatives may be more appropriate. alternatives may be more appropriate.
If the main goal is to avoid PKIs, another possibility worth If the main goal is to avoid PKIs, another possibility worth
considering is to use self-signed certificates with public key considering is to use self-signed certificates with public key
fingerprints. Instead of manually configuring a shared secret in, fingerprints. Instead of manually configuring a shared secret in,
for instance, some configuration file, a fingerprint (hash) of the for instance, some configuration file, a fingerprint (hash) of the
other party's public key (or certificate) could be placed there other party's public key (or certificate) could be placed there
instead. instead.
It is also possible to use the SRP (Secure Remote Password) It is also possible to use the SRP (Secure Remote Password)
ciphersuites for shared secret authentication [TLS-SRP]. While SRP ciphersuites for shared secret authentication [13]. SRP was designed
protects against dictionary attacks, it requires more computational to be used with passwords, and incorporates protection against
resources. dictionary attacks. However, it is computationally more expensive
than the PSK ciphersuites in Section 2.
1.2 Conventions used in this document 1.2 Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS]. document are to be interpreted as described in [1].
2. Protocol 2. PSK key exchange algorithm
This section defines the PSK key exchange algorithm and associated
ciphersuites. These ciphersuites use only symmetric key algorithms.
It is assumed that the reader is familiar with ordinary TLS It is assumed that the reader is familiar with ordinary TLS
handshake, shown below. The elements in parenthesis are not included handshake, shown below. The elements in parenthesis are not included
in PSK-based ciphersuites. when PSK key exchange algorithm is used.
Client Server Client Server
------ ------ ------ ------
ClientHello --------> ClientHello -------->
ServerHello ServerHello
(Certificate) (Certificate)
ServerKeyExchange ServerKeyExchange
(CertificateRequest) (CertificateRequest)
<-------- ServerHelloDone <-------- ServerHelloDone
(Certificate) (Certificate)
ClientKeyExchange ClientKeyExchange
(CertificateVerify) (CertificateVerify)
ChangeCipherSpec ChangeCipherSpec
Finished --------> Finished -------->
ChangeCipherSpec ChangeCipherSpec
<-------- Finished <-------- Finished
Application Data <-------> Application Data Application Data <-------> Application Data
The client indicates its willingness to use pre-shared key The client indicates its willingness to use pre-shared key
authentication by including one or more PSK-based ciphersuites in the authentication by including one or more PSK ciphersuites in the
ClientHello message. The following ciphersuites are defined in this ClientHello message. If the TLS server also wants to use pre-shared
document: keys, it selects one of the PSK ciphersuites, places the selected
ciphersuite in the ServerHello message, and includes an appropriate
CipherSuite TLS_PSK_WITH_RC4_128_SHA = { 0x00, 0xTBD }; ServerKeyExchange message (see below). The Certificate and
CipherSuite TLS_PSK_WITH_3DES_EDE_CBC_SHA = { 0x00, 0xTBD }; CertificateRequest payloads are omitted from the response.
CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA = { 0x00, 0xTBD };
CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA = { 0x00, 0xTBD };
Note that this document defines only a new authentication and key
exchange algorithm; see [TLS] and [TLS-AES] for description of the
cipher and MAC algorithms.
If the TLS server also wants to use pre-shared keys, it selects one
of the PSK ciphersuites, places the selected ciphersuite in the
ServerHello message, and includes an appropriate ServerKeyExchange
message (see below). The Certificate and CertificateRequest payloads
are omitted from the response.
Both clients and servers may have pre-shared keys with several Both clients and servers may have pre-shared keys with several
different parties. The client indicates which key to use by different parties. The client indicates which key to use by
including a "PSK identity" in the ClientKeyExchange message (note including a "PSK identity" in the ClientKeyExchange message (note
that unlike in [TLS-SHAREDKEYS], the session_id field in ClientHello that unlike in [6], the session_id field in ClientHello message keeps
message keeps its usual meaning). To help the client in selecting its usual meaning). To help the client in selecting which identity
which identity to use, the server can provide a "PSK identity hint" to use, the server can provide a "PSK identity hint" in the
in the ServerKeyExchange message (note that if no hint is provided, a ServerKeyExchange message (note that if no hint is provided, a
ServerKeyExchange message is still sent). ServerKeyExchange message is still sent).
This document does not specify the format of the PSK identity or PSK This document does not specify the format of the PSK identity or PSK
identity hint; neither is specified how exactly the client uses the identity hint; neither is specified how exactly the client uses the
hint (if it uses it at all). The parties have to agree on the hint (if it uses it at all). The parties have to agree on the
identities when the shared secret is configured (however, see Section identities when the shared secret is configured (however, see Section
4 for related security considerations). In situations where the 6 for related security considerations). In situations where the
identity is entered by a person, it is RECOMMENDED that the input is identity is entered by a person, it is RECOMMENDED that the input is
processed using an appropriate stringprep [STRINGPREP] profile and processed using an appropriate stringprep [9] profile and encoded in
encoded in octets using UTF-8 encoding [UTF8]. One possible octets using UTF-8 encoding [14]. One possible stringprep profile is
stringprep profile is described in [SASLPREP]. described in [8].
The format of the ServerKeyExchange and ClientKeyExchange messages is The format of the ServerKeyExchange and ClientKeyExchange messages is
shown below. shown below.
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case diffie_hellman: /* other cases for rsa, diffie_hellman, etc. */
ServerDHParams params;
Signature signed_params;
case rsa:
ServerRSAParams params;
Signature signed_params;
case psk: /* NEW */ case psk: /* NEW */
opaque psk_identity_hint<0..2^16-1>; opaque psk_identity_hint<0..2^16-1>;
}; };
} ServerKeyExchange; } ServerKeyExchange;
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case rsa: EncryptedPreMasterSecret; /* other cases for rsa, diffie_hellman, etc. */
case diffie_hellman: ClientDiffieHellmanPublic; case psk: /* NEW */
case psk: opaque psk_identity<0..2^16-1>; /* NEW */ opaque psk_identity<0..2^16-1>;
} exchange_keys; } exchange_keys;
} ClientKeyExchange; } ClientKeyExchange;
The premaster secret is formed as follows: concatenate 24 zero The premaster secret is formed as follows: If the PSK is N octets
octets, followed by SHA-1 hash [FIPS180-2] of the PSK itself, long, concatenate N zero octets and the PSK.
followed by 4 zero octets.
Note: This effectively means that only the HMAC-SHA1 part of the Note: This effectively means that only the HMAC-SHA1 part of the
TLS PRF is used, and the HMAC-MD5 part is not used. See TLS PRF is used, and the HMAC-MD5 part is not used. See [7] for a
[Krawczyk20040113] for a more detailed rationale. The PSK is more detailed rationale.
first hashed so that PSKs longer than 24 octets can be used; this
is similar to what is done in [HMAC] if the key length is longer
than the hash block size.
If the server does not recognize the PSK identity, it SHOULD respond The TLS handshake is authenticated using the Finished messages as
with a decrypt_error alert message. This alert is also sent if usual.
validating the Finished message fails. The use of the same alert
message makes it more difficult to find out which PSK identities are
known to the server.
3. IANA considerations If the server does not recognize the PSK identity, it MAY respond
with an "unknown_psk_identity" alert message. Alternatively, if the
server wishes to hide the fact that the PSK identity was not known,
it MAY continue the protocol as if the PSK identity existed but the
key was incorrect: that is, respond with a "decrypt_error" alert.
This document does not define any new namespaces to be managed by 3. DHE_PSK key exchange algorithm
IANA. It does require assignment of several new ciphersuite numbers,
but it is unclear how this is done, since the TLS spec does not say
who is responsible for assigning them :-)
4. Security Considerations This section defines additional ciphersuites that use a PSK to
authenticate a Diffie-Hellman exchange. These ciphersuites give some
additional protection against dictionary attacks, and also provide
Perfect Forward Secrecy (PFS). See Section 6 for discussion of
related security considerations.
When these ciphersuites are used, the ServerKeyExchange and
ClientKeyExchange also include the Diffie-Hellman parameters. The
PSK identity and identity hint fields have the same meaning as in the
previous section.
The format of the ServerKeyExchange and ClientKeyExchange messages is
shown below.
struct {
select (KeyExchangeAlgorithm) {
/* other cases for rsa, diffie_hellman, etc. */
case diffie_hellman_psk: /* NEW */
opaque psk_identity_hint<0..2^16-1>;
ServerDHParams params;
};
} ServerKeyExchange;
struct {
select (KeyExchangeAlgorithm) {
/* other cases for rsa, diffie_hellman, etc. */
case diffie_hellman_psk: /* NEW */
opaque psk_identity<0..2^16-1>;
ClientDiffieHellmanPublic public;
} exchange_keys;
} ClientKeyExchange;
The premaster secret is formed as follows: concatenate the value
produced by the Diffie-Hellman exchange (with leading zero bytes
stripped as in other Diffie-Hellman based ciphersuites) and the PSK,
in this order.
4. RSA_PSK key exchange algorithm
The ciphersuites in this section use RSA and certificates to
authenticate the server, in addition to using a PSK.
As in normal RSA ciphersuites, the server must send a Certificate
message. The format of the ServerKeyExchange and ClientKeyExchange
messages is shown below.
struct {
select (KeyExchangeAlgorithm) {
/* other cases for rsa, diffie_hellman, etc. */
case rsa_psk: /* NEW */
opaque psk_identity_hint<0..2^16-1>;
};
} ServerKeyExchange;
struct {
select (KeyExchangeAlgorithm) {
/* other cases for rsa, diffie_hellman, etc. */
case rsa_psk: /* NEW */
opaque psk_identity<0..2^16-1>;
EncryptedPreMasterSecret;
} exchange_keys;
} ClientKeyExchange;
The premaster secret is formed as follows: concatenate the 48-byte
value generated by the client (and sent to the server in
ClientKeyExchange message) and the PSK, in this order.
5. IANA considerations
(This depends on whether this document is published before or after
TLS 1.1.)
(If after 1.1) This document does not create any new namespaces to be
maintained by IANA, but it requires new values in the ciphersuite
namespace defined in TLS 1.1 specification.
(If before 1.1) There are no IANA actions associated with this
document. For easier reference in the future, the ciphersuite
numbers defined in this document are summarized below.
CipherSuite TLS_PSK_WITH_RC4_128_SHA = { 0x00, 0xTBD };
CipherSuite TLS_PSK_WITH_3DES_EDE_CBC_SHA = { 0x00, 0xTBD };
CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA = { 0x00, 0xTBD };
CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA = { 0x00, 0xTBD };
CipherSuite TLS_DHE_PSK_WITH_RC4_128_SHA = { 0x00, 0xTBD };
CipherSuite TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA = { 0x00, 0xTBD };
CipherSuite TLS_DHE_PSK_WITH_AES_128_CBC_SHA = { 0x00, 0xTBD };
CipherSuite TLS_DHE_PSK_WITH_AES_256_CBC_SHA = { 0x00, 0xTBD };
CipherSuite TLS_RSA_PSK_WITH_RC4_128_SHA = { 0x00, 0xTBD };
CipherSuite TLS_RSA_PSK_WITH_3DES_EDE_CBC_SHA = { 0x00, 0xTBD };
CipherSuite TLS_RSA_PSK_WITH_AES_128_CBC_SHA = { 0x00, 0xTBD };
CipherSuite TLS_RSA_PSK_WITH_AES_256_CBC_SHA = { 0x00, 0xTBD };
This document also defines a new TLS alert message,
unknown_psk_identity(TBD). Since IANA does not maintain a registry
of TLS alert messages, no IANA action is needed for this.
6. Security Considerations
As with all schemes involving shared keys, special care should be As with all schemes involving shared keys, special care should be
taken to protect the shared values and to limit their exposure over taken to protect the shared values and to limit their exposure over
time. time.
The ciphersuites defined in this document do not provide Perfect 6.1 Perfect forward secrecy (PFS)
Forward Secrecy (PFS). That is, if the shared secret key is somehow
compromised, an attacker can decrypt old conversations. (Note that The PSK and RSA_PSK ciphersuites defined in this document do not
the most popular TLS key exchange algorithm, RSA, does not provide provide Perfect Forward Secrecy (PFS). That is, if the shared secret
PFS either.) key (in PSK ciphersuites), or both the shared secret key and the RSA
private key (in RSA_PSK ciphersuites), is somehow compromised, an
attacker can decrypt old conversations.
The DHE_PSK ciphersuites provide Perfect Forward Secrecy if a fresh
DH private key is generated for each handshake.
6.2 Brute-force and dictionary attacks
Use of a fixed shared secret of limited entropy (such as a password) Use of a fixed shared secret of limited entropy (such as a password)
allows an attacker to perform a brute-force or dictionary attack to may allow an attacker to perform a brute-force or dictionary attack
recover the secret. This may be either an off-line attack (against a to recover the secret. This may be either an off-line attack
captured TLS conversation), or an on-line attack where the attacker (against a captured TLS handshake messages), or an on-line attack
attempts to connect to the server and tries different keys. An where the attacker attempts to connect to the server and tries
attacker can also get the information required for an off-line attack different keys.
if a valid client attempts to connect with the attacker. It is
RECOMMENDED that implementations that allow the administrator to For the PSK ciphersuites, an attacker can get the information
manually configure the PSK also provide a functionality for required for an off-line attack by eavesdropping a TLS handshake, or
generating a new random PSK, taking [RANDOMNESS] into account. by getting a valid client to attempt connection with the attacker (by
tricking the client to connect to wrong address, or intercepting a
connection attempt to the correct address, for instance).
For the DHE_PSK ciphersuites, an attacker can obtain the information
by getting a valid client to attempt connection with the attacker.
Passive eavesdropping alone is not sufficient.
For the RSA_PSK ciphersuites, only the server (authenticated using
RSA and certificates) can obtain sufficient information for an
off-line attack.
It is RECOMMENDED that implementations that allow the administrator
to manually configure the PSK also provide a functionality for
generating a new random PSK, taking [4] into account.
6.3 Identity privacy
The PSK identity is sent in cleartext. While using a user name or The PSK identity is sent in cleartext. While using a user name or
other similar string as the PSK identity is the most straightforward other similar string as the PSK identity is the most straightforward
option, it may lead to problems in some environments since an option, it may lead to problems in some environments since an
eavesdropper is able to identify the communicating parties. Even eavesdropper is able to identify the communicating parties. Even
when the identity does not reveal any information itself, reusing the when the identity does not reveal any information itself, reusing the
same identity over time may eventually allow an attacker to perform same identity over time may eventually allow an attacker to perform
traffic analysis to the identify parties. It should be noted that traffic analysis to identify the parties. It should be noted that
this is no worse than client certificates, since they are also sent this is no worse than client certificates, since they are also sent
in cleartext. in cleartext.
5. Acknowledgments 6.4 Implementation notes
The implementation notes in [10] about correct implementation and use
of RSA (including Section 7.4.7.1) and Diffie-Hellman (including
Appendix F.1.1.3) apply to the DHE_PSK and RSA_PSK ciphersuites as
well.
7. Acknowledgments
The protocol defined in this document is heavily based on work by Tim The protocol defined in this document is heavily based on work by Tim
Dierks and Peter Gutmann, and borrows some text from [TLS-SHAREDKEYS] Dierks and Peter Gutmann, and borrows some text from [6] and [2].
and [TLS-AES]. Valuable feedback was also provided by Philip Valuable feedback was also provided by Philip Ginzboorg, Peter
Ginzboorg, Peter Gutmann, David Jablon, Nikos Mavroyanopoulos, Bodo Gutmann, David Jablon, Nikos Mavroyanopoulos, Bodo Moeller, and Mika
Moeller, and Mika Tervonen. Tervonen.
When the first version of this draft was almost ready, the authors When the first version of this draft was almost ready, the authors
learned that something similar had been proposed already in 1996 learned that something similar had been proposed already in 1996
[TLS-PASSAUTH]. However, this draft is not intended for web password [12]. However, this draft is not intended for web password
authentication, but rather for other uses of TLS. authentication, but rather for other uses of TLS.
6. References The DHE_PSK and RSA_PSK ciphersuites borrow heavily from [5].
6.1 Normative References 8. Open issues
[KEYWORDS] o Identity privacy could be provided (in DHE_PSK/RSA_PSK versions)
Bradner, S., "Key words for use in RFCs to Indicate by encrypting the psk_identity payload with keys derived from the
Requirement Levels", RFC 2119, March 1997. DH value/RSA-encrypted random (but not PSK). But perhaps this
would be an unnecessary complication.
[TLS-AES] Chown, P., "Advanced Encryption Standard (AES) o The way the PSK is combined with DH value (and is then used to
Ciphersuites for Transport Layer Security (TLS)", RFC calculate the Finished message) is not exactly the traditional
3268, June 2002. way. It should be OK with TLS-PRF, though.
[TLS] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", 9. References
RFC 2246, January 1999.
[RANDOMNESS] 9.1 Normative References
Eastlake, D., Crocker, S. and J. Schiller, "Randomness
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[2] Chown, P., "Advanced Encryption Standard (AES) Ciphersuites for
Transport Layer Security (TLS)", RFC 3268, June 2002.
[3] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
2246, January 1999.
[4] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994. Recommendations for Security", RFC 1750, December 1994.
[FIPS180-2] 9.2 Informative References
National Institute of Standards and Technology,
"Specifications for the Secure Hash Standard", Federal
Information Processing Standard (FIPS) Publication 180-2,
August 2002.
6.2 Informative References [5] Badra, M., Cherkaoui, O., Hajjeh, I. and A. Serhrouchni,
"Pre-Shared-Key key Exchange methods for TLS",
draft-badra-tls-key-exchange-00 (work in progress), August
2004.
[TLS-SHAREDKEYS] [6] Gutmann, P., "Use of Shared Keys in the TLS Protocol",
Gutmann, P., "Use of Shared Keys in the TLS Protocol",
draft-ietf-tls-sharedkeys-02 (expired), October 2003. draft-ietf-tls-sharedkeys-02 (expired), October 2003.
[HMAC] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: [7] Krawczyk, H., "Re: TLS shared keys PRF", message on
Keyed-Hashing for Message Authentication", RFC 2104,
February 1997.
[Krawczyk20040113]
Krawczyk, H., "Re: TLS shared keys PRF", message on
ietf-tls@lists.certicom.com mailing list 2004-01-13, ietf-tls@lists.certicom.com mailing list 2004-01-13,
http://www.imc.org/ietf-tls/mail-archive/msg04098.html. http://www.imc.org/ietf-tls/mail-archive/msg04098.html.
[SASLPREP] [8] Zeilenga, K., "SASLprep: Stringprep profile for user names and
Zeilenga, K., "SASLprep: Stringprep profile for user names passwords", draft-ietf-sasl-saslprep-10 (work in progress),
and passwords", draft-ietf-sasl-saslprep-09 (work in July 2004.
progress), April 2004.
[STRINGPREP] [9] Hoffman, P. and M. Blanchet, "Preparation of Internationalized
Hoffman, P. and M. Blanchet, "Preparation of Strings ("stringprep")", RFC 3454, December 2002.
Internationalized Strings ("stringprep")", RFC 3454,
December 2002.
[TLS-KRB] Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher [10] Dierks, T. and E. Rescorla, "The TLS Protocol Version 1.1",
Suites to Transport Layer Security (TLS)", RFC 2712, draft-ietf-tls-rfc2246-bis-08 (work in progress), August 2004.
October 1999.
[TLS-PASSAUTH] [11] Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher Suites
Simon, D., "Addition of Shared Key Authentication to to Transport Layer Security (TLS)", RFC 2712, October 1999.
Transport Layer Security (TLS)",
draft-ietf-tls-passauth-00 (expired), November 1996.
[TLS-SRP] Taylor, D., Wu, T., Mavroyanopoulos, N. and T. Perrin, [12] Simon, D., "Addition of Shared Key Authentication to Transport
"Using SRP for TLS Authentication", draft-ietf-tls-srp-06 Layer Security (TLS)", draft-ietf-tls-passauth-00 (expired),
(work in progress), January 2004. November 1996.
[UTF8] Yergeau, F., "UTF-8, a transformation format of ISO [13] Taylor, D., Wu, T., Mavroyanopoulos, N. and T. Perrin, "Using
10646", RFC 3629, November 2003. SRP for TLS Authentication", draft-ietf-tls-srp-07 (work in
progress), June 2004.
[14] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
3629, November 2003.
Authors' Addresses Authors' Addresses
Pasi Eronen Pasi Eronen
Nokia Research Center Nokia Research Center
P.O. Box 407 P.O. Box 407
FIN-00045 Nokia Group FIN-00045 Nokia Group
Finland Finland
EMail: pasi.eronen@nokia.com EMail: pasi.eronen@nokia.com
skipping to change at page 8, line 16 skipping to change at page 11, line 32
Otto-Hahn-Ring 6 Otto-Hahn-Ring 6
Munich, Bayern 81739 Munich, Bayern 81739
Germany Germany
EMail: Hannes.Tschofenig@siemens.com EMail: Hannes.Tschofenig@siemens.com
Appendix A. Changelog Appendix A. Changelog
(This section should be removed by the RFC Editor before (This section should be removed by the RFC Editor before
publication.) publication.)
Changes from draft-ietf-tls-psk-00 to -01:
o Added DHE_PSK and RSA_PSK key exchange algorithms, and updated
other text accordingly
o Removed SHA-1 hash from PSK key exchange premaster secret
construction (since premaster secret doesn't need to be 48 bytes).
o Added unknown_psk_identity alert message.
o Updated IANA considerations section.
Changes from draft-eronen-tls-psk-00 to draft-ietf-tls-psk-00: Changes from draft-eronen-tls-psk-00 to draft-ietf-tls-psk-00:
o Updated dictionary attack considerations based on comments from o Updated dictionary attack considerations based on comments from
David Jablon. David Jablon.
o Added a recommendation about using UTF-8 in the identity field. o Added a recommendation about using UTF-8 in the identity field.
o Removed Appendix A comparing this document with o Removed Appendix A comparing this document with
draft-ietf-tls-sharedkeys-02. draft-ietf-tls-sharedkeys-02.
 End of changes. 

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