draft-ietf-tls-ciphersuite-02.txt   draft-ietf-tls-ciphersuite-03.txt 
Network Working Group Pete Chown Network Working Group Pete Chown
INTERNET DRAFT Skygate Technology INTERNET DRAFT Skygate Technology
<draft-ietf-tls-ciphersuite-02.txt> 15 November 2000 <draft-ietf-tls-ciphersuite-03.txt> 22 January 2001
AES Ciphersuites for TLS AES Ciphersuites for TLS
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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claims. RSA Security Inc has trademark rights in the names RC2 claims. RSA Security Inc has trademark rights in the names RC2
and RC4, and claims that the RC4 algorithm itself is a trade and RC4, and claims that the RC4 algorithm itself is a trade
secret. Ascom Systec Ltd owns a patent on the IDEA algorithm. secret. Ascom Systec Ltd owns a patent on the IDEA algorithm.
2. Triple DES is much less efficient than more modern ciphers. 2. Triple DES is much less efficient than more modern ciphers.
3. Now the AES process is completed there will be commercial pres¡ 3. Now the AES process is completed there will be commercial pres¡
sure to use the selected cipher. The AES is efficient and has sure to use the selected cipher. The AES is efficient and has
withstood extensive cryptanalytic efforts. The AES is withstood extensive cryptanalytic efforts. The AES is
ietf-tls-ciphersuite-02 AES Ciphersuites for TLS 15 November 2000 ietf-tls-ciphersuite-03 AES Ciphersuites for TLS 22 January 2001
therefore a desirable choice. therefore a desirable choice.
4. Currently the DHE ciphersuites only allow triple DES (along 4. Currently the DHE ciphersuites only allow triple DES (along
with some ``export'' variants which offer reduced key lengths). with some ``export'' variants which do not use a satisfactory
At the same time the DHE ciphersuites are the only ones to key length). At the same time the DHE ciphersuites are the
offer forward secrecy. only ones to offer forward secrecy.
This document proposes several new ciphersuites, with the aim of This document proposes several new ciphersuites, with the aim of
overcoming these problems. overcoming these problems.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119.
Cipher Usage Cipher Usage
The new ciphersuites proposed here are very similar to the follow¡ The new ciphersuites proposed here are very similar to the follow¡
ing, defined in [TLS]: ing, defined in [TLS]:
TLS_RSA_WITH_3DES_EDE_CBC_SHA TLS_RSA_WITH_3DES_EDE_CBC_SHA
TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA
TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA
TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA
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All the ciphersuites described here use the AES in cipher block All the ciphersuites described here use the AES in cipher block
chaining (CBC) mode. Furthermore, they use SHA-1 [SHA-1] in an chaining (CBC) mode. Furthermore, they use SHA-1 [SHA-1] in an
HMAC construction as described in section 5 of [TLS]. (Although HMAC construction as described in section 5 of [TLS]. (Although
the TLS ciphersuite names include the text ``SHA'', this actually the TLS ciphersuite names include the text ``SHA'', this actually
refers to the modified SHA-1 version of the algorithm.) refers to the modified SHA-1 version of the algorithm.)
The ciphersuites differ in the type of certificate and key exchange The ciphersuites differ in the type of certificate and key exchange
method. The ciphersuites defined here use the following options method. The ciphersuites defined here use the following options
for this part of the protocol: for this part of the protocol:
ietf-tls-ciphersuite-03 AES Ciphersuites for TLS 22 January 2001
CipherSuite Certificate type (if applicable) CipherSuite Certificate type (if applicable)
and key exchange algorithm and key exchange algorithm
TLS_RSA_WITH_AES_128_CBC_SHA RSA TLS_RSA_WITH_AES_128_CBC_SHA RSA
TLS_DH_DSS_WITH_AES_128_CBC_SHA DH_DSS TLS_DH_DSS_WITH_AES_128_CBC_SHA DH_DSS
TLS_DH_RSA_WITH_AES_128_CBC_SHA DH_RSA TLS_DH_RSA_WITH_AES_128_CBC_SHA DH_RSA
TLS_DHE_DSS_WITH_AES_128_CBC_SHA DHE_DSS TLS_DHE_DSS_WITH_AES_128_CBC_SHA DHE_DSS
TLS_DHE_RSA_WITH_AES_128_CBC_SHA DHE_RSA TLS_DHE_RSA_WITH_AES_128_CBC_SHA DHE_RSA
TLS_DH_anon_WITH_AES_128_CBC_SHA DH_anon TLS_DH_anon_WITH_AES_128_CBC_SHA DH_anon
TLS_RSA_WITH_AES_256_CBC_SHA RSA
TLS_DH_DSS_WITH_AES_256_CBC_SHA DH_DSS
TLS_DH_RSA_WITH_AES_256_CBC_SHA DH_RSA
TLS_DHE_DSS_WITH_AES_256_CBC_SHA DHE_DSS
TLS_DHE_RSA_WITH_AES_256_CBC_SHA DHE_RSA
TLS_DH_anon_WITH_AES_256_CBC_SHA DH_anon
For the meanings of the terms RSA, DH_DSS, DH_RSA, DHE_DSS, DHE_RSA For the meanings of the terms RSA, DH_DSS, DH_RSA, DHE_DSS, DHE_RSA
and DH_anon, please refer to sections 7.4.2 and 7.4.3 of [TLS]. and DH_anon, please refer to sections 7.4.2 and 7.4.3 of [TLS].
ietf-tls-ciphersuite-02 AES Ciphersuites for TLS 15 November 2000 The AES supports key lengths of 128, 192 and 256 bits. However,
this document only defines ciphersuites for 128- and 256-bit keys.
The AES supports key lengths of 128, 192 and 256 bits. At the pre¡ This is to avoid unnecessary proliferation of ciphersuites. Rijn¡
sent time, all of these are believed to be secure against even the dael actually allows for 192- and 256-bit block sizes as well as
best equipped attackers. The overall strength of TLS is such that the 128-bit blocks mandated by the AES process. The ciphersuites
there is no gain from using a key length longer than 128 bits. defined here all use 128-bit blocks.
Accordingly the AES will use 128 bit keys.
The new ciphersuites will have the following definitions: The new ciphersuites will have the following definitions:
CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x2F }; CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x2F };
CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x30 }; CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x30 };
CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x31 }; CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x31 };
CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x32 }; CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x32 };
CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x33 }; CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x33 };
CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA = { 0x00, 0x34 }; CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA = { 0x00, 0x34 };
In the absence of an application profile standard specifying other¡ CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x35 };
wise: CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA = { 0x00, 0x36 };
CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x37 };
1. Servers MUST provide at least one of CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA = { 0x00, 0x38 };
TLS_RSA_WITH_AES_128_CBC_SHA and CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x39 };
TLS_DHE_RSA_WITH_AES_128_CBC_SHA. CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA = { 0x00, 0x3A };
2. Clients MUST provide both TLS_RSA_WITH_AES_128_CBC_SHA and
TLS_DHE_RSA_WITH_AES_128_CBC_SHA.
(A TLS implementation which does not follow this requirement is
non-compliant with this RFC. However, it will still be a valid TLS
implementation if it complies with [TLS].)
Implementations MAY provide any of the other ciphersuites described
above.
Security Considerations Security Considerations
It is not believed that the new ciphersuites are ever less secure It is not believed that the new ciphersuites are ever less secure
than the corresponding older ones. The AES is believed to be than the corresponding older ones. The AES is believed to be
ietf-tls-ciphersuite-03 AES Ciphersuites for TLS 22 January 2001
secure, and it has withstood extensive cryptanalytic attack. secure, and it has withstood extensive cryptanalytic attack.
The ephemeral Diffie-Hellman ciphersuites provide forward secrecy The ephemeral Diffie-Hellman ciphersuites provide forward secrecy
without any known reduction in security in other areas. To obtain without any known reduction in security in other areas. To obtain
the maximum benefit from these ciphersuites: the maximum benefit from these ciphersuites:
1. The ephemeral keys should only be used once. With the TLS pro¡ 1. The ephemeral keys should only be used once. With the TLS pro¡
tocol as currently defined there is no efficiency gain from tocol as currently defined there is no significant efficiency
reusing ephemeral keys. gain from reusing ephemeral keys.
2. Ephemeral keys should be destroyed securely when they are no 2. Ephemeral keys should be destroyed securely when they are no
longer required. longer required.
ietf-tls-ciphersuite-02 AES Ciphersuites for TLS 15 November 2000
3. The random number generator used to create ephemeral keys must 3. The random number generator used to create ephemeral keys must
not reveal past output even when its internal state is compro¡ not reveal past output even when its internal state is compro¡
mised. mised.
[TLS] describes the anonymous Diffie-Hellman (ADH) ciphersuites as [TLS] describes the anonymous Diffie-Hellman (ADH) ciphersuites as
deprecated. The ADH ciphersuite defined here is not deprecated. deprecated. The ADH ciphersuites defined here are not deprecated.
However, when it is used, particular care must be taken: However, when they are used, particular care must be taken:
1. ADH provides confidentiality but not authentication. This 1. ADH provides confidentiality but not authentication. This
means that (if authentication is required) the communicating means that (if authentication is required) the communicating
parties must authenticate to each other by some means other parties must authenticate to each other by some means other
than TLS. than TLS.
2. ADH is vulnerable to man-in-the-middle attacks, as a conse¡ 2. ADH is vulnerable to man-in-the-middle attacks, as a conse¡
quence of the lack of authentication. The parties must have a quence of the lack of authentication. The parties must have a
way of determining whether they are participating in the same way of determining whether they are participating in the same
TLS connection. If they are not, they can deduce that they are TLS connection. If they are not, they can deduce that they are
under attack, and presumably abort the connection. under attack, and presumably abort the connection.
For example, if the parties share a secret, it is possible to For example, if the parties share a secret, it is possible to
compute a MAC of the TLS Finished message. An attacker would compute a MAC of the TLS Finished message. An attacker would
have to negotiate two different TLS connections; one with each have to negotiate two different TLS connections; one with each
communicating party. The Finished messages would be different communicating party. The Finished messages would be different
in each case, because they depend on the master secret. For in each case, because they depend on the parties' public keys
this reason, the MACs computed by each party would be differ¡ (among other things). For this reason, the MACs computed by
ent. each party would be different.
It is important to note that authentication techniques which do It is important to note that authentication techniques which do
not use the Finished message do not usually provide protection not use the Finished message do not usually provide protection
from this attack. For example, the client could authenticate from this attack. For example, the client could authenticate
to the server with a password, but it would still be vulnerable to the server with a password, but it would still be vulnerable
to man-in-the-middle attacks. to man-in-the-middle attacks.
Copyright Copyright
Copyright (C) The Internet Society 2000. All Rights Reserved. ietf-tls-ciphersuite-03 AES Ciphersuites for TLS 22 January 2001
Copyright (C) The Internet Society 2001. All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain others, and derivative works that comment on or otherwise explain
it or assist in its implementation may be prepared, copied, pub¡ it or assist in its implementation may be prepared, copied, pub¡
lished and distributed, in whole or in part, without restriction of lished and distributed, in whole or in part, without restriction of
any kind, provided that the above copyright notice and this para¡ any kind, provided that the above copyright notice and this para¡
graph are included on all such copies and derivative works. How¡ graph are included on all such copies and derivative works. How¡
ever, this document itself may not be modified in any way, such as ever, this document itself may not be modified in any way, such as
by removing the copyright notice or references to the Internet by removing the copyright notice or references to the Internet
Society or other Internet organizations, except as needed for the Society or other Internet organizations, except as needed for the
purpose of developing Internet standards in which case the proce¡ purpose of developing Internet standards in which case the proce¡
dures for copyrights defined in the Internet Standards process must dures for copyrights defined in the Internet Standards process must
ietf-tls-ciphersuite-02 AES Ciphersuites for TLS 15 November 2000
be followed, or as required to translate it into languages other be followed, or as required to translate it into languages other
than English. than English.
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees. revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on This document and the information contained herein is provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGI¡ an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGI¡
NEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, NEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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to obtain a general license or permission for the use of such pro¡ to obtain a general license or permission for the use of such pro¡
prietary rights by implementors or users of this specification can prietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat. be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive this standard. Please address the information to the IETF Executive
Director. Director.
ietf-tls-ciphersuite-03 AES Ciphersuites for TLS 22 January 2001
During the development of the AES, NIST published the following During the development of the AES, NIST published the following
statement on intellectual property: statement on intellectual property:
SPECIAL NOTE - Intellectual Property SPECIAL NOTE - Intellectual Property
NIST reminds all interested parties that the adoption of NIST reminds all interested parties that the adoption of
AES is being conducted as an open standards-setting AES is being conducted as an open standards-setting
activity. Specifically, NIST has requested that all activity. Specifically, NIST has requested that all
interested parties identify to NIST any patents or inven¡ interested parties identify to NIST any patents or inven¡
tions that may be required for the use of AES. NIST tions that may be required for the use of AES. NIST
hereby gives public notice that it may seek redress under hereby gives public notice that it may seek redress under
the antitrust laws of the United States against any party the antitrust laws of the United States against any party
in the future who might seek to exercise patent rights in the future who might seek to exercise patent rights
ietf-tls-ciphersuite-02 AES Ciphersuites for TLS 15 November 2000
against any user of AES that have not been disclosed to against any user of AES that have not been disclosed to
NIST in response to this request for information. NIST in response to this request for information.
One of the authors of Rijndael signed the following disclaimer when One of the authors of Rijndael signed the following disclaimer when
submitting the algorithm to NIST for consideration in the AES pro¡ submitting the algorithm to NIST for consideration in the AES pro¡
cess: cess:
I, Joan Daemen, do hereby declare that to the best of my I, Joan Daemen, do hereby declare that to the best of my
knowledge the practice of the algorithm, reference imple¡ knowledge the practice of the algorithm, reference imple¡
mentation, and mathematically optimized implementations, mentation, and mathematically optimized implementations,
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withdrawn from public consideration for inclusion in the withdrawn from public consideration for inclusion in the
Federal Information Processing Standard (FIPS) for Federal Information Processing Standard (FIPS) for
Advanced Encryption Standard (AES). I further understand Advanced Encryption Standard (AES). I further understand
that I will not receive financial compensation from the that I will not receive financial compensation from the
government for my submission. I certify that, to the government for my submission. I certify that, to the
best of my knowledge, I have fully disclosed all patents best of my knowledge, I have fully disclosed all patents
and patent applications relating to my algorithm. I also and patent applications relating to my algorithm. I also
understand that the U.S. Government may, during the understand that the U.S. Government may, during the
course of the lifetime of the AES or during the FIPS pub¡ course of the lifetime of the AES or during the FIPS pub¡
lic review process, modify the algorithm's specifications lic review process, modify the algorithm's specifications
(e.g., to protect against a newly discovered vulnerabil¡ (e.g., to protect against a newly discovered
ity). Should my submission be selected for inclusion in
the AES, I hereby agree not to place any restrictions on ietf-tls-ciphersuite-03 AES Ciphersuites for TLS 22 January 2001
the use of the algorithm intending it to be available on
a worldwide, non-exclusive, royalty-free basis. vulnerability). Should my submission be selected for
inclusion in the AES, I hereby agree not to place any
restrictions on the use of the algorithm intending it to
be available on a worldwide, non-exclusive, royalty-free
basis.
I do hereby agree to provide the statements for any I do hereby agree to provide the statements for any
patent or patent application identified to cover practice patent or patent application identified to cover practice
of my algorithm, reference implementation or mathemati¡ of my algorithm, reference implementation or mathemati¡
cally optimized implementations and the right to use such cally optimized implementations and the right to use such
implementations for the purposes of the AES evaluation implementations for the purposes of the AES evaluation
process. process.
ietf-tls-ciphersuite-02 AES Ciphersuites for TLS 15 November 2000
I understand that NIST will announce the selected algo¡ I understand that NIST will announce the selected algo¡
rithm(s) and proceed to publish the draft FIPS for public rithm(s) and proceed to publish the draft FIPS for public
comment. If my algorithm (or the derived algorithm) is comment. If my algorithm (or the derived algorithm) is
not selected for inclusion in the FIPS (including those not selected for inclusion in the FIPS (including those
not selected for second round of public evaluation), I not selected for second round of public evaluation), I
understand that all rights, including use rights of the understand that all rights, including use rights of the
reference and mathematically optimized implementations, reference and mathematically optimized implementations,
revert back to the submitter (and other owner[s] as revert back to the submitter (and other owner[s] as
appropriate). Additionally, should the U.S. Government appropriate). Additionally, should the U.S. Government
not select my algorithm for inclusion in the AES after a not select my algorithm for inclusion in the AES after a
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Dear Mr Foti [of NIST], Dear Mr Foti [of NIST],
Hereby we confirm that the original patent and patent Hereby we confirm that the original patent and patent
application information, as provided to NIST with our application information, as provided to NIST with our
original submission in June 1998, has not changed. To original submission in June 1998, has not changed. To
the best of our knowledge, there are no patents or patent the best of our knowledge, there are no patents or patent
applications covering the practice of the algorithm, ref¡ applications covering the practice of the algorithm, ref¡
erence implementation or the mathematically optimized erence implementation or the mathematically optimized
implementations. implementations.
ietf-tls-ciphersuite-03 AES Ciphersuites for TLS 22 January 2001
[signed] [signed]
Joan Daemen, Vincent Rijmen Joan Daemen, Vincent Rijmen
Acknowledgements Acknowledgements
I would like to thank the ietf-tls mailing list contributors who I would like to thank the ietf-tls mailing list contributors who
have made helpful suggestions for this document. have made helpful suggestions for this document.
References References
[TLS] T. Dierks, C. Allen, "The TLS Protocol Version 1.0" RFC-2246. [TLS] T. Dierks, C. Allen, "The TLS Protocol Version 1.0" RFC-2246.
January, 1999. January, 1999.
ietf-tls-ciphersuite-02 AES Ciphersuites for TLS 15 November 2000
[AES] J. Daemen, V. Rijmen, "The Rijndael Block Cipher" [AES] J. Daemen, V. Rijmen, "The Rijndael Block Cipher"
http://csrc.nist.gov/encryption/aes/rijndael/Rijndael.pdf 3rd http://csrc.nist.gov/encryption/aes/rijndael/Rijndael.pdf 3rd
September 1999. September 1999.
[SHA-1] FIPS PUB 180-1, "Secure Hash Standard," National Institute [SHA-1] FIPS PUB 180-1, "Secure Hash Standard," National Institute
of Standards and Technology, U.S. Department of Commerce, April 17, of Standards and Technology, U.S. Department of Commerce, April 17,
1995. 1995.
Author's Address Author's Address
 End of changes. 

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