draft-ietf-tls-ciphersuite-00.txt   draft-ietf-tls-ciphersuite-01.txt 
Network Working Group Pete Chown Network Working Group Pete Chown
INTERNET DRAFT Skygate Technology INTERNET DRAFT Skygate Technology
<draft-ietf-tls-ciphersuite-00.txt> 02 October 2000 <draft-ietf-tls-ciphersuite-01.txt> 27 October 2000
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-00 AES Ciphersuites for TLS 02 October 2000 ietf-tls-ciphersuite-01 AES Ciphersuites for TLS 27 October 2000
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 offer reduced key lengths).
At the same time the DHE ciphersuites are the only ones to At the same time the DHE ciphersuites are the only ones to
offer forward secrecy. offer forward secrecy.
This document proposes two new ciphersuites, with the aim of over¡ This document proposes several new ciphersuites, with the aim of
coming these problems. overcoming these problems.
Rationale
Certain of the TLS ciphersuites use an ephemeral Diffie-Hellman key
exchange. These ciphersuites provide forward secrecy. The other
ciphersuites do not; if either party's key is ever compromised, all
the sessions which it secured can be decrypted.
The additional overhead associated with ephemeral Diffie-Hellman is
not believed to be significant, and forward secrecy is an extremely
desirable property for a system like TLS. For this reason, both
the new ciphersuites employ an ephemeral Diffie-Hellman key
exchange.
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_DH_DSS_WITH_3DES_EDE_CBC_SHA
TLS_DH_RSA_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
and All the ciphersuites described here use the AES in cipher block
chaining (CBC) mode. Furthermore, they use SHA-1 in an HMAC con¡
struction as described in section 5 of [TLS]. (Although the TLS
ciphersuite names include the text ``SHA'', this actually refers to
the modified SHA-1 version of the algorithm.)
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA The ciphersuites differ in the type of certificate and key exchange
method. The ciphersuites defined here use the following options
for this part of the protocol:
Both the ciphersuites proposed in this document use either RSA or CipherSuite Certificate type and key
DSS certificates. They use the AES in cipher block chaining (CBC) exchange algorithm
mode. Furthermore, they use SHA-1 in an HMAC construction as
described in section 5 of [TLS]. (Although the TLS ciphersuite TLS_RSA_WITH_AES_128_CBC_SHA RSA
names include the text ``SHA'', this actually refers to the modi¡ TLS_DH_DSS_WITH_AES_128_CBC_SHA DH_DSS
fied SHA-1 version of the algorithm.) TLS_DH_RSA_WITH_AES_128_CBC_SHA DH_RSA
TLS_DHE_DSS_WITH_AES_128_CBC_SHA DHE_DSS
TLS_DHE_RSA_WITH_AES_128_CBC_SHA DHE_RSA
For the meanings of the terms RSA, DH_DSS, DH_RSA, DHE_DSS and
DHE_RSA, please refer to section 7.4.2 of [TLS].
The AES supports key lengths of 128, 192 and 256 bits. At the pre¡ The AES supports key lengths of 128, 192 and 256 bits. At the pre¡
sent time, all of these are believed to be secure against even the sent time, all of these are believed to be secure against even the
best equipped attackers. The overall strength of TLS is such that best equipped attackers. The overall strength of TLS is such that
there is no gain from using a key length longer than 128 bits. there is no gain from using a key length longer than 128 bits.
Accordingly the AES will use 128 bit keys. Accordingly the AES will use 128 bit keys.
The new ciphersuites will have the following definitions: ietf-tls-ciphersuite-01 AES Ciphersuites for TLS 27 October 2000
ietf-tls-ciphersuite-00 AES Ciphersuites for TLS 02 October 2000 The new ciphersuites will have the following definitions:
CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x2F }; CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x2F };
CipherSuite TLS_DHE_RSA_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_DHE_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x32 };
CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x33 };
TLS implementations SHOULD implement the AES ciphersuites. Implementations SHOULD provide TLS_RSA_WITH_AES_128_CBC_SHA and
TLS_DHE_RSA_WITH_AES_128_CBC_SHA. Implementations MAY provide any
of the other ciphersuites described above.
Security Considerations Security Considerations
It is not believed that adding these ciphersuites will ever reduce It is not believed that the new ciphersuites are ever less secure
security. The AES is believed to be secure, and it has withstood than the corresponding older ones. The AES is believed to be
extensive cryptanalytic attack. The ephemeral Diffie-Hellman secure, and it has withstood extensive cryptanalytic attack.
ciphersuites provide forward secrecy without any reduction in secu¡
rity in other areas. The ephemeral Diffie-Hellman ciphersuites provide forward secrecy
without any known reduction in security in other areas. To obtain
the maximum benefit from these ciphersuites:
1. The ephemeral keys should only be used once. With the TLS pro¡
tocol as currently defined there is no efficiency gain from
reusing ephemeral keys.
2. Ephemeral keys should be destroyed securely when they are no
longer required.
3. The random number generator used to create ephemeral keys must
not reveal past output even when its internal state is compro¡
mised.
Copyright Copyright
Copyright (C) The Internet Society 2000. All Rights Reserved. Copyright (C) The Internet Society 2000. 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-01 AES Ciphersuites for TLS 27 October 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
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WAR¡ INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WAR¡
RANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. RANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to per¡ intellectual property or other rights that might be claimed to per¡
tain to the implementation or use other technology described in tain to the implementation or use other technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it might or might not be available; neither does it represent that it
ietf-tls-ciphersuite-00 AES Ciphersuites for TLS 02 October 2000
has made any effort to identify any such rights. Information on the has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances claims of rights made available for publication and any assurances
of licenses to be made available, or the result of an attempt made of licenses to be made available, or the result of an attempt made
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
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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-01 AES Ciphersuites for TLS 27 October 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,
I have submitted, known as Rijndael may be covered by the I have submitted, known as Rijndael may be covered by the
following U.S. and/or foreign patents: following U.S. and/or foreign patents:
none none
I do hereby declare that I am aware of no patent applica¡ I do hereby declare that I am aware of no patent applica¡
tions which may cover the practice of my submitted algo¡ tions which may cover the practice of my submitted algo¡
rithm, reference implementation or mathematically opti¡ rithm, reference implementation or mathematically opti¡
mized implementations. mized implementations.
ietf-tls-ciphersuite-00 AES Ciphersuites for TLS 02 October 2000
I do hereby understand that my submitted algorithm may I do hereby understand that my submitted algorithm may
not be selected for inclusion in the Advanced Encryption not be selected for inclusion in the Advanced Encryption
Standard. I also understand and agree that after the Standard. I also understand and agree that after the
close of the submission period, my submission may not be close of the submission period, my submission may not be
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
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the use of the algorithm intending it to be available on the use of the algorithm intending it to be available on
a worldwide, non-exclusive, royalty-free basis. 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-01 AES Ciphersuites for TLS 27 October 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
period of four years from the close of the submission period of four years from the close of the submission
date for candidate algorithms, all rights revert to the date for candidate algorithms, all rights revert to the
submitter (and other owner[s] as appropriate). submitter (and other owner[s] as appropriate).
[signed] [signed]
Title: Cryptographer Title: Cryptographer
Dated: 10-6-98 Dated: 10-6-98
Place: Brussels Place: Brussels
ietf-tls-ciphersuite-00 AES Ciphersuites for TLS 02 October 2000
The following disclaimer was signed at the start of the second The following disclaimer was signed at the start of the second
"round" of the AES process: "round" of the AES process:
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¡
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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-01 AES Ciphersuites for TLS 27 October 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/round2/AESAlgs/Rijndael/Rijn¡ http://csrc.nist.gov/encryption/aes/rijndael/Rijndael.pdf 3rd
dael.pdf 3rd September 1999. September 1999.
Author's Address Author's Address
Pete Chown Pete Chown
Skygate Technology Ltd Skygate Technology Ltd
8 Lombard Road 8 Lombard Road
London London
SW19 3TZ SW19 3TZ
United Kingdom United Kingdom
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