Network Working Group IPsec Working Group INTERNET DRAFT S. Frankel, NIST March 2000 R. Glenn, NIST Expiration Date: September 2000 S. Kelly, RedCreek The Candidate AES Cipher Algorithms and Their Use With IPsec Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Drafts Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This document is a submission to the IETF Internet Protocol Security (IPSEC) Working Group. Comments are solicited and should be addressed to the working group mailing list (ipsec@tis.com) or to the editors. Distribution of this memo is unlimited. Abstract This document describes the use of the AES Cipher Algorithms in Ci- pher Block Chaining Mode, with an explicit IV, as a confidentiality mechanism within the context of the IPsec Encapsulating Security Pay- load (ESP). This Internet Draft specifies the use of each of the 5 AES finalist candidates in the ESP Header. Once the AES cipher is chosen, this document will be changed to reflect that choice. Frankel,Glenn,Kelly [Page 1] INTERNET DRAFT March 2000 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Specification of Requirements . . . . . . . . . . . . . . . . . 4 2. The Candidate AES Cipher Algorithms . . . . . . . . . . . . . . 4 2.1 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Key Size . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 Weak Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.4 Block Size and Padding . . . . . . . . . . . . . . . . . . . . 6 2.5 Rounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.6 Cipher-specific Information . . . . . . . . . . . . . . . . . . 6 2.7 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. ESP Payload . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1 ESP Algorithmic Interactions . . . . . . . . . . . . . . . . . 8 3.2 Keying Material . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3 IKE Interactions . . . . . . . . . . . . . . . . . . . . . . . 8 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 10 5. Intellectual Property Rights Statement . . . . . . . . . . . . 11 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 11 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14 9. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 14 Frankel,Glenn,Kelly [Page 2] INTERNET DRAFT March 2000 1. Introduction Recognizing that the venerable DES cipher was reaching the end of its useful life, in January 1997 NIST (the National Institute of Stan- dards and Technology) announced a plan to select its successor, the AES (Advanced Encryption Standard). The AES will be the government's designated encryption cipher, and will be definitively described in a FIPS (Federal Information Processing Standard). The expectation is that the AES will suffice to protect sensitive government information at least until the next century. It is also expected to be widely adopted by businesses and financial institutions. The initial call for AES candidates specified the following require- ments: + unclassified + publicly disclosed + available royalty-free worldwide + capable of handling a block size of at least 128 bits + at a minimum, capable of handling key sizes of 128, 192, and 256 bits The distinguishing characteristics on which the final AES cipher will be selected are: + security + computational efficiency and memory requirements on a variety of software and hardware, including smart cards + flexibility and simplicity Of the 15 ciphers that were submitted as AES candidates in August 1998, 5 were designated as finalists. Analysis and discussion of the candidates continues. Either 1 or 2 of the finalists will be selected as the AES cipher; the AES FIPS is expected to be completed by summer 2001. It is the intention of the IETF IPsec Working Group that AES will eventually be adopted as the default IPsec ESP cipher and will obtain the status of MUST be included in compliant IPsec implementations. However, until 1 or 2 of the finalists are selected and until there is more experience with regard to the cryptographic strengths and weaknesses of the algorithms, this document should be used to experi- ment with the AES candidates and determine how they can best be used in IPsec implementations. This document should be considered experi- mental. Frankel,Glenn,Kelly [Page 3] INTERNET DRAFT March 2000 The remainder of this document specifies the use of the five finalist AES candidate ciphers within the context of IPsec ESP. For further information on how the various pieces of ESP fit together to provide security services, refer to [ARCH], [ESP], and [ROAD]. 1.1 Specification of Requirements The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" that appear in this document are to be interpreted as described in [RFC-2119]. 2. The Candidate AES Cipher Algorithms All symmetric block cipher algorithms share common characteristics and variables, including mode, key size, weak keys, block size, and rounds. The following sections contain descriptions of the relevant characteristics of the candidate AES ciphers. Some of the candidate AES ciphers are covered by copyrights, patents or patent applications. Each submitter has sworn that, if selected as the AES cipher algorithm, the algorithm will be made available world-wide on a royalty-free basis. The AES homepage, http://www.nist.gov/aes, contains a wealth of in- formation about the 5 finalists, including definitive descriptions of each algorithm, comparative analyses, performance statistics, test vectors and intellectual property information. This site also con- tains information on how to obtain reference implementations from NIST for each of the candidate algorithms. 2.1 Mode No operational modes are currently defined for the AES ciphers. How- ever, the Cipher Block Chaining (CBC) mode is well-defined and well- understood for symmetric ciphers, and is currently required for all other ESP ciphers. This document specifies the use of the AES ci- phers in CBC mode within ESP. This mode requires an Initialization Vector (IV) that is the same size as the block size. Use of a ran- domly generated IV prevents generation of identical ciphertext from packets which have identical data that spans the first block of the cipher algorithm's block size. The IV is XOR'd with the first plaintext block before it is encrypt- ed. Then for successive blocks, the previous ciphertext block is XOR'd with the current plaintext, before it is encrypted. More information on CBC mode can be obtained in [CRYPTO-S]. For the use of CBC mode in ESP with 64-bit ciphers, see [CBC]. [AUTHORS' NOTE: Should we require CBC mode using the ciphertext from the previously generated block? On the AES discussion list, it has been suggested that a Counter Feedback Mode be defined, which allows parallel encryption of blocks. Should we stick with CBC, use some Frankel,Glenn,Kelly [Page 4] INTERNET DRAFT March 2000 variant of a Counter Feedback Mode, or wait for the AES FIPS to de- cide?] 2.2 Key Size Some cipher algorithms allow for variable sized keys, while others only allow specific, pre-defined key sizes. The length of the key typically correlates with the strength of the algorithm; thus larger keys are usually harder to break than shorter ones. This document stipulates that all key sizes MUST be a multiple of 8 bits. This document specifies the default (i.e. MUST be supported) key size for all of the AES cipher algorithms. All of the candidate ciphers were required to accept key sizes of 128, 192 and 256 bits. The de- fault key size that implementations MUST support for IPsec is 128 bits. +============+=========================+===========+ | Algorithm | Key Sizes (bits) | Default | +============+=========================+===========+ | MARS | 128 - 448* | 128 | +------------+-------------------------+-----------+ | RC6 | variable up to 2040 | 128 | +------------+-------------------------+-----------+ | Rijndael | 128, 192, 256 | 128 | +------------+-------------------------+-----------+ | Serpent | variable up to 256** | 128 | +------------+-------------------------+-----------+ | Twofish | variable up to 256*** | 128 | +------------+-------------------------+-----------+ *NOTE1: MARS key lengths must be multiples of 32 bits. **NOTE2: Serpent keys are always padded to 256 bits. The padding con- sists of a "1" bit followed by "0" bits. ***NOTE3: Twofish keys, other than the default sizes, are always padded with "0" bits up to the next default size. 2.3 Weak Keys At the time of writing this document there are no known weak keys for any of the AES ciphers. Some cipher algorithms have weak keys or keys that MUST not be used due to their interaction with some aspect of the cipher's definition. If weak keys are discovered for any of the AES ciphers, then weak keys SHOULD be checked for and discarded when using manual key man- agement. When using dynamic key management, such as [IKE], weak key checks SHOULD NOT be performed as they are seen as an unnecessary added code complexity that could weaken the intended security [EVALU- ATION]. Frankel,Glenn,Kelly [Page 5] INTERNET DRAFT March 2000 2.4 Block Size and Padding All of the algorithms described in this document use a block size of sixteen octets (128 bits), as required in the AES specifications. Some of the algorithms can handle larger block sizes as well. Padding is required by the candidate AES algorithms to maintain a 16-octet (128-bit) blocksize. Padding MUST be added, as specified in [ESP], such that the data to be encrypted (which includes the ESP Pad Length and Next Header fields) has a length that is a multiple of 16 octets. Because of the algorithm specific padding requirement, no additional padding is required to ensure that the ciphertext terminates on a 4-octet boundary (i.e. maintaining a 16-octet blocksize guarantees that the ESP Pad Length and Next Header fields will be right aligned within a 4-octet word). Additional padding may be included, as specifed in [ESP], as long as the 16-octet blocksize is maintained. 2.5 Rounds This variable determines how many times a block is encrypted. While this variable MAY be negotiated, a default value MUST always exist when it is not negotiated. +============+===============+=======================+ | Algorithm | Negotiable? | Default # of Rounds | +============+===============+=======================+ | MARS | Yes | 32 | +------------+---------------+-----------------------+ | RC6 | Yes | 20 | +------------+---------------+-----------------------+ | Rijndael | Yes | 10, 12, 14* | +------------+---------------+-----------------------+ | Serpent | Yes | 32 | +------------+---------------+-----------------------+ | Twofish | Yes | 16 | +------------+---------------+-----------------------+ *NOTE1: Rijndael's Default # of Rounds is dependent on key size. De- fault # of Rounds = keylen/32 + 6. 2.6 Cipher-specific Information MARS: MARS is IBM's submission to the AES competition. The inventors, who are from the US and Switzerland, are: Carolynn Burwick, Don Copper- smith, Edward D'Avignon, Rosario Gennaro, Shai Halevi, Charanjit Jut- la, Sstephen Matyas Jr., Luke O'Connor, Mohammad Peyravian, David Safford, and Nevenko Zunic, A patent application, IBM application CR99802, is pending. However, the MARS homepage contains the follow- Frankel,Glenn,Kelly [Page 6] INTERNET DRAFT March 2000 ing statement: "MARS is now available world-wide under a royalty-free license from Tivoli." MARS is defined in [MARS-1] and [MARS-2]. A change to the key generation technique is described in [MARS-3]. The MARS homepage is: http://www.research.ibm.com/security/mars.html. RC6: RC6 was invented by Ronald Rivest of MIT, and by Matthew Robshaw, Ray Sidney, and Yiqun Lisa Yin, all from RSA Laboratories. The name RC6 is protected by a copyright. The algorithm is covered by USA patent number 5,724,428 (granted March 3, 1998); two other US patents are pending: application serial numbers 08/854,210 (filed April 21, 1997) and 09/094,649 (filed June 15, 1998). The RC6 family of algorithms is defined in [RC6]. The RC6 homepage is: http://www.rsasecurity.com/rsalabs/aes/. Rijndael: Rijndael was invented by Joan Daemen from Banksys/PWI and Vincent Ri- jmen from ESAT-COSIC, both in Belgium. It is not covered by any patents, and the Rijndael homepage contains the following statement: "Rijndael is available for free. You can use it for whatever purposes you want, irrespective of whether it is accepted as AES or not." Ri- jndael's description can be found in [RIJNDAEL]. The Rijndael home- page is: http://www.esat.kuleuven.ac.be/~rijmen/rijndael/. Serpent: Serpent was invented by Ross Anderson of Cambridge University, Eli Biham of the Technion, Israel and Lars Knudsen of the University of Bergen, Norway. Two UK patent applications are pending: 9722789.7 (filed October 29, 1997) and 9722798.9 (filed October 30, 1997). However, the Serpent homepage contains the following statement: "Ser- pent is now completely in the public domain, and we impose no re- strictions on its use." Serpent is defined in [SERPENT-1] and [SER- PENT-2]. The Serpent homepage is: http://www.cl.cam.ac.uk/~rja14/serpent.html. Twofish: Twofish was invented by Bruce Schneier, John Kelsey, Chris Hall and Niels Ferguson, all from Counterpane Systems, Doug Whiting of Hi/fn, and David Wagner from the University of California Berkeley. It is not covered by any patents, and the Twofish homepage contains the following statement: "Twofish is unpatented, and the source code is uncopyrighted and license-free; it is free for all uses." Twofish is defined in [TWOFISH-1] and [TWOFISH-2]. The Twofish homepage is: http://www.counterpane.com/twofish.html. 2.7 Performance For a comparison table of the estimated speeds of these and other ci- pher algorithms, please see [PERF-1], [PERF-2], [PERF-3], or [PERF-4]. The AES homepage, http://www.nist.gov/aes, has pointers to Frankel,Glenn,Kelly [Page 7] INTERNET DRAFT March 2000 other analyses. The individual cypher documents, [MARS-1], [MARS-2], [RC6], [RIJNDAEL], [SERPENT-1], [SERPENT-2], [TWOFISH-1] and [TWOFISH-2] also contain performance statistics. 3. ESP Payload The ESP payload is made up of the IV followed by raw cipher-text. Thus the payload field, as defined in [ESP], is broken down according to the following diagram: +---------------+---------------+---------------+---------------+ | | + Initialization Vector (16 octets) + | | +---------------+---------------+---------------+---------------+ | | ~ Encrypted Payload (variable length, a multiple of 16 octets) ~ | | +---------------------------------------------------------------+ The IV field MUST be the same size as the block size of the cipher algorithm being used. The IV MUST be chosen at random. Common prac- tice is to use random data for the first IV and the last block of en- crypted data from an encryption process as the IV for the next en- cryption process. Including the IV in each datagram ensures that decryption of each re- ceived datagram can be performed, even when some datagrams are dropped, or datagrams are re-ordered in transit. To avoid ECB encryption of very similar plaintext blocks in different packets, implementations MUST NOT use a counter or other low-Hamming distance source for IVs. 3.1 ESP Algorithmic Interactions Currently, there are no known issues regarding interactions between these algorithms and other aspects of ESP, such as use of certain au- thentication schemes. 3.2 Keying Material The minimum number of bits sent from the key exchange protocol to the ESP algorithm must be greater than or equal to the key size. The cipher's encryption and decryption key is taken from the first bits of the keying material, where represents the required key size. 3.3 IKE Interactions To facilitate the experimental use of the AES candidate ciphers, it would be useful to temporarily define standard IPsec ESP Transform Identifiers for each of the AES algorithms. [DOI] reserves the val- Frankel,Glenn,Kelly [Page 8] INTERNET DRAFT March 2000 ues 249-255 for "private use amongst cooperating systems." The fol- lowing IPsec ESP Transform Identifiers are suggested for IKE interop- erability using the AES candidate ciphers: +===================+=========+ | Transform ID | Value | +===================+=========+ | ESP_AES_MARS | 249 | +-------------------+---------+ | ESP_AES_RC6 | 250 | +-------------------+---------+ | ESP_AES_RIJNDAEL | 251 | +-------------------+---------+ | ESP_AES_SERPENT | 252 | +-------------------+---------+ | ESP_AES_TWOFISH | 253 | +-------------------+---------+ Since the AES candidate ciphers allow variable key lengths, the Key Length attribute MUST be specified in a Phase 2 exchange [DOI]. The Key Length attribute MAY be specified in a Phase 1 exchange [IKE]; if it is not specified, the default key length is 128 bits. If IKE is used to negotiate keys for the AES candidate ciphers, the recommended characteristics of the groups governing the Diffie-Hell- man exchange are as follows: +===========+=================+================+===============+ | Key Size | Exponent Size | Modulus Size | Group Type | +===========+=================+================+===============+ | 128 | 256 | 3240 | MODP | +-----------+-----------------+----------------+---------------+ | 192 | 384 | 7945 | MODP | +-----------+-----------------+----------------+---------------+ | 256 | 512 | 15430 | MODP | +-----------+-----------------+----------------+---------------+ | 128 | 248 | 248 | EC2N | +-----------+-----------------+----------------+---------------+ | 192 | 376 | 376 | EC2N | +-----------+-----------------+----------------+---------------+ | 256 | 504 | 504 | EC2N | +-----------+-----------------+----------------+---------------+ NOTE: This table is based on Section 4.5 in [KEYLEN-1] and on email communications with Hilarie Orman [KEYLEN-2]. Additional information about the relationship between the group gov- erning a Diffie-Hellman exchange and the symmetric keys derived from the exchange can be found in [KEYLEN-1]. For symmetric key lengths that exceed the output of the hash used to generate the key, the Diffie-Hellman shared secret MUST be hashed Frankel,Glenn,Kelly [Page 9] INTERNET DRAFT March 2000 twice, and the resulting values combined to form the keying material [KEYLEN-2], as follows: P1 = Hash(0|shared_secret) P2 = Hash(1|shared_secret) keying_material = (P1 << shift_bits XOR P2) The first hash output, P1, is shifted left a variable number of bits, depending upon the hash and the key length, prior to XOR'ing it with the second hash output, P2. +===========+=========+============+===================+ | Key Size | Hash | Dual DH? | # of Shift Bits | +===========+=========+============+===================+ | 128 | MD5 | N | - | +-----------+---------+------------+-------------------+ | 128 | SHA-1 | N | - | +-----------+---------+------------+-------------------+ | 192 | MD5 | Y | 64 | +-----------+---------+------------+-------------------+ | 192 | SHA-1 | Y | 32 | +-----------+---------+------------+-------------------+ | 256 | MD5 | Y | 128 | +-----------+---------+------------+-------------------+ | 256 | SHA-1 | Y | 96 | +-----------+---------+------------+-------------------+ If additional keying material is required for an authentication key, IKE's iterative key-boosting algorithm MUST be used [IKE, Section 6.2]. 4. Security Considerations Implementations are encouraged to use the largest key sizes they can when taking into account performance considerations for their partic- ular hardware and software configuration. Note that encryption nec- essarily impacts both sides of a secure channel, so such considera- tion must take into account not only the client side, but the server as well. Because these candidate AES algorithms are relatively new and have only undergone limited cryptographic analysis, their use in IPsec im- plementations should be considered experimental. Once NIST has pub- lished the AES FIPS, and at the recommendation of cryptographic ex- perts, AES should become a default and mandatory-to-implement cipher algorithm for IPsec. For more information regarding the necessary use of random IV values, see [CRYPTO-B]. For further security considerations, the reader is encouraged to read the documents that describe the actual cipher algorithms. Frankel,Glenn,Kelly [Page 10] INTERNET DRAFT March 2000 5. Intellectual Property Rights Statement Pursuant to the provisions of [RFC-2026], the authors represent that they have disclosed the existence of any proprietary or intellectual property rights in the contribution that are reasonably and personal- ly known to the authors. The authors do not represent that they per- sonally know of all potentially pertinent proprietary and intellectu- al property rights owned or claimed by the organizations they repre- sent or third parties. The IETF takes no position regarding the validity or scope of any in- tellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this doc- ument or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards- related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances 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 proprietary rights by implementers or users of this specification can be obtained from the IETF Secretariat. 6. Acknowledgments Portions of this text, as well as its general structure, were un- abashedly lifted from [CBC]. The authors want to thank Hilarie Orman for providing expert advice (and a sanity check) on key sizes, requirements for Diffie-Hellman groups, and IKE interactions. 7. References [ARCH] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [CBC] Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher Algorithms," RFC 2451, November 1998. [CRYPTO-B] Bellovin, S., "Probable Plaintext Cryptanalysis of the IP Security Protocols", Proceedings of the Symposium on Network and Distributed System Security, San Diego, CA, pp. 155-160, February 1997. http://www.research.att.com/~smb/probtxt.{ps, pdf}). [CRYPTO-M] A. Menezes, P. Van Oorschot, S. Vanstone, "Handbook of Applied Cryptography", CRC Press, 1997, ISBN 0-8493-8523-7. Frankel,Glenn,Kelly [Page 11] INTERNET DRAFT March 2000 [CRYPTO-S] B. Schneier, "Applied Cryptography Second Edition", John Wiley & Sons, New York, NY, 1995, ISBN 0-471-12845-7. [DOI] Piper, D., "The Internet IP Security Domain of Interpretation for ISAKMP," RFC 2407, November 1998. [ESP] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload (ESP)", RFC 2406, November 1998. [EVALUATION] Ferguson, N. and B. Schneier, "A Cryptographic Evaluation of IPsec," Counterpane Internet Security, Inc., January 2000. [IKE] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", draft-ietf-ipsec-ike-01.txt, May 1999. [IKE-ECC] Panjwani, P. and Y. Poeluev, "Additional ECC Groups For IKE," draft-ietf-ipsec-ike-ecc-groups-01.txt, Septermber 1999. [ISAKMP] Maughan, D., M. Schertler, M. Schneider, and J. Turner, "The Internet Security Association and Key Management Protocol (ISAKMP)," [KEYLEN-1] Orman, H. and P. Hoffman, "Determining Strengths For Public Keys Used For Exchanging Symmetric Keys," draft- orman-public-key-lengths-00.txt, February 2000. [KEYLEN-2] Orman, H., email communications, February 2000. [MARS-1] Burwick, C., D. Coppersmith, E. D'Avignon, R. Gennaro, S. Halevi, C. Jutla, S. Matyas Jr., L. O'Connor, M. Peyravian, D. Safford, and N. Zunic, "MARS - a candidate cipher for AES," NIST AES Proposal, Jun 1998. http://csrc.nist.gov/encryption/aes/round2/AESAlgs/MARS/mars.pdf http://www.research.ibm.com/security/mars.html [MARS-2] Burwick, C., D. Coppersmith, E. D'Avignon, R. Gennaro, S. Halevi, C. Jutla, S. Matyas Jr., L. O'Connor, M. Peyravian, D. Safford, and N. Zunic, "The MARS Encryption Algorithm," NIST AES Proposal, Jun 1998. http://csrc.nist.gov/encryption/aes/round2/AESAlgs/MARS/mars-int.pdf [MARS-3] Zunic, N., "Suggested 'tweaks' for the MARS cipher," NIST AES Proposal, May 1999. http://csrc.nist.gov/encryption/aes/round2/AESAlgs/MARS/mars-twk.txt [PERF-1] Bassham, L. III, "Efficiency Testing of ANSI C Implementations of Round1 Candidate Algorithms for the Advanced Encryption Standard". http://csrc.nist.gov/encryption/aes/round1/r1-ansic.pdf Frankel,Glenn,Kelly [Page 12] INTERNET DRAFT March 2000 [PERF-2] Lipmaa, Helger, "Efficiency Testing Table." http://home.cyber.ee/helger/aes [PERF-3] Nechvetal, J., E. Barker, D. Dodson, M. Dworkin, J. Foti and E. Roback, "Status Report on the First Round of the Development of the Advanced Encryption Standard". http://csrc.nist.gov/encryption/aes/round1/r1report.pdf [PERF-4] Schneier, B., J. Kelsey, D. Whiting, D. Wagner, C. Hall, and N. Ferguson, "Performance Comparison of the AES Submissions." http://www.counterpane.com/AES-performance.html [RC6] Rivest, R., M. Robshaw, R. Sidney, and Y. Yin, "The RC6[TM] Block Cipher," NIST AES Proposal, Jun 1998. http://csrc.nist.gov/encryption/aes/round2/AESAlgs/RC6/cipher.pdf [RFC-2026] Bradner, S., "The Internet Standards Process -- Revision 3", RFC2026, October 1996. [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC-2119, March 1997. [RIJNDAEL] Daemen, J. and V. Rijman, "AES Proposal: Rijndael," NIST AES Proposal, Jun 1998. http://csrc.nist.gov/encryption/aes/round2/AESAlgs/Rijndael/Rijndael.pdf [ROAD] Thayer, R., N. Doraswamy and R. Glenn, "IP Security Document Roadmap", RFC 2411, November 1998. [SERPENT-1] Anderson, R., E. Biham, and L. Knudsen, "Serpent: A Proposal for the Advanced Encryption Standard," NIST AES Proposal, Jun 1998. http://csrc.nist.gov/encryption/aes/round2/AESAlgs/Serpent/Serpent.pdf [SERPENT-2] Biham, E., R. Anderson, L. Knudsen, "Serpent: A New Block Cipher Proposal," Fast Software Encryption - FSE98, Springer LNCS, vol. 1372, pp. 222-238. [TWOFISH-1] Schneier, B., J. Kelsey, D. Whiting, D. Wagner, C. Hall, and N. Ferguson, "Twofish: A 128-Bit Block Cipher," NIST AES Proposal, Jun 1998. http://csrc.nist.gov/encryption/aes/round2/AESAlgs/Twofish/Twofish.pdf [TWOFISH-2] Schneier, B., J. Kelsey, D. Whiting, D. Wagner, C. Hall, and N. Ferguson, "The Twofish Encryption Algorithm: A 128-Bit Block Cipher," John Wiley & Sons, 1999. http://www.counterpane.com/ipsec.html Frankel,Glenn,Kelly [Page 13] INTERNET DRAFT March 2000 8. Authors' Addresses Sheila Frankel NIST 820 West Diamond Ave. Room 680 Gaithersburg, MD 20899 Phone: +1 (301) 975-3297 Email: sheila.frankel@nist.gov Rob Glenn NIST 820 West Diamond Ave. Room 455 Gaithersburg, MD 20899 Phone: +1 (301) 975-3667 Email: rob.glenn@nist.gov Scott Kelly RedCreek Communications 3900 Newpark Mall Road Newark, CA 94560 Phone: +1 (510) 745-3969 Email: skelly@redcreek.com The IPsec working group can be contacted through the chair: Ted T'so Massachusetts Institute of Technology e-mail: tytso@mit.edu 9. Full Copyright Statement Copyright (C) The Internet Society (1998). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this doc- ument itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other In- ternet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights de- fined in the Internet Standards process must be followed, or as re- quired to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING Frankel,Glenn,Kelly [Page 14] INTERNET DRAFT March 2000 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HERE- IN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MER- CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Frankel,Glenn,Kelly [Page 15]