Internet Draft IPsec Working Group October 2001 S. Frankel, NIST Expiration Date: April 2002 S. Kelly, RedCreek R. Glenn, NIST The AES Cipher Algorithm and Its 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@lists.tislabs.com) or to the editors. Distribution of this memo is unlimited. Abstract This document describes the use of the AES Cipher Algorithm in Cipher Block Chaining Mode, with an explicit IV, as a confidentiality mecha- nism within the context of the IPsec Encapsulating Security Payload (ESP). This Internet Draft also describes the use of the four other AES fi- nalist candidate algorithms in the ESP Header. Frankel,Glenn,Kelly [Page 1] INTERNET DRAFT October 2001 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Specification of Requirements . . . . . . . . . . . . . . . 3 2. The AES Cipher Algorithm . . . . . . . . . . . . . . . . . . . . 4 2.1 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Key Size . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.3 Weak Keys . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.4 Block Size and Padding . . . . . . . . . . . . . . . . . . . 5 2.5 Rounds . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.6 Cipher-specific Information . . . . . . . . . . . . . . . . 6 2.7 Performance . . . . . . . . . . . . . . . . . . . . . . . . 7 3. ESP Payload . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1 ESP Algorithmic Interactions . . . . . . . . . . . . . . . . 8 3.2 Keying Material . . . . . . . . . . . . . . . . . . . . . . 8 4. IKE Interactions . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1 Phase 1 Identifiers . . . . . . . . . . . . . . . . . . . . 8 4.2 Phase 2 Identifiers . . . . . . . . . . . . . . . . . . . . 9 4.3 Key Length Attribute . . . . . . . . . . . . . . . . . . . . 9 4.4 Diffie-Hellman Groups . . . . . . . . . . . . . . . . . . . 9 4.4.1 Relative Strength . . . . . . . . . . . . . . . . . . 10 4.5 Hash Algorithm Considerations . . . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 12 7. Intellectual Property Rights Statement . . . . . . . . . . . . . 12 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 11. Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 16 Frankel,Glenn,Kelly [Page 2] INTERNET DRAFT October 2001 1. Introduction As the culmination of a four-year competitive process, NIST (the Na- tional Institute of Standards and Technology) has selected the AES (Advanced Encryption Standard), the successor to the venerable DES. The competition was an open one, with public participation and com- ment solicited at each step of the process. The AES, formerly known as Rijndael, was chosen from the five finalists. The four other fi- nalists, MARS, RC6, Serpent and Twofish, were all adjudged to be suf- ficiently secure. The final AES selection was made on the basis of several additional characteristics: + computational efficiency and memory requirements on a variety of software and hardware, including smart cards + flexibility, simplicity and ease of implementation The AES will be the government's designated encryption cipher, and will be definitively described in a FIPS (Federal Information Pro- cessing Standard), expected to be completed by summer 2001. The expectation is that the AES will suffice to protect sensitive (unclassified) government information at least until the next cen- tury. It is also expected to be widely adopted by businesses and financial institutions. 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 there is more experience with regard to the crypto- graphic strengths and weaknesses of the algorithm, this document should be used to experiment with the AES algorithm and determine how it can best be used in IPsec implementations. This document should be considered experimental. The remainder of this document specifies the use of the AES and the other four 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]. Frankel,Glenn,Kelly [Page 3] INTERNET DRAFT October 2001 2. The AES Cipher Algorithm 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 AES cipher and the other finalists. The AES will be made available world-wide on a royalty-free basis. Some of the other finalists are covered by copyrights, patents or patent applications. The AES homepage, http://www.nist.gov/aes, contains a wealth of in- formation about the AES and the other finalists, including definitive descriptions of each algorithm, comparative analyses, performance statistics, test vectors and intellectual property information. This site also contains information on how to obtain reference implementa- tions from NIST for each of the algorithms. 2.1 Mode No operational modes are currently defined for the AES cipher. NIST is in the process of developing a modes of operation FIPS for AES [MODES]. However, the Cipher Block Chaining (CBC) mode is well-de- fined and well-understood for symmetric ciphers, and is currently re- quired for all other ESP ciphers. This document specifies the use of the AES cipher and the other finalists in CBC mode within ESP. This mode requires an Initialization Vector (IV) that is the same size as the block size. Use of a randomly 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]. 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 the AES cipher algorithm. The default key size that implementa- tions MUST support for IPsec is 128 bits. In addition, all of the ciphers accept key sizes of 192 and 256 bits. Frankel,Glenn,Kelly [Page 4] INTERNET DRAFT October 2001 +============+=========================+===========+ | Algorithm | Key Sizes (bits) | Default | +============+=========================+===========+ | AES | 128, 192, 256 | 128 | +------------+-------------------------+-----------+ | MARS | 128 - 448* | 128 | +------------+-------------------------+-----------+ | RC6 | variable up to 2040 | 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 the AES or any of the other finalists. 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 the AES or any of the other final- ists, then weak keys SHOULD be checked for and discarded when using manual key management. 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 se- curity [EVALUATION]. 2.4 Block Size and Padding All of the algorithms described in this document use a block size of sixteen octets (128 bits), mandatory for the AES. Some of the algo- rithms can handle larger block sizes as well. Padding is required by the 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. Frankel,Glenn,Kelly [Page 5] INTERNET DRAFT October 2001 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. Within IPsec, the AES MUST support 10 rounds, corresponding to the mandatory 128-bit keysize. +============+===============+=======================+ | Algorithm | Negotiable? | Default # of Rounds | +============+===============+=======================+ | AES | Yes | 10, 12, 14* | +------------+---------------+-----------------------+ | MARS | Yes | 32 | +------------+---------------+-----------------------+ | RC6 | Yes | 20 | +------------+---------------+-----------------------+ | Serpent | Yes | 32 | +------------+---------------+-----------------------+ | Twofish | Yes | 16 | +------------+---------------+-----------------------+ *NOTE1: AES's Default # of Rounds is dependent on key size. Default # of Rounds = keylen/32 + 6. 2.6 Cipher-specific Information AES: AES was invented by Joan Daemen from Banksys/PWI and Vincent Rijmen 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." AES's de- scription can be found in [RIJNDAEL]. The Rijndael homepage is: http://www.esat.kuleuven.ac.be/~rijmen/rijndael/. 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- 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 Frankel,Glenn,Kelly [Page 6] INTERNET DRAFT October 2001 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/. 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 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) ~ | | +---------------------------------------------------------------+ Frankel,Glenn,Kelly [Page 7] INTERNET DRAFT October 2001 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 CBC 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. 4. IKE Interactions 4.1 Phase 1 Identifiers For Phase 1 negotiations, IANA has already assigned an Encryption Al- gorithm ID of 7 for AES-CBC. To facilitate the experimental use of the other finalist ciphers, it would be useful to temporarily define standard IKE Encryption Algorithm Identifiers for each of them as well. [IKE] reserves the values 65001-65535 "for private use among mutually consenting parties". The following IKE Encryption Algorithm Identifiers are suggested for IKE interoperability using the finalist ciphers: Frankel,Glenn,Kelly [Page 8] INTERNET DRAFT October 2001 +=======================+=========+ | Encryption Algorithm | Value | +=======================+=========+ | MARS-CBC | 65001 | +-----------------------+---------+ | RC6-CBC | 65002 | +-----------------------+---------+ | SERPENT-CBC | 65004 | +-----------------------+---------+ | TWOFISH-CBC | 65005 | +-----------------------+---------+ 4.2 Phase 2 Identifiers For Phase 2 negotiations, IANA has already assigned an ESP Transform Identifier of 12 for ESP_AES. To facilitate the experimental use of the other finalist ciphers, it would be useful to temporarily define standard IPsec ESP Transform Identifiers for each of them as well. [DOI] reserves the values 249-255 for "private use amongst cooperat- ing systems." The following IPsec ESP Transform Identifiers are sug- gested for IKE interoperability using the finalist ciphers: +===============+=========+ | Transform ID | Value | +===============+=========+ | ESP_MARS | 249 | +---------------+---------+ | ESP_RC6 | 250 | +---------------+---------+ | ESP_SERPENT | 252 | +---------------+---------+ | ESP_TWOFISH | 253 | +---------------+---------+ 4.3 Key Length Attribute Since the AES and other finalist 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 ex- change [IKE]; if it is not specified, the default key length is 128 bits. 4.4 Diffie-Hellman Groups The Diffie-Hellman algorithm is the basis of cryptographic key ex- change within IPsec. The algorithm may be implemented using either "MODP" (modulus-exponent) groups or "EC" (elliptic curve) groups. The general procedure is as follows: the initiator chooses a random expo- nent x with K bits of entropy that is 2K bits in length (the K bits may be hashed to produce 2K bits), and then computes g^x using the group operation: X = g^x Frankel,Glenn,Kelly [Page 9] INTERNET DRAFT October 2001 For MODP the group operation is modular multiplication, while for EC the operation is point addition on the curve. The notation "g^x" means "iterate the group operation x times". X is then sent to the responder. The responder chooses a secret number y, and similarly computes Y = g^y which is in turn sent to the initiator. At this point, both the ini- tiator and responder may compute a shared secret value by combining their own secret value with the exponential and applying the group operation: Z = g^(xy) = Y^x = X^y From Z, both derive identical cryptographic keys. This description is simplified in the interest of brevity, and an in- depth descriptions of this mechanism is beyond the scope of this memo. For further details, refer to the wealth of published litera- ture on this topic. 4.4.1 Relative Strength The relative strength of the encryption keys derived via the Diffie- Hellman exchange may be characterized in terms the randomness of the participant's exponents and the strength of Diffie-Hellman group; if an exponent has at least 128 completely random bits, it is said to have 128-bits of "entropy". If the Diffie-Hellman group cannot be broken in less time than searching a 128-bit key space, then the de- rived 128-bit key is said to have 128 bits of "strength". For an in- depth discussion regarding relative strength of values derived from DH exchanges, see [KEYLEN-1]. In some cases, one may choose to settle for an amount of entropy which is less than that of a completely random key of the given size. There are numerous reasons for making such a choice, among which might include a concern for the computational effort required to com- plete the key exchange. For example, the following table lists recom- mended modulus and exponent sizes for various key lengths using ei- ther MODP or EC groups. Frankel,Glenn,Kelly [Page 10] INTERNET DRAFT October 2001 +===========+=================+================+===============+ | 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]. Note that the sizes of the moduli and exponents for the MODP groups in the table above are very large, and the computational effort re- quired to complete the exponentiation and modulo operations with such large values is quite significant using hardware commonly available in the year 2000. If such considerations are deemed important, then keys larger than 128 bits SHOULD NOT be used. Further, if it is de- termined that less than 128 bits of strength will suffice for the se- curity requirements of the given application, then smaller exponents and moduli may be used. [GROUPS] defines four additional Diffie-Hellman MODP groups for IKE. Two of these groups, a 3072-bit MODP group and a 4096-bit MODP group, could be used to establish 128-bit AES keys. [IKE-ECC] defines four additional Diffie-Hellman ECC groups for IKE. Two of these groups, Group 8 and 9, both of which are 283-bit ECC groups, could be used to establish 128-bit AES keys. Additional information about the rela- tionship between the group governing a Diffie-Hellman exchange and the symmetric keys derived from the exchange can be found in [KEYLEN-1]. 4.5 Hash Algorithm Considerations A companion competition, to select the successor to SHA-1, the wide- ly-used hash algorithm, recently concluded. The resulting hashes, called SHA-256, SHA-384 and SHA-512 [SHA2-1] are capable of producing output of three different lengths (256, 384 and 512 bits), sufficient for the generation of the three AES key sizes (128, 192 and 256 bits). IANA has already assigned Phase 1 Hash Algorithm values of 4, 5 and 6 to SHA2-256, SHA2-384, and SHA2-512. IANA has also assigned AH Transform Identifiers of 5, 6 and 7 to AH_SHA2_256, AH_SHA2_384, and AH_SHA2_512.) The use of these hashes in ESP, AH and IKE is de- scribed in [SHA2-2]. Frankel,Glenn,Kelly [Page 11] INTERNET DRAFT October 2001 5. 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. However, a key size of 128 bits is considered secure for the foreseeable future. Because the AES algorithm is relatively new and has only undergone limited cryptographic analysis, its use in IPsec implementations should be considered experimental. Once NIST has published the AES FIPS, and at the recommendation of cryptographic experts, 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. 6. IANA Considerations IANA has assigned Encryption Algorithm ID 7 to AES-CBC. IANA has assigned ESP Transform Identifier 12 to ESP_AES. 7. 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. Frankel,Glenn,Kelly [Page 12] INTERNET DRAFT October 2001 8. 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. 9. 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. [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. [GROUPS] Kivinen, T. and M. Kojo, "More MODP Diffie-Hellman groups for IKE," draft-ietf-ipsec-ike-modp- groups-00.txt, October 2000. [IKE] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, November 1998. [IKE-ECC] Panjwani, P. and Y. Poeluev, "Additional ECC Groups For IKE," draft-ietf-ipsec-ike-ecc-groups-02.txt, May 2000. Frankel,Glenn,Kelly [Page 13] INTERNET DRAFT October 2001 [KEYLEN-1] Orman, H. and P. Hoffman, "Determining Strengths For Public Keys Used For Exchanging Symmetric Keys," draft- orman-public-key-lengths-01.txt, August 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 [MODES] "Symmetric Key Block Cipher Modes of Operation." http://www.nist.gov/modes [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 [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. Frankel,Glenn,Kelly [Page 14] INTERNET DRAFT October 2001 [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. [SHA2-1] "Descriptions of SHA-256, SHA-384, and SHA-512." http://csrc.nist.gov/cryptval/shs/sha256-384-512.pdf. [SHA2-2] Frankel, S. and S. Kelly, "The Use of SHA-256, SHA-384, and SHA-512 within ESP, AH and IKE," Work in progress. [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 10. Authors' Addresses Sheila Frankel NIST 820 West Diamond Ave. Room 680 Gaithersburg, MD 20899 Phone: +1 (301) 975-3297 Email: sheila.frankel@nist.gov Scott Kelly RedCreek Communications 3900 Newpark Mall Road Newark, CA 94560 Phone: +1 (510) 745-3969 Email: skelly@redcreek.com Rob Glenn NIST Frankel,Glenn,Kelly [Page 15] INTERNET DRAFT October 2001 820 West Diamond Ave. Room 455 Gaithersburg, MD 20899 Phone: +1 (301) 975-3667 Email: rob.glenn@nist.gov The IPsec working group can be contacted through the chair: Ted T'so Massachusetts Institute of Technology e-mail: tytso@mit.edu 11. 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. 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