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
<draft-ietf-ipsec-ciph-aes-cbc-00.txt>
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,
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This document is a submission to the IETF Internet Protocol Security
(IPSEC) Working Group. Comments are solicited and should be addressed
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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.
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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
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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.
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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
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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].
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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-
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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
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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
<x> bits of the keying material, where <x> 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-
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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
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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.
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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.
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[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
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[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
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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]
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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]
