[Docs] [txt|pdf] [draft-ietf-ipsec-...] [Diff1] [Diff2]

PROPOSED STANDARD

Network Working Group                                         S. Frankel
Request for Comments: 3602                                      R. Glenn
Category: Standards Track                                           NIST
                                                                S. Kelly
                                                               Airespace
                                                          September 2003


          The AES-CBC Cipher Algorithm and Its Use with IPsec

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes the use of the Advanced Encryption Standard
   (AES) Cipher Algorithm in Cipher Block Chaining (CBC) Mode, with an
   explicit Initialization Vector (IV), as a confidentiality mechanism
   within the context of the IPsec Encapsulating Security Payload (ESP).

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
       1.1.  Specification of Requirements. . . . . . . . . . . . . .  3
   2.  The AES Cipher Algorithm . . . . . . . . . . . . . . . . . . .  3
       2.1.  Mode . . . . . . . . . . . . . . . . . . . . . . . . . .  3
       2.2.  Key Size and Number of Rounds. . . . . . . . . . . . . .  4
       2.3.  Weak Keys. . . . . . . . . . . . . . . . . . . . . . . .  4
       2.4.  Block Size and Padding . . . . . . . . . . . . . . . . .  4
       2.5.  Additional Information . . . . . . . . . . . . . . . . .  4
       2.6.  Performance. . . . . . . . . . . . . . . . . . . . . . .  5
   3.  ESP Payload  . . . . . . . . . . . . . . . . . . . . . . . . .  5
       3.1.  ESP Algorithmic Interactions . . . . . . . . . . . . . .  6
       3.2.  Keying Material. . . . . . . . . . . . . . . . . . . . .  6
   4.  Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  IKE Interactions . . . . . . . . . . . . . . . . . . . . . . . 10
       5.1.  Phase 1 Identifier . . . . . . . . . . . . . . . . . . . 10
       5.2.  Phase 2 Identifier . . . . . . . . . . . . . . . . . . . 10
       5.3.  Key Length Attribute . . . . . . . . . . . . . . . . . . 10



Frankel, et al.             Standards Track                     [Page 1]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


       5.4.  Hash Algorithm Considerations. . . . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   8.  Intellectual Property Rights Statement . . . . . . . . . . . . 11
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
       9.1.  Normative References . . . . . . . . . . . . . . . . . . 12
       9.2.  Informative References . . . . . . . . . . . . . . . . . 12
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   11. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14
   12. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 15

1.  Introduction

   As the culmination of a four-year competitive process, NIST (the
   National Institute of Standards and Technology) has selected the AES
   (Advanced Encryption Standard), the successor to the venerable DES
   (Data Encryption Standard).  The competition was an open one, with
   public participation and comment solicited at each step of the
   process.  The AES [AES], formerly known as Rijndael, was chosen from
   a field of five finalists.

   The AES selection was made on the basis of several characteristics:

      +  security

      +  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

      +  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.  The
   expectation is that the AES will suffice to protect sensitive
   (unclassified) government information until at least the next
   century.  It is also expected to be widely adopted by businesses and
   financial institutions.





Frankel, et al.             Standards Track                     [Page 2]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


   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.

   The remainder of this document specifies the use of the AES 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 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.

2.1.  Mode

   NIST has defined 5 modes of operation for AES and other FIPS-approved
   ciphers [MODES]: CBC (Cipher Block Chaining), ECB (Electronic
   CodeBook), CFB (Cipher FeedBack), OFB (Output FeedBack) and CTR
   (Counter).  The 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 cipher 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
   encrypted.  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 [MODES, CRYPTO-S].
   For the use of CBC mode in ESP with 64-bit ciphers, see [CBC].








Frankel, et al.             Standards Track                     [Page 3]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


2.2.  Key Size and Number of Rounds

   AES supports three key sizes: 128 bits, 192 bits, and 256 bits.  The
   default key size is 128 bits, and all implementations MUST support
   this key size.  Implementations MAY also support key sizes of 192
   bits and 256 bits.

   AES uses a different number of rounds for each of the defined key
   sizes.  When a 128-bit key is used, implementations MUST use 10
   rounds.  When a 192-bit key is used, implementations MUST use 12
   rounds.  When a 256-bit key is used, implementations MUST use 14
   rounds.

2.3.  Weak Keys

   At the time of writing this document there are no known weak keys for
   the AES.

   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, 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 security [EVALUATION].

2.4.  Block Size and Padding

   The AES uses a block size of sixteen octets (128 bits).

   Padding is required by the AES 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
   specified in [ESP], as long as the 16-octet blocksize is maintained.

2.5.  Additional Information

   AES was invented by Joan Daemen from Banksys/PWI and Vincent Rijmen
   from ESAT-COSIC, both in Belgium, and is available world-wide on a
   royalty-free basis.  It is not covered by any patents, and the
   Rijndael homepage contains the following statement: "Rijndael is



Frankel, et al.             Standards Track                     [Page 4]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


   available for free.  You can use it for whatever purposes you want,
   irrespective of whether it is accepted as AES or not."  AES's
   description can be found in [AES].  The Rijndael homepage is:
   http://www.esat.kuleuven.ac.be/~rijmen/rijndael/.

   The AES homepage, http://www.nist.gov/aes, contains a wealth of
   information about the AES, including a definitive description of the
   AES algorithm, performance statistics, test vectors and intellectual
   property information.  This site also contains information on how to
   obtain an AES reference implementation from NIST.

2.6.  Performance

   For a comparison table of the estimated speeds of AES and other
   cipher algorithms, please see [PERF-1], [PERF-2], [PERF-3], or
   [PERF-4].  The AES homepage has pointers to other analyses.

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, and MUST be
   unpredictable.

   Including the IV in each datagram ensures that decryption of each
   received 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.







Frankel, et al.             Standards Track                     [Page 5]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


3.1.  ESP Algorithmic Interactions

   Currently, there are no known issues regarding interactions between
   the AES and other aspects of ESP, such as use of certain
   authentication 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.

4.  Test Vectors

   The first 4 test cases test AES-CBC encryption.  Each test case
   includes the key, the plaintext, and the resulting ciphertext.  The
   values of keys and data are either hexadecimal numbers (prefixed by
   "0x") or ASCII character strings (surrounded by double quotes).  If a
   value is an ASCII character string, then the AES-CBC computation for
   the corresponding test case DOES NOT include the trailing null
   character ('\0') of the string.  The computed cyphertext values are
   all hexadecimal numbers.

   The last 4 test cases illustrate sample ESP packets using AES-CBC for
   encryption.  All data are hexadecimal numbers (not prefixed by "0x").

   These test cases were verified using 2 independent implementations:
   the NIST AES-CBC reference implementation and an implementation
   provided by the authors of the Rijndael algorithm
   (http://csrc.nist.gov/encryption/aes/rijndael/
                          rijndael-unix-refc.tar).

Case #1: Encrypting 16 bytes (1 block) using AES-CBC with 128-bit key
Key       : 0x06a9214036b8a15b512e03d534120006
IV        : 0x3dafba429d9eb430b422da802c9fac41
Plaintext : "Single block msg"
Ciphertext: 0xe353779c1079aeb82708942dbe77181a

Case #2: Encrypting 32 bytes (2 blocks) using AES-CBC with 128-bit key
Key       : 0xc286696d887c9aa0611bbb3e2025a45a
IV        : 0x562e17996d093d28ddb3ba695a2e6f58
Plaintext : 0x000102030405060708090a0b0c0d0e0f
              101112131415161718191a1b1c1d1e1f
Ciphertext: 0xd296cd94c2cccf8a3a863028b5e1dc0a
              7586602d253cfff91b8266bea6d61ab1



Frankel, et al.             Standards Track                     [Page 6]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


Case #3: Encrypting 48 bytes (3 blocks) using AES-CBC with 128-bit key
Key       : 0x6c3ea0477630ce21a2ce334aa746c2cd
IV        : 0xc782dc4c098c66cbd9cd27d825682c81
Plaintext : "This is a 48-byte message (exactly 3 AES blocks)"
Ciphertext: 0xd0a02b3836451753d493665d33f0e886
              2dea54cdb293abc7506939276772f8d5
              021c19216bad525c8579695d83ba2684

Case #4: Encrypting 64 bytes (4 blocks) using AES-CBC with 128-bit key
Key       : 0x56e47a38c5598974bc46903dba290349
IV        : 0x8ce82eefbea0da3c44699ed7db51b7d9
Plaintext : 0xa0a1a2a3a4a5a6a7a8a9aaabacadaeaf
              b0b1b2b3b4b5b6b7b8b9babbbcbdbebf
              c0c1c2c3c4c5c6c7c8c9cacbcccdcecf
              d0d1d2d3d4d5d6d7d8d9dadbdcdddedf
Ciphertext: 0xc30e32ffedc0774e6aff6af0869f71aa
              0f3af07a9a31a9c684db207eb0ef8e4e
              35907aa632c3ffdf868bb7b29d3d46ad
              83ce9f9a102ee99d49a53e87f4c3da55

Case #5: Sample transport-mode ESP packet (ping 192.168.123.100)
Key: 90d382b4 10eeba7a d938c46c ec1a82bf
SPI: 4321
Source address: 192.168.123.3
Destination address: 192.168.123.100
Sequence number: 1
IV: e96e8c08 ab465763 fd098d45 dd3ff893

Original packet:
IP header (20 bytes): 45000054 08f20000 4001f9fe c0a87b03 c0a87b64
Data (64 bytes):
08000ebd a70a0000 8e9c083d b95b0700 08090a0b 0c0d0e0f 10111213 14151617
18191a1b 1c1d1e1f 20212223 24252627 28292a2b 2c2d2e2f 30313233 34353637

Augment data with:
Padding: 01020304 05060708 090a0b0c 0d0e
Pad length: 0e
Next header: 01 (ICMP)

Pre-encryption Data with padding, pad length and next header (80 bytes):
08000ebd a70a0000 8e9c083d b95b0700 08090a0b 0c0d0e0f 10111213 14151617
18191a1b 1c1d1e1f 20212223 24252627 28292a2b 2c2d2e2f 30313233 34353637
01020304 05060708 090a0b0c 0d0e0e01








Frankel, et al.             Standards Track                     [Page 7]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


Post-encryption packet with SPI, Sequence number, IV:
IP header: 4500007c 08f20000 4032f9a5 c0a87b03 c0a87b64
SPI/Seq #: 00004321 00000001
IV: e96e8c08 ab465763 fd098d45 dd3ff893
Encrypted Data (80 bytes):
f663c25d 325c18c6 a9453e19 4e120849 a4870b66 cc6b9965 330013b4 898dc856
a4699e52 3a55db08 0b59ec3a 8e4b7e52 775b07d1 db34ed9c 538ab50c 551b874a
a269add0 47ad2d59 13ac19b7 cfbad4a6

Case #6: Sample transport-mode ESP packet
         (ping -p 77 -s 20 192.168.123.100)
Key: 90d382b4 10eeba7a d938c46c ec1a82bf
SPI: 4321
Source address: 192.168.123.3
Destination address: 192.168.123.100
Sequence number: 8
IV: 69d08df7 d203329d b093fc49 24e5bd80

Original packet:
IP header (20 bytes): 45000030 08fe0000 4001fa16 c0a87b03 c0a87b64
Data (28 bytes):
0800b5e8 a80a0500 a69c083d 0b660e00 77777777 77777777 77777777

Augment data with:
Padding: 0102
Pad length: 02
Next header: 01 (ICMP)

Pre-encryption Data with padding, pad length and next header (32 bytes):
0800b5e8 a80a0500 a69c083d 0b660e00 77777777 77777777 77777777 01020201

Post-encryption packet with SPI, Sequence number, IV:
IP header: 4500004c 08fe0000 4032f9c9 c0a87b03 c0a87b64
SPI/Seq #: 00004321 00000008
IV: 69d08df7 d203329d b093fc49 24e5bd80
Encrypted Data (32 bytes):
f5199588 1ec4e0c4 488987ce 742e8109 689bb379 d2d750c0 d915dca3 46a89f75

Case #7: Sample tunnel-mode ESP packet (ping 192.168.123.200)
Key: 01234567 89abcdef 01234567 89abcdef
SPI: 8765
Source address: 192.168.123.3
Destination address: 192.168.123.200
Sequence number: 2
IV: f4e76524 4f6407ad f13dc138 0f673f37






Frankel, et al.             Standards Track                     [Page 8]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


Original packet:
IP header (20 bytes): 45000054 09040000 4001f988 c0a87b03 c0a87bc8
Data (64 bytes):
08009f76 a90a0100 b49c083d 02a20400 08090a0b 0c0d0e0f 10111213 14151617
18191a1b 1c1d1e1f 20212223 24252627 28292a2b 2c2d2e2f 30313233 34353637

Augment data with:
Padding: 01020304 05060708 090a
Pad length: 0a
Next header: 04 (IP-in-IP)

Pre-encryption Data with original IP header, padding, pad length and
                         next header (96 bytes):
45000054 09040000 4001f988 c0a87b03 c0a87bc8 08009f76 a90a0100 b49c083d
02a20400 08090a0b 0c0d0e0f 10111213 14151617 18191a1b 1c1d1e1f 20212223
24252627 28292a2b 2c2d2e2f 30313233 34353637 01020304 05060708 090a0a04

Post-encryption packet with SPI, Sequence number, IV:
IP header: 4500008c 09050000 4032f91e c0a87b03 c0a87bc8
SPI/Seq #: 00008765 00000002
IV: f4e76524 4f6407ad f13dc138 0f673f37
Encrypted Data (96 bytes):
773b5241 a4c44922 5e4f3ce5 ed611b0c 237ca96c f74a9301 3c1b0ea1 a0cf70f8
e4ecaec7 8ac53aad 7a0f022b 859243c6 47752e94 a859352b 8a4d4d2d ecd136e5
c177f132 ad3fbfb2 201ac990 4c74ee0a 109e0ca1 e4dfe9d5 a100b842 f1c22f0d

Case #8: Sample tunnel-mode ESP packet
         (ping -p ff -s 40 192.168.123.200)
Key: 01234567 89abcdef 01234567 89abcdef
SPI: 8765
Source address: 192.168.123.3
Destination address: 192.168.123.200
Sequence number: 5
IV: 85d47224 b5f3dd5d 2101d4ea 8dffab22

Original packet:
IP header (20 bytes): 45000044 090c0000 4001f990 c0a87b03 c0a87bc8
Data (48 bytes):
0800d63c aa0a0200 c69c083d a3de0300 ffffffff ffffffff ffffffff ffffffff
ffffffff ffffffff ffffffff ffffffff

Augment data with:
Padding: 01020304 05060708 090a
Pad length: 0a
Next header: 04 (IP-in-IP)






Frankel, et al.             Standards Track                     [Page 9]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


Pre-encryption Data with original IP header, padding, pad length and
                         next header (80 bytes):
45000044 090c0000 4001f990 c0a87b03 c0a87bc8 0800d63c aa0a0200 c69c083d
a3de0300 ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff
ffffffff 01020304 05060708 090a0a04

Post-encryption packet with SPI, Sequence number, IV:
IP header: 4500007c 090d0000 4032f926 c0a87b03 c0a87bc8
SPI/Seq #: 00008765 00000005
IV: 85d47224 b5f3dd5d 2101d4ea 8dffab22
Encrypted Data (80 bytes):
15b92683 819596a8 047232cc 00f7048f e45318e1 1f8a0f62 ede3c3fc 61203bb5
0f980a08 c9843fd3 a1b06d5c 07ff9639 b7eb7dfb 3512e5de 435e7207 ed971ef3
d2726d9b 5ef6affc 6d17a0de cbb13892

5.  IKE Interactions

5.1.  Phase 1 Identifier

   For Phase 1 negotiations, IANA has assigned an Encryption Algorithm
   ID of 7 for AES-CBC.

5.2.  Phase 2 Identifier

   For Phase 2 negotiations, IANA has assigned an ESP Transform
   Identifier of 12 for ESP_AES.

5.3.  Key Length Attribute

   Since the AES allows variable key lengths, the Key Length attribute
   MUST be specified in both a Phase 1 exchange [IKE] and a Phase 2
   exchange [DOI].

5.4.  Hash Algorithm Considerations

   A companion competition, to select the successor to SHA-1, the
   widely-used hash algorithm, recently concluded.  The resulting
   hashes, called SHA-256, SHA-384 and SHA-512 [SHA2-1, SHA2-2] are
   capable of producing output of three different lengths (256, 384 and
   512 bits), sufficient for the generation (within IKE) and
   authentication (within ESP) of the three AES key sizes (128, 192 and
   256 bits).

   However, HMAC-SHA-1 [HMAC-SHA] and HMAC-MD5 [HMAC-MD5] are currently
   considered of sufficient strength to serve both as IKE generators of
   128-bit AES keys and as ESP authenticators for AES encryption using
   128-bit keys.




Frankel, et al.             Standards Track                    [Page 10]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


6.  Security Considerations

   Implementations are encouraged to use the largest key sizes they can
   when taking into account performance considerations for their
   particular hardware and software configuration.  Note that encryption
   necessarily impacts both sides of a secure channel, so such
   consideration 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.

   For more information regarding the necessary use of random IV values,
   see [CRYPTO-B].

   For further security considerations, the reader is encouraged to read
   [AES].

7.  IANA Considerations

   IANA has assigned Encryption Algorithm ID 7 to AES-CBC.
   IANA has assigned ESP Transform Identifier 12 to ESP_AES.

8.  Intellectual Property Rights Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document 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.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.









Frankel, et al.             Standards Track                    [Page 11]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


9.  References

9.1.  Normative References

   [AES]        NIST, FIPS PUB 197, "Advanced Encryption Standard
                (AES)," November 2001.
                http://csrc.nist.gov/publications/fips/fips197/
                fips-197.{ps,pdf}

   [CBC]        Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher
                Algorithms", RFC 2451, November 1998.

   [ESP]        Kent, S. and R. Atkinson, "IP Encapsulating Security
                Payload (ESP)", RFC 2406, November 1998.

9.2.  Informative References

   [ARCH]       Kent, S. and R. Atkinson, "Security Architecture for the
                Internet Protocol", RFC 2401, 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/papers/probtxt.pdf

   [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.

   [EVALUATION] Ferguson, N. and B. Schneier, "A Cryptographic
                Evaluation of IPsec," Counterpane Internet Security,
                Inc., January 2000.
                http://www.counterpane.com/ipsec.pdf

   [HMAC-MD5]   Madson, C. and R. Glenn, "The Use of HMAC-MD5-96 within
                ESP and AH", RFC 2403, November 1998.

   [HMAC-SHA]   Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96
                within ESP and AH", RFC 2404, November 1998.

   [IKE]        Harkins, D. and D. Carrel, "The Internet Key Exchange
                (IKE)", RFC 2409, November 1998.






Frankel, et al.             Standards Track                    [Page 12]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


   [MODES]      Dworkin, M., "Recommendation for Block Cipher Modes of
                Operation: Methods and Techniques," NIST Special
                Publication 800-38A, December 2001.
                http://csrc.nist.gov/publications/nistpubs/
                800-38a/sp800-38a.pdf

   [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, "AES/Rijndael: speed."
                http://www.tcs.hut.fi/~helger/aes/rijndael.html

   [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.pdf

   [RFC-2119]   Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.

   [ROAD]       Thayer, R., Doraswamy, N. and R. Glenn, "IP Security
                Document Roadmap", RFC 2411, November 1998.

   [SHA2-1]     NIST, FIPS PUB 180-2 "Specifications for the Secure Hash
                Standard," August 2002.
                http://csrc.nist.gov/publications/fips/fips180-2/
                fips180-2.pdf

   [SHA2-2]     "Descriptions of SHA-256, SHA-384, and SHA-512."
                http://csrc.nist.gov/cryptval/shs/sha256-384-512.pdf

10.  Acknowledgments

   Portions of this text, as well as its general structure, were
   unabashedly 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.  We also thank Scott Fluhrer for his
   helpful comments and recommendations.




Frankel, et al.             Standards Track                    [Page 13]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


11.  Authors' Addresses

   Sheila Frankel
   NIST
   820 West Diamond Ave.
   Room 677
   Gaithersburg, MD 20899

   Phone: +1 (301) 975-3297
   EMail: sheila.frankel@nist.gov


   Scott Kelly
   Airespace
   110 Nortech Pkwy
   San Jose CA 95134

   Phone: +1 408 635 2000
   EMail: scott@hyperthought.com


   Rob Glenn
   NIST
   820 West Diamond Ave.
   Room 605
   Gaithersburg, MD 20899

   Phone: +1 (301) 975-3667
   EMail: rob.glenn@nist.gov






















Frankel, et al.             Standards Track                    [Page 14]

RFC 3602        AES-CBC Cipher Algorithm Use with IPsec   September 2003


12.  Full Copyright Statement

   Copyright (C) The Internet Society (2003).  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
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required 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 assignees.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















Frankel, et al.             Standards Track                    [Page 15]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/