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RFC 4196

The SEED Cipher Algorithm and Its Use with IPsec

Pages: 12
Proposed Standard

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Network Working Group                                           H.J. Lee
Request for Comments: 4196                                     J.H. Yoon
Category: Standards Track                                       S.L. Lee
                                                                J.I. Lee
                                                                    KISA
                                                            October 2005


            The SEED 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 (2005).

Abstract

This document describes the use of the SEED block cipher algorithm in the Cipher Block Chaining Mode, with an explicit IV, as a confidentiality mechanism within the context of the IPsec Encapsulating Security Payload (ESP).

1. Introduction

1.1. SEED

SEED is a national industrial association standard [TTASSEED] and is widely used in South Korea for electronic commerce and financial services that are operated on wired and wireless communications. SEED is a 128-bit symmetric key block cipher that has been developed by KISA (Korea Information Security Agency) and a group of experts since 1998. The input/output block size of SEED is 128-bit and the key length is also 128-bit. SEED has the 16-round Feistel structure. A 128-bit input is divided into two 64-bit blocks, and the right 64- bit block is an input to the round function with a 64-bit subkey that is generated from the key scheduling. SEED is easily implemented in various software and hardware, and it can be effectively adopted to a computing environment with restricted resources, such as mobile devices and smart cards.
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   SEED is robust against known attacks including DC (Differential
   cryptanalysis), LC (Linear cryptanalysis), and related key attacks.
   SEED has gone through wide public scrutinizing procedures.  It has
   been evaluated and is considered cryptographically secure by credible
   organizations such as ISO/IEC JTC 1/SC 27 and Japan CRYPTREC
   (Cryptography Research and Evaluation Committees)[ISOSEED][CRYPTREC].

   The remainder of this document specifies the use of SEED within the
   context of IPsec ESP.  For further information on how the various
   pieces of ESP fit together to provide security services, please refer
   to [ARCH], [ESP], and [ROAD].

1.2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase, as shown) are to be interpreted as described in RFC 2119 [KEYWORDS].

2. The SEED 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 SEED. The algorithm specification and object identifiers are described in [ISOSEED] [SEED]. The SEED homepage, http://www.kisa.or.kr/seed/seed_eng.html, contains a wealth of information about SEED, including a detailed specification, evaluation report, test vectors, and so on.

2.1. Mode

NIST has defined 5 modes of operation for the Advanced Encryption Standard (AES) [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 SEED cipher in the 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 that 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.
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   More information on the CBC mode can be obtained in [MODES]
   [CRYPTO-S].  For use of the CBC mode in ESP with 64-bit ciphers,
   please see [CBC].

2.2. Key Size and Numbers of Rounds

SEED supports 128-bit key and has the 16-round Feistel structure.

2.3. Weak Keys

At the time this document was written, there were no known weak keys for SEED.

2.4. Block Size and Padding

SEED uses a block size of 16 octets (128 bits). Padding is required by SEED 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. Performance

Performance figures of SEED are available at http://www.kisa.or.kr/seed/seed_eng.html
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3. ESP Payload

The ESP Payload is made up of the Initialization Vector(IV) of 16 octets followed by the encrypted payload. 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 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.

4. Test Vectors

The first 2 test cases test SEED-CBC encryption. Each test case includes key, the plaintext, and the resulting ciphertext. All data are hexadecimal numbers (not prefixed by "0x"). The last 4 test cases illustrate sample ESP packets using SEED-CBC for encryption. All data are hexadecimal numbers (not prefixed by "0x"). Case #1 : Encrypting 32 bytes (2 blocks) using SEED-CBC with 128-bit key Key : ed2401ad 22fa2559 91bafdb0 1fefd697 IV : 93eb149f 92c9905b ae5cd34d a06c3c8e PlainText : b40d7003 d9b6904b 35622750 c91a2457 5bb9a632 364aa26e 3ac0cf3a 9c9d0dcb CipherText : f072c5b1 a0588c10 5af8301a dcd91dd0 67f68221 55304bf3 aad75ceb 44341c25
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   Case #2    : Encrypting 64 bytes (4 blocks) using SEED-CBC with
                128-bit key
   Key        : 88e34f8f  081779f1  e9f39437  0ad40589
   IV         : 268d66a7  35a81a81  6fbad9fa  36162501
   PlainText  : d76d0d18  327ec562  b15e6bc3  65ac0c0f
                8d41e0bb  938568ae  ebfd92ed  1affa096
                394d20fc  5277ddfc  4de8b0fc  e1eb2b93
                d4ae40ef  4768c613  b50b8942  f7d4b9b3
   CipherText : a293eae9  d9aebfac  37ba714b  d774e427
                e8b706d7  e7d9a097  228639e0  b62b3b34
                ced11609  cef2abaa  ec2edf97  9308f379
                c31527a8  267783e5  cba35389  82b48d06

   Case #3  : 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
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   Post-encryption packet with SPI, Sequence number, IV :
   IP Header : 45000054 08f20000 4001f9fe  c0a87b03  c0a87b64
   SPI/Seq # : 00004321 00000001
   IV        : e96e8c08  ab465763  fd098d45  dd3ff893
   Encrypted Data (80 bytes) :
   e7ebaa03  cf45ef09  021b3011  b40d3769
   be96ebae  cd4222f6  b6f84ce5  b2d5cdd1
   60eb6b0e  5a47d16a  501a4d10  7b2d7cc8
   ab86ba03  9a000972  66374fa8  f87ee0fb
   ef3805db  faa144a2  334a34db  0b0f81ca

   Case #4 : 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) :
   b9ad6e19  e9a6a2fa  02569160  2c0af541
   db0b0807  e1f660c7  3ae2700b  5bb5efd1
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   Case #5 : 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

   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):
   2638aa7b  05e71b54  9348082b  67b47b26
   c565aed4  737f0bcb  439c0f00  73e7913c
   3c8a3e4f  5f7a5062  003b78ed  7ca54a08
   c7ce047d  5bec14e4  8cba1005  32a12097
   8d7f5503  204ef661  729b4ea1  ae6a9178
   59a5caac  46e810bd  7875bd13  d6f57b3d
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   Case #6 : 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)

   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) :
   311168e0  bc36ac4e  59802bd5  192c5734
   8f3d29c8  90bab276  e9db4702  91f79ac7
   79571929  c170f902  ffb2f08b  d448f782
   31671414  ff29b7e0  168e1c87  09ba2b67
   a56e0fbc  4ff6a936  d859ed57  6c16ef1b
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5. Interaction with IKE

This section describes the use of IKE [IKE] to establish IPsec ESP security associations (SAs) that employ SEED in CBC mode.

5.1. Phase 1 Identifier

For Phase 1 negotiations, the object identifier of SEED-CBC is defined in [SEED]. algorithm OBJECT IDENTIFIER ::= { iso(1) member-body(2) korea(410) kisa(200004) algorithm(1) } id-seedCBC OBJECT IDENTIFIER ::= { algorithm seedCBC(4) }

5.2. Phase 2 Identifier

For Phase 2 negotiations, IANA has assigned an ESP Transform Identifier of (21) for ESP_SEED_CBC.

5.3. Key Length Attribute

Since the SEED supports 128-bit key lengths, the Key Length attribute is set with 128 bits.

5.4. Hash Algorithm Considerations

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 SEED keys and as ESP authenticators for SEED encryption using 128-bit keys.

6. Security Considerations

No security problem has been found on SEED. SEED is secure against all known attacks including Differential cryptanalysis, Linear cryptanalysis, and related key attacks. The best known attack is only an exhaustive search for the key (by [CRYPTREC]). For further security considerations, the reader is encouraged to read [CRYPTREC], [ISOSEED], and [SEED-EVAL].

7. IANA Considerations

IANA has assigned ESP Transform Identifier (21) to ESP_SEED_CBC.
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8. Acknowledgments

The authors want to thank Ph.D Haesuk Kim of Future Systems Inc. and Brian Kim of OULLIM Information Technology Inc. for providing expert advice on Test Vector examples.

9. References

9.1. Normative References

[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. [IKE] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, November 1998. [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [SEED] Park, J., Lee, S., Kim, J., and J. Lee, "The SEED Encryption Algorithm", RFC 4009, February 2005. [TTASSEED] Telecommunications Technology Association (TTA), South Korea, "128-bit Symmetric Block Cipher (SEED)", TTAS.KO- 12.0004, September, 1998 (In Korean) http://www.tta.or.kr/English/new/main/index.htm

9.2. Informative Reference

[AES] NIST, FIPS PUB 197, "Advanced Encryption Standard(AES), November 2001. http://csrc.nist.gov/publications/fips/fips197/fips-197. {ps,pdf} [ARCH] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [CRYPTO-S] Schneier, B., "Applied Cryptography Second Edition", John Wiley & Sons, New York, NY, 1995, ISBN 0-471-12845-7. [CRYPTREC] Information-technology Promotion Agency (IPA), Japan, CRYPTREC. "SEED Evaluation Report", February, 2002 http://www.kisa.or.kr/seed/seed_eng.html
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   [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.

   [ISOSEED]   ISO/IEC JTC 1/SC 27 N3979, "IT Security techniques -
               Encryption Algorithms - Part3 : Block ciphers", June
               2004.

   [MODES]     Symmetric Key Block Cipher Modes of Operation,
               http://www.nist.gov/modes/.

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

   [SEED-EVAL] KISA, "Self Evaluation Report",
               http://www.kisa.or.kr/seed/data/Document_pdf/
               SEED_Self_Evaluation.pdf"

Authors' Address

Hyangjin Lee Korea Information Security Agency Phone: +82-2-405-5446 Fax : +82-2-405-5319 EMail : jiinii@kisa.or.kr Jaeho Yoon Korea Information Security Agency Phone: +82-2-405-5434 Fax : +82-2-405-5219 EMail : jhyoon@kisa.or.kr Seoklae Lee Korea Information Security Agency Phone: +82-2-405-5230 Fax : +82-2-405-5219 EMail : sllee@kisa.or.kr Jaeil Lee Korea Information Security Agency Phone: +82-2-405-5200 Fax : +82-2-405-5219 EMail: jilee@kisa.or.kr
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Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   This document is subject to the rights, licenses and restrictions
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