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| block size = 64 bits
| block size = 64 bits
| structure = [[Feistel cipher|Feistel network]]
| structure = [[Feistel cipher|Feistel network]]
| rounds = 10
| rounds = Variable
| cryptanalysis =
| cryptanalysis =
}}
}}
In [[cryptography]], '''M8''' is a [[block cipher]] designed by [[Hitachi, Ltd.|Hitachi]] in 1999. It is a modification of Hitachi's earlier [[M6 (cipher)|M6]] algorithm, designed for greater security and high performance in both hardware and 32-bit software implementations. M8 was registered under ISO/IEC 9979 with the registration number 20.<ref>{{cite web
In [[cryptography]], '''M8''' is a [[block cipher]] designed by [[Hitachi, Ltd.|Hitachi]] in 1999. It is a modification of Hitachi's earlier [[M6 (cipher)|M6]] algorithm, designed for greater security and high performance in both hardware and 32-bit software implementations. M8 was registered by Hitachi in March 1999 as ISO/IEC 9979-0020.<ref>{{cite web
|url=http://www.chrismitchell.net/ISO-register/0020.pdf
|url=http://www.chrismitchell.net/ISO-register/0020.pdf
|title=ISO/IEC9979-0020 Register Entry
|title=ISO/IEC9979-0020 Register Entry
Line 19: Line 19:
}} </ref>
}} </ref>


Like M6, M8 is a 10-round [[Feistel cipher]] with a [[block size (cryptography)|block size]] of 64 bits. The round function can include [[bit rotation]]s, [[XOR]]s, and [[modular arithmetic|modular addition]], but the structure of each round function used is determined by the [[key (cryptography)|key]]. Making these variations key-dependent is intended to make [[cryptanalysis]] more difficult (see [[FROG]] for a similar design philosophy).
Like M6, M8 is a [[Feistel cipher]] with a [[block size (cryptography)|block size]] of 64 bits. The round function can include 32-bit [[bit rotation|rotation]]s, [[XOR]]s, and [[modular arithmetic|modular addition]], making it an early example of an [[ARX cipher]].
The cipher features a variable number of rounds (any positive integer N), each of which has a structure determined by a round-specific "algorithm decision [[key (cryptography)|]". Making the rounds key-dependent is intended to make [[cryptanalysis]] more difficult (see [[FROG]] for a similar design philosophy).

==Cipher description==

The round count is customizable, and can be any positive integer N. The key consists of four components: a 64-bit data key, 256-bit key expansion key, a set of N 24-bit algorithm decision keys, and a set of N 96-bit algorithm expansion keys.


==Test vectors==
The published version of ISO/IEC 9979-0020 includes the following test data:

<blockquote>
- Round number: 126
- Key expansion key: 0<sup>256</sup> (an all-zeros vector)
- Data key: 0123 4567 89AB CDEF in hex
- Algorithm decision key:
- rounds 1, 5, 9, ...: 848B6D hex
- rounds 2, 6, 10, ...: 8489BB hex
- rounds 3, 7, 11, ...: 84B762 hex
- rounds 4, 8, 12, ...: 84EDA2 hex
- Algorithm expansion key: 0000 0001 0000 0000 0000 0000 hex for all rounds

- Plaintext: 0000 0000 0000 0001 hex
- Ciphertext after 7 rounds: C5D6 FBAD 76AB A53B hex
- Ciphertext after 14 rounds: 6380 4805 68DB 1895 hex
- Ciphertext after 21 rounds: 2BFB 806E 1292 5B18 hex
- Ciphertext after 28 rounds: F610 6A41 88C5 8747 hex
- Ciphertext after 56 rounds: D3E1 66E9 C50A 10A2 hex
- Final ciphertext after 126 rounds: FE4B 1622 E446 36C0 hex
</blockquote>


==Cryptanalysis==
==Cryptanalysis==

Revision as of 03:22, 6 December 2021

M8
General
DesignersHitachi
First published1999
Derived fromM6
Cipher detail
Block sizes64 bits
StructureFeistel network
RoundsVariable

In cryptography, M8 is a block cipher designed by Hitachi in 1999. It is a modification of Hitachi's earlier M6 algorithm, designed for greater security and high performance in both hardware and 32-bit software implementations. M8 was registered by Hitachi in March 1999 as ISO/IEC 9979-0020.[1]

Like M6, M8 is a Feistel cipher with a block size of 64 bits. The round function can include 32-bit rotations, XORs, and modular addition, making it an early example of an ARX cipher.

The cipher features a variable number of rounds (any positive integer N), each of which has a structure determined by a round-specific "algorithm decision [[key (cryptography)|]". Making the rounds key-dependent is intended to make cryptanalysis more difficult (see FROG for a similar design philosophy).

Cipher description

The round count is customizable, and can be any positive integer N. The key consists of four components: a 64-bit data key, 256-bit key expansion key, a set of N 24-bit algorithm decision keys, and a set of N 96-bit algorithm expansion keys.


Test vectors

The published version of ISO/IEC 9979-0020 includes the following test data:

- Round number: 126 - Key expansion key: 0256 (an all-zeros vector) - Data key: 0123 4567 89AB CDEF in hex - Algorithm decision key: - rounds 1, 5, 9, ...: 848B6D hex - rounds 2, 6, 10, ...: 8489BB hex - rounds 3, 7, 11, ...: 84B762 hex - rounds 4, 8, 12, ...: 84EDA2 hex - Algorithm expansion key: 0000 0001 0000 0000 0000 0000 hex for all rounds

- Plaintext: 0000 0000 0000 0001 hex - Ciphertext after 7 rounds: C5D6 FBAD 76AB A53B hex - Ciphertext after 14 rounds: 6380 4805 68DB 1895 hex - Ciphertext after 21 rounds: 2BFB 806E 1292 5B18 hex - Ciphertext after 28 rounds: F610 6A41 88C5 8747 hex - Ciphertext after 56 rounds: D3E1 66E9 C50A 10A2 hex - Final ciphertext after 126 rounds: FE4B 1622 E446 36C0 hex

Cryptanalysis

The key-dependent behaviour of the cipher results in a large class of weak keys which expose the cipher to a range of attacks, including differential cryptanalysis, linear cryptanalysis and mod n cryptanalysis[2].

References

  1. ^ "ISO/IEC9979-0020 Register Entry" (PDF). Professor Chris Mitchell, Information Security Group, Royal Holloway, University of London. ISO/IEC 9979 Register of Cryptographic Algorithms.
  2. ^ Toshio Tokita; Tsutomu Matsumoto. "On Applicability of Differential Cryptanalysis, Linear Cryptanalysis and Mod n Cryptanalysis to an Encryption Algorithm M8 (ISO9979-20)". Ipsj Journal. 42 (8).


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