SM4 (cipher)

SM4
General
Designers	Chinese Government
First published	2006 (declassified; standardized March 21, 2012)
Cipher detail
Key sizes	128 bits
Block sizes	128 bits
Structure	unbalanced Feistel network
Rounds	32
Best public cryptanalysis
	linear and differential attacks against 22 rounds

SM4 (formerly SMS4)^[1] is a block cipher used in the Chinese National Standard for Wireless LAN WAPI (Wired Authentication and Privacy Infrastructure).

SMS4 was a proposed cipher to be used in IEEE 802.11i standard, but has so far been rejected by ISO. One of the reasons for the rejection has been opposition to the WAPI fast-track proposal by the IEEE.

The SMS4 algorithm was invented by Prof. LU Shu-wang (吕述望). The algorithm was declassified in January, 2006. A few details of the SMS4 cipher are:

It has a block size of 128 bits.
It uses an 8-bit S-box.
The key size is 128 bits.
The only operations used are XOR, 32-bit circular shifts and S-Box applications
Encryption or decryption of one block of data is composed of 32 rounds.
Each round updates a quarter of the internal state (i.e., 32 bits).
A non-linear key schedule is used to produce the round keys.
Decryption uses the same round keys as for encryption, except that they are in reversed order.

Terms and Definitions

Word and Byte

Define $Z_{2}^{e}$ as a vector set of e bits.

$Z_{2}^{{32}}$ is a word.

$Z_{2}^{8}$ is a byte.

S-box

S-box is fixed for 8-bit input and 8-bit output, noted as Sbox().

Keys and Key Parameters

The length of encryption keys are 128-bit, represented as $MK=(MK_{0},\ MK_{1},\ MK_{2},\ MK_{3})$ , in which $MK_{i}\ (i=0,\ 1,\ 2,\ 3)$ is a word.

A round key is represented as $(rk_{0},\ rk_{1},\ \ldots ,\ rk_{{31}})$ ,where each $rk_{i}(i=0,\ \ldots ,\ 31)$ is a word. It is generated by the encryption key.

$FK=(FK_{0},\ FK_{1},\ FK_{2},\ FK_{3})$ is a system parameter.

$CK=(CK_{0},\ CK_{1},\ \ldots ,\ CK_{{31}})$ is a fixed parameter, used to generate $rk_{i}$ .

$FK_{i}$ and $CK_{i}$ are words, used for extension of the algorithm.

Remark

On Mar 21, 2012, the Chinese government published the industrial standard <GM/T 0002-2012 SM4 Block Cipher Algorithm Standard>, officially renaming SMS4 to SM4.

References

↑ "国家密码管理局公告（第23号）". The Office of Security Commercial Code Administration (OSCCA). 2012-03-21. Retrieved 2016-07-24.

External links

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[1] "国家密码管理局公告（第23号）". The Office of Security Commercial Code Administration (OSCCA). 2012-03-21. Retrieved 2016-07-24.