SMS4

SMS4
General
Designers	Chinese Government
First published	2006 (declassified),(standardized in 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

SMS4 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.
Uses an 8-bit S-box
The key size is 128 bits.
The only operations used are XOR, circular shifts and S-Box applications
Performs 32 rounds to process one block.
Each round updates a quarter (32 bits) of the internal state.
A non-linear key schedule is used to produce the round keys.
Decryption is using the same keys as encryption, but in reversed order.

Terms and Definitions

Word and Byte

Define $Z^e_2$ as a vector set of e bits.

$Z^{32}_2$ is a word.

$Z^8_2$ 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

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

External links

Block ciphers (security summary)

Common algorithms	AES Blowfish DES (Internal Mechanics, Triple DES) Serpent Twofish

Less common algorithms	Camellia CAST-128 IDEA RC2 RC5 SEED ARIA Skipjack TEA XTEA

Other algorithms	3-Way Akelarre Anubis BaseKing BassOmatic BATON BEAR and LION CAST-256 Chiasmus CIKS-1 CIPHERUNICORN-A CIPHERUNICORN-E CLEFIA CMEA Cobra COCONUT98 Crab Cryptomeria/C2 CRYPTON CS-Cipher DEAL DES-X DFC E2 FEAL FEA-M FROG G-DES GOST Grand Cru Hasty Pudding cipher Hierocrypt ICE IDEA NXT Intel Cascade Cipher Iraqi KASUMI KeeLoq KHAZAD Khufu and Khafre KN-Cipher Ladder-DES Libelle LOKI (97, 89/91) Lucifer M6 M8 MacGuffin Madryga MAGENTA MARS Mercy MESH MISTY1 MMB MULTI2 MultiSwap New Data Seal NewDES Nimbus NOEKEON NUSH PRESENT Q RC6 REDOC Red Pike S-1 SAFER SAVILLE SC2000 SHACAL SHARK Simon SMS4 Speck Spectr-H64 Square SXAL/MBAL Threefish Treyfer UES Xenon xmx XXTEA Zodiac

Design	Feistel network Key schedule Lai-Massey scheme Product cipher S-box P-box SPN Avalanche effect Block size Key size Key whitening (Whitening transformation)

Attack (cryptanalysis)	Brute-force (EFF DES cracker) MITM (Biclique attack, 3-subset MITM attack) Linear (Piling-up lemma) Differential (Impossible Truncated Higher-order) Differential-linear Distinguishing (Known-key) Integral/Square Boomerang Mod n Related-key Slide Rotational Timing XSL Interpolation Partitioning Davies' Rebound Weak key Tau Chi-square Time/memory/data tradeoff

Standardization	AES process CRYPTREC NESSIE

Utilization	Initialization vector Mode of operation Padding

Cryptography

History of cryptography Cryptanalysis Outline of cryptography

Symmetric-key algorithm Block cipher Stream cipher Public-key cryptography Cryptographic hash function Message authentication code Random numbers Steganography

Portal

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