 | |
| General | |
|---|---|
| Designers | Data Assurance & Communication Security Center,Chinese Academy of Sciences |
| First published | 2006 (declassified; standardized March 21, 2012)[1] |
| Cipher detail | |
| Key sizes | 128 bits |
| Block sizes | 128 bits |
| Structure | Unbalanced Feistel network |
| Rounds | 32 |
| Best publiccryptanalysis | |
| Linear anddifferential attacks against 22 rounds | |
ShāngMì 4 (SM4, 商密4) (formerlySMS4)[2] is ablock cipher, standardised for commercial cryptography in China.[3] It is used in theChinese National Standard for Wireless LANWAPI (WLAN Authentication and Privacy Infrastructure), and withTransport Layer Security.[4]
SM4 was a cipher proposed for theIEEE 802.11i standard, but it has so far been rejected. One of the reasons for the rejection has been opposition to the WAPI fast-track proposal by theIEEE.[citation needed]
SM4 was published asISO/IEC 18033-3/Amd 1 in 2021.
The SM4 algorithm was drafted by Data Assurance & Communication Security Center,Chinese Academy of Sciences (CAS), and Commercial Cryptography Testing Center, National Cryptography Administration. It is mainly developed by Lü Shuwang (Chinese:吕述望). The algorithm was declassified in January, 2006, and it became a national standard (GB/T 32907-2016) in August 2016.[5]
The SM4 cipher has a key size and a block size of 128 bits each.[6][7] Encryption or decryption of one block of data is composed of 32 rounds. A non-linearkey schedule is used to produce the round keys and the decryption uses the same round keys as for encryption, except that they are in reversed order.
The length of encryption keys is 128 bits, represented as, in which is a 32-bit word. The round keys are represented by, where each is a word. It is generated by the encryption key and the following parameters:
and are words, used to generate the round keys.
Each round are computed from the four previous round outputs such that:
Where is a substitution function composed of a non-linear transform, the S-box and linear transform
SM4's S-box is fixed for 8-bit input and 8-bit output, noted as Sbox(). As withAdvanced Encryption Standard (AES), the S-box is based on themultiplicative inverse overGF(28). The affine transforms and polynomial bases are different from that of AES, but due toaffine isomorphism it can be calculated efficiently given anAES S-Box.[8]
On March 21, 2012, the Chinese government published the industrial standard "GM/T 0002-2012 SM4 Block Cipher Algorithm", officially renaming SMS4 to SM4.[2]
A description of SM4 in English is available as anInternet Draft. It contains areference implementation inANSI C.[9]
SM4 is part of theARMv8.4-A expansion to the ARM architecture.[10] SM4 support for theRISC-V architecture was ratified in 2021 as the Zksed extension.[11]
SM4 is supported by Intel processors, starting fromArrow Lake S,Lunar Lake, Diamond Rapids and Clearwater Forest.[12]
