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SM4 (cipher)

Block cipher used predominately in China

ShāngMì 4 (SM4, 商密4) (formerly SMS4) is a block cipher, standardised for commercial cryptography in China. It is used in the Chinese National Standard for Wireless LAN WAPI (WLAN Authentication and Privacy Infrastructure), and with Transport Layer Security.

SM4 was a cipher proposed for the IEEE 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 the IEEE. SM4 was published as GM/T 0002 in 2012 and ISO/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. The SM4 cipher has a key size and a block size of 128 bits each. Encryption or decryption of one block of data is composed of 32 rounds.

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