Template:Infobox block cipher 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 fasttrack proposal by the IEEE.
The SMS4 algorithm was invented by Prof. LU Shuwang(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 8bit Sbox
 The key size is 128 bits.
 The only operations used are XOR, circular shifts and SBox applications
 Performs 32 rounds to process one block.
 Each round updates a quarter (32 bits) of the internal state.
 A nonlinear 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 as a vector set of e bits.
is a word.
is a byte.
Sbox[]
Sbox is fixed for 8bit input and 8bit output, noted as Sbox().
Keys and Key Parameters[]
The length of encryption keys are 128bit, represented as , in which is a word.
A round key is represented as . It is generated by the encryption key.
is a system parameter.
is a fixed parameter.
and are words, used for extension of the algorithm.
External links[]
 Chinese document describing the SMS4 cipher
 English translation of the Chinese document
 Linear and Differential Cryptanalysis of Reduced SMS4 Block Cipher
 Example of SMS4 implemented as a Spreadsheet
 Page of Prof. LU Shuwang(吕述望) in Chinese
 Example of SMS4 implemented in ANSI C
