SMS4 is a block cipher

Block cipher

In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation. A block cipher encryption algorithm might take a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext...

 used in the Chinese

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 National Standard for Wireless LAN WAPI (Wired Authentication and Privacy Infrastructure).

SMS4 was a proposed cipher to be used in IEEE 802.11i

IEEE 802.11i

IEEE 802.11i-2004 or 802.11i, implemented as WPA2, is an amendment to the original IEEE 802.11. The draft standard was ratified on 24 June 2004. This standard specifies security mechanisms for wireless networks. It replaced the short Authentication and privacy clause of the original standard with...

 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
  Key schedule
  [[Image:DES-key-schedule.png|thumbnail|220px|The key schedule of DES [[Image:DES-key-schedule.png|thumbnail|220px|The key schedule of DES [[Image:DES-key-schedule.png|thumbnail|220px|The key schedule of DES ("[[Image:DES-key-schedule.png|thumbnail|220px|The key schedule of DES ("...
  
  is used to produce the round keys.
• Decryption is using the same keys as encryption, but in reversed order.

Word and Byte

Define as a vector set of e bits.

is a word.

is a byte.

Keys and Key Parameters

The length of encryption keys are 128-bit, 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 Shu-wang(吕述望) in Chinese
• Example of SMS4 implemented in ANSI C