SMS4

SMS4 is a block cipher used in the WAPI Chinese WLAN security standard with a key length and block size of 128 bits. After the algorithm was initially classified as secret, it was published in 2006.

Method

The 128- bit key is expanded to 32 round keys, each with 32 bits. The 128-bit input is divided into four words of 32 bits. The encryption is done in 32 rounds, in the round function in each round only operates on a 32- bit word. Structurally, it is at SMS4 by an unbalanced Feistelchiffre with 32 rounds. The round function is composed of a non-linear substitution, based on an 8-bit S-box, and a linear replacement.

Security

In the cryptanalysis of SMS4 researchers found security problems in the round function.

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