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| {{Infobox block cipher
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| | name = SMS4
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| | image =
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| | caption =
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| | designers =
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| | publish date = 2006 (declassified)
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| | derived from =
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| | derived to =
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| | key size = 128 bits
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| | block size = 128 bits
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| | structure = [[Feistel cipher|unbalanced Feistel network]]
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| | rounds = 32
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| | cryptanalysis = [[linear cryptanalysis|linear]] and [[differential cryptanalysis|differential]] attacks against 22 rounds
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| }}
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| '''SMS4''' is a [[block cipher]] used in the [[China|Chinese]] National Standard for Wireless LAN [[WLAN Authentication and Privacy Infrastructure|WAPI]] (Wired Authentication and Privacy Infrastructure). | |
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| SMS4 was a proposed cipher to be used in [[IEEE 802.11i]] standard, but has so far been rejected by [[International Organization for Standardization|ISO]]. One of the reasons for the rejection has been opposition to the WAPI fast-track proposal by the [[IEEE]].
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| 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:
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| * It has a block size of 128 bits.
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| * Uses an 8-bit [[S-box]]
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| * The key size is 128 bits.
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| * The only operations used are XOR, circular shifts and S-Box applications
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| * Performs 32 rounds to process one block.
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| * Each round updates a quarter (32 bits) of the internal state.
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| * A non-linear [[key schedule]] is used to produce the round keys.
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| * Decryption is using the same keys as encryption, but in reversed order.
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| ==Terms and Definitions==
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| ===Word and Byte===
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| Define <math>Z^e_2</math> as a vector set of ''e'' bits.
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| <math>Z^{32}_2</math> is a '''word'''. | |
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| <math>Z^8_2</math> is a '''byte'''.
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| ===S-box===
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| S-box is fixed for 8-bit input and 8-bit output, noted as Sbox().
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| ===Keys and Key Parameters===
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| The length of encryption keys are 128-bit, represented as <math>MK=(MK_0,\ MK_1,\ MK_2,\ MK_3)</math>, in which <math>MK_i\ (i=0,\ 1,\ 2,\ 3)</math> is a word.
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| A round key is represented as <math>(rk_0,\ rk_1,\ \ldots,\ rk_{31})</math>. It is generated by the encryption key.
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| <math>FK=(FK_0,\ FK_1,\ FK_2,\ FK_3)</math> is a system parameter.
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| <math>CK=(CK_0,\ CK_1,\ \ldots,\ CK_{31})</math> is a fixed parameter.
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| <math>FK_i</math> and <math>CK_i</math> are words, used for extension of the algorithm.
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| ==External links==
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| * [http://www.oscca.gov.cn/UpFile/200621016423197990.pdf Chinese document describing the SMS4 cipher]
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| * [http://eprint.iacr.org/2008/329.pdf English translation of the Chinese document]
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| * [http://eprint.iacr.org/2008/281 Linear and Differential Cryptanalysis of Reduced SMS4 Block Cipher]
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| * [http://www.cryptoclarity.com/CryptoClarityLLC/Welcome/Entries/2009/2/24_SMS4_Cipher_as_a_Spreadsheet.html Example of SMS4 implemented as a Spreadsheet]
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| * [http://www.lois.labs.gov.cn/personnel/lvshuwang.htm Page of Prof. LU Shu-wang(吕述望) in Chinese]
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| * [http://hi.baidu.com/numax/blog/item/80addfefddfb93e4cf1b3e61.html Example of SMS4 implemented in ANSI C]
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| {{Cryptography navbox | block}}
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| [[Category:Block ciphers]]
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