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GM/T 0002-2012: SM4 Block Cipher Algorithm
GM/T 0002-2012
GM
CRYPTOGRAPHIC INDUSTRY STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
ICS 35.040
L 80
Record no.. 36825-2012
SM4 block cipher algorithm
ISSUED ON. MARCH 21, 2012
IMPLEMENTED ON. MARCH 21, 2012
Issued by. State Cryptography Administration of the People’s Republic of
China
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Terms and definitions ... 4
3 Symbols and abbreviations ... 5
4 Algorithm structure ... 5
5 Key and key parameters ... 5
6 Round function ... 5
6.1 Structure of round function ... 5
6.2 Compound replacement T ... 6
7 Algorithm description ... 7
7.1 Encryption algorithm ... 7
7.2 Decryption algorithm ... 7
7.3 Key expansion algorithm ... 7
Annex A (Informative) Examples of operation ... 9
A.1 Example 1 ... 9
A.2 Example 2 ... 10
SM4 block cipher algorithm
1 Scope
This Standard specifies the algorithm structure and algorithm description of SM4 block
cipher algorithm and gives examples for computation.
This Standard applies to the requirements for the use of block cipher algorithm in
cryptographic applications.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
block length
Number of bits of an information block.
2.2
key length
Number of bits of key.
2.3
key expansion algorithm
Arithmetic unit in which a key is converted into a round key.
2.4
rounds
Number of iterations of round function.
2.5
word
Block (string) of 32-bit length.
2.6
S-box
S-box is the fixed replacement of 8-bit input with 8-bit output, expressed as Sbox(.).
3 Symbols and abbreviations
32-bit exclusive-OR operation
Left shift of 32-bit words by i bits
4 Algorithm structure
SM4 cipher algorithm is a block algorithm. The block length of the algorithm is 128 bits;
the key length is 128 bits. Both encryption algorithm and key expansion algorithm are
of a 32-round nonlinear iteration structure. Data decryption and data encryption are of
the same algorithm structure, but the use orders of round keys are opposite. A
decryption round key is the reverse order of an encryption round key.
5 Key and key parameters
The length of an encryption key is 128 bits, expressed as MK = (MK0, MK1, MK2, MK3),
where MKi (i = 0, 1, 2, 3) is a word.
Round keys are expressed as (rk0, Fk1, FK2, FK3), where rki (i = 0, ..., 31) is a 32-bit
word. Round keys are generated by encryption keys.
FK = (FK0, FK1, FK2, FK3), a system parameter, and CK = (CK0, CK1, ..., CK31), a fixed
parameter, are used for key expansion algorithm, where FKi (i =0, ..., 3) and CKi (i =
0, ..., 31) are words.
6 Round function
6.1 Structure of round function
Let the input be and the round key , then the round
function F is.