SM4 introduction
The SM4 algorithm is a symmetric encryption algorithm , also known as the national secret algorithm. It was designed by Chinese cryptographers and has been included in the standards of the State Cryptozoology Bureau.
The SM4 algorithm uses a 128-bit key and block size , and uses 32 rounds of iterative encryption, which can be used to encrypt data and verify message authentication codes. Its encryption efficiency is very high and its security is also very good. It is widely used in various security fields, such as e-commerce, mobile communications and cloud computing.
Algorithm implementation flow chart
Encryption Algorithm
Key expansion algorithm
Among them, the generation process of K0~K3 is as follows:
Assume the input key is MK = (MK0, MK1, MK2, MK3), then (K0, K1, K2, K3) = (MK0 ^ FK0, MK1 ^ FK1, MK2 ^ FK2, MK3^FK3)
Note:
- CKi and FKi are constants ;
- The value of i is i=0,1,...31, and a total of 32 subkeys are generated .
Source code
encryption
S_BOX = [0xD6, 0x90, 0xE9, 0xFE, 0xCC, 0xE1, 0x3D, 0xB7, 0x16, 0xB6, 0x14, 0xC2, 0x28, 0xFB, 0x2C, 0x05,
0x2B, 0x67, 0x9A, 0x76, 0x2A, 0xBE, 0x04, 0xC3, 0xAA, 0x44, 0x13, 0x26, 0x49, 0x86, 0x06, 0x99,
0x9C, 0x42, 0x50, 0xF4, 0x91, 0xEF, 0x98, 0x7A, 0x33, 0x54, 0x0B, 0x43, 0xED, 0xCF, 0xAC, 0x62,
0xE4, 0xB3, 0x1C, 0xA9, 0xC9, 0x08, 0xE8, 0x95, 0x80, 0xDF, 0x94, 0xFA, 0x75, 0x8F, 0x3F, 0xA6,
0x47, 0x07, 0xA7, 0xFC, 0xF3, 0x73, 0x17, 0xBA, 0x83, 0x59, 0x3C, 0x19, 0xE6, 0x85, 0x4F, 0xA8,
0x68, 0x6B, 0x81, 0xB2, 0x71, 0x64, 0xDA, 0x8B, 0xF8, 0xEB, 0x0F, 0x4B, 0x70, 0x56, 0x9D, 0x35,
0x1E, 0x24, 0x0E, 0x5E, 0x63, 0x58, 0xD1, 0xA2, 0x25, 0x22, 0x7C, 0x3B, 0x01, 0x21, 0x78, 0x87,
0xD4, 0x00, 0x46, 0x57, 0x9F, 0xD3, 0x27, 0x52, 0x4C, 0x36, 0x02, 0xE7, 0xA0, 0xC4, 0xC8, 0x9E,
0xEA, 0xBF, 0x8A, 0xD2, 0x40, 0xC7, 0x38, 0xB5, 0xA3, 0xF7, 0xF2, 0xCE, 0xF9, 0x61, 0x15, 0xA1,
0xE0, 0xAE, 0x5D, 0xA4, 0x9B, 0x34, 0x1A, 0x55, 0xAD, 0x93, 0x32, 0x30, 0xF5, 0x8C, 0xB1, 0xE3,
0x1D, 0xF6, 0xE2, 0x2E, 0x82, 0x66, 0xCA, 0x60, 0xC0, 0x29, 0x23, 0xAB, 0x0D, 0x53, 0x4E, 0x6F,
0xD5, 0xDB, 0x37, 0x45, 0xDE, 0xFD, 0x8E, 0x2F, 0x03, 0xFF, 0x6A, 0x72, 0x6D, 0x6C, 0x5B, 0x51,
0x8D, 0x1B, 0xAF, 0x92, 0xBB, 0xDD, 0xBC, 0x7F, 0x11, 0xD9, 0x5C, 0x41, 0x1F, 0x10, 0x5A, 0xD8,
0x0A, 0xC1, 0x31, 0x88, 0xA5, 0xCD, 0x7B, 0xBD, 0x2D, 0x74, 0xD0, 0x12, 0xB8, 0xE5, 0xB4, 0xB0,
0x89, 0x69, 0x97, 0x4A, 0x0C, 0x96, 0x77, 0x7E, 0x65, 0xB9, 0xF1, 0x09, 0xC5, 0x6E, 0xC6, 0x84,
0x18, 0xF0, 0x7D, 0xEC, 0x3A, 0xDC, 0x4D, 0x20, 0x79, 0xEE, 0x5F, 0x3E, 0xD7, 0xCB, 0x39, 0x48
]
FK = [0xa3b1bac6, 0x56aa3350, 0x677d9197, 0xb27022dc]
CK = [
0x00070e15, 0x1c232a31, 0x383f464d, 0x545b6269,
0x70777e85, 0x8c939aa1, 0xa8afb6bd, 0xc4cbd2d9,
0xe0e7eef5, 0xfc030a11, 0x181f262d, 0x343b4249,
0x50575e65, 0x6c737a81, 0x888f969d, 0xa4abb2b9,
0xc0c7ced5, 0xdce3eaf1, 0xf8ff060d, 0x141b2229,
0x30373e45, 0x4c535a61, 0x686f767d, 0x848b9299,
0xa0a7aeb5, 0xbcc3cad1, 0xd8dfe6ed, 0xf4fb0209,
0x10171e25, 0x2c333a41, 0x484f565d, 0x646b7279
]
def wd_to_byte(wd, bys):
bys.extend([(wd >> i) & 0xff for i in range(24, -1, -8)])
def bys_to_wd(bys):
ret = 0
for i in range(4):
bits = 24 - i * 8
ret |= (bys[i] << bits)
return ret
def s_box(wd):
"""
进行非线性变换，查S盒
:param wd: 输入一个32bits字
:return: 返回一个32bits字 ->int
"""
ret = []
for i in range(0, 4):
byte = (wd >> (24 - i * 8)) & 0xff
row = byte >> 4
col = byte & 0x0f
index = (row * 16 + col)
ret.append(S_BOX[index])
return bys_to_wd(ret)
def rotate_left(wd, bit):
"""
:param wd: 待移位的字
:param bit: 循环左移位数
:return:
"""
return (wd << bit & 0xffffffff) | (wd >> (32 - bit))
def Linear_transformation(wd):
"""
进行线性变换L
:param wd: 32bits输入
"""
return wd ^ rotate_left(wd, 2) ^ rotate_left(wd, 10) ^ rotate_left(wd, 18) ^ rotate_left(wd, 24)
def Tx(k1, k2, k3, ck):
"""
密钥扩展算法的合成变换
"""
xor = k1 ^ k2 ^ k3 ^ ck
t = s_box(k1 ^ k2 ^ k3 ^ ck)
return t ^ rotate_left(t, 13) ^ rotate_left(t, 23)
def T(x1, x2, x3, rk):
"""
加密算法轮函数的合成变换
"""
t = x1 ^ x2 ^ x3 ^ rk
t = s_box(t)
return t ^ rotate_left(t, 2) ^ rotate_left(t, 10) ^ rotate_left(t, 18) ^ rotate_left(t, 24)
def key_extend(main_key):
MK = [(main_key >> (128 - (i + 1) * 32)) & 0xffffffff for i in range(4)]
# 将128bits分为4个字
keys = [FK[i] ^ MK[i] for i in range(4)]
# 生成K0~K3
RK = []
for i in range(32):
t = Tx(keys[i + 1], keys[i + 2], keys[i + 3], CK[i])
k = keys[i] ^ t
keys.append(k)
RK.append(k)
return RK
def R(x0, x1, x2, x3):
# 使用位运算符将数值限制在32位范围内
x0 &= 0xffffffff
x1 &= 0xffffffff
x2 &= 0xffffffff
x3 &= 0xffffffff
s = f"{
x3:08x}{
x2:08x}{
x1:08x}{
x0:08x}"
return s
def encode(plaintext, rk):
X = [plaintext >> (128 - (i + 1) * 32) & 0xffffffff for i in range(4)]
for i in range(32):
t = T(X[1], X[2], X[3], rk[i])
c = (t ^ X[0])
X = X[1:] + [c]
ciphertext = R(X[0], X[1], X[2], X[3])
# 进行反序处理
return ciphertext
def decode(ciphertext, rk):
ciphertext = int(ciphertext, 16)
X = [ciphertext >> (128 - (i + 1) * 32) & 0xffffffff for i in range(4)]
for i in range(32):
t = T(X[1], X[2], X[3], rk[31 - i])
c = (t ^ X[0])
X = X[1:] + [c]
m = R(X[0], X[1], X[2], X[3])
return m
def output(s, name):
out = ""
for i in range(0, len(s), 2):
out += s[i:i + 2] + " "
print(f"{
name}:", end="")
print(out.strip())
if __name__ == '__main__':
plaintext = 0x0123456789abcdeffedcba9876543210
main_key = 0x0123456789abcdeffedcba9876543210
rk = key_extend(main_key)
print("加密:")
ciphertext = encode(plaintext, rk)
output(ciphertext, "ciphertext")
print("解密:")
m = decode(ciphertext, rk)
output(m, "plaintext")
Decrypt
Since the SM4 algorithm is an involution operation, the decryption algorithm is the same as the encryption algorithm, except that the round keys are used in the opposite order.
operation result
加密:
ciphertext:68 1e df 34 d2 06 96 5e 86 b3 e9 4f 53 6e 42 46
解密
plaintext:01 23 45 67 89 ab cd ef fe dc ba 98 76 54 32 10