国密算法 SM4加密算法 Python完整实现

青旅半醒 2024-03-24 13:03 70阅读 0赞

## SM4介绍 ##

SM4算法是一种**对称加密算法**，也被称为国密算法。它是由中国密码学家设计的，已被列入国家密码局的标准。

SM4算法使用**128位的密钥和分组大小**，使用**32轮迭代**加密，可以用于加密数据和验证消息认证码。它的加密效率很高，安全性也很好，被广泛应用于各种安全领域，如电子商务、移动通信和云计算等。

## 算法实现流程图 ##

### 加密算法 ###

![SM4加密算法][SM4]

### 密钥扩展算法 ###

![密钥扩展算法][f16d95ee81554b808598fc219c410564.png]  
其中，K0~K3的生成过程如下：  
设输入的密钥为MK=（MK0，MK1，MK2，MK3），则（K0，K1，K2，K3）=（MK0 ^ FK0，MK1 ^ FK1，MK2 ^ FK2，MK3 ^ FK3）  
注：

1.  CKi以及FKi为**常数**；
2.  i 的取值为 i=0,1,…31,共生成**32个子密钥**。

## 源码 ##

### 加密 ###

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")

### 解密 ###

由于SM4算法是对合运算，因此解密算法与加密算法相同，只是轮密钥的使用顺序相反。

### 运行结果 ###

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

[SM4]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/24/c4813a9de6214ef28f1b7071a7f97413.png
[f16d95ee81554b808598fc219c410564.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/24/6729a0de5ce24a21beede1185dc019b9.png