SM4分组密码算法，原名SMS4，国家密码管理局于2012年3月21日发布。该算法的分组长度为128比特，密钥长度为128比特。加密算法与密钥扩展算法都采用32轮非线性迭代结构。解密算法与加密算法的结构相同，只是轮密钥的使用顺序相反，解密轮密钥是加密轮密钥的逆序。

• 算法中采用的三种种基本运算：

1. ⊕: 32比特异；
2. <<<i : 特循环左移i位；
3. 反序变换R(A₀, A₁, A₂, A₃) = (A₃, A₂, A₁, A₀)；

   #define Reverse(_x, _y) (((_x) << (_y)) | ((_x) >> (32 - (_y))))
   

   
   

• 密钥相关变量的定义：

1：轮密钥：表示为(rk0,rk1 … rk31)，每4个字节一组，共32组，由加密密钥计算；
2：加密密钥：长度128比特，表示为MK=(MK0，MK1， MK2，MK3)，每4个字节一组；
3：FK=(FK0,FK1,FK2,FK3)为系统固定参数， FK₀=(A3B1BAC6)，FKj=(56AA3350)，FK₂=(677D9197)，FK₃=(B27022DC)；

4：CK=(CK0,CK1...CK31)为系统固定参数。

/*CK为固定参数*/
const unsigned int CK[32] = {
	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 };

5：S盒置换：计算过程为查表过程，Sbox(69) = 22，即S表中第六行第九列的值为22；

const unsigned char Sbox[256] = {
	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
};

• 算法中使用的置换运算：

1.非线性变换t：t由4个并行的S盒构成，设输入为 A = (a₀,a₁,a₂,a₃)，输出为 B = (b₀,b₁,b₂,b₃)，t变换计算公式如下：

(b₀,b₁,b₂,b₃） = t(a₀,a₁,a₂,a₃) = (Sbox (a₀), Sbox (a₁), Sbox (a₂), Sbox (a₃))

#define SboxTrans(_A) (Sbox[(_A) >> 24 & 0xFF] << 24 ^ Sbox[(_A) >> 16 & 0xFF] << 16 ^ Sbox[(_A) >>  8 & 0xFF] <<  8 ^ Sbox[(_A) & 0xFF])

2.线性变换L：非线性变换t的输出是线性变换L的输入，本算法中使用的L变换计算公式有两处：

加密算法： L1(B) = B ⊕ (B <<< 2) ⊕ ( B <<< 10) ⊕ (B <<< 18) ⊕ (B <<< 24)；

密钥扩展算法：L2(B) = B⊕(B <<< 13)⊕(B <<< 23)； 

#define L1(_B) ((_B) ^ Rotl(_B, 2) ^ Rotl(_B, 10) ^ Rotl(_B, 18) ^ Rotl(_B, 24))
#define L2(_B) ((_B) ^ Rotl(_B, 13) ^ Rotl(_B, 23))

• 密钥扩展算法

本算法中加密算法的轮密钥由加密密钥通过密钥扩展算法生成，扩展密钥生成公式：

(K_0, K_1, K_2,K₃) =(MK₀⊕FK₀,MK₁⊕FK₁,MK₂⊕FK₂,MK₃⊕FK₃);

rk _i = K ₄ = K _i ⊕ T(K _i+1⊕ K _i+2⊕ K _i+3⊕CK _i);

void SM4KeyExt(unsigned char *key, unsigned int *rk, unsigned int CryptFlag)
{
	unsigned int r, tmp, k0, k1, k2, k3;
	/*(k0,k1,k2,k3) = (key0 xor FK0, key1 xor FK1, key2 xor FK2, key3 xor FK3)*/
	/*系统参数FK0 = 0xa3b1bac6、FK1 = 0x56aa3350、FK2 = 0x677d9197、FK3 = 0xb27022dc; */
	k0 = key[0] ^ 0xa3b1bac6;
	k1 = key[1] ^ 0x56aa3350;
	k2 = key[2] ^ 0x677d9197;
	k3 = key[3] ^ 0xb27022dc;
	for (r = 0; r < 32; r += 4)
	{
		/*rk(i) = k(4+i) = k(i) xor T[k(i+1) xor k(i+2) xor k(i+3) xor CK(i)]*/
		/*合成置换T的过程包括非线性变换（ByteSub函数，从SBox中查找）和线性变换（L2函数，移位和异或运算）*/
		tmp = k1 ^ k2 ^ k3 ^ CK[r + 0];
		tmp = SboxTrans(tmp);
		k0 = k0 ^ L2(tmp);
		rk[r + 0] = k0;

		tmp = k2 ^ k3 ^ k0 ^ CK[r + 1];
		tmp = SboxTrans(tmp);
		k1 = k1 ^ L2(tmp);
		rk[r + 1] = k1;
		
		tmp = k3 ^ k0 ^ k1 ^ CK[r + 2];
		tmp = SboxTrans(tmp);
		k2 = k2 ^ L2(tmp);
		rk[r + 2] = k2;

		tmp = k0 ^ k1 ^ k2 ^ CK[r + 3];
		tmp = SboxTrans(tmp);
		k3 = k3 ^ L2(tmp);
		rk[r + 3] = k3;
	}
	if (CryptFlag == 1)
	{
		for (r = 0; r < 16; r++)
			tmp = rk[r], rk[r] = rk[31 - r], rk[31 - r] = tmp;
	}
}

• 加密算法

加密变换公式为：

X_i+4= F(X_i, X_i+1, X_i+2,X_i+3, rk_i)= X_i ⊕ T(X_i+1⊕X_i+2⊕X_i+3⊕rk_i);

(Y_0, Y_1, Y_2,Y₃) = R(X_32, X_33, X_34，X₃₅) =(X_35,X_34,X_33,X₃₂);

本算法的解密变换与加密变换结构相同，不同的仅是轮密钥的使用顺序。 加密时轮密钥的使用顺序为： (rk0,rk1 … rk31) ,   解密时轮密钥的使用顺序为： (rk 31,rk30 … rk0 )。

void SM4Crypt(unsigned char *Input, unsigned char *Output, unsigned int *rk)
{
	unsigned int r, tmp, x0, x1, x2, x3, *y;
	y = (unsigned int *)Input;
	x0 = y[0];
	x1 = y[1];
	x2 = y[2];
	x3 = y[3];
	for (r = 0; r < 32; r += 4)
	{
		/*x4 = x0 ^ T(x1 ^ x2 ^ x3 ^ rk[0])*/
		tmp = x1 ^ x2 ^ x3 ^ rk[r + 0];
		tmp = SboxTrans(tmp);
		x0 ^= L1(tmp);

		tmp = x2 ^ x3 ^ x0 ^ rk[r + 1];
		tmp = SboxTrans(tmp);
		x1 ^= L1(tmp);

		tmp = x3 ^ x0 ^ x1 ^ rk[r + 2];
		tmp = SboxTrans(tmp);
		x2 ^= L1(tmp);

		tmp = x0 ^ x1 ^ x2 ^ rk[r + 3];
		tmp = SboxTrans(tmp);
		x3 ^= L1(tmp);
	}
	y = (unsigned int *)Output;
	/*(y0,y1,y2,y3) = (x35,x34,x33,x32)*/
	y[0] = x3;
	y[1] = x2;
	y[2] = x1;
	y[3] = x0;
}

• 加密实例

明文:01 23 45 67 89 ab cd ef fe dc ba 98 76 54 32 10 
加密密钥: 01 23 45 67 89 ab cd ef fe dc ba 98 76 54 32 10

轮密钥与每轮输出状态： 
rk[ 0] = f12186f9    rk[ 1] = 41662b61    rk[ 2] = 5a6ab19a      rk[ 3] = 7ba92077      
rk[ 4] = 367360f4    rk[ 5] = 776a0c61     rk[ 6] = b6bb89b3    rk[ 7] = 24763151     
rk[ 8] = a520307c     rk[ 9] = b7584dbd     rk[10] = c30753ed      rk[11] = 7ee55b57      
rk[12] = 6988608c    rk[13] = 30d895b7   rk[14] = 44ba14af    rk[15] = 104495a1     
rk[16] = d120b428    rk[17] = 73b55fa3     rk[18] = cc874966     rk[19] = 92244439     
rk[20] = e89e641f      rk[21] = 98ca015a      rk[22] = c7159060     rk[23] = 99e1fd2e     
rk[24] = b79bd80c     rk[25] = 1d2115b0     rk[26] = 0e228aeb      rk[27] = f1780c81     
rk[28] = 428d3654     rk[29] = 62293496    rk[30] = 01cf72e5     rk[31] = 9124a012    

X[0] = 27fad345, X[1] = a18b4cb2, X[2] = 11c1e22a, X[3] = cc13e2ee, 

X[4] = f87c5bd5,  X[5] = 33220757, X[6] = 77f4c297, X[7] = 7a96f2eb, 

X[8] = 27dac07f, X[9] = 42dd0f19, X[10] = b8a5da02,  X[11] = 907127fa, 

X[12] = 8b952b83,  X[13] = d42b7c59, X[14] = 2ffc5831,X[15] = f69e6888,

X[16] = af2432c4,  X[17] = ed1ec85e, X[18] = 55a3ba22, X[19] = 124b18aa, 

X[20] = 6ae7725f, X[21] = f4cba1f9, X[22] = 1dcdfa10, X[23] = 2ff60603,

X[24] = eff24fdc, X[25] = 6fe46b75, X[26] = 893450ad, X[27] = 7b938f4c , 

X[28] = 536e4246, X[29] = 86b3e94f, X[30] = d206965e, X[31] = 681edf34.

轮密钥计算方法：

密文: 68 1e df 34 d2 06 96 5e 86 b3 e9 4f 53 6e 42 46

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