1.SM4算法介绍

SM4 算法是一种分组密码算法。其分组长度为 16字节，密钥长度也为 16字节。
加密算法与密钥扩展算法均采用 32 轮非线性迭代结构，以字（32 位）为单位进
行加密运算，每一次迭代运算均为一轮变换函数 F。SM4 算法加/解密算法的结构
相同，只是使用轮密钥相反，其中解密轮密钥是加密轮密钥的逆序。

2.代码例子

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int main(int argc, char *argv[])
{
    unsigned char sm4_en[512],sm4_de[512];
    int sm4enStrLen,sm4deStrLen;
    unsigned char source[20]={0x41,0x12,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x10, 0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0x20};
    unsigned char keyStr[16]={0x15,0x67,0x28,0xe1,0x5f,0x9a,0xfc,0x01,0xd4,0xb6,0x1b,0x4e,0x44,0x5d,0xbb,0x26};
    sm4enStrLen=my_sm4encrpt(keyStr,source,20,sm4_en);
    printf("sm4enStrLen:%d",sm4enStrLen);
    for(int i=0;i<sm4enStrLen;++i)
    {
        printf("0x%x",sm4_en[i]);
    }
    printf("\n");
    sm4deStrLen=dencryptStr(keyStr,sm4_en,sm4enStrLen,sm4_de);
    printf("sm4deStrLen:%d",sm4deStrLen);
    for(int i=0;i<sm4deStrLen;++i)
    {
        printf("0x%x",sm4_de[i]);
    }
    printf("\n");
}
int my_sm4encrpt(unsigned char * keyStr,unsigned char * surbuf,int surlen,unsigned char * enbuf)
{
    unsigned char *out_buf = enbuf;
    int out_len;
    int out_padding_len;
    int i;
    unsigned char *iv;
    EVP_CIPHER_CTX *ctx;
    ctx = EVP_CIPHER_CTX_new();
    EVP_EncryptInit(ctx, EVP_sm4_ecb(), keyStr, iv);
    if( 0 == surlen % 16 )
    {
        EVP_CIPHER_CTX_set_padding( ctx, 0 );
    }
    out_len = 0;
    EVP_EncryptUpdate(ctx, out_buf, &out_len, surbuf, surlen);
    out_padding_len = 0;
    EVP_EncryptFinal(ctx, out_buf + out_len, &out_padding_len);

    EVP_CIPHER_CTX_free(ctx);
    return out_len + out_padding_len;
}


int dencryptStr(unsigned char * sm4PriKey, unsigned char *cEnStr, int cEnstrlen, unsigned char *deStr)
{
    unsigned char *iv;
    EVP_CIPHER_CTX *ctx;
    int len;
    int temlen;
    int deStrLen;
    if (!(ctx = EVP_CIPHER_CTX_new())) {
       printf("EVP_CIPHER_CTX_new failed");
    }
    if (1 != EVP_DecryptInit(ctx, EVP_sm4_ecb(), sm4PriKey, iv)) {
        printf("EVP_DecryptInit_ex failed");
    }


    if (1 != EVP_DecryptUpdate(ctx, deStr, &len, cEnStr, cEnstrlen)) {
        printf("EVP_DecryptUpdate failed");
    }
    if( 0 == len % 16 )
    {
        EVP_CIPHER_CTX_set_padding( ctx, 0 );
        len += 16;

    }
    if( !EVP_DecryptFinal( ctx, deStr + len, &temlen ) )
    {
        printf("EVP_DecryptFinal failed");
        return EXIT_FAILURE;
    }
    deStrLen=len+temlen;
    printf("解密数据：%d\n",deStrLen);
    for (int i = 0;i < deStrLen;i++) {
        printf("0x%02x ",*(deStr + i));
    }
    printf("\n");
    EVP_CIPHER_CTX_free(ctx);
    return deStrLen;
}