c++实现SM2算法

SM2算法是一种基于椭圆曲线密码学的公钥密码算法，下面是C++实现SM2算法的基本步骤：

1. 选取椭圆曲线参数，确定基点G和曲线阶n。

2. 生成密钥对：随机生成私钥d，并计算公钥Q=dG。

3. 加密过程：选择随机数k，计算点C1=kG，计算点S=kPb，计算点T=M⊕KDF(S)，其中M为明文，KDF为密钥派生函数。

4. 解密过程：计算点S=dC1，计算点T=M⊕KDF(S)。

下面是一个基于OpenSSL库实现SM2算法的示例代码：

#include <openssl/ec.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/bn.h>

int SM2_encrypt(unsigned char *in, size_t inlen, unsigned char *out, size_t *outlen, EC_KEY *ec_key)
{
    int ret = 0;
    const EC_GROUP *group = EC_KEY_get0_group(ec_key);
    const EC_POINT *pub_key = EC_KEY_get0_public_key(ec_key);
    const BIGNUM *order = EC_GROUP_get0_order(group);
    const EVP_MD *md = EVP_sm3();
    unsigned char Z[32];
    unsigned char kdf[32];
    unsigned char C1[65], C2[1024], C3[32];
    size_t C1len = 65, C2len = inlen, C3len = 32;
    EC_POINT *kG = NULL, *Pb = NULL;
    BIGNUM *k = NULL, *S = NULL, *T = NULL;
    EVP_MD_CTX *ctx = NULL;

    kG = EC_POINT_new(group);
    Pb = EC_POINT_new(group);
    k = BN_new();
    S = BN_new();
    T = BN_new();
    ctx = EVP_MD_CTX_new();

    // 生成随机数k
    do {
        if (!BN_rand_range(k, order)) {
            ret = -1;
            break;
        }
    } while (BN_is_zero(k));

    // 计算点C1=kG
    if (!EC_POINT_mul(group, kG, k, NULL, NULL, NULL)) {
        ret = -1;
        break;
    }
    if (!EC_POINT_point2oct(group, kG, POINT_CONVERSION_UNCOMPRESSED, C1, C1len, NULL)) {
        ret = -1;
        break;
    }

    // 计算点S=kPb
    if (!EC_POINT_mul(group, Pb, NULL, pub_key, k, NULL)) {
        ret = -1;
        break;
    }
    if (!EC_POINT_point2bn(group, Pb, POINT_CONVERSION_UNCOMPRESSED, S, NULL)) {
        ret = -1;
        break;
    }

    // 计算Z=Hash(ENTLA||ZA||M)
    if (!EVP_Digest(in, inlen, Z, NULL, md, NULL)) {
        ret = -1;
        break;
    }
    if (!EC_POINT_point2oct(group, pub_key, POINT_CONVERSION_UNCOMPRESSED, Z + 1, 64, NULL)) {
        ret = -1;
        break;
    }
    Z[0] = 0x03;

    // 计算点C2=M⊕KDF(S)
    if (!EVP_DigestInit_ex(ctx, md, NULL) ||
        !EVP_DigestUpdate(ctx, Z, sizeof(Z)) ||
        !EVP_DigestUpdate(ctx, in, inlen) ||
        !EVP_DigestFinal_ex(ctx, kdf, NULL)) {
        ret = -1;
        break;
    }
    for (size_t i = 0; i < sizeof(kdf); i++) {
        C2[i] = in[i] ^ kdf[i];
    }

    // 计算点C3=Hash(Z||C2)
    if (!EVP_DigestInit_ex(ctx, md, NULL) ||
        !EVP_DigestUpdate(ctx, Z, sizeof(Z)) ||
        !EVP_DigestUpdate(ctx, C2, C2len) ||
        !EVP_DigestFinal_ex(ctx, C3, NULL)) {
        ret = -1;
        break;
    }

    // 组装密文
    memcpy(out, C1, C1len);
    memcpy(out + C1len, C3, C3len);
    memcpy(out + C1len + C3len, C2, C2len);
    *outlen = C1len + C3len + C2len;

    ret = 1;

done:
    EVP_MD_CTX_free(ctx);
    BN_free(T);
    BN_free(S);
    BN_free(k);
    EC_POINT_free(Pb);
    EC_POINT_free(kG);

    return ret;
}

int SM2_decrypt(unsigned char *in, size_t inlen, unsigned char *out, size_t *outlen, EC_KEY *ec_key)
{
    int ret = 0;
    const EC_GROUP *group = EC_KEY_get0_group(ec_key);
    const BIGNUM *d = EC_KEY_get0_private_key(ec_key);
    const EVP_MD *md = EVP_sm3();
    unsigned char Z[32];
    unsigned char kdf[32];
    unsigned char C1[65], C2[1024], C3[32];
    size_t C1len = 65, C2len = inlen - C1len - C3len, C3len = 32;
    EC_POINT *kG = NULL, *Sb = NULL;
    BIGNUM *S = NULL, *T = NULL;
    EVP_MD_CTX *ctx = NULL;

    kG = EC_POINT_new(group);
    Sb = EC_POINT_new(group);
    S = BN_new();
    T = BN_new();
    ctx = EVP_MD_CTX_new();

    // 解析密文
    memcpy(C1, in, C1len);
    memcpy(C3, in + C1len, C3len);
    memcpy(C2, in + C1len + C3len, C2len);

    // 计算点S=dC1
    if (!EC_POINT_oct2point(group, kG, C1, C1len, NULL) ||
        !EC_POINT_mul(group, Sb, NULL, kG, d, NULL) ||
        !EC_POINT_point2bn(group, Sb, POINT_CONVERSION_UNCOMPRESSED, S, NULL)) {
        ret = -1;
        break;
    }

    // 计算Z=Hash(ENTLA||ZA||M)
    if (!EVP_Digest(C2, C2len, Z, NULL, md, NULL) ||
        !EC_POINT_point2oct(group, Sb, POINT_CONVERSION_UNCOMPRESSED, Z + 1, 64, NULL)) {
        ret = -1;
        break;
    }
    Z[0] = 0x03;

    // 计算点T=M⊕KDF(S)
    if (!EVP_DigestInit_ex(ctx, md, NULL) ||
        !EVP_DigestUpdate(ctx, Z, sizeof(Z)) ||
        !EVP_DigestUpdate(ctx, C2, C2len) ||
        !EVP_DigestFinal_ex(ctx, kdf, NULL)) {
        ret = -1;
        break;
    }
    for (size_t i = 0; i < sizeof(kdf); i++) {
        out[i] = C2[i] ^ kdf[i];
    }
    *outlen = sizeof(kdf);

    ret = 1;

done:
    EVP_MD_CTX_free(ctx);
    BN_free(T);
    BN_free(S);
    EC_POINT_free(Sb);
    EC_POINT_free(kG);

    return ret;
}

此代码实现的SM2算法需要依赖OpenSSL库，并且仅提供了加密和解密的基本实现，还需要根据具体应用场景进行适当的调整和优化。