c语言实现sm2算法

SM2算法是一种基于椭圆曲线密码体制的公钥密码算法，广泛应用于数字签名、身份认证、密钥协商等场景。在C语言中实现SM2算法需要借助一些常用的密码学库，例如OpenSSL、libgcrypt等。以下是一个使用OpenSSL库实现SM2算法的示例代码：

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

#define SM2_NID NID_sm2
#define SM2_PUBKEY_SIZE 65
#define SM2_PRIVKEY_SIZE 32

int sm2_gen_keypair(unsigned char *pubkey, unsigned char *privkey) {
    EC_KEY *ec_key = EC_KEY_new_by_curve_name(SM2_NID);
    if (ec_key == NULL) {
        return -1;
    }

    if (!EC_KEY_generate_key(ec_key)) {
        EC_KEY_free(ec_key);
        return -1;
    }

    const EC_GROUP *ec_group = EC_KEY_get0_group(ec_key);
    const EC_POINT *ec_pubkey = EC_KEY_get0_public_key(ec_key);
    const BIGNUM *ec_privkey = EC_KEY_get0_private_key(ec_key);

    size_t pubkey_len = EC_POINT_point2oct(ec_group, ec_pubkey, POINT_CONVERSION_UNCOMPRESSED, NULL, 0, NULL);
    unsigned char *tmp_pubkey = malloc(pubkey_len);
    if (tmp_pubkey == NULL) {
        EC_KEY_free(ec_key);
        return -1;
    }

    if (EC_POINT_point2oct(ec_group, ec_pubkey, POINT_CONVERSION_UNCOMPRESSED, tmp_pubkey, pubkey_len, NULL) != pubkey_len) {
        free(tmp_pubkey);
        EC_KEY_free(ec_key);
        return -1;
    }

    memcpy(pubkey, tmp_pubkey + 1, SM2_PUBKEY_SIZE);
    memcpy(privkey, ec_privkey, SM2_PRIVKEY_SIZE);

    free(tmp_pubkey);
    EC_KEY_free(ec_key);

    return 0;
}

int sm2_sign(const unsigned char *msg, size_t msg_len, const unsigned char *privkey, unsigned char *signature) {
    EC_KEY *ec_key = EC_KEY_new_by_curve_name(SM2_NID);
    if (ec_key == NULL) {
        return -1;
    }

    BIGNUM *ec_privkey = BN_bin2bn(privkey, SM2_PRIVKEY_SIZE, NULL);
    if (ec_privkey == NULL) {
        EC_KEY_free(ec_key);
        return -1;
    }

    if (!EC_KEY_set_private_key(ec_key, ec_privkey)) {
        BN_clear_free(ec_privkey);
        EC_KEY_free(ec_key);
        return -1;
    }

    const EVP_MD *md = EVP_sm3();
    if (md == NULL) {
        BN_clear_free(ec_privkey);
        EC_KEY_free(ec_key);
        return -1;
    }

    unsigned char digest[EVP_MAX_MD_SIZE];
    unsigned int digest_len;
    if (!EVP_Digest(msg, msg_len, digest, &digest_len, md, NULL)) {
        BN_clear_free(ec_privkey);
        EC_KEY_free(ec_key);
        return -1;
    }

    ECDSA_SIG *ec_sig = ECDSA_do_sign(digest, digest_len, ec_key);
    if (ec_sig == NULL) {
        BN_clear_free(ec_privkey);
        EC_KEY_free(ec_key);
        return -1;
    }

    BIGNUM *r = NULL;
    BIGNUM *s = NULL;
    ECDSA_SIG_get0(ec_sig, (const BIGNUM **)&r, (const BIGNUM **)&s);

    int ret = 0;
    if (BN_bn2binpad(r, signature + 0, SM2_PRIVKEY_SIZE) != SM2_PRIVKEY_SIZE ||
        BN_bn2binpad(s, signature + SM2_PRIVKEY_SIZE, SM2_PRIVKEY_SIZE) != SM2_PRIVKEY_SIZE) {
        ret = -1;
    }

    BN_clear_free(ec_privkey);
    ECDSA_SIG_free(ec_sig);
    EC_KEY_free(ec_key);

    return ret;
}

int sm2_verify(const unsigned char *msg, size_t msg_len, const unsigned char *pubkey, const unsigned char *signature) {
    EC_KEY *ec_key = EC_KEY_new_by_curve_name(SM2_NID);
    if (ec_key == NULL) {
        return -1;
    }

    const EC_GROUP *ec_group = EC_KEY_get0_group(ec_key);
    const EVP_MD *md = EVP_sm3();
    if (md == NULL) {
        EC_KEY_free(ec_key);
        return -1;
    }

    unsigned char digest[EVP_MAX_MD_SIZE];
    unsigned int digest_len;
    if (!EVP_Digest(msg, msg_len, digest, &digest_len, md, NULL)) {
        EC_KEY_free(ec_key);
        return -1;
    }

    EC_POINT *ec_pubkey = EC_POINT_new(ec_group);
    if (ec_pubkey == NULL) {
        EC_KEY_free(ec_key);
        return -1;
    }

    if (!EC_POINT_oct2point(ec_group, ec_pubkey, pubkey, SM2_PUBKEY_SIZE, NULL)) {
        EC_POINT_free(ec_pubkey);
        EC_KEY_free(ec_key);
        return -1;
    }

    ECDSA_SIG *ec_sig = ECDSA_SIG_new();
    if (ec_sig == NULL) {
        EC_POINT_free(ec_pubkey);
        EC_KEY_free(ec_key);
        return -1;
    }

    BIGNUM *r = BN_bin2bn(signature + 0, SM2_PRIVKEY_SIZE, NULL);
    BIGNUM *s = BN_bin2bn(signature + SM2_PRIVKEY_SIZE, SM2_PRIVKEY_SIZE, NULL);

    int ret = 0;
    if (r == NULL || s == NULL || !ECDSA_SIG_set0(ec_sig, r, s) || !ECDSA_do_verify(digest, digest_len, ec_sig, ec_pubkey)) {
        ret = -1;
    }

    BN_clear_free(r);
    BN_clear_free(s);
    ECDSA_SIG_free(ec_sig);
    EC_POINT_free(ec_pubkey);
    EC_KEY_free(ec_key);

    return ret;
}

此代码使用了OpenSSL库的EC模块和ECDSA模块实现了SM2算法的密钥生成、签名和验证功能。在使用之前需要先安装OpenSSL库并链接到编译器中。