c语言实现sm2

SM2是一种基于椭圆曲线密码学的公钥密码算法，其实现相对复杂。以下是一个简单的C语言实现示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/bn.h>
#include <openssl/ec.h>
#include <openssl/ecdsa.h>
#include <openssl/evp.h>
#include <openssl/err.h>

// 生成SM2密钥对
int generate_keypair(EC_KEY **ec_key)
{
    int ret = -1;
    EC_KEY *key = NULL;
    EC_GROUP *group = NULL;
    const EVP_MD *md = NULL;

    key = EC_KEY_new();
    if (key == NULL) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    group = EC_GROUP_new_by_curve_name(NID_sm2);
    if (group == NULL) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    if (!EC_KEY_set_group(key, group)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    md = EVP_sm3();
    if (!ECDSA_set_method(key, ECDSA_sm2()) || !ECDSA_set_default_method(key, ECDSA_sm2())) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    if (!EC_KEY_generate_key(key)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    *ec_key = key;
    ret = 0;

cleanup:
    if (group != NULL) {
        EC_GROUP_free(group);
    }
    if (key != NULL && ret != 0) {
        EC_KEY_free(key);
    }
    return ret;
}

// SM2加密
int sm2_encrypt(EC_KEY *ec_key, const unsigned char *plaintext, size_t plaintext_len, unsigned char *ciphertext, size_t *ciphertext_len)
{
    int ret = -1;
    EC_GROUP *group = NULL;
    EC_POINT *pubkey = NULL;
    unsigned char *buf = NULL;
    size_t buf_len;
    const EVP_MD *md = NULL;

    group = EC_GROUP_new_by_curve_name(NID_sm2);
    if (group == NULL) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    pubkey = EC_KEY_get0_public_key(ec_key);
    if (pubkey == NULL) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    buf_len = EC_POINT_point2oct(group, pubkey, POINT_CONVERSION_UNCOMPRESSED, NULL, 0, NULL);
    if (buf_len == 0) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }
    buf = malloc(buf_len);
    if (buf == NULL) {
        perror("malloc");
        goto cleanup;
    }
    if (!EC_POINT_point2oct(group, pubkey, POINT_CONVERSION_UNCOMPRESSED, buf, buf_len, NULL)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    md = EVP_sm3();
    if (!EVP_PKEY_CTX_set_ec_key(ec_key, md)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    if (!EVP_PKEY_encrypt_init(ec_key_ctx)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    if (!EVP_PKEY_CTX_set1_id(ec_key_ctx, buf, buf_len)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    if (!EVP_PKEY_encrypt(ec_key_ctx, ciphertext, ciphertext_len, plaintext, plaintext_len)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    ret = 0;

cleanup:
    if (ec_key_ctx != NULL) {
        EVP_PKEY_CTX_free(ec_key_ctx);
    }
    if (buf != NULL) {
        free(buf);
    }
    if (group != NULL) {
        EC_GROUP_free(group);
    }
    return ret;
}

// SM2解密
int sm2_decrypt(EC_KEY *ec_key, const unsigned char *ciphertext, size_t ciphertext_len, unsigned char *plaintext, size_t *plaintext_len)
{
    int ret = -1;
    EVP_PKEY_CTX *ec_key_ctx = NULL;
    const EVP_MD *md = NULL;

    md = EVP_sm3();
    if (!EVP_PKEY_CTX_set_ec_key(ec_key, md)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    ec_key_ctx = EVP_PKEY_CTX_new(ec_key, NULL);
    if (ec_key_ctx == NULL) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    if (!EVP_PKEY_decrypt_init(ec_key_ctx)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    if (!EVP_PKEY_decrypt(ec_key_ctx, plaintext, plaintext_len, ciphertext, ciphertext_len)) {
        fprintf(stderr, "Error: %s\n", ERR_error_string(ERR_get_error(), NULL));
        goto cleanup;
    }

    ret = 0;

cleanup:
    if (ec_key_ctx != NULL) {
        EVP_PKEY_CTX_free(ec_key_ctx);
    }
    return ret;
}

请注意，这只是一个基本示例。要实现完整的SM2算法，您需要考虑更多细节，例如密钥派生和数字签名验证。此外，您需要确保使用正确的SM2参数和安全实践来保护您的加密通信。