用c语言写一段签名验签代码

由于签名验签的具体实现涉及到不同的加密算法和密钥管理方法，因此无法提供通用的代码。以下是一个基于 OpenSSL 库实现 RSA 签名验签的示例代码，仅供参考：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/rsa.h>
#include <openssl/pem.h>

// RSA 密钥文件路径
#define PRIVATE_KEY_PATH "private_key.pem"
#define PUBLIC_KEY_PATH "public_key.pem"

// 待签名数据
const char *data = "hello, world";

// RSA 签名函数
int rsa_sign(const char *data, size_t data_len, unsigned char *signature, size_t *sig_len, RSA *private_key) {
    int ret = -1;
    EVP_MD_CTX *mdctx = EVP_MD_CTX_new();

    if (mdctx != NULL) {
        if (EVP_SignInit(mdctx, EVP_sha256()) == 1) {
            if (EVP_SignUpdate(mdctx, data, data_len) == 1) {
                if (EVP_SignFinal(mdctx, signature, sig_len, private_key) == 1) {
                    ret = 0;
                }
            }
        }

        EVP_MD_CTX_free(mdctx);
    }

    return ret;
}

// RSA 验签函数
int rsa_verify(const char *data, size_t data_len, const unsigned char *signature, size_t sig_len, RSA *public_key) {
    int ret = -1;
    EVP_MD_CTX *mdctx = EVP_MD_CTX_new();

    if (mdctx != NULL) {
        if (EVP_VerifyInit(mdctx, EVP_sha256()) == 1) {
            if (EVP_VerifyUpdate(mdctx, data, data_len) == 1) {
                if (EVP_VerifyFinal(mdctx, signature, sig_len, public_key) == 1) {
                    ret = 0;
                }
            }
        }

        EVP_MD_CTX_free(mdctx);
    }

    return ret;
}

int main() {
    int ret = 0;
    RSA *private_key = NULL;
    RSA *public_key = NULL;
    unsigned char signature[2048] = {0};
    size_t sig_len = sizeof(signature);

    // 读取 RSA 密钥文件
    FILE *fp = fopen(PRIVATE_KEY_PATH, "r");
    if (fp != NULL) {
        private_key = PEM_read_RSAPrivateKey(fp, NULL, NULL, NULL);
        fclose(fp);
    }

    fp = fopen(PUBLIC_KEY_PATH, "r");
    if (fp != NULL) {
        public_key = PEM_read_RSA_PUBKEY(fp, NULL, NULL, NULL);
        fclose(fp);
    }

    // RSA 签名
    if (private_key != NULL) {
        if (rsa_sign(data, strlen(data), signature, &sig_len, private_key) == 0) {
            printf("RSA signature:\n");
            for (size_t i = 0; i < sig_len; i++) {
                printf("%02x", signature[i]);
            }
            printf("\n");

            // RSA 验签
            if (public_key != NULL) {
                ret = rsa_verify(data, strlen(data), signature, sig_len, public_key);
                if (ret == 0) {
                    printf("RSA signature verified successfully\n");
                } else {
                    printf("RSA signature verification failed\n");
                }
            }
        }

        RSA_free(private_key);
    }

    RSA_free(public_key);

    return ret;
}