数字签名算法C语言代码

数字签名算法常用的是RSA算法，下面是RSA数字签名算法的C语言实现代码：

#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <openssl/err.h>

//RSA私钥签名
int rsa_sign(const unsigned char *data, int data_len, const char *private_key_file, unsigned char *signature, unsigned int *signature_len) {
    int ret = 0;
    RSA *rsa = NULL;
    FILE *fp = NULL;

    //读取私钥文件
    fp = fopen(private_key_file, "r");
    if (fp == NULL) {
        printf("Failed to open private key file: %s\n", private_key_file);
        goto end;
    }

    //从文件中获取RSA私钥
    rsa = PEM_read_RSAPrivateKey(fp, NULL, NULL, NULL);
    if (rsa == NULL) {
        printf("Failed to read private key file: %s\n", private_key_file);
        goto end;
    }

    //签名
    ret = RSA_sign(NID_sha256, data, data_len, signature, signature_len, rsa);
    if (ret != 1) {
        printf("Failed to sign data.\n");
        goto end;
    }

    end:
    if (fp != NULL) {
        fclose(fp);
    }
    if (rsa != NULL) {
        RSA_free(rsa);
    }
    return ret;
}

//RSA公钥验证签名
int rsa_verify(const unsigned char *data, int data_len, const char *public_key_file, const unsigned char *signature, unsigned int signature_len) {
    int ret = 0;
    RSA *rsa = NULL;
    FILE *fp = NULL;

    //读取公钥文件
    fp = fopen(public_key_file, "r");
    if (fp == NULL) {
        printf("Failed to open public key file: %s\n", public_key_file);
        goto end;
    }

    //从文件中获取RSA公钥
    rsa = PEM_read_RSA_PUBKEY(fp, NULL, NULL, NULL);
    if (rsa == NULL) {
        printf("Failed to read public key file: %s\n", public_key_file);
        goto end;
    }

    //验证签名
    ret = RSA_verify(NID_sha256, data, data_len, signature, signature_len, rsa);
    if (ret != 1) {
        printf("Failed to verify signature.\n");
        goto end;
    }

    end:
    if (fp != NULL) {
        fclose(fp);
    }
    if (rsa != NULL) {
        RSA_free(rsa);
    }
    return ret;
}

这里使用了OpenSSL库来实现RSA数字签名算法。在签名时，需要提供待签名的数据、私钥文件路径以及用于存储签名结果的缓冲区和缓冲区长度；在验证签名时，需要提供待验证的数据、公钥文件路径以及签名结果。