RSA加密解密算法C语言

RSA加密解密算法是一种非对称加密算法，它是由Ron Rivest、Adi Shamir和Leonard Adleman在1977年提出的。RSA算法的安全性基于大数分解的困难性，即将一个大数分解成两个质数的乘积。RSA算法的加密过程是将明文先转换成数字，然后使用公钥进行加密，得到密文；解密过程是使用私钥对密文进行解密，得到明文。RSA算法在数字签名、密钥协商等领域有着广泛的应用。

以下是一个简单的C语言实现RSA加密解密算法的范例：

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

#define PUBLIC_KEY_FILE "public_key.pem"
#define PRIVATE_KEY_FILE "private_key.pem"

int main()
{
    RSA *rsa = NULL;
    FILE *fp = NULL;
    char *plain_text = "Hello, RSA!";
    char *cipher_text = NULL;
    char *decrypted_text = NULL;
    int plain_text_len = strlen(plain_text);
    int cipher_text_len = 0;
    int decrypted_text_len = 0;

    // 生成RSA密钥对
    rsa = RSA_generate_key(1024, RSA_F4, NULL, NULL);
    if (rsa == NULL) {
        printf("Failed to generate RSA key pair!\n");
        return -1;
    }

    // 将公钥写入文件
    fp = fopen(PUBLIC_KEY_FILE, "w");
    if (fp == NULL) {
        printf("Failed to open public key file!\n");
        return -1;
    }
    PEM_write_RSAPublicKey(fp, rsa);
    fclose(fp);

    // 将私钥写入文件
    fp = fopen(PRIVATE_KEY_FILE, "w");
    if (fp == NULL) {
        printf("Failed to open private key file!\n");
        return -1;
    }
    PEM_write_RSAPrivateKey(fp, rsa, NULL, NULL, 0, NULL, NULL);
    fclose(fp);

    // 加密明文
    cipher_text_len = RSA_size(rsa);
    cipher_text = (char *)malloc(cipher_text_len);
    memset(cipher_text, 0, cipher_text_len);
    RSA_public_encrypt(plain_text_len, (unsigned char *)plain_text, (unsigned char *)cipher_text, rsa, RSA_PKCS1_PADDING);

    // 解密密文
    decrypted_text_len = RSA_size(rsa);
    decrypted_text = (char *)malloc(decrypted_text_len);
    memset(decrypted_text, 0, decrypted_text_len);    RSA_private_decrypt(cipher_text_len, (unsigned char *)cipher_text, (unsigned char *)decrypted_text, rsa, RSA_PKCS1_PADDING);

    // 输出结果
    printf("Plain text: %s\n", plain_text);
    printf("Cipher text: ");
    for (int i = 0; i < cipher_text_len; i++) {
        printf("%02x", (unsigned char)cipher_text[i]);
    }
    printf("\n");
    printf("Decrypted text: %s\n", decrypted_text);

    // 释放资源
    RSA_free(rsa);
    free(cipher_text);
    free(decrypted_text);

    return 0;
}