rsa加密算法代码C语言

以下是一个简单的RSA加密算法C语言代码示例：

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

#define RSA_KEY_SIZE 2048

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

    // 将公钥和私钥分别保存到文件中
    FILE *fp = fopen("public_key.pem", "w");
    if (!fp) {
        printf("failed to open file public_key.pem\n");
        return -1;
    }
    PEM_write_RSAPublicKey(fp, rsa);
    fclose(fp);

    fp = fopen("private_key.pem", "w");
    if (!fp) {
        printf("failed to open file private_key.pem\n");
        return -1;
    }
    PEM_write_RSAPrivateKey(fp, rsa, NULL, NULL, 0, NULL, NULL);
    fclose(fp);

    // 加密和解密测试
    const char *message = "Hello World!";
    int message_len = strlen(message);

    // 加密
    int encrypted_size = RSA_size(rsa);
    unsigned char *encrypted = malloc(encrypted_size);
    int result = RSA_public_encrypt(message_len, (unsigned char *)message, encrypted, rsa, RSA_PKCS1_PADDING);
    if (result == -1) {
        printf("failed to encrypt message\n");
        return -1;
    }

    // 解密
    int decrypted_size = RSA_size(rsa);
    unsigned char *decrypted = malloc(decrypted_size);
    result = RSA_private_decrypt(result, encrypted, decrypted, rsa, RSA_PKCS1_PADDING);
    if (result == -1) {
        printf("failed to decrypt message\n");
        return -1;
    }

    printf("Original message: %s\n", message);
    printf("Decrypted message: %s\n", decrypted);

    // 释放RSA密钥对和加解密缓冲区
    RSA_free(rsa);
    free(encrypted);
    free(decrypted);

    return 0;
}

该代码使用OpenSSL库，首先生成一个RSA密钥对，然后将公钥和私钥保存到文件中。接着，使用公钥对一条消息进行加密，再使用私钥对密文进行解密，并输出原始消息和解密后的消息。最后，释放RSA密钥对和加解密缓冲区。