使用openssl编写RSA加解密算法

好的，以下是使用 OpenSSL 库编写 RSA 加解密算法的示例代码：

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

#define KEY_LENGTH  2048
#define PUB_KEY_FILE "public.pem"
#define PRI_KEY_FILE "private.pem"

int generate_keypair()
{
    int ret = 0;
    RSA *rsa = NULL;
    BIGNUM *e = NULL;
    BIO *pri_bio = NULL, *pub_bio = NULL;

    // 创建 RSA 结构体
    rsa = RSA_new();
    if (!rsa) {
        printf("Failed to create RSA struct.\n");
        return -1;
    }

    // 设置 RSA 公钥指数
    e = BN_new();
    ret = BN_set_word(e, RSA_F4);
    if (ret != 1) {
        printf("Failed to set RSA exponent.\n");
        RSA_free(rsa);
        return -1;
    }

    // 生成 RSA 密钥对
    ret = RSA_generate_key_ex(rsa, KEY_LENGTH, e, NULL);
    if (ret != 1) {
        printf("Failed to generate RSA key pair.\n");
        RSA_free(rsa);
        return -1;
    }

    // 保存 RSA 公钥
    pub_bio = BIO_new_file(PUB_KEY_FILE, "w");
    if (!pub_bio) {
        printf("Failed to create public key file.\n");
        RSA_free(rsa);
        return -1;
    }
    ret = PEM_write_bio_RSAPublicKey(pub_bio, rsa);
    if (ret != 1) {
        printf("Failed to write public key.\n");
        RSA_free(rsa);
        BIO_free(pub_bio);
        return -1;
    }
    BIO_free(pub_bio);

    // 保存 RSA 私钥
    pri_bio = BIO_new_file(PRI_KEY_FILE, "w");
    if (!pri_bio) {
        printf("Failed to create private key file.\n");
        RSA_free(rsa);
        return -1;
    }
    ret = PEM_write_bio_RSAPrivateKey(pri_bio, rsa, NULL, NULL, 0, NULL, NULL);
    if (ret != 1) {
        printf("Failed to write private key.\n");
        RSA_free(rsa);
        BIO_free(pri_bio);
        return -1;
    }
    BIO_free(pri_bio);

    RSA_free(rsa);
    return 0;
}

int rsa_encrypt(const char *plain_text, char *cipher_text)
{
    int ret = 0;
    RSA *rsa = NULL;
    BIO *pub_bio = NULL;
    int len = 0;

    // 从文件读取 RSA 公钥
    pub_bio = BIO_new_file(PUB_KEY_FILE, "r");
    if (!pub_bio) {
        printf("Failed to read public key file.\n");
        return -1;
    }
    rsa = PEM_read_bio_RSAPublicKey(pub_bio, NULL, NULL, NULL);
    if (!rsa) {
        printf("Failed to read public key.\n");
        BIO_free(pub_bio);
        return -1;
    }
    BIO_free(pub_bio);

    // 加密明文
    len = RSA_public_encrypt(strlen(plain_text), (unsigned char *)plain_text, (unsigned char *)cipher_text, rsa, RSA_PKCS1_PADDING);
    if (len < 0) {
        printf("Failed to encrypt plain text.\n");
        RSA_free(rsa);
        return -1;
    }

    RSA_free(rsa);
    return len;
}

int rsa_decrypt(const char *cipher_text, char *plain_text)
{
    int ret = 0;
    RSA *rsa = NULL;
    BIO *pri_bio = NULL;
    int len = 0;

    // 从文件读取 RSA 私钥
    pri_bio = BIO_new_file(PRI_KEY_FILE, "r");
    if (!pri_bio) {
        printf("Failed to read private key file.\n");
        return -1;
    }
    rsa = PEM_read_bio_RSAPrivateKey(pri_bio, NULL, NULL, NULL);
    if (!rsa) {
        printf("Failed to read private key.\n");
        BIO_free(pri_bio);
        return -1;
    }
    BIO_free(pri_bio);

    // 解密密文
    len = RSA_private_decrypt(KEY_LENGTH/8, (unsigned char *)cipher_text, (unsigned char *)plain_text, rsa, RSA_PKCS1_PADDING);
    if (len < 0) {
        printf("Failed to decrypt cipher text.\n");
        RSA_free(rsa);
        return -1;
    }

    RSA_free(rsa);
    return len;
}

int main()
{
    char plain_text[] = "Hello, world!";
    char cipher_text[KEY_LENGTH/8] = {0};
    char decrypted_text[KEY_LENGTH/8] = {0};
    int len = 0;

    // 生成 RSA 密钥对
    if (generate_keypair() != 0) {
        printf("Failed to generate RSA key pair.\n");
        return -1;
    }

    // 加密明文
    len = rsa_encrypt(plain_text, cipher_text);
    if (len < 0) {
        printf("Failed to encrypt plain text.\n");
        return -1;
    }
    printf("Cipher text: %s\n", cipher_text);

    // 解密密文
    len = rsa_decrypt(cipher_text, decrypted_text);
    if (len < 0) {
        printf("Failed to decrypt cipher text.\n");
        return -1;
    }
    printf("Decrypted text: %s\n", decrypted_text);

    return 0;
}

这个示例代码中，我们使用 OpenSSL 库中的 RSA 函数实现了 RSA 加解密算法。在程序启动时，我们使用 `generate_keypair()` 函数生成 RSA 密钥对，并将公钥和私钥保存到文件中。接着，我们使用 `rsa_encrypt()` 函数加密明文，使用 `rsa_decrypt()` 函数解密密文，最后输出解密后的明文。需要注意的是，在解密密文时，我们需要使用私钥进行解密。