基于Linux系统下的文件加密解密技术

该示例代码演示了在Linux系统下利用openssl库对文件进行加密和解密的实现方式。其中包括了采用对称加密算法AES和非对称加密算法RSA的代码示例。通过使用不同的密钥进行加密和解密，确保文件的安全性。

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

// 使用AES加密文件
void aes_encrypt_file(char *in_filename, char *out_filename, unsigned char *key) {
    AES_KEY aes_key;
    unsigned char iv[AES_BLOCK_SIZE];
    int bytesRead, bytesWrite;

    FILE *fin = fopen(in_filename, "rb");
    FILE *fout = fopen(out_filename, "wb");

    // 初始化iv向量
    memset(iv, 0, AES_BLOCK_SIZE);

    // 设置加密密钥
    AES_set_encrypt_key(key, 256, &aes_key);

    // 逐段加密文件内容
    while (1) { 
        unsigned char in_data[AES_BLOCK_SIZE];
        unsigned char out_data[AES_BLOCK_SIZE];

        bytesRead = fread(in_data, 1, AES_BLOCK_SIZE, fin);
        AES_cbc_encrypt(in_data, out_data, bytesRead, &aes_key, iv, AES_ENCRYPT);

        bytesWrite = fwrite(out_data, 1, bytesRead, fout);
        if (bytesRead < AES_BLOCK_SIZE) {
            break;
        }
    }

    fclose(fin);
    fclose(fout);
}

// 使用AES解密文件
void aes_decrypt_file(char *in_filename, char *out_filename, unsigned char *key) {
    AES_KEY aes_key;
    unsigned char iv[AES_BLOCK_SIZE];
    int bytesRead, bytesWrite;

    FILE *fin = fopen(in_filename, "rb");
    FILE *fout = fopen(out_filename, "wb");

    // 初始化iv向量
    memset(iv, 0, AES_BLOCK_SIZE);

    // 设置解密密钥
    AES_set_decrypt_key(key, 256, &aes_key);

    // 逐段解密文件内容
    while (1) {
        unsigned char in_data[AES_BLOCK_SIZE];
        unsigned char out_data[AES_BLOCK_SIZE];

        bytesRead = fread(in_data, 1, AES_BLOCK_SIZE, fin);
        AES_cbc_encrypt(in_data, out_data, bytesRead, &aes_key, iv, AES_DECRYPT);

        bytesWrite = fwrite(out_data, 1, bytesRead, fout);
        if (bytesRead < AES_BLOCK_SIZE) {
            break;
        }
    }

    fclose(fin);
    fclose(fout);
}

// 使用RSA加密AES密钥
void rsa_encrypt_key(unsigned char *key, int key_len, char *pemfile, char *cipherfile) {
    FILE * fp = fopen(pemfile, "rb");
    RSA *rsa = PEM_read_RSA_PUBKEY(fp, NULL, NULL, NULL);
    fclose(fp);

    int flen = RSA_size(rsa);
    unsigned char *out = (unsigned char*)malloc(flen);

    RSA_public_encrypt(key_len, key, out, rsa, RSA_PKCS1_OAEP_PADDING);

    FILE *fout = fopen(cipherfile, "wb");
    fwrite(out, 1, flen, fout);

    fclose(fout);
    RSA_free(rsa);
    free(out);
}

// 使用RSA解密AES密钥
void rsa_decrypt_key(unsigned char *cipher, int cipher_len, char *pemfile, unsigned char *dec) {
    FILE * fp = fopen(pemfile, "rb");
    RSA *rsa = PEM_read_RSAPrivateKey(fp, NULL, NULL, NULL);
    fclose(fp);

    int flen = RSA_size(rsa);

    RSA_private_decrypt(cipher_len, cipher, dec, rsa, RSA_PKCS1_OAEP_PADDING);

    RSA_free(rsa);
}

int main() {
    // 生成随机密钥
    unsigned char key[32];
    RAND_bytes(key, 32);

    // 加密文件
    aes_encrypt_file("test.txt", "test.aes", key);

    // 加密密钥
    rsa_encrypt_key(key, 32, "public.pem", "key.cipher");

    // 解密密钥
    unsigned char out_key[32];
    memset(out_key, 0, 32);
    unsigned char cipher[256];
    int cipher_len;
    FILE *fp = fopen("key.cipher", "rb");
    cipher_len = fread(cipher, 1, 256, fp);
    rsa_decrypt_key(cipher, cipher_len, "private.pem", out_key);
    fclose(fp);

    // 解密文件
    aes_decrypt_file("test.aes", "test.dec", out_key);

    printf("Done!\n");
    return 0;
}

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