如何加密.bmp文件

Question

在理解如何使用用于AES的开放SSL库加密文件时，我有些麻烦。任务是使用AES ECB模式和AES CBC模式为图像文件实现加密解决方案。 假设加密密钥为“ 12345678”

对于第0步和第1步：我已经提出了我认为需要的内容，但在确定第2-5步的内容时需要帮助。

#include <openssl/evp.h>
#include <openssl/err.h>

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

void handleErrors()
{
   printf("Wrong encryption progress\n");
}

int encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key, unsigned char *iv, unsigned char *ciphertext)
{
    EVP_CIPHER_CTX *ctx;
    int len;
    int ciphertext_len;

    /* Create and initialise the context */
    if(!(ctx = EVP_CIPHER_CTX_new()))
        handleErrors();

    /* Initialise the encryption operation. IMPORTANT - ensure you use a key
     * and IV size appropriate for your cipher
     */
    if(1 != EVP_EncryptInit_ex(ctx, EVP_aes_128_cbc(), NULL, key, iv))
        handleErrors();

    /* Provide the message to be encrypted, and obtain the encrypted output.
     * EVP_EncryptUpdate can be called multiple times if necessary
     */
    if(1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
        handleErrors();

    ciphertext_len = len;

    /* Finalise the encryption. Further ciphertext bytes may be written at
     * this stage.
     */
    if(1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len))
        handleErrors();

    ciphertext_len += len;

    /* Clean up */
    EVP_CIPHER_CTX_free(ctx);

    return ciphertext_len;

}

int main(int argc, char **argv)
{

    char * fileName="pic_original.bmp";
    int encryptionkey = 12345678;
    int mode;

    //======================= STEP 0=====================================//
    /*Key initialization.
     It will be automaticalledly padded to 128 bit key
     */

    unsigned char *key = (unsigned char *)"01234567890123456789012345678901";


    //======================= STEP 1=====================================//
    /*IV initialization.
     The IV size for *most* modes is the same as the block size.
     For AES128 this is 128 bits
     */

    unsigned char *iv = (unsigned char *)"0123456789012345";


    //======================= STEP 2=====================================//
    /*read the file from given filename in binary mode*/
    printf("Start to read the .bmp file \n");



    //======================= STEP 3=====================================//
    /*allocate memory for bitmapHeader and bitmapImage,
     then read bytes for these variables.*/



    //allocate memory for the final ciphertext

    /*as this is a .bmpfile, we need to read the header
     (the first 54 bytes) into bitmapHeader*/

    //read the bitmap image content until the end of the .bmp file

    //======================= STEP 4=====================================//
    //encrypt the bitmapImage with the given key

    //======================= STEP 5=====================================//
    /*merge header and bitmap to the final ciphertext
     and output it into a .bmp file*/

    return 1;
}

要编译程序（假设您的程序是图像加密。c并且可执行文件被命名为图像加密）：

$ gcc -I / usr / local / ssl / include -L / usr / local / ssl / lib -o \ image_encryption image_encryption.c -lcrypto -ldl

输出应为加密文件。