OpenSSL AES 256 CBC通过EVP api在C

Question

我想做的是：用C编写一个程序，打开任意大小的文件并读取其内容。一旦内容被读取，它将在AES 256 CBC中对其进行加密，并将密文保存到名为ciphertext的文件中。保存后，它将关闭两个文件。然后将打开刚刚保存的文件中的密码文本，解密密码文本并将其保存到名为decrypted的文件中。

我的问题是：它似乎永远不会解密我的密文。我收到垃圾，我不知道我做错了什么。请帮忙。

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

void encrypt(FILE *ifp, FILE *ofp)
{
  //Get file size
  fseek(ifp, 0L, SEEK_END);
  int fsize = ftell(ifp);
  //set back to normal
  fseek(ifp, 0L, SEEK_SET);

  int outLen1 = 0; int outLen2 = 0;
  unsigned char *indata = malloc(fsize);
  unsigned char *outdata = malloc(fsize*2);
  unsigned char ckey[] =  "thiskeyisverybad";
  unsigned char ivec[] = "dontusethisinput";

  //Read File
  fread(indata,sizeof(char),fsize, ifp);//Read Entire File

  //Set up encryption
  EVP_CIPHER_CTX ctx;
  EVP_EncryptInit(&ctx,EVP_aes_256_cbc(),ckey,ivec);
  EVP_EncryptUpdate(&ctx,outdata,&outLen1,indata,fsize);
  EVP_EncryptFinal(&ctx,outdata,&outLen2);
  fwrite(outdata,sizeof(char),fsize,ofp);
}

void decrypt(FILE *ifp, FILE *ofp)
{
  //Get file size
  fseek(ifp, 0L, SEEK_END);
  int fsize = ftell(ifp);
  //set back to normal
  fseek(ifp, 0L, SEEK_SET);

  int outLen1 = 0; int outLen2 = 0;
  unsigned char *indata = malloc(fsize);
  unsigned char *outdata = malloc(fsize*2);
  unsigned char ckey[] =  "thiskeyisverybad";
  unsigned char ivec[] = "dontusethisinput";

  //Read File
  fread(indata,sizeof(char),fsize, ifp);//Read Entire File

  //setup decryption
  EVP_CIPHER_CTX ctx;
  EVP_DecryptInit(&ctx,EVP_aes_256_cbc(),ckey,ivec);
  EVP_DecryptUpdate(&ctx,outdata,&outLen1,indata,fsize);
  EVP_DecryptFinal(&ctx,outdata,&outLen2);
  fwrite(outdata,sizeof(char),fsize,ofp);
}

int main(int argc, char *argv[])
{    
  FILE *fIN, *fOUT;

  fIN = fopen("plain.txt", "rb");//File to be encrypted; plain text
  fOUT = fopen("cyphertext.txt", "wb");//File to be written; cipher text    
  encrypt(fIN, fOUT);

  fclose(fIN);
  fclose(fOUT);

  //Decrypt file now
  fIN = fopen("cyphertext.txt", "rb");//File to be written; cipher text
  fOUT = fopen("decrypted.txt", "wb");//File to be written; cipher text
  decrypt(fIN,fOUT);

  fclose(fIN);
  fclose(fOUT);

  return 0;
}

注意：可能有一些拼写错误。编辑：好像我在密钥和IV上犯了一个错误，它们都是128位的，我正在尝试使用256位的CBC。这是我的问题，一旦我把它改成

EVP_aes_128_cbc()

Answer 1

此代码有效，如果任何人对如何更干净或更高效有一些建议，请发表评论。

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

void encrypt(FILE *ifp, FILE *ofp)
{
    //Get file size
    fseek(ifp, 0L, SEEK_END);
    int fsize = ftell(ifp);
    //set back to normal
    fseek(ifp, 0L, SEEK_SET);

    int outLen1 = 0; int outLen2 = 0;
    unsigned char *indata = malloc(fsize);
    unsigned char *outdata = malloc(fsize*2);
    unsigned char ckey[] =  "thiskeyisverybad";
    unsigned char ivec[] = "dontusethisinput";

    //Read File
    fread(indata,sizeof(char),fsize, ifp);//Read Entire File

    //Set up encryption
    EVP_CIPHER_CTX ctx;
    EVP_EncryptInit(&ctx,EVP_aes_128_cbc(),ckey,ivec);
    EVP_EncryptUpdate(&ctx,outdata,&outLen1,indata,fsize);
    EVP_EncryptFinal(&ctx,outdata + outLen1,&outLen2);
    fwrite(outdata,sizeof(char),outLen1 + outLen2,ofp);
}

void decrypt(FILE *ifp, FILE *ofp)
{
    //Get file size
    fseek(ifp, 0L, SEEK_END);
    int fsize = ftell(ifp);
    //set back to normal
    fseek(ifp, 0L, SEEK_SET);

    int outLen1 = 0; int outLen2 = 0;
    unsigned char *indata = malloc(fsize);
    unsigned char *outdata = malloc(fsize);
    unsigned char ckey[] =  "thiskeyisverybad";
    unsigned char ivec[] = "dontusethisinput";

    //Read File
    fread(indata,sizeof(char),fsize, ifp);//Read Entire File

    //setup decryption
    EVP_CIPHER_CTX ctx;
    EVP_DecryptInit(&ctx,EVP_aes_128_cbc(),ckey,ivec);
    EVP_DecryptUpdate(&ctx,outdata,&outLen1,indata,fsize);
    EVP_DecryptFinal(&ctx,outdata + outLen1,&outLen2);
    fwrite(outdata,sizeof(char),outLen1 + outLen2,ofp);
}

int main(int argc, char *argv[])
{        
    if(argc != 2){
        printf("Usage: <executable> /path/to/file/exe");
        return -1;
    }
    FILE *fIN, *fOUT;
    fIN = fopen("plain.txt", "rb");//File to be encrypted; plain text
    fOUT = fopen("cyphertext.txt", "wb");//File to be written; cipher text

    encrypt(fIN, fOUT);
    fclose(fIN);
    fclose(fOUT);
    //Decrypt file now
    fIN = fopen("cyphertext.txt", "rb");//File to be written; cipher text
    fOUT = fopen("decrypted.txt", "wb");//File to be written; cipher text
    decrypt(fIN,fOUT);
    fclose(fIN);
    fclose(fOUT);

    return 0;
}

此外，根据这篇文章，EVP api将处理任意大小的输入

AES加密-大文件

Answer 2

这是我的代码版本。当然，我更喜欢它，但我提供它只是作为一种选择。请注意，完全没有错误检查：真正的代码会有错误检查。

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

#ifndef TRUE
#define TRUE 1
#endif

#ifndef FALSE
#define FALSE 0
#endif


/**
 * Encrypt or decrypt, depending on flag 'should_encrypt'
 */
void en_de_crypt(int should_encrypt, FILE *ifp, FILE *ofp, unsigned char *ckey, unsigned char *ivec) {

    const unsigned BUFSIZE=4096;
    unsigned char *read_buf = malloc(BUFSIZE);
    unsigned char *cipher_buf;
    unsigned blocksize;
    int out_len;
    EVP_CIPHER_CTX ctx;

    EVP_CipherInit(&ctx, EVP_aes_256_cbc(), ckey, ivec, should_encrypt);
    blocksize = EVP_CIPHER_CTX_block_size(&ctx);
    cipher_buf = malloc(BUFSIZE + blocksize);

    while (1) {

        // Read in data in blocks until EOF. Update the ciphering with each read.

        int numRead = fread(read_buf, sizeof(unsigned char), BUFSIZE, ifp);
        EVP_CipherUpdate(&ctx, cipher_buf, &out_len, read_buf, numRead);
        fwrite(cipher_buf, sizeof(unsigned char), out_len, ofp);
        if (numRead < BUFSIZE) { // EOF
            break;
        }
    }

    // Now cipher the final block and write it out.

    EVP_CipherFinal(&ctx, cipher_buf, &out_len);
    fwrite(cipher_buf, sizeof(unsigned char), out_len, ofp);

    // Free memory

    free(cipher_buf);
    free(read_buf);
}

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

    unsigned char ckey[] = "thiskeyisverybad";
    unsigned char ivec[] = "dontusethisinput";
    FILE *fIN, *fOUT;

    if (argc != 2) {
        printf("Usage: <executable> /path/to/file/exe");
        return -1;
    }

    // First encrypt the file

    fIN = fopen("plain.txt", "rb"); //File to be encrypted; plain text
    fOUT = fopen("cyphertext.txt", "wb"); //File to be written; cipher text

    en_de_crypt(TRUE, fIN, fOUT, ckey, ivec);

    fclose(fIN);
    fclose(fOUT);

    //Decrypt file now

    fIN = fopen("cyphertext.txt", "rb"); //File to be read; cipher text
    fOUT = fopen("decrypted.txt", "wb"); //File to be written; cipher text

    en_de_crypt(FALSE, fIN, fOUT, ckey, ivec);

    fclose(fIN);
    fclose(fOUT);

    return 0;
}