[iassael]

Hi how can i encrypt a file in aes with 256 key in c?
Thank you very much!

[iassael]

Originally Posted by iassael

Hi how can i encrypt a file in aes with 256 key in c?
Thank you very much!

or c++
any suggestions?

[h4rdc0ded]

Alright...
First, get a decent AES- implementation.
There are many freely available; I picked this one at random; it's BSD- licensed (meaning you can use it for whatever you want, just mention Brian Gladman in a copyright notice).

For building the library (I didn't bother with the slightly faster ASM- version), I just used:

gcc -c -O2 -fomit-frame-pointer aescrypt.c aeskey.c aestab.c aes_modes.c
ar rcs libaes.a *.o

If you use Visual Studio, get the corresponding project files...

Here is an example of how your program could look like:

#include <stdlib.h>
#include <time.h>
#include <stdio.h>
#include "aes.h"
 
 
void encrypt(const char *fileIn, const char *fileOut,
    const unsigned char *key);
void decrypt(const char *fileIn, const char *fileOut,
    const unsigned char *key);
 
int main() {
  const unsigned char key[] = "my key";
 
  srand(time(NULL));
 
  aes_init();
  encrypt("main.c", "main.c.encrypted", key);
  decrypt("main.c.encrypted", "main.c.decrypted", key);
 
  return 0;
}
 
void encrypt(const char *fileIn, const char *fileOut, 
    const unsigned char *key) {
  int i;
  aes_encrypt_ctx ctx[1];
  unsigned char iv[16]; /* initialisation vector */
  unsigned char inBuffer[200], outBuffer[200];
  FILE *inFile = fopen(fileIn, "rb");
  FILE *outFile = fopen(fileOut, "wb");
 
  /* pick a random initialisation vector */
  for(i = 0; i < 16; ++i)
    iv[i] = rand() & 0xFF;
  fwrite(iv, 1, 16, outFile);
 
  aes_encrypt_key256(key, ctx);
  while((i = fread(inBuffer, 1, sizeof(inBuffer), inFile)) > 0) {
    aes_ofb_crypt(inBuffer, outBuffer, i, iv, ctx);
    fwrite(outBuffer, 1, i, outFile);
  }
 
  fclose(inFile);
  fclose(outFile);
}
 
void decrypt(const char *fileIn, const char *fileOut, 
    const unsigned char *key) {
  int i;
  aes_encrypt_ctx ctx[1];
  unsigned char iv[16]; /* initialisation vector */
  unsigned char inBuffer[200], outBuffer[200];
  FILE *inFile = fopen(fileIn, "rb");
  FILE *outFile = fopen(fileOut, "wb");
 
  /* read initialization vector from file */
  if(fread(iv, 1, 16, inFile) < 16) {
    fclose(inFile);
    fclose(outFile);
    return; /* error: file doesn't even contain an initialisation vector */
  }
 
  aes_encrypt_key256(key, ctx);
  while((i = fread(inBuffer, 1, sizeof(inBuffer), inFile)) > 0) {
    aes_ofb_crypt(inBuffer, outBuffer, i, iv, ctx);
    fwrite(outBuffer, 1, i, outFile);
  }
 
  fclose(inFile);
  fclose(outFile);
}

You have to link with the library you previously created, and "aes.h", "brg_types.h" must be in your includepath.

Note that I'm pretty clueless about cryptography- storing the initialisation vector as plaintext inside the encrypted file may or may not be "secure", but I guess it's better than using always the same one, and seems to be common practise...

--edit: fixed typos

[iassael]

Originally Posted by h4rdc0ded

Alright...
First, get a decent AES- implementation.
There are many freely available; I picked this one at random; it's BSD- licensed (meaning you can use it for whatever you want, just mention Brian Gladman in a copyright notice).

For building the library (I didn't bother with the slightly faster ASM- version), I just used:

gcc -c -O2 -fomit-frame-pointer aescrypt.c aeskey.c aestab.c aes_modes.c
ar rcs libaes.a *.o

If you use Visual Studio, get the corresponding project files...

Here is an example of how your program could look like:

#include <stdlib.h>
#include <time.h>
#include <stdio.h>
#include "aes.h"
 
 
void encrypt(const char *fileIn, const char *fileOut,
    const unsigned char *key);
void decrypt(const char *fileIn, const char *fileOut,
    const unsigned char *key);
 
int main() {
  const unsigned char key[] = "my key";
 
  srand(time(NULL));
 
  aes_init();
  encrypt("main.c", "main.c.encrypted", key);
  decrypt("main.c.encrypted", "main.c.decrypted", key);
 
  return 0;
}
 
void encrypt(const char *fileIn, const char *fileOut, 
    const unsigned char *key) {
  int i;
  aes_encrypt_ctx ctx[1];
  unsigned char iv[16]; /* initialisation vector */
  unsigned char inBuffer[200], outBuffer[200];
  FILE *inFile = fopen(fileIn, "rb");
  FILE *outFile = fopen(fileOut, "wb");
 
  /* pick a random initialisation vector */
  for(i = 0; i < 16; ++i)
    iv[i] = rand() & 0xFF;
  fwrite(iv, 1, 16, outFile);
 
  aes_encrypt_key256(key, ctx);
  while((i = fread(inBuffer, 1, sizeof(inBuffer), inFile)) > 0) {
    aes_ofb_crypt(inBuffer, outBuffer, i, iv, ctx);
    fwrite(outBuffer, 1, i, outFile);
  }
  aes_ofb_crypt(inBuffer, outBuffer, i, iv, ctx);
  fwrite(outBuffer, 1, i, outFile);
 
  fclose(inFile);
  fclose(outFile);
}
 
void decrypt(const char *fileIn, const char *fileOut, 
    const unsigned char *key) {
  int i;
  aes_encrypt_ctx ctx[1];
  unsigned char iv[16]; /* initialisation vector */
  unsigned char inBuffer[200], outBuffer[200];
  FILE *inFile = fopen(fileIn, "rb");
  FILE *outFile = fopen(fileOut, "wb");
 
  /* read initialization vector from file */
  if(fread(iv, 1, 16, inFile) < 16)
    return; /* error: file doesn't even contain an initialisation vector */
 
  aes_encrypt_key256(key, ctx);
  while((i = fread(inBuffer, 1, sizeof(inBuffer), inFile)) > 0) {
    aes_ofb_crypt(inBuffer, outBuffer, i, iv, ctx);
    fwrite(outBuffer, 1, i, outFile);
  }
 
  fclose(inFile);
  fclose(outFile);
}

You have to link with the library you previously created, and "aes.h", "brg_types.h" must be in your includepath.

Note that I'm pretty clueless about cryptography- storing the initialisation vector as plaintext inside the encrypted file may or may not be "secure", but I guess it's better than using always the same one, and seems to be common practise...

--edit: fixed typos

thanks man!!! Its perfect i will check it in a couple of hours :)

[iassael]

Originally Posted by iassael

thanks man!!! Its perfect i will check it in a couple of hours :)

although i included the source and was found i get a lot of "unidentified reference to aes_init()" like errors ...
Any suggestions?
Thanks!

[Scorpions4ever]

Set your project path settings to point to the AES lib

[iassael]

Originally Posted by Scorpions4ever

Set your project path settings to point to the AES lib

of course i did it.... :)

[iassael]

u r right it works perfect many thanks! :)

[7anoun]

hi :hi:
I try to execute the code but it doesn't work :( please if you don't mind telling me the steps in details because I don't have a good experience in c and I will be thankful :D

[BobS0327]

Originally Posted by 7anoun

hi :hi:
I try to execute the code but it doesn't work :( please if you don't mind telling me the steps in details because I don't have a good experience in c and I will be thankful :D

Do you have a text file named main.c in the same folder as your successfully compiled binary?

Have you built the library as follows?

gcc -c -O2 -fomit-frame-pointer aescrypt.c aeskey.c aestab.c aes_modes.c
ar rcs libaes.a *.o

Have you compiled your test app as follows (assuming the source is named test.cpp?

gcc test.cpp libaes.a