I just want to test AES from openSSL with this 3 modes: with 128,192 and 256 key length but my decrypted text is different from my input and I dont know why. Also, when I pass a huge inputs length (lets say 1024 bytes) my program shows core dumped
... My input is always the same but it doesnt matter, at least for now. Heres the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/aes.h>
int main(int argc, char **argv)
{
int i;
int keylength;
printf("Give a key length [only 128 or 192 or 256!]:\n");
scanf("%d", &keylength);
/* generate a key with a given length */
unsigned char aes_key[keylength];
memset(aes_key, 0, sizeof(aes_key));
if (!RAND_bytes(aes_key, keylength))
{
exit(-1);
}
aes_key[keylength-1] = '\0';
int inputslength;
printf("Give an input's length:\n");
scanf("%d", &inputslength);
/* generate input with a given length */
unsigned char aes_input[inputslength+1];
memset(aes_input, '0', sizeof(aes_input));
aes_input[inputslength] = '\0';
/*printf("original:\t");
for(i=0; i<inputslength; i++)
{
printf("%c ", aes_input[i]);
}
printf("\n");*/
/* init vector */
unsigned char iv[AES_BLOCK_SIZE];
if (!RAND_bytes(iv, AES_BLOCK_SIZE))
{
exit(-1);
}
//printf("AES_BLOCK_SIZE = %d\n", AES_BLOCK_SIZE); // aes block size is 16 bytes = 128 bits
AES_KEY enc_key, dec_key;
unsigned char enc_out[AES_BLOCK_SIZE];
unsigned char dec_out[AES_BLOCK_SIZE];
// so i can do with this aes-cbc-128 aes-cbc-192 aes-cbc-256
AES_set_encrypt_key(aes_key, keylength, &enc_key);
AES_cbc_encrypt(aes_input, enc_out, inputslength, &enc_key, iv, AES_ENCRYPT);
AES_set_decrypt_key(aes_key, keylength, &dec_key);
AES_decrypt(enc_out, dec_out, &dec_key);
printf("original:\t");
for(i=0;*(aes_input+i)!=0x00;i++)
printf("%X ",*(aes_input+i));
printf("\nencrypted:\t");
for(i=0;*(enc_out+i)!=0x00;i++)
printf("%X ",*(enc_out+i));
printf("\ndecrypted:\t");
for(i=0;*(dec_out+i)!=0x00;i++)
printf("%X ",*(dec_out+i));
printf("\n");
/*printf("\n\noriginal:\t");
for(i=0; i<inputslength; i++)
{
printf("%x ", dec_out[i]);
}
printf("\n");*/
return 0;
}
EDIT:
When I changed outputs sizes to inputslength
instead of AES_BLOCK_SIZE
I got results:
Give a key length [only 128 or 192 or 256!]:
128
Give an input's length:
5
original: 30 30 30 30 30
encrypted: 94 56 50 7E 19 B2 1C CE 20 23 4A E7 10 AF DB E3 30 30 30 30 30
decrypted: E1 5F F4 3D E8 8D 91 19 CD 3E 22 1E AF 1C 8F 5A 94 56 50 7E 19 B2 1C CE 20 23 4A E7 10 AF DB E3 30 30 30 30 30
So is it possible that theres an issue with outpus sizes and the size of the iv? What sizes they should have (for AES-CBC-128, AES-CBC-192, AES-CBC-256)?
Take a peek at this modified version of your code. Note the following:
AES_cbc_encrypt()
is used for both encryption and decryption (see the last parameter in the call).Source Code
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/aes.h>
#include <openssl/rand.h>
// a simple hex-print routine. could be modified to print 16 bytes-per-line
static void hex_print(const void* pv, size_t len)
{
const unsigned char * p = (const unsigned char*)pv;
if (NULL == pv)
printf("NULL");
else
{
size_t i = 0;
for (; i<len;++i)
printf("%02X ", *p++);
}
printf("\n");
}
// main entrypoint
int main(int argc, char **argv)
{
int keylength;
printf("Give a key length [only 128 or 192 or 256!]:\n");
scanf("%d", &keylength);
/* generate a key with a given length */
unsigned char aes_key[keylength/8];
memset(aes_key, 0, keylength/8);
if (!RAND_bytes(aes_key, keylength/8))
exit(-1);
size_t inputslength = 0;
printf("Give an input's length:\n");
scanf("%lu", &inputslength);
/* generate input with a given length */
unsigned char aes_input[inputslength];
memset(aes_input, 'X', inputslength);
/* init vector */
unsigned char iv_enc[AES_BLOCK_SIZE], iv_dec[AES_BLOCK_SIZE];
RAND_bytes(iv_enc, AES_BLOCK_SIZE);
memcpy(iv_dec, iv_enc, AES_BLOCK_SIZE);
// buffers for encryption and decryption
const size_t encslength = ((inputslength + AES_BLOCK_SIZE) / AES_BLOCK_SIZE) * AES_BLOCK_SIZE;
unsigned char enc_out[encslength];
unsigned char dec_out[inputslength];
memset(enc_out, 0, sizeof(enc_out));
memset(dec_out, 0, sizeof(dec_out));
// so i can do with this aes-cbc-128 aes-cbc-192 aes-cbc-256
AES_KEY enc_key, dec_key;
AES_set_encrypt_key(aes_key, keylength, &enc_key);
AES_cbc_encrypt(aes_input, enc_out, inputslength, &enc_key, iv_enc, AES_ENCRYPT);
AES_set_decrypt_key(aes_key, keylength, &dec_key);
AES_cbc_encrypt(enc_out, dec_out, encslength, &dec_key, iv_dec, AES_DECRYPT);
printf("original:\t");
hex_print(aes_input, sizeof(aes_input));
printf("encrypt:\t");
hex_print(enc_out, sizeof(enc_out));
printf("decrypt:\t");
hex_print(dec_out, sizeof(dec_out));
return 0;
}
Test Output
Give a key length [only 128 or 192 or 256!]:
128
Give an input's length:
10
original: 58 58 58 58 58 58 58 58 58 58
encrypt: A9 66 C5 24 A4 02 AB 96 08 65 F7 22 A5 FB BE 26
decrypt: 58 58 58 58 58 58 58 58 58 58
Second Test Output
Give a key length [only 128 or 192 or 256!]:
128
Give an input's length:
10
original: 58 58 58 58 58 58 58 58 58 58
encrypt: C2 47 6D B1 A1 68 29 53 55 74 C5 CC 3F 27 0A 3F
decrypt: 58 58 58 58 58 58 58 58 58 58
I sincerely hope this helps.