Hi,
I am using aes-128-cbc encryption using openssl. I have to encrypt the
plain text using the words I have in the file which act as key. I have
a cipher text. I have to compare the encrypted text with the cipher
text already declared in the program.
The following is the program I have written. My plain text is 21 bytes
and key is sometimes <16 or > 16 bytes in length because the word list
is a dictionary of words.
When I run my code I am getting different cipher texts every single
time. I am not sure why this is happening. Is there any thing that is
going wrong in my code.
The following is my code. Please let me know where I am making a
mistake.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <openssl/evp.h>
int main()
{
int i;
char words[32], t;
FILE *key, *outFile;
const char *out = "Output.txt";
unsigned char outbuf[1024 + EVP_MAX_BLOCK_LENGTH];
unsigned char iv[] = "0000000000000000";
int outlen, tmplen;
int num;
EVP_CIPHER_CTX ctx;
EVP_CIPHER_CTX_init(&ctx);
char inText[] = "This is a top secret.";
char cipherText[] =
"8d20e5056a8d24d0462ce74e4904c1b513e10d1df4a2ef2ad4540fae1ca0aaf9";
key = fopen("words.txt", "r");
if( remove("ciphertext.txt") == -1 ) {
perror("Error deleting file");
}
outFile = fopen("ciphertext.txt", "a+");
if( key < 0 || outFile < 0 )
{
perror ("Cannot open file");
exit(1);
}
char pbuffer[1024];
while ( fgets(words,32, key) )
{
i=strlen(words);
words[i-1]='\0';
//printf("%s",words);
i = 0;
EVP_EncryptInit_ex(&ctx, EVP_aes_128_cbc(), NULL, words, iv);
if(!EVP_EncryptUpdate(&ctx, outbuf, &outlen, inText,
strlen(inText)))
{
EVP_CIPHER_CTX_cleanup(&ctx);
return 0;
}
if(!EVP_EncryptFinal_ex(&ctx, outbuf + outlen, &tmplen))
{
EVP_CIPHER_CTX_cleanup(&ctx);
return 0;
}
outlen += tmplen;
print_hex(outbuf, outlen, outFile);
}
fclose(key);
fclose(outFile);
return 1;
}
int print_hex(unsigned char *buf, int len, FILE *outFile)
{
int i,n;
char x='\n';
for ( i = 0; i < len; i++ )
{
fprintf(outFile,"%02x",buf[i]);
}
fprintf(outFile,"%c",x);
return(0);
}
Harish K Bayyavarapu
Master's Computer Science
University of Texas at El Paso
Phone: 915-929-0999
