Question

I am using openssl libraries for purpose of encoding and decoding to base64, This is my encryption code

#include <openssl/buffer.h>
#include <stdlib.h>
char *base64(const unsigned char *input, int length);

int main(int argc, char **argv)
{
   char nonce[10];
   srand(time(NULL));
   printf("rand():%d\n", rand());
   sprintf(nonce, "%d", rand());
   char *output = base64(nonce, sizeof(nonce));
   printf("Base64: *%s*\n", output);
   free(output);
}

char *base64(const unsigned char *input, int length)
{
  BIO *bmem, *b64;
  BUF_MEM *bptr;
  char *buff;
  b64 = BIO_new(BIO_f_base64());
  bmem = BIO_new(BIO_s_mem());
  b64 = BIO_push(b64, bmem);
  BIO_write(b64, input, length);
  BIO_flush(b64);
  BIO_get_mem_ptr(b64, &bptr);
  buff = (char *) malloc(bptr->length);
  memcpy(buff, bptr->data, bptr->length-1);
  buff[bptr->length-1] = '\0';
  BIO_free_all(b64);
  return buff;
}

The o/p of this when was NjI0MjQ3MwAECA== the rand() output was 1308702736 (This is a an example for one instance of rand gen o/p), when i used the decode function to decode this value i get 6242473, which is totally diff, i have to get 1308702736 when decoded,

My decode function is as follows

#include <string.h>
#include <openssl/sha.h>
#include <openssl/hmac.h>
#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/buffer.h>

char *unbase64(unsigned char *input, int length);

int main(int argc, char **argv)
{
   char *output = unbase64("NjI0MjQ3MwAECA==\n", strlen("NjI0MjQ3MwAECA==\n"));
   printf("Unbase64: *%s*\n", output);
   free(output);
}
char *unbase64(unsigned char *input, int length)
{
   BIO *b64, *bmem;
   char *buffer = (char *)malloc(length);
   memset(buffer, 0, length);
   b64 = BIO_new(BIO_f_base64());
   bmem = BIO_new_mem_buf(input, length);
   bmem = BIO_push(b64, bmem);
   BIO_read(bmem, buffer, length);
   BIO_free_all(bmem);

   return buffer;
}

NOTE: to compile this code v have to use -lcrypto
I need a help in solving this i am stuck here, googled for solutions but didn’t get any,and have one more doubt why input to base64 decoder b terminated by \n ? can one one help me out in this

Answer 1

printf("rand():%d\n", rand());
sprintf(nonce, "%d", rand());

You call rand twice, giving you two different numbers. NjI0MjQ3MwAECA== decodes to 624247.