C Mcrypt Rijndael-256 en/decryptor

rijndael256.c

/*
Encrypts and decrypts text in Rijndael-256.
When compiling, make sure you have libmcrypt installed and use the -lmcrypt flag for GCC.
To install libmcrypt on Ubuntu/Debian/Elementary: (sudo) apt-get install libmcrypt-dev

Copyright Roemer Bakker - 2015
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <mcrypt.h>

#include <math.h>
#include <stdint.h>

int encrypt(
    void* buffer,
    int buffer_len,
    char* IV,
    char* key,
    int key_len
    ) {
  MCRYPT td = mcrypt_module_open("rijndael-256", NULL, "cbc", NULL);
  int blocksize = mcrypt_enc_get_block_size(td);
  if (buffer_len % blocksize != 0) {return 1;}

  mcrypt_generic_init(td, key, key_len, IV);
  mcrypt_generic(td, buffer, buffer_len);
  mcrypt_generic_deinit(td);
  mcrypt_module_close(td);

  return 0;
}

int decrypt(
    void* buffer,
    int buffer_len,
    char* IV,
    char* key,
    int key_len
    ) {
  MCRYPT td = mcrypt_module_open("rijndael-256", NULL, "cbc", NULL);
  int blocksize = mcrypt_enc_get_block_size(td);
  if (buffer_len % blocksize != 0) {return 1;}

  mcrypt_generic_init(td,key,key_len,IV);
  mdecrypt_generic(td,buffer,buffer_len);
  mcrypt_generic_deinit(td);
  mcrypt_module_close(td);

  return 0;
}

void display(char* ciphertext,int len) {
  int v;
  for(v=0;v<len;v++) {
    printf("%d",ciphertext[v]);
  }
  printf("\n");
}

int main() {
  MCRYPT td, td2;
  char * plaintext= "w0w such secret.";
  char* IV = "AAAAAAAAAAAAAAAA";
  char *key = "0123456789abcdef0123456789abcdef";
  int keysize = 16;
  char* buffer;
  int buffer_len = 16;

  buffer = calloc(1, buffer_len);
  strncpy(buffer, plaintext, buffer_len);

  printf("plain: %s\n", plaintext);
  encrypt(buffer, buffer_len, IV, key, keysize);
  printf("Encrypted: "); display(buffer, buffer_len);
  decrypt(buffer, buffer_len, IV, key, keysize);
  printf("Decrypted: %s\n",buffer);

  return 0;
}