/*
 * An example of using the AES block cipher,
 * with key (in hex) 01000000000000000000000000000000
 * and input (in hex) 01000000000000000000000000000000.
 * The result should be the output (in hex) FAEB01888D2E92AEE70ECC1C638BF6D6
 * (AES_encrypt corresponds to computing AES in the forward direction.)
 * We then compute the inverse, and check that we recovered the original input.
 * (AES_decrypt corresponds to computing the inverse of AES.)
 * (The terminology "AES_encrypt" and "AES_decrypt" is unfortunate since,
 * as discussed in class, AES is a block cipher, not an encryption scheme.
 */

/*
 * To compile (on unix): 
 * gcc -c aes_core.c
 * gcc -c example.c
 * (make sure to #include "aes.h" in your program)
 * gcc -o example example.o aes_core.o
 */

#include "aes.h"
#include <stdio.h>

main(){
  AES_KEY AESkey;
  unsigned char MBlock[16];
  unsigned char MBlock2[16];
  unsigned char CBlock[16];
  unsigned char Key[16];
  int i;

  /* 
   * Key contains the actual 128-bit AES key. AESkey is a data structure 
   * holding a transformed version of the key, for efficiency. 
   */

  Key[0]=1;

  for (i=1; i<=15; i++) {
    Key[i] = 0;
    } 

  AES_set_encrypt_key((const unsigned char *) Key, 128, &AESkey);

  MBlock[0] = 1;

  for (i=1; i<16; i++)
    MBlock[i] = 0;

  AES_encrypt((const unsigned char *) MBlock, CBlock, (const AES_KEY *) &AESkey);
  
  for (i=0; i<16; i++) 
    printf("%X", CBlock[i]/16), printf("%X", CBlock[i]%16);
  printf("\n");

  /* 
   * We need to set AESkey appropriately before inverting AES. 
   * Note that the underlying key Key is the same; just the data structure
   * AESkey is changing (for reasons of efficiency).
   */
  AES_set_decrypt_key((const unsigned char *) Key, 128, &AESkey);
  
  AES_decrypt((const unsigned char *) CBlock, MBlock2, (const AES_KEY *) &AESkey); 

  for (i=0; i<16; i++) 
    printf("%X", MBlock2[i]/16), printf("%X", MBlock2[i]%16);
  printf("\n");
}