main.c

#include "des56.h"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

//Use these constants to specify ENCRYPT or DECRYPT in the fencrypt function call.  (The middle parameter)
#define ENCRYPT    0
#define DECRYPT    1

/*This function takes the XOR of block A and block B and stores the result in block "result"*/
/*Note that it is possible that "result" is the same as "A" (or "B").*/
/*For example:
 XORblock(block1,IV,block1);
 Would XOR the first block with the IV and put the result in block1*/
void XORblock(char A[8], char B[8], char result[8])
{
    int i = 0;
    for(;i<8;i++)
        result[i] = A[i]^B[i];
}

/*This function takes a block as input and prints the corresponding hex to the terminal*/
void printhex(unsigned char block[8])
{
    int i=0;
    for(;i<8;i++)
        printf(" 0x%x ",block[i]);
    puts("");
}

void cbc_enc_three_blocks(char block1[8], char block2[8], char block3[8], char IV[8],keysched *ks)
{
    XORblock(block1, IV, block1);
    fencrypt(block1, 0, ks);
    XORblock(block2, block1, block2);
    fencrypt(block2, 0, ks);
    XORblock(block3, block2, block3);
    fencrypt(block3, 0, ks);
}

void cbc_dec_three_blocks(char block1[8], char block2[8], char block3[8], char IV[8],keysched *ks)
{
    char temp1[8];
    char temp2[8];
    char temp3[8];

    for(int i = 0; i < 8; i++)
    {
        temp1[i] = block1[i];
        temp2[i] = block2[i];
        temp3[i] = block3[i];
    }

    fencrypt(block1,1,ks);
    XORblock(block1, IV, block1);
    fencrypt(block2,1,ks);
    XORblock(block2, temp1, block2);
    fencrypt(block3,1,ks);
    XORblock(block3, temp2, block3);
}

int main()
{
    unsigned char key[8] = {1,2,3,4,5,6,7,8};  //This will be the key
    keysched *ks = malloc(sizeof(keysched));   //Initialize the key schedule data structure
    fsetkey(key,ks);                           //Build the key schedule
    unsigned char* all_blocks = malloc(3*8*sizeof(char)); //24 bytes of memory, representing 3 DES blocks
    bzero(all_blocks,8*3);                     //Initialize the blocks to all 0s

    all_blocks[0] = 'A';                       //Put 0x41=='A' into the first byte of the first block

    /*The file "plaintext.txt", created below, will be useful for testing.*/
    FILE* pt_f = fopen("plaintext.txt","wb");
    fwrite(all_blocks,8,3,pt_f); //write 3 blocks, each of length 8 bytes
    fclose(pt_f);

    unsigned char IV[8] = {0};                  //The IV will be all zeros

    cbc_enc_three_blocks(all_blocks,all_blocks+8,all_blocks+16,IV,ks);   //Do the encryption
    FILE* fp = fopen("encryption.des","wb");                             //Save the result
    fwrite(all_blocks,8,3,fp); //write 3 blocks, each of length 8 bytes
    fclose(fp);

    cbc_dec_three_blocks(all_blocks,all_blocks+8,all_blocks+16,IV,ks);   //Do the decryption
    fp = fopen("decryption.txt","wb");                                   //Save the result
    fwrite(all_blocks,8,3,fp); //write 3 blocks, each of length 8 bytes
    fclose(fp);
}