/* Ryan Nichols
* 2/19/17
* CEG4750 - Undergraduate
* Project 1 - CBC Mode DES Decoder
*/
#include<iostream>
#include<fstream>
#include<sstream>
#include<string>
#include<cstring>
using namespace std;

#include"cryptopp/cryptlib.h"
#include"cryptopp/hex.h"
#include"cryptopp/filters.h"
#include"cryptopp/des.h"
#include"cryptopp/modes.h"

using namespace CryptoPP;

void des_decryption_8(unsigned char *input, unsigned char *key, unsigned char *output)
{
	DESDecryption desDecryptor;
	unsigned char xorBlock[8];
	memset(xorBlock,0,8);
	desDecryptor.SetKey(key,8);
	desDecryptor.ProcessAndXorBlock(input,xorBlock,output);
}

int main(int argc, char * argv[])
{
    //Assign init vector
    unsigned char iv[DES::BLOCKSIZE] = {0x4c, 0xa0, 0x0f, 0xd6, 0xdb, 0xf1, 0xfb, 0x28}; //Test case 1
    //unsigned char iv[DES::BLOCKSIZE] = {0x0f, 0xf4, 0xc8, 0xd6, 0x1e, 0x80, 0x06, 0x18}; //Test case 2

    //Files
    fstream pFile; //Output plaintext file
    fstream cFile; //Input ciphertext file
    fstream kFile; //Input key file

    //Incorrect commandline usage
    if(argc!=4)
    {
        cout<<"usage:cbc_des_encode infile outfile keyfile"<<endl;
    }

    //Open files
    cFile.open(argv[1],ios::in);
    pFile.open(argv[2],ios::out);
    kFile.open(argv[3],ios::in);

    //Read ciphertext
    stringstream buffer;
    buffer << cFile.rdbuf();
    string cString(buffer.str());
    cout<< "Ciphertext: " << cString << endl;

    //Read Key
    stringstream buffer2;
    buffer2 << kFile.rdbuf();
    string kString(buffer2.str());
    cout << "Key: " << kString;
    unsigned char key[DES::DEFAULT_KEYLENGTH];
    for (int i = 0; i < DES::DEFAULT_KEYLENGTH; i++) {
       	key[i] = kString.at(i);
    }

    //Get block count
    int numblocks = (cString.size() / DES::BLOCKSIZE);
    cout << "number of blocks: " << numblocks << endl;



    unsigned char cipherblock[numblocks][DES::BLOCKSIZE];
    unsigned char plainblock [numblocks][DES::BLOCKSIZE];
    unsigned char plaintext [numblocks * DES::BLOCKSIZE];
    unsigned char thisblock[DES::BLOCKSIZE];
    for (int block = numblocks - 1; block >= 0; block--) {
     	for (int i = block * 8, j = 0; j < 8; i++, j++) {
          	cipherblock[block][j] = (unsigned char)cString.at(i);	//Get a block
        }
	unsigned char tempblock[DES::BLOCKSIZE];
	for(int i = 0; i < 8; i++)
	{
		tempblock[i] = cipherblock[block][i]; //Fill a temporary array which is passed to the decoding function
	}
	des_decryption_8(tempblock, key, thisblock); //decrpyt block, plaintext written to this block. Still need xored

	for(int i = 0; i < 8; i++) {
		plainblock[block][i] = thisblock[i]; //Save decrypted blocks to xor them after
	}

    }
    for(int i = numblocks-1; i > 0; i--) {		//For all but the first block
	for (int j = 0; j < 8; j++){
           	plainblock[i][j] ^= cipherblock[i-1][j];  //xor with previous ciphertext for CBC implementation
        }
    }
    for (int j = 0; j < 8; j++){
           plainblock[0][j] ^= iv[j];  //xor first block with the IV
    }

    for (int block = 0; block < numblocks; block++) {
    	for(int i = block *8, j =0; j<8; i++, j++)
    	{
     		plaintext[i]=plainblock[block][j]; //Recombine the plaintext
    	}
    }

    //Remove padding
    int padAmount = plaintext[numblocks * DES::BLOCKSIZE -1];

    cout << "Plaintext: ";
    for (int i =0; i < (numblocks * DES::BLOCKSIZE) - padAmount; i++)	{
       	pFile<< plaintext [i];  //write plaintext to file
	cout << plaintext[i];   //write plaintext to console
    }
    cout <<endl;
}