/* 

Modified RC4 source code in which a cryptographically secure hash
is xored against the RC4 keystream before the actual encryption/decryption process

Regarding lincense information of any cipher algorithm used in the tests
please refer to:

RC4  		Ron Rivest (RSA Security)

MD5			Ron Rivest (RSA Security)

The modification is made by Karl-Uwe Frank and licensed as:

This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to <http://unlicense.org/>

*/

#include <stdlib.h>
#include <stdio.h> 
#include <stdint.h>
#include <string.h>
#include <time.h>
#include <math.h>

#include "md5/md5.h"
#include "md5/md5.c"


#define swap(X,Y) { uint8_t T = X; X = Y; Y = T; }


/*
-----------------------------------------
 
rm -f rc4_mdX_keystream && gcc -O3 -std=c99 rc4_mdX_keystream.c -o rc4_mdX_keystream

Usage:
./rc4_mdX_keystream key out_size-in-64bit > rc4_mdX_keystream_out.bin


-----------------------------------------

Test Vector

./rc4_mdX_keystream 0102030405 128 | xxd -g 1

0000000: a3 6c 25 14 d5 51 d0 61 c2 65 1d 6b c0 01 6e 7c  .l%..Q.a.e.k..n|
0000010: 23 89 7c 6b e7 8a ce 6b 9d d1 14 57 99 45 df 59  #.|k...k...W.E.Y
0000020: ad 4c b3 44 fb 0d 9a 8b 1f cc 9d d5 fa 7b e6 ed  .L.D.........{..
0000030: 33 97 30 6c f9 10 4f 49 7d 7b e4 f9 0f 74 e4 7e  3.0l..OI}{...t.~
0000040: f8 de 7e 17 bd c0 e6 e9 6f 25 ce 82 de 67 67 26  ..~.....o%...gg&
0000050: dd c3 e6 dd 1a 5d 98 43 78 44 09 15 f7 fe 41 94  .....].CxD....A.
0000060: 24 f5 ff ff fa 9c 17 48 e9 13 90 e7 94 80 5d e4  $......H......].
0000070: ce 57 ca cd c1 db c9 15 99 21 27 45 06 76 ef cf  .W.......!'E.v..


./rc4_mdX_keystream 0c8c8279b04c4430d69a6454d069458e 128 | xxd -g 1

0000000: 69 e4 6b ad 91 51 14 82 d6 e1 62 ef e6 6c b4 db  i.k..Q....b..l..
0000010: de ad be 2f 12 b5 a3 c5 10 c5 6b cf c4 8f bb aa  .../......k.....
0000020: d3 35 98 8f 56 cf 0c 75 1d ff 4a 60 68 82 c2 d0  .5..V..u..J`h...
0000030: b9 73 d8 0e 9f c1 4e 5f fc 38 5a 55 ae 80 10 d2  .s....N_.8ZU....
0000040: 0f 08 ff f0 32 fa c8 9f 1a 3f ee bd 1d 23 f1 f3  ....2....?...#..
0000050: f1 d0 3e 0d a9 57 5c 0c f9 9f 77 75 1b aa da 93  ..>..W\...wu....
0000060: 52 0c 30 0d 20 94 ea 68 a7 c2 ae 84 67 d7 59 2e  R.0. ..h....g.Y.
0000070: 11 e5 d1 54 25 65 51 4b 2f 7f 9c a1 aa bb 31 e4  ...T%eQK/.....1.

-----------------------------------------

./rc4_mdX_keystream 00 10000000 > rc4_mdX_keystream_out.bin

*/


static uint8_t a, b, j, k, t, out_8bit;
static uint8_t SBox[256];

void rc4_KSA(uint8_t key[], uint8_t keyLen);
uint8_t rc4_PRGA();



void MD5hash(unsigned char *data, unsigned int dataLen, unsigned char *digest) {
    MD5_CTX c;
    MD5Init(&c);
    MD5Update(&c, data, dataLen);
    MD5Final(digest, &c);
}


//-----------------------------------------
// KSA = Key Schedule Algorithm
//
void rc4_KSA(uint8_t key[], uint8_t keyLen) {
  uint8_t j = k = 0;

  for (int i=0; i<256; i++) {
    SBox[i] = i;
  }
	
	for (int i=0; i<256; i++) {
		k = (i % keyLen);
		j = (j + SBox[i] + key[k]);
		swap(SBox[i], SBox[j]);
	}
		
	a=0; b=0;
}


//-----------------------------------------
//
// Pseudo Random Generation Algorithm
//
uint8_t rc4_PRGA() {
  uint8_t t = 0;

  a = a + 1;
  b = b + SBox[a];
  
  swap(SBox[a], SBox[b]);
  
  t = SBox[a] + SBox[b];
  
  return SBox[t];
}


//-----------------------------------------
// Main 
//
int main (int argc, char *argv[]) 
{ 
	// 
	int Debug = 0;

  // initialisation
  char* PrgName;

	uint8_t DigestLen 			= 16; // md5
	uint8_t keystream[16] 	= {0,};
	uint8_t hashDigest[16]  = {0,};
	uint64_t output_size;

	// Check if a Seed is passed through
 	if (argc < 3) {
 		fprintf(stderr,"\nError: key (hex in format) > 0x0");
 		fprintf(stderr,"\n       and size of output must be byte value >0 and max. 64bit\n\n");
 		return 1;
 	}	
		
 	output_size = (uint64_t)strtoul(argv[2], NULL, 0);
 	
 	if (output_size == 0) {
		fprintf(stderr,"\nError: size of output must be byte value >0 and max. 64bit\n\n");
	 	exit(1);
	}


	// We have a key
	uint8_t key[256];
	uint8_t keyLen;
	uint8_t hexKey[256];
	uint8_t hex[3]; 

	// Make sure the arrays get initialised properly
	// and wipe out anything which might be there
	memset(key,    0, 256);
	memset(hexKey, 0, 256);
	memset(hex,    0, 3);

	// Rebuild key[] from KeyHash
	strcpy(hexKey, argv[1]);
	keyLen = strlen(hexKey);
	hexKey[keyLen] = 0;

	keyLen = keyLen/2;
	for (uint8_t i=0; i<keyLen; i++) {
		strncpy(hex, hexKey +(i*2), 2);
		key[i] = strtol(hex, NULL, 16);
	}

	/*
	fprintf(stderr, "========= Start Values (rc4_md 8-bit) ============\n\n");
	fprintf(stderr, "             key = %s\n\n", argv[1]); 
	fprintf(stderr, "  Output size (byte) = %s\n\n", argv[2]); 
	fprintf(stderr, "===================================================\n\n");
	*/

  //-----------------------------------------
  // Initialisation of rc4
  //
  // perform the Key Schedule
	rc4_KSA(key, keyLen);   

  fflush(stdout);

	// Output the keystream
	for (uint64_t i=0; i<(output_size/DigestLen); i++) {
		// Capture 16 Byte of the Keystream
		for (int n=0; n<DigestLen; n++) keystream[n] = rc4_PRGA();
		
		// Hash the captured Keystream
		MD5hash(keystream, DigestLen, hashDigest);
			
		// XOR the Hash Digest against the captured Keystream
		for (int n=0; n<DigestLen; n++) keystream[n] ^= hashDigest[n];
	
		// Write the XORed keystream to stdout
		fwrite(&keystream, sizeof(uint8_t), DigestLen, stdout);
	}

  fflush(stdout);

  return 0;
}