/* SBox8: 8 bit Pseudo-Random Number Generator Algorithm/Source Code */

/*
Copyright(c) 2015, Karl-Uwe Frank
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

  1. Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright
  notice, this list of conditions and the following disclaimer in the
  documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES(INCLUDING, BUT NOT LIMITED
TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT(INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#** SBox8 algorithm designed and developed by Karl-Uwe Frank

06.01.2016: Update of the Shifting Function inside SBox8_PIA
thanks to the recommendation of Bob Harris on sci.crpyt
*/
//**********************************************************************



//-----------------------------------------
//
// rm -f ./SBox8_keystream; gcc -std=c99 -O3 -fomit-frame-pointer -mtune=native SBox8_keystream.c -o SBox8_keystream
//
// Usage:
// ./SBox8_keystream seed key out_size-in-64bit > SBox8_keystream_out.bin
//
// ./SBox8_keystream 0x2ddd6a2c 0c8c8279b04c4430d69a6454d069458e 256 > SBox8_keystream_out.bin
// 
// ./SBox8_keystream 0xdeadbeef 04c7a580a0c8e7bf7ec5a0c9aef63c81 1024000 > SBox8_keystream_out.bin
//
//-----------------------------------------
//
// ./SBox8_keystream 00f75bce 50617373776f7264 16 | xxd -g 1
// 
// 0000000: d2 89 ea 66 f9 01 33 56 ca e8 d5 4f e0 72 49 e8
//
//-----------------------------------------
//
// ./SBox8_keystream 0 00 10000000 > SBox8_keystream_out.bin
//
// dieharder -a -g 201 -f SBox8_keystream_out.bin



#include <stdlib.h>
#include <stdio.h> 
#include <string.h>
#include <time.h>
// needed to generate uint32 on a 64bit OS
#include <stdint.h>

///////////////////////////////////////////

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



int main (int argc, char *argv[]) { 
	uint8_t  a, b, c, d, j, t, out_8bit;
	uint8_t SBox[256];
	uint32_t seed;
	uint64_t output_size, i;

	// Check if a Seed is passed through
 	if (argc < 4) {
 		fprintf(stderr,"\nError: seed (hex in format) value can be < 0x%08x and > 0x0", 0xffffffff);
 		fprintf(stderr,"\n       key  (hex in format) > 00\n");
 		fprintf(stderr,"\n       and size of output must be > 0 and max. 64bit\n\n");
 		return 1;
 	}	
		
 	seed				= (int)strtoul(argv[1], NULL, 16); 	
 	output_size = (uint64_t)strtoul(argv[3], NULL, 0);
 	
 	if (output_size == 0) {
		fprintf(stderr,"\nError: size of output must be > 0 and max. 64bit\n\n");
	 	exit(1);
	}

	if (seed == 0) {
		a = 14;
		b = 59;
		c = 23;
		d = 77;	
	} else {	
		a = ( seed        & 0xff);
		b = ((seed >>  8) & 0xff);
		c = ((seed >> 16) & 0xff);
		d = ((seed >> 24) & 0xff);
	}

	// 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
	strncpy(hexKey, argv[2], strlen(argv[2]));
	keyLen = strlen(hexKey);
	hexKey[keyLen] = 0;

	keyLen = keyLen/2;
	for (uint16_t i=0; i<keyLen; i++) {
		strncpy(hex, hexKey +(i*2), 2);
		key[i] = strtol(hex, NULL, 16);
	}

	// Shifting to the next odd Value of each Variable
	// in Order to generate an alternating Permutation
	t = ((b ^ c) + d);
	t |= 1;

	fprintf(stderr, "========= Start Values (SBox8 8-bit) ============\n\n");
	fprintf(stderr, "                   a = %3i\n",	a); 
	fprintf(stderr, "                   b = %3i\n",	b); 
	fprintf(stderr, "                   c = %3i\n",	c); 
	fprintf(stderr, "                   d = %3i\n\n",	d); 
 	fprintf(stderr, "                Seed = %s\n\n", argv[1]); 
	fprintf(stderr, "                 key = %s\n\n", argv[2]); 
	fprintf(stderr, "  Output size (byte) = %s\n\n", argv[3]); 
	fprintf(stderr, "===================================================\n\n");

	// Initialise the alternating Permutation
	for (int i=0; i<256; i++) {
		a += t;
		SBox[i] = a;
	}

	//for (int i=0; i<256; i++) fprintf(stderr, "%02x ", SBox[i]);
	//fprintf(stderr, "\n");

	// Shuffle the key into the Permutation
	for (int i=0; i<256; i++) {
		d  = i % keyLen;
		
		a += SBox[b];
		b += SBox[a];
		c  = a + b + i + key[d];
		
		swap(SBox[c], SBox[i]);		

    //fprintf(stderr, "i=%3d   a=%3d, b=%3d, c=%3d, SBox[c]=%3d, SBox[d]=%3d <== key[d]=%3d\n", i, a, b, c, SBox[c], SBox[d], key[d]);
	}

  fflush(stdout);

	j=0;
	
	// Output the keystream
	for (i=0; i<output_size; i++) {
		a += SBox[b];
		b += SBox[a];
		c  = a + b + j + SBox[j];
		
		swap(SBox[c], SBox[j]);		

		d  = SBox[(SBox[c] + SBox[d]) &0xff];

    //fprintf(stderr, "j=%3d  c=%3d, SBox[c]=%3d, SBox[d]=%3d\n", j, c, SBox[c], SBox[d]);

		out_8bit = ((a + b) ^ (c + d));
    
    j++;

		// write keystream to stdout
    fwrite(&out_8bit, sizeof(out_8bit), 1, stdout);
	}

  fflush(stdout);

	return 0;
}