/* serpent.c */
/*
    This file is part of the AVR-Crypto-Lib.
    Copyright (C) 2006-2015 Daniel Otte (bg@nerilex.org)

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
/* serpent.c
 * a bitsliced implementation of the serpent cipher for avr microcontrollers
 * author: Daniel Otte 
 * email:  bg@nerilex.org
 * license: GPLv3
 */

#include <stdint.h>
#include <string.h> /* memset() */
#include <avr/pgmspace.h>
#include "memxor.h"
#include "serpent.h"
#include "serpent-sboxes.h"

/******************************************************************************/

uint32_t rotl32(uint32_t a, uint8_t n){
	return ((a<<n) | (a>>(32-n)));
}


uint32_t rotr32(uint32_t a, uint8_t n){
	return ((a>>n) | (a<<(32-n)));
}


#define X0 (((uint32_t*)b)[0])
#define X1 (((uint32_t*)b)[1])
#define X2 (((uint32_t*)b)[2])
#define X3 (((uint32_t*)b)[3])

static void serpent_lt(uint8_t *b){
	X0 = rotl32(X0, 13);
	X2 = rotl32(X2,  3);
	X1 ^= X0 ^ X2;
	X3 ^= X2 ^ (X0 << 3);
	X1 = rotl32(X1, 1);
	X3 = rotl32(X3, 7);
	X0 ^= X1 ^ X3;
	X2 ^= X3 ^ (X1 << 7);
	X0 = rotl32(X0, 5);
	X2 = rotr32(X2, 10);
}

static void serpent_inv_lt(uint8_t *b){
	X2 = rotl32(X2, 10);
	X0 = rotr32(X0, 5);
	X2 ^= X3 ^ (X1 << 7);
	X0 ^= X1 ^ X3;
	X3 = rotr32(X3, 7);
	X1 = rotr32(X1, 1);
	X3 ^= X2 ^ (X0 << 3);
	X1 ^= X0 ^ X2;
	X2 = rotr32(X2,  3);
	X0 = rotr32(X0, 13);
}

#define GOLDEN_RATIO 0x9e3779b9l

static uint32_t serpent_gen_w(uint32_t * b, uint8_t i){
	uint32_t ret;
	ret = b[0] ^ b[3] ^ b[5] ^ b[7] ^ GOLDEN_RATIO ^ (uint32_t)i;
	ret = rotl32(ret, 11);
	return ret;
} 

void serpent_init(const void *key, uint16_t keysize_b, serpent_ctx_t *ctx){
	uint32_t buffer[8];
	uint8_t i,j;
	if(keysize_b<256){
		/* keysize is less than 256 bit, padding needed */
		memset(buffer, 0, 32);
		memcpy(buffer, key, (keysize_b+7)/8);
		((uint8_t*)buffer)[keysize_b/8] |= 1<<(keysize_b%8);
	} else {
		/* keysize is 256 bit */
		memcpy(buffer, key, 32); 
	}
	for(i=0; i<33; ++i){
		for(j=0; j<4; ++j){
			ctx->k[i][j] = serpent_gen_w(buffer, i*4+j);
			memmove(buffer, &(buffer[1]), 7*4); /* shift buffer one to the "left" */
			buffer[7] = ctx->k[i][j];
		}
	}
	for(i=0; i<33; ++i){
		sbox128(ctx->k[i],3-i);
	}
}

void serpent_enc(void *buffer, const serpent_ctx_t *ctx){
	uint8_t i;
	for(i=0; i<31; ++i){
		memxor(buffer, ctx->k[i], 16);
		sbox128(buffer, i);
		serpent_lt((uint8_t*)buffer);
	}
	memxor(buffer, ctx->k[i], 16);
	sbox128(buffer, i);
	++i;
	memxor(buffer, ctx->k[i], 16);
}

void serpent_dec(void *buffer, const serpent_ctx_t *ctx){
	int8_t i=32;
	
	memxor(buffer, ctx->k[i], 16);
	--i;
	inv_sbox128(buffer, i);
	memxor((uint8_t*)buffer, ctx->k[i], 16);
	--i;
	for(; i>=0; --i){
		serpent_inv_lt(buffer);
		inv_sbox128(buffer, i);
		memxor(buffer, ctx->k[i], 16);
	}
}