present.h

/*
 * Copyright (c) 2009, Shanghai Jiao Tong University
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - 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.
 * - Neither the name of the Shanghai Jiao Tong University nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * 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 OWNER 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.
 */

/*
 * The core function of PRESENT block cipher.
 * 1kB look-up tables are used for perferment tunning.
 *
 * @author Bo Zhu, http://about.bozhu.me
 * @author Zheng Gong, DIES Group, University of Twente
 * @date   July 21, 2009
 */

#ifndef PRESENT_H
#define PRESENT_H

// comment this out if this is used on PC
#define __UINT_T__

#ifndef __UINT_T__
#define __UINT_T__
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned long uint32_t;
typedef unsigned long long uint64_t;
#endif /* __UINT_T__ */

// full-round PRESENT block cipher
#define present(plain, key, cipher) present_rounds((plain), (key), 31, (cipher))

// actually is (sbox[] << 4)
static const uint8_t sbox[16] = {
	0xC0, 0x50, 0x60, 0xB0, 0x90, 0x00, 0xA0, 0xD0, 0x30, 0xE0, 0xF0, 0x80, 0x40, 0x70, 0x10, 0x20,
};

// look-up tables for speeding up permutation layer
static const uint8_t sbox_pmt_3[256] = {
	0xF0, 0xB1, 0xB4, 0xE5, 0xE1, 0xA0, 0xE4, 0xF1, 0xA5, 0xF4, 0xF5, 0xE0, 0xB0, 0xB5, 0xA1, 0xA4, 
	0x72, 0x33, 0x36, 0x67, 0x63, 0x22, 0x66, 0x73, 0x27, 0x76, 0x77, 0x62, 0x32, 0x37, 0x23, 0x26, 
	0x78, 0x39, 0x3C, 0x6D, 0x69, 0x28, 0x6C, 0x79, 0x2D, 0x7C, 0x7D, 0x68, 0x38, 0x3D, 0x29, 0x2C, 
	0xDA, 0x9B, 0x9E, 0xCF, 0xCB, 0x8A, 0xCE, 0xDB, 0x8F, 0xDE, 0xDF, 0xCA, 0x9A, 0x9F, 0x8B, 0x8E, 
	0xD2, 0x93, 0x96, 0xC7, 0xC3, 0x82, 0xC6, 0xD3, 0x87, 0xD6, 0xD7, 0xC2, 0x92, 0x97, 0x83, 0x86, 
	0x50, 0x11, 0x14, 0x45, 0x41, 0x00, 0x44, 0x51, 0x05, 0x54, 0x55, 0x40, 0x10, 0x15, 0x01, 0x04, 
	0xD8, 0x99, 0x9C, 0xCD, 0xC9, 0x88, 0xCC, 0xD9, 0x8D, 0xDC, 0xDD, 0xC8, 0x98, 0x9D, 0x89, 0x8C, 
	0xF2, 0xB3, 0xB6, 0xE7, 0xE3, 0xA2, 0xE6, 0xF3, 0xA7, 0xF6, 0xF7, 0xE2, 0xB2, 0xB7, 0xA3, 0xA6, 
	0x5A, 0x1B, 0x1E, 0x4F, 0x4B, 0x0A, 0x4E, 0x5B, 0x0F, 0x5E, 0x5F, 0x4A, 0x1A, 0x1F, 0x0B, 0x0E, 
	0xF8, 0xB9, 0xBC, 0xED, 0xE9, 0xA8, 0xEC, 0xF9, 0xAD, 0xFC, 0xFD, 0xE8, 0xB8, 0xBD, 0xA9, 0xAC, 
	0xFA, 0xBB, 0xBE, 0xEF, 0xEB, 0xAA, 0xEE, 0xFB, 0xAF, 0xFE, 0xFF, 0xEA, 0xBA, 0xBF, 0xAB, 0xAE, 
	0xD0, 0x91, 0x94, 0xC5, 0xC1, 0x80, 0xC4, 0xD1, 0x85, 0xD4, 0xD5, 0xC0, 0x90, 0x95, 0x81, 0x84, 
	0x70, 0x31, 0x34, 0x65, 0x61, 0x20, 0x64, 0x71, 0x25, 0x74, 0x75, 0x60, 0x30, 0x35, 0x21, 0x24, 
	0x7A, 0x3B, 0x3E, 0x6F, 0x6B, 0x2A, 0x6E, 0x7B, 0x2F, 0x7E, 0x7F, 0x6A, 0x3A, 0x3F, 0x2B, 0x2E, 
	0x52, 0x13, 0x16, 0x47, 0x43, 0x02, 0x46, 0x53, 0x07, 0x56, 0x57, 0x42, 0x12, 0x17, 0x03, 0x06, 
	0x58, 0x19, 0x1C, 0x4D, 0x49, 0x08, 0x4C, 0x59, 0x0D, 0x5C, 0x5D, 0x48, 0x18, 0x1D, 0x09, 0x0C,
};

static const uint8_t sbox_pmt_2[256] = {
	0x3C, 0x6C, 0x2D, 0x79, 0x78, 0x28, 0x39, 0x7C, 0x69, 0x3D, 0x7D, 0x38, 0x2C, 0x6D, 0x68, 0x29, 
	0x9C, 0xCC, 0x8D, 0xD9, 0xD8, 0x88, 0x99, 0xDC, 0xC9, 0x9D, 0xDD, 0x98, 0x8C, 0xCD, 0xC8, 0x89, 
	0x1E, 0x4E, 0x0F, 0x5B, 0x5A, 0x0A, 0x1B, 0x5E, 0x4B, 0x1F, 0x5F, 0x1A, 0x0E, 0x4F, 0x4A, 0x0B, 
	0xB6, 0xE6, 0xA7, 0xF3, 0xF2, 0xA2, 0xB3, 0xF6, 0xE3, 0xB7, 0xF7, 0xB2, 0xA6, 0xE7, 0xE2, 0xA3, 
	0xB4, 0xE4, 0xA5, 0xF1, 0xF0, 0xA0, 0xB1, 0xF4, 0xE1, 0xB5, 0xF5, 0xB0, 0xA4, 0xE5, 0xE0, 0xA1, 
	0x14, 0x44, 0x05, 0x51, 0x50, 0x00, 0x11, 0x54, 0x41, 0x15, 0x55, 0x10, 0x04, 0x45, 0x40, 0x01, 
	0x36, 0x66, 0x27, 0x73, 0x72, 0x22, 0x33, 0x76, 0x63, 0x37, 0x77, 0x32, 0x26, 0x67, 0x62, 0x23, 
	0xBC, 0xEC, 0xAD, 0xF9, 0xF8, 0xA8, 0xB9, 0xFC, 0xE9, 0xBD, 0xFD, 0xB8, 0xAC, 0xED, 0xE8, 0xA9, 
	0x96, 0xC6, 0x87, 0xD3, 0xD2, 0x82, 0x93, 0xD6, 0xC3, 0x97, 0xD7, 0x92, 0x86, 0xC7, 0xC2, 0x83, 
	0x3E, 0x6E, 0x2F, 0x7B, 0x7A, 0x2A, 0x3B, 0x7E, 0x6B, 0x3F, 0x7F, 0x3A, 0x2E, 0x6F, 0x6A, 0x2B, 
	0xBE, 0xEE, 0xAF, 0xFB, 0xFA, 0xAA, 0xBB, 0xFE, 0xEB, 0xBF, 0xFF, 0xBA, 0xAE, 0xEF, 0xEA, 0xAB, 
	0x34, 0x64, 0x25, 0x71, 0x70, 0x20, 0x31, 0x74, 0x61, 0x35, 0x75, 0x30, 0x24, 0x65, 0x60, 0x21, 
	0x1C, 0x4C, 0x0D, 0x59, 0x58, 0x08, 0x19, 0x5C, 0x49, 0x1D, 0x5D, 0x18, 0x0C, 0x4D, 0x48, 0x09, 
	0x9E, 0xCE, 0x8F, 0xDB, 0xDA, 0x8A, 0x9B, 0xDE, 0xCB, 0x9F, 0xDF, 0x9A, 0x8E, 0xCF, 0xCA, 0x8B, 
	0x94, 0xC4, 0x85, 0xD1, 0xD0, 0x80, 0x91, 0xD4, 0xC1, 0x95, 0xD5, 0x90, 0x84, 0xC5, 0xC0, 0x81, 
	0x16, 0x46, 0x07, 0x53, 0x52, 0x02, 0x13, 0x56, 0x43, 0x17, 0x57, 0x12, 0x06, 0x47, 0x42, 0x03,
};

static const uint8_t sbox_pmt_1[256] = {
	0x0F, 0x1B, 0x4B, 0x5E, 0x1E, 0x0A, 0x4E, 0x1F, 0x5A, 0x4F, 0x5F, 0x0E, 0x0B, 0x5B, 0x1A, 0x4A, 
	0x27, 0x33, 0x63, 0x76, 0x36, 0x22, 0x66, 0x37, 0x72, 0x67, 0x77, 0x26, 0x23, 0x73, 0x32, 0x62, 
	0x87, 0x93, 0xC3, 0xD6, 0x96, 0x82, 0xC6, 0x97, 0xD2, 0xC7, 0xD7, 0x86, 0x83, 0xD3, 0x92, 0xC2, 
	0xAD, 0xB9, 0xE9, 0xFC, 0xBC, 0xA8, 0xEC, 0xBD, 0xF8, 0xED, 0xFD, 0xAC, 0xA9, 0xF9, 0xB8, 0xE8, 
	0x2D, 0x39, 0x69, 0x7C, 0x3C, 0x28, 0x6C, 0x3D, 0x78, 0x6D, 0x7D, 0x2C, 0x29, 0x79, 0x38, 0x68, 
	0x05, 0x11, 0x41, 0x54, 0x14, 0x00, 0x44, 0x15, 0x50, 0x45, 0x55, 0x04, 0x01, 0x51, 0x10, 0x40, 
	0x8D, 0x99, 0xC9, 0xDC, 0x9C, 0x88, 0xCC, 0x9D, 0xD8, 0xCD, 0xDD, 0x8C, 0x89, 0xD9, 0x98, 0xC8, 
	0x2F, 0x3B, 0x6B, 0x7E, 0x3E, 0x2A, 0x6E, 0x3F, 0x7A, 0x6F, 0x7F, 0x2E, 0x2B, 0x7B, 0x3A, 0x6A, 
	0xA5, 0xB1, 0xE1, 0xF4, 0xB4, 0xA0, 0xE4, 0xB5, 0xF0, 0xE5, 0xF5, 0xA4, 0xA1, 0xF1, 0xB0, 0xE0, 
	0x8F, 0x9B, 0xCB, 0xDE, 0x9E, 0x8A, 0xCE, 0x9F, 0xDA, 0xCF, 0xDF, 0x8E, 0x8B, 0xDB, 0x9A, 0xCA, 
	0xAF, 0xBB, 0xEB, 0xFE, 0xBE, 0xAA, 0xEE, 0xBF, 0xFA, 0xEF, 0xFF, 0xAE, 0xAB, 0xFB, 0xBA, 0xEA, 
	0x0D, 0x19, 0x49, 0x5C, 0x1C, 0x08, 0x4C, 0x1D, 0x58, 0x4D, 0x5D, 0x0C, 0x09, 0x59, 0x18, 0x48, 
	0x07, 0x13, 0x43, 0x56, 0x16, 0x02, 0x46, 0x17, 0x52, 0x47, 0x57, 0x06, 0x03, 0x53, 0x12, 0x42, 
	0xA7, 0xB3, 0xE3, 0xF6, 0xB6, 0xA2, 0xE6, 0xB7, 0xF2, 0xE7, 0xF7, 0xA6, 0xA3, 0xF3, 0xB2, 0xE2, 
	0x25, 0x31, 0x61, 0x74, 0x34, 0x20, 0x64, 0x35, 0x70, 0x65, 0x75, 0x24, 0x21, 0x71, 0x30, 0x60, 
	0x85, 0x91, 0xC1, 0xD4, 0x94, 0x80, 0xC4, 0x95, 0xD0, 0xC5, 0xD5, 0x84, 0x81, 0xD1, 0x90, 0xC0,
};

static const uint8_t sbox_pmt_0[256] = {
	0xC3, 0xC6, 0xD2, 0x97, 0x87, 0x82, 0x93, 0xC7, 0x96, 0xD3, 0xD7, 0x83, 0xC2, 0xD6, 0x86, 0x92, 
	0xC9, 0xCC, 0xD8, 0x9D, 0x8D, 0x88, 0x99, 0xCD, 0x9C, 0xD9, 0xDD, 0x89, 0xC8, 0xDC, 0x8C, 0x98, 
	0xE1, 0xE4, 0xF0, 0xB5, 0xA5, 0xA0, 0xB1, 0xE5, 0xB4, 0xF1, 0xF5, 0xA1, 0xE0, 0xF4, 0xA4, 0xB0, 
	0x6B, 0x6E, 0x7A, 0x3F, 0x2F, 0x2A, 0x3B, 0x6F, 0x3E, 0x7B, 0x7F, 0x2B, 0x6A, 0x7E, 0x2E, 0x3A, 
	0x4B, 0x4E, 0x5A, 0x1F, 0x0F, 0x0A, 0x1B, 0x4F, 0x1E, 0x5B, 0x5F, 0x0B, 0x4A, 0x5E, 0x0E, 0x1A, 
	0x41, 0x44, 0x50, 0x15, 0x05, 0x00, 0x11, 0x45, 0x14, 0x51, 0x55, 0x01, 0x40, 0x54, 0x04, 0x10, 
	0x63, 0x66, 0x72, 0x37, 0x27, 0x22, 0x33, 0x67, 0x36, 0x73, 0x77, 0x23, 0x62, 0x76, 0x26, 0x32, 
	0xCB, 0xCE, 0xDA, 0x9F, 0x8F, 0x8A, 0x9B, 0xCF, 0x9E, 0xDB, 0xDF, 0x8B, 0xCA, 0xDE, 0x8E, 0x9A, 
	0x69, 0x6C, 0x78, 0x3D, 0x2D, 0x28, 0x39, 0x6D, 0x3C, 0x79, 0x7D, 0x29, 0x68, 0x7C, 0x2C, 0x38, 
	0xE3, 0xE6, 0xF2, 0xB7, 0xA7, 0xA2, 0xB3, 0xE7, 0xB6, 0xF3, 0xF7, 0xA3, 0xE2, 0xF6, 0xA6, 0xB2, 
	0xEB, 0xEE, 0xFA, 0xBF, 0xAF, 0xAA, 0xBB, 0xEF, 0xBE, 0xFB, 0xFF, 0xAB, 0xEA, 0xFE, 0xAE, 0xBA, 
	0x43, 0x46, 0x52, 0x17, 0x07, 0x02, 0x13, 0x47, 0x16, 0x53, 0x57, 0x03, 0x42, 0x56, 0x06, 0x12, 
	0xC1, 0xC4, 0xD0, 0x95, 0x85, 0x80, 0x91, 0xC5, 0x94, 0xD1, 0xD5, 0x81, 0xC0, 0xD4, 0x84, 0x90, 
	0xE9, 0xEC, 0xF8, 0xBD, 0xAD, 0xA8, 0xB9, 0xED, 0xBC, 0xF9, 0xFD, 0xA9, 0xE8, 0xFC, 0xAC, 0xB8, 
	0x49, 0x4C, 0x58, 0x1D, 0x0D, 0x08, 0x19, 0x4D, 0x1C, 0x59, 0x5D, 0x09, 0x48, 0x5C, 0x0C, 0x18, 
	0x61, 0x64, 0x70, 0x35, 0x25, 0x20, 0x31, 0x65, 0x34, 0x71, 0x75, 0x21, 0x60, 0x74, 0x24, 0x30,
};

// full-round should be 31, i.e. rounds = 31
// plain and cipher can overlap, so do key and cipher
void present_rounds(const uint8_t *plain, const uint8_t *key, const uint8_t rounds, uint8_t *cipher)
{
	uint8_t round_counter = 1;
	
	uint8_t state[8];
	uint8_t round_key[10];

	// add key
	state[0] = plain[0] ^ key[0];
	state[1] = plain[1] ^ key[1];
	state[2] = plain[2] ^ key[2];
	state[3] = plain[3] ^ key[3];
	state[4] = plain[4] ^ key[4];
	state[5] = plain[5] ^ key[5];
	state[6] = plain[6] ^ key[6];
	state[7] = plain[7] ^ key[7];

	// update key
	round_key[9] = key[6] << 5 | key[7] >> 3;
	round_key[8] = key[5] << 5 | key[6] >> 3;
	round_key[7] = key[4] << 5 | key[5] >> 3;
	round_key[6] = key[3] << 5 | key[4] >> 3;
	round_key[5] = key[2] << 5 | key[3] >> 3;
	round_key[4] = key[1] << 5 | key[2] >> 3;
	round_key[3] = key[0] << 5 | key[1] >> 3;
	round_key[2] = key[9] << 5 | key[0] >> 3;
	round_key[1] = key[8] << 5 | key[9] >> 3;
	round_key[0] = key[7] << 5 | key[8] >> 3;

	round_key[0] = (round_key[0] & 0x0F) | sbox[round_key[0] >> 4];

	round_key[7] ^= round_counter >> 1;
	round_key[8] ^= round_counter << 7;

	// substitution and permutation
	cipher[0] = 
		(sbox_pmt_3[state[0]] & 0xC0) | 
		(sbox_pmt_2[state[1]] & 0x30) |
		(sbox_pmt_1[state[2]] & 0x0C) |
		(sbox_pmt_0[state[3]] & 0x03);
	cipher[1] = 
		(sbox_pmt_3[state[4]] & 0xC0) | 
		(sbox_pmt_2[state[5]] & 0x30) |
		(sbox_pmt_1[state[6]] & 0x0C) | 
		(sbox_pmt_0[state[7]] & 0x03);

	cipher[2] = 
		(sbox_pmt_0[state[0]] & 0xC0) | 
		(sbox_pmt_3[state[1]] & 0x30) |
		(sbox_pmt_2[state[2]] & 0x0C) |
		(sbox_pmt_1[state[3]] & 0x03);
	cipher[3] = 
		(sbox_pmt_0[state[4]] & 0xC0) | 
		(sbox_pmt_3[state[5]] & 0x30) |
		(sbox_pmt_2[state[6]] & 0x0C) |
		(sbox_pmt_1[state[7]] & 0x03);

	cipher[4] = 
		(sbox_pmt_1[state[0]] & 0xC0) | 
		(sbox_pmt_0[state[1]] & 0x30) |
		(sbox_pmt_3[state[2]] & 0x0C) |
		(sbox_pmt_2[state[3]] & 0x03);
	cipher[5] = 
		(sbox_pmt_1[state[4]] & 0xC0) | 
		(sbox_pmt_0[state[5]] & 0x30) |
		(sbox_pmt_3[state[6]] & 0x0C) |
		(sbox_pmt_2[state[7]] & 0x03);

	cipher[6] = 
		(sbox_pmt_2[state[0]] & 0xC0) | 
		(sbox_pmt_1[state[1]] & 0x30) |
		(sbox_pmt_0[state[2]] & 0x0C) |
		(sbox_pmt_3[state[3]] & 0x03);
	cipher[7] = 
		(sbox_pmt_2[state[4]] & 0xC0) | 
		(sbox_pmt_1[state[5]] & 0x30) |
		(sbox_pmt_0[state[6]] & 0x0C) |
		(sbox_pmt_3[state[7]] & 0x03);

	for (round_counter = 2; round_counter <= rounds; round_counter++) {
		state[0] = cipher[0] ^ round_key[0];
		state[1] = cipher[1] ^ round_key[1];
		state[2] = cipher[2] ^ round_key[2];
		state[3] = cipher[3] ^ round_key[3];
		state[4] = cipher[4] ^ round_key[4];
		state[5] = cipher[5] ^ round_key[5];
		state[6] = cipher[6] ^ round_key[6];
		state[7] = cipher[7] ^ round_key[7];

		cipher[0] = 
			(sbox_pmt_3[state[0]] & 0xC0) | 
			(sbox_pmt_2[state[1]] & 0x30) |
			(sbox_pmt_1[state[2]] & 0x0C) |
			(sbox_pmt_0[state[3]] & 0x03);
		cipher[1] = 
			(sbox_pmt_3[state[4]] & 0xC0) | 
			(sbox_pmt_2[state[5]] & 0x30) |
			(sbox_pmt_1[state[6]] & 0x0C) | 
			(sbox_pmt_0[state[7]] & 0x03);

		cipher[2] = 
			(sbox_pmt_0[state[0]] & 0xC0) | 
			(sbox_pmt_3[state[1]] & 0x30) |
			(sbox_pmt_2[state[2]] & 0x0C) |
			(sbox_pmt_1[state[3]] & 0x03);
		cipher[3] = 
			(sbox_pmt_0[state[4]] & 0xC0) | 
			(sbox_pmt_3[state[5]] & 0x30) |
			(sbox_pmt_2[state[6]] & 0x0C) |
			(sbox_pmt_1[state[7]] & 0x03);

		cipher[4] = 
			(sbox_pmt_1[state[0]] & 0xC0) | 
			(sbox_pmt_0[state[1]] & 0x30) |
			(sbox_pmt_3[state[2]] & 0x0C) |
			(sbox_pmt_2[state[3]] & 0x03);
		cipher[5] = 
			(sbox_pmt_1[state[4]] & 0xC0) | 
			(sbox_pmt_0[state[5]] & 0x30) |
			(sbox_pmt_3[state[6]] & 0x0C) |
			(sbox_pmt_2[state[7]] & 0x03);

		cipher[6] = 
			(sbox_pmt_2[state[0]] & 0xC0) | 
			(sbox_pmt_1[state[1]] & 0x30) |
			(sbox_pmt_0[state[2]] & 0x0C) |
			(sbox_pmt_3[state[3]] & 0x03);
		cipher[7] = 
			(sbox_pmt_2[state[4]] & 0xC0) | 
			(sbox_pmt_1[state[5]] & 0x30) |
			(sbox_pmt_0[state[6]] & 0x0C) |
			(sbox_pmt_3[state[7]] & 0x03);

		round_key[5] ^= round_counter << 2; // do this first, which may be faster

		// use state[] for temporary storage
		state[2] = round_key[9];
		state[1] = round_key[8];
		state[0] = round_key[7];

		round_key[9] = round_key[6] << 5 | round_key[7] >> 3;
		round_key[8] = round_key[5] << 5 | round_key[6] >> 3;
		round_key[7] = round_key[4] << 5 | round_key[5] >> 3;
		round_key[6] = round_key[3] << 5 | round_key[4] >> 3;
		round_key[5] = round_key[2] << 5 | round_key[3] >> 3;
		round_key[4] = round_key[1] << 5 | round_key[2] >> 3;
		round_key[3] = round_key[0] << 5 | round_key[1] >> 3;
		round_key[2] = state[2] << 5 | round_key[0] >> 3;
		round_key[1] = state[1] << 5 | state[2] >> 3;
		round_key[0] = state[0] << 5 | state[1] >> 3;

		round_key[0] = (round_key[0] & 0x0F) | sbox[round_key[0] >> 4];
	}

	// if round is not equal to 31, then do not perform the last adding key operation
	// this can be used in constructing PRESENT based algorithm, such as MAC
	if (31 == rounds) {
		cipher[0] ^= round_key[0];
		cipher[1] ^= round_key[1];
		cipher[2] ^= round_key[2];
		cipher[3] ^= round_key[3];
		cipher[4] ^= round_key[4];
		cipher[5] ^= round_key[5];
		cipher[6] ^= round_key[6];
		cipher[7] ^= round_key[7];
	}
}

#endif /* PRESENT_H */