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/**
* \file
* <!--
* This file is part of BeRTOS.
*
* Bertos 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 2 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, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
* As a special exception, you may use this file as part of a free software
* library without restriction. Specifically, if other files instantiate
* templates or use macros or inline functions from this file, or you compile
* this file and link it with other files to produce an executable, this
* file does not by itself cause the resulting executable to be covered by
* the GNU General Public License. This exception does not however
* invalidate any other reasons why the executable file might be covered by
* the GNU General Public License.
*
* Copyright 2006 Develer S.r.l. (http://www.develer.com/)
*
* -->
*
* \brief TEA Tiny Encription Algorith functions (implementation).
*
* \author Francesco Sacchi <batt@develer.com>
*
* The Tiny Encryption Algorithm (TEA) by David Wheeler and Roger Needham
* of the Cambridge Computer Laboratory
*
* Placed in the Public Domain by David Wheeler and Roger Needham.
*
* **** ANSI C VERSION ****
*
* Notes:
*
* TEA is a Feistel cipher with XOR and and addition as the non-linear
* mixing functions.
*
* Takes 64 bits of data in v[0] and v[1]. Returns 64 bits of data in w[0]
* and w[1]. Takes 128 bits of key in k[0] - k[3].
*
* TEA can be operated in any of the modes of DES. Cipher Block Chaining is,
* for example, simple to implement.
*
* n is the number of iterations. 32 is ample, 16 is sufficient, as few
* as eight may be OK. The algorithm achieves good dispersion after six
* iterations. The iteration count can be made variable if required.
*
* Note this is optimised for 32-bit CPUs with fast shift capabilities. It
* can very easily be ported to assembly language on most CPUs.
*
* delta is chosen to be the real part of (the golden ratio Sqrt(5/4) -
* 1/2 ~ 0.618034 multiplied by 2^32).
*/
#include "tea.h"
#include <cpu/byteorder.h>
static uint32_t tea_func(uint32_t *in, uint32_t *sum, uint32_t *k)
{
return ((*in << 4) + cpu_to_le32(k[0])) ^ (*in + *sum) ^ ((*in >> 5) + cpu_to_le32(k[1]));
}
/**
* \brief TEA encryption function.
* This function encrypts <EM>v</EM> with <EM>k</EM> and returns the
* encrypted data in <EM>v</EM>.
* \param _v Array of two long values containing the data block.
* \param _k Array of four long values containing the key.
*/
void tea_enc(void *_v, void *_k)
{
uint32_t y, z;
uint32_t sum = 0;
uint8_t n = ROUNDS;
uint32_t *v = (uint32_t *)_v;
uint32_t *k = (uint32_t *)_k;
y=cpu_to_le32(v[0]);
z=cpu_to_le32(v[1]);
while(n-- > 0)
{
sum += DELTA;
y += tea_func(&z, &sum, &(k[0]));
z += tea_func(&y, &sum, &(k[2]));
}
v[0] = le32_to_cpu(y);
v[1] = le32_to_cpu(z);
}
/**
* \brief TEA decryption function.
* This function decrypts <EM>v</EM> with <EM>k</EM> and returns the
* decrypted data in <EM>v</EM>.
* \param _v Array of two long values containing the data block.
* \param _k Array of four long values containing the key.
*/
void tea_dec(void *_v, void *_k)
{
uint32_t y, z;
uint32_t sum = DELTA * ROUNDS;
uint8_t n = ROUNDS;
uint32_t *v = (uint32_t *)_v;
uint32_t *k = (uint32_t *)_k;
y = cpu_to_le32(v[0]);
z = cpu_to_le32(v[1]);
while(n-- > 0)
{
z -= tea_func(&y, &sum, &(k[2]));
y -= tea_func(&z, &sum, &(k[0]));
sum -= DELTA;
}
v[0] = le32_to_cpu(y);
v[1] = le32_to_cpu(z);
}