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