/** * \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); }