89 lines
3.4 KiB
C
89 lines
3.4 KiB
C
/****************************************************************************
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* libc/misc/lib_tea_decrypt.c
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* Tiny Encryption Algorithm - Decryption support
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*
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* Copyright (C) 2016 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* https://en.wikipedia.org/wiki/Tiny_Encryption_Algorithm: "Following is
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* an adaptation of the reference encryption and decryption routines in C,
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* released into the public domain by David Wheeler and Roger Needham."
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <stdint.h>
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#include <nuttx/crypto/tea.h>
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#define TEA_KEY_SCHEDULE_CONSTANT 0x9e3779b9
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#define TEA_SUM_SETUP_CONSTANT 0xc6ef3720
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: tea_decrypt
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*
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* Input Parameters:
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* value = 2 x 32-bit value (input/output)
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* key = 4 x 32-bit Cache key (input)
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*
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****************************************************************************/
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void tea_decrypt(FAR uint32_t *value, FAR const uint32_t *key)
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{
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uint32_t v0 = value[0];
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uint32_t v1 = value[1];
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uint32_t sum = TEA_SUM_SETUP_CONSTANT;
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int i;
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/* Basic cycle start */
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for (i = 0; i < 32; i++)
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{
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v1 -= ((v0 << 4) + key[2]) ^ (v0 + sum) ^ ((v0 >> 5) + key[3]);
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v0 -= ((v1 << 4) + key[0]) ^ (v1 + sum) ^ ((v1 >> 5) + key[1]);
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sum -= TEA_KEY_SCHEDULE_CONSTANT;
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}
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/* End cycle */
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value[0] = v0;
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value[1] = v1;
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}
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