74 lines
2.6 KiB
C
74 lines
2.6 KiB
C
/****************************************************************************
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* libs/libc/misc/lib_tea_decrypt.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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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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/****************************************************************************
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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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