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AES256.cpp
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AES256.cpp
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/*
* Copyright (C) 2015 Southern Storm Software, Pty Ltd.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
#include "AES.h"
#include "Crypto.h"
#include <string.h>
/**
* \class AES256 AES.h <AES.h>
* \brief AES block cipher with 256-bit keys.
*
* \sa AES128, AES192
*/
/**
* \brief Constructs an AES 256-bit block cipher with no initial key.
*
* This constructor must be followed by a call to setKey() before the
* block cipher can be used for encryption or decryption.
*/
AES256::AES256()
{
rounds = 14;
schedule = sched;
}
AES256::~AES256()
{
clean(sched);
}
/**
* \brief Size of a 256-bit AES key in bytes.
* \return Always returns 32.
*/
size_t AES256::keySize() const
{
return 32;
}
bool AES256::setKey(const uint8_t *key, size_t len)
{
if (len != 32)
return false;
// Copy the key itself into the first 32 bytes of the schedule.
uint8_t *schedule = sched;
memcpy(schedule, key, 32);
// Expand the key schedule until we have 240 bytes of expanded key.
uint8_t iteration = 1;
uint8_t n = 32;
uint8_t w = 8;
while (n < 240) {
if (w == 8) {
// Every 32 bytes (8 words) we need to apply the key schedule core.
keyScheduleCore(schedule + 32, schedule + 28, iteration);
schedule[32] ^= schedule[0];
schedule[33] ^= schedule[1];
schedule[34] ^= schedule[2];
schedule[35] ^= schedule[3];
++iteration;
w = 0;
} else if (w == 4) {
// At the 16 byte mark we need to apply the S-box.
applySbox(schedule + 32, schedule + 28);
schedule[32] ^= schedule[0];
schedule[33] ^= schedule[1];
schedule[34] ^= schedule[2];
schedule[35] ^= schedule[3];
} else {
// Otherwise just XOR the word with the one 32 bytes previous.
schedule[32] = schedule[28] ^ schedule[0];
schedule[33] = schedule[29] ^ schedule[1];
schedule[34] = schedule[30] ^ schedule[2];
schedule[35] = schedule[31] ^ schedule[3];
}
// Advance to the next word in the schedule.
schedule += 4;
n += 4;
++w;
}
return true;
}