libcruft-util/crypto/xxtea.cpp

105 lines
2.8 KiB
C++

/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright 2015 Danny Robson <danny@nerdcruft.net>
*/
#include "xxtea.hpp"
#include <cstring>
// test vectors: http://www.cix.co.uk/~klockstone/teavect.htm
using util::crypto::XXTEA;
//-----------------------------------------------------------------------------
static const uint32_t MAGIC = 0x9E3779B9;
static const unsigned ITERATIONS = 32; // each iteration performs two feistel rounds
//-----------------------------------------------------------------------------
static constexpr uint32_t mix (uint32_t Z,
uint32_t Y,
uint32_t S,
size_t E,
size_t P,
const uint32_t *restrict K)
{
return ((Z >> 5 ^ Y << 2) + (Y >> 3 ^ Z << 4)) ^ ((S ^ Y) + (K[(P & 3) ^ E] ^ Z));
}
//-----------------------------------------------------------------------------
XXTEA::XXTEA (key_t _key):
m_key (_key)
{ ; }
//-----------------------------------------------------------------------------
void
XXTEA::encrypt (uint32_t *restrict data, size_t count)
{
if (count < 2)
throw std::invalid_argument ("minimum blocksize is 64 bits");
uint32_t sum = 0;
uint32_t z = data[count - 1];
uint32_t y, e, p;
unsigned rounds = 6 + 52 / count;
do {
sum += MAGIC;
e = (sum >> 2) & 3;
for (p = 0; p < count - 1; p++) {
y = data[p + 1];
z = data[p] += mix (z, y, sum, e, p, m_key.data ());
}
y = data[0];
z = data[count - 1] += mix (z, y, sum, e, p, m_key.data ());
} while (--rounds);
}
//-----------------------------------------------------------------------------
void
XXTEA::decrypt (uint32_t *restrict data, size_t count)
{
if (count < 2)
throw std::invalid_argument ("minimum blocksize is 64 bits");
uint32_t y, z, sum;
unsigned p, rounds, e;
rounds = 6 + 52 / count;
sum = rounds * MAGIC;
y = data[0];
do {
e = (sum >> 2) & 3;
for (p = count - 1; p > 0; p--) {
z = data[p - 1];
y = data[p ] -= mix (z, y, sum, e, p, m_key.data ());
}
z = data[count - 1];
y = data[ 0] -= mix (z, y, sum, e, p, m_key.data ());
sum -= MAGIC;
} while (--rounds);
}