libcruft-crypto/block/xtea.cpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2015 Danny Robson <danny@nerdcruft.net>
 */

#include "xtea.hpp"

using cruft::crypto::block::XTEA;


///////////////////////////////////////////////////////////////////////////////
static const uint32_t MAGIC = 0x9E3779B9;

// each iteration performs two feistel rounds, for a total of 64
static const unsigned ITERATIONS = 32;


///////////////////////////////////////////////////////////////////////////////
XTEA::XTEA (key_t _key):
    m_key (_key)
{ }


//-----------------------------------------------------------------------------
void
XTEA::encrypt (uint32_t *restrict data, size_t count)
{
    if (count % 2)
        throw std::invalid_argument ("XTEA requires even data count");

    auto last = data + count;

    while (data < last) {
        uint32_t sum = 0;
        uint32_t v0 = data[0];
        uint32_t v1 = data[1];

        for (unsigned i = 0; i < ITERATIONS; ++i) {
            v0  += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + m_key[sum & 3]);
            sum += MAGIC;
            v1  += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + m_key[(sum >> 11) & 3]);
        }

        *data++ = v0;
        *data++ = v1;
    }
}


//-----------------------------------------------------------------------------
void
XTEA::decrypt (uint32_t *restrict data, size_t count)
{
    if (count % 2)
        throw std::invalid_argument ("XTEA requires even data count");

    auto last = data + count;

    while (data < last) {
        uint32_t sum = ITERATIONS * MAGIC;
        uint32_t v0 = data[0];
        uint32_t v1 = data[1];

        for (unsigned i = 0; i < ITERATIONS; ++i) {
            v1  -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + m_key[(sum >> 11) & 3]);
            sum -= MAGIC;
            v0  -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + m_key[sum & 3]);
        }

        *data++ = v0;
        *data++ = v1;
    }
}