/*
 * 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 2015-2018 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 (cruft::view<word_t*> dst, cruft::view<word_t const*> src)
{
    if (dst.size () != src.size ())
        throw std::invalid_argument ("mismatching encode/decode buffer sizes");
    if (src.size () % 2)
        throw std::invalid_argument ("XTEA requires even data count");

    for (size_t i = 0, last = src.size (); i != last; i += 2) {
        uint32_t sum = 0;
        uint32_t v0 = src[i + 0];
        uint32_t v1 = src[i + 1];

        for (unsigned j = 0; j < ITERATIONS; ++j) {
            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]);
        }

        dst[i + 0] = v0;
        dst[i + 1] = v1;
    }
}


//-----------------------------------------------------------------------------
void
XTEA::decrypt (cruft::view<word_t*> dst, cruft::view<word_t const*> src)
{
    if (dst.size () != src.size ())
        throw std::invalid_argument ("mismatching encode/decode buffer sizes");
    if (src.size () % 2)
        throw std::invalid_argument ("XTEA requires even data count");

    for (size_t i = 0, last = src.size (); i != last; i += 2) {
        uint32_t sum = ITERATIONS * MAGIC;
        uint32_t v0 = src[i + 0];
        uint32_t v1 = src[i + 1];

        for (unsigned j = 0; j < ITERATIONS; ++j) {
            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]);
        }

        dst[i + 0] = v0;
        dst[i + 1] = v1;
    }
}