libcruft-crypto/block/tea.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 2015-2018 Danny Robson <danny@nerdcruft.net>
 */

#include "tea.hpp"

#include <cstdint>
#include <stdexcept>

using cruft::crypto::block::TEA;


///////////////////////////////////////////////////////////////////////////////
static const u32 MAGIC = 0x9E3779B9;


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


///////////////////////////////////////////////////////////////////////////////
TEA::TEA (key_t _key)
    : m_key (_key)
{ ; }


///////////////////////////////////////////////////////////////////////////////
void
TEA::encrypt (cruft::view<word_t*> data)
{
    if (data.size () % 2)
        throw std::invalid_argument ("TEA requires even data count");

    for (auto cursor = data.begin (), last = data.end (); cursor < last; ) {
        word_t sum = 0;
        word_t v0 = cursor[0];
        word_t v1 = cursor[1];

        for (unsigned i = 0; i < ITERATIONS; ++i) {
            sum += MAGIC;
            v0  += ((v1 << 4) + m_key[0]) ^ (v1 + sum) ^ ((v1 >> 5) + m_key[1]);
            v1  += ((v0 << 4) + m_key[2]) ^ (v0 + sum) ^ ((v0 >> 5) + m_key[3]);
        }

        *cursor++ = v0;
        *cursor++ = v1;
    }
}


//-----------------------------------------------------------------------------
void
TEA::decrypt (cruft::view<word_t*> data)
{
    if (data.size () % 2)
        throw std::invalid_argument ("TEA requires even data count");

    for (auto cursor = data.begin (), last = data.end (); cursor < last; ) {
        word_t sum = MAGIC << 5;
        word_t v0 = cursor[0];
        word_t v1 = cursor[1];

        for (unsigned i = 0; i < ITERATIONS; ++i) {
            v1  -= ((v0 << 4) + m_key[2]) ^ (v0 + sum) ^ ((v0 >> 5) + m_key[3]);
            v0  -= ((v1 << 4) + m_key[0]) ^ (v1 + sum) ^ ((v1 >> 5) + m_key[1]);
            sum -= MAGIC;
        }

        *cursor++ = v0;
        *cursor++ = v1;
    }
}