CTR.cpp

/*
 * 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 "CTR.h"
#include "Crypto.h"
#include <string.h>
 
CTRCommon::CTRCommon()
    : blockCipher(0)
    , posn(16)
    , counterStart(0)
{
}
 
CTRCommon::~CTRCommon()
{
    // It is assumed that the subclass will clear sensitive
    // information in the block cipher.
    clean(counter);
    clean(state);
}
 
size_t CTRCommon::keySize() const
{
    return blockCipher->keySize();
}
 
size_t CTRCommon::ivSize() const
{
    return 16;
}
 
bool CTRCommon::setCounterSize(size_t size)
{
    if (size < 1 || size > 16)
        return false;
    counterStart = 16 - size;
    return true;
}
 
bool CTRCommon::setKey(const uint8_t *key, size_t len)
{
    // Verify the cipher's block size, just in case.
    if (blockCipher->blockSize() != 16)
        return false;
 
    // Set the key on the underlying block cipher.
    return blockCipher->setKey(key, len);
}
 
bool CTRCommon::setIV(const uint8_t *iv, size_t len)
{
    if (len != 16)
        return false;
    memcpy(counter, iv, len);
    posn = 16;
    return true;
}
 
void CTRCommon::encrypt(uint8_t *output, const uint8_t *input, size_t len)
{
    while (len > 0) {
        if (posn >= 16) {
            // Generate a new encrypted counter block.
            blockCipher->encryptBlock(state, counter);
            posn = 0;
 
            // Increment the counter, taking care not to reveal
            // any timing information about the starting value.
            // We iterate through the entire counter region even
            // if we could stop earlier because a byte is non-zero.
            uint16_t temp = 1;
            uint8_t index = 16;
            while (index > counterStart) {
                --index;
                temp += counter[index];
                counter[index] = (uint8_t)temp;
                temp >>= 8;
            }
        }
        uint8_t templen = 16 - posn;
        if (templen > len)
            templen = len;
        len -= templen;
        while (templen > 0) {
            *output++ = *input++ ^ state[posn++];
            --templen;
        }
    }
}
 
void CTRCommon::decrypt(uint8_t *output, const uint8_t *input, size_t len)
{
    encrypt(output, input, len);
}
 
void CTRCommon::clear()
{
    blockCipher->clear();
    clean(counter);
    clean(state);
    posn = 16;
}