CFB.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 "CFB.h"
#include "Crypto.h"
#include <string.h>
 
CFBCommon::CFBCommon()
    : blockCipher(0)
    , posn(16)
{
}
 
CFBCommon::~CFBCommon()
{
    clean(iv);
}
 
size_t CFBCommon::keySize() const
{
    return blockCipher->keySize();
}
 
size_t CFBCommon::ivSize() const
{
    return 16;
}
 
bool CFBCommon::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 CFBCommon::setIV(const uint8_t *iv, size_t len)
{
    if (len != 16)
        return false;
    memcpy(this->iv, iv, 16);
    posn = 16;
    return true;
}
 
void CFBCommon::encrypt(uint8_t *output, const uint8_t *input, size_t len)
{
    uint8_t size;
    while (len > 0) {
        // If we have exhausted the current keystream block, then encrypt
        // the IV/ciphertext to get another keystream block.
        if (posn >= 16) {
            blockCipher->encryptBlock(iv, iv);
            posn = 0;
        }
 
        // XOR the plaintext with the encrypted IV to get the new ciphertext.
        // We keep building up the ciphertext byte by byte in the IV buffer
        // until we have a full block's worth, and then the IV is encrypted
        // again by the code above.
        size = 16 - posn;
        if (size > len)
            size = len;
        len -= size;
        while (size > 0) {
            iv[posn] ^= *input++;
            *output++ = iv[posn++];
            --size;
        }
    }
}
 
void CFBCommon::decrypt(uint8_t *output, const uint8_t *input, size_t len)
{
    uint8_t size;
    while (len > 0) {
        // If we have exhausted the current keystream block, then encrypt
        // the IV/ciphertext to get another keystream block.
        if (posn >= 16) {
            blockCipher->encryptBlock(iv, iv);
            posn = 0;
        }
 
        // XOR the ciphertext with the encrypted IV to get the new plaintext.
        // We keep building up the ciphertext byte by byte in the IV buffer
        // until we have a full block's worth, and then the IV is encrypted
        // again by the code above.
        size = 16 - posn;
        if (size > len)
            size = len;
        len -= size;
        while (size > 0) {
            uint8_t in = *input++;
            *output++ = iv[posn] ^ in;
            iv[posn++] = in;
            --size;
        }
    }
}
 
void CFBCommon::clear()
{
    blockCipher->clear();
    clean(iv);
    posn = 16;
}