CBC.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"),
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 * 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
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 * DEALINGS IN THE SOFTWARE.
 */

#include "CBC.h"
#include "Crypto.h"
#include <string.h>

/**
 * \class CBCCommon CBC.h <CBC.h>
 * \brief Concrete base class to assist with implementing CBC for
 * 128-bit block ciphers.
 *
 * Reference: http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation
 *
 * \sa CBC
 */

/**
 * \brief Constructs a new cipher in CBC mode.
 *
 * This constructor should be followed by a call to setBlockCipher().
 */
CBCCommon::CBCCommon()
    : blockCipher(0)
    , posn(16)
{
}

/**
 * \brief Destroys this cipher object after clearing sensitive information.
 */
CBCCommon::~CBCCommon()
{
    clean(iv);
    clean(temp);
}

size_t CBCCommon::keySize() const
{
    return blockCipher->keySize();
}

size_t CBCCommon::ivSize() const
{
    return 16;
}

bool CBCCommon::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 CBCCommon::setIV(const uint8_t *iv, size_t len)
{
    if (len != 16)
        return false;
    memcpy(this->iv, iv, 16);
    posn = 16;
    return true;
}

void CBCCommon::encrypt(uint8_t *output, const uint8_t *input, size_t len)
{
    uint8_t posn;
    while (len >= 16) {
        for (posn = 0; posn < 16; ++posn)
            iv[posn] ^= *input++;
        blockCipher->encryptBlock(iv, iv);
        for (posn = 0; posn < 16; ++posn)
            *output++ = iv[posn];
        len -= 16;
    }
}

void CBCCommon::decrypt(uint8_t *output, const uint8_t *input, size_t len)
{
    uint8_t posn;
    while (len >= 16) {
        blockCipher->decryptBlock(temp, input);
        for (posn = 0; posn < 16; ++posn) {
            uint8_t in = *input++;
            *output++ = temp[posn] ^ iv[posn];
            iv[posn] = in;
        }
        len -= 16;
    }
}

void CBCCommon::clear()
{
    blockCipher->clear();
    clean(iv);
    clean(temp);
    posn = 16;
}

/**
 * \fn void CBCCommon::setBlockCipher(BlockCipher *cipher)
 * \brief Sets the block cipher to use for this CBC object.
 *
 * \param cipher The block cipher to use to implement CBC mode,
 * which must have a block size of 16 bytes (128 bits).
 */

/**
 * \class CBC CBC.h <CBC.h>
 * \brief Implementation of the Cipher Block Chaining (CBC) mode for
 * 128-bit block ciphers.
 *
 * The template parameter T must be a concrete subclass of BlockCipher
 * indicating the specific block cipher to use.  T must have a block size
 * of 16 bytes (128 bits).
 *
 * For example, the following creates a CBC object using AES192 as the
 * underlying cipher:
 *
 * \code
 * CBC<AES192> cbc;
 * cbc.setKey(key, 24);
 * cbc.setIV(iv, 16);
 * cbc.encrypt(output, input, len);
 * \endcode
 *
 * Decryption is similar:
 *
 * \code
 * CBC<AES192> cbc;
 * cbc.setKey(key, 24);
 * cbc.setIV(iv, 16);
 * cbc.decrypt(output, input, len);
 * \endcode
 *
 * The size of the ciphertext will always be the same as the size of
 * the plaintext.  Also, the length of the plaintext/ciphertext must be a
 * multiple of 16.  Extra bytes are ignored and not encrypted.  The caller
 * is responsible for padding the underlying data to a multiple of 16
 * using an appropriate padding scheme for the application.
 *
 * Reference: http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation
 *
 * \sa CTR, CFB, OFB
 */

/**
 * \fn CBC::CBC()
 * \brief Constructs a new CBC object for the block cipher T.
 */