/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4 -*- */

/* libwpd

 * Version: MPL 2.0 / LGPLv2.1+

 *

 * 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/.

 *

 * Major Contributor(s):

 * Copyright (C) 2007 Fridrich Strba (fridrich.strba@bluewin.ch)

 *

 * For minor contributions see the git repository.

 *

 * Alternatively, the contents of this file may be used under the terms

 * of the GNU Lesser General Public License Version 2.1 or later

 * (LGPLv2.1+), in which case the provisions of the LGPLv2.1+ are

 * applicable instead of those above.

 *

 * For further information visit http://libwpd.sourceforge.net

 */

/* "This product is not manufactured, approved, or supported by

 * Corel Corporation or Corel Corporation Limited."

 */

#include "WPXEncryption.h"

#include "libwpd_internal.h"

#include <string.h>

WPXEncryption::WPXEncryption(const char *password, const unsigned long encryptionStartOffset) :

  m_buffer(nullptr),

  m_password(),

  m_encryptionStartOffset(encryptionStartOffset),

  m_encryptionMaskBase(0)

{

  if (password)

  {

    for (unsigned long i = 0; i < strlen(password); i++)

      if (password[i] >= 'a' && password[i] <= 'z')

        m_password.append((char)(password[i] - 'a' + 'A'));

      else

        m_password.append(password[i]);

    m_encryptionMaskBase = (unsigned char)(m_password.len() + 1);

  }

}

WPXEncryption::~WPXEncryption()

{

}

unsigned short WPXEncryption::getCheckSum() const

{

  if (m_password.len() <= 0)

    return 0;

  librevenge::RVNGString::Iter i(m_password);

  unsigned short checkSum = 0;

  for (i.rewind(); i.next();)

    checkSum = (unsigned short)(((checkSum >> 1) | (checkSum << 15)) ^ (((unsigned short)*(i())) << 8));

  WPD_DEBUG_MSG(("CheckSum: 0x%.4x\n", checkSum));

  return checkSum;

}

const unsigned char *WPXEncryption::readAndDecrypt(librevenge::RVNGInputStream *input, unsigned long numBytes, unsigned long &numBytesRead)

{

  if ((m_password.len() <= 0) || (m_encryptionStartOffset > input->tell() + numBytes))

    return input->read(numBytes, numBytesRead);

  unsigned long readStartPosition = input->tell();

  if (readStartPosition == (unsigned long)-1)

    return nullptr;

  const unsigned char *encryptedBuffer = input->read(numBytes, numBytesRead);

  m_buffer.reset(new unsigned char[numBytesRead]);

  for (unsigned long i=0; i<numBytesRead; i++)

  {

    if (readStartPosition + i < m_encryptionStartOffset)

      m_buffer[i] = encryptedBuffer[i];

    else

    {

      unsigned long passwordOffset = (readStartPosition + i - m_encryptionStartOffset) % m_password.len();

      auto encryptionMask = (unsigned char)(m_encryptionMaskBase + readStartPosition + i - m_encryptionStartOffset);

      m_buffer[i] = (unsigned char)(encryptedBuffer[i] ^ (m_password.cstr()[passwordOffset] ^ encryptionMask));

    }

  }

  return m_buffer.get();

}

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