encfs/fs/BlockNameIO.cpp

/*****************************************************************************
 * Author:   Valient Gough <vgough@pobox.com>
 *
 *****************************************************************************
 * Copyright (c) 2004-2011, Valient Gough
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.  
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "fs/BlockNameIO.h"

#include "base/base64.h"
#include "base/Error.h"
#include "base/i18n.h"
#include "cipher/CipherV1.h"

#include <cstring>
#include <glog/logging.h>

namespace encfs {

static shared_ptr<NameIO> NewBlockNameIO( const Interface &iface,
    const shared_ptr<CipherV1> &cipher )
{
  return shared_ptr<NameIO>( 
      new BlockNameIO( iface, cipher, false));
}

static shared_ptr<NameIO> NewBlockNameIO32( const Interface &iface,
    const shared_ptr<CipherV1> &cipher )
{
  return shared_ptr<NameIO>( 
      new BlockNameIO( iface, cipher, true));
}

static bool BlockIO_registered = NameIO::Register("Block",
    // description of block name encoding algorithm..
    // xgroup(setup)
    gettext_noop("Block encoding, hides file name size somewhat"),
    BlockNameIO::CurrentInterface(false),
    NewBlockNameIO, false);

static bool BlockIO32_registered = NameIO::Register("Block32",
    // description of block name encoding algorithm..
    // xgroup(setup)
    gettext_noop("Block encoding with base32 output for case-sensitive systems"),
    BlockNameIO::CurrentInterface(true),
    NewBlockNameIO32, false);

/*
    - Version 1.0 computed MAC over the filename, but not the padding bytes.
    This version was from pre-release 1.1, never publically released, so no
    backward compatibility necessary.

    - Version 2.0 includes padding bytes in MAC computation.  This way the MAC
    computation uses the same number of bytes regardless of the number of
    padding bytes.

    - Version 3.0 uses full 64 bit initialization vector during IV chaining.
    Prior versions used only the output from the MAC_16 call, giving a 1 in
    2^16 chance of the same name being produced.  Using the full 64 bit IV
    changes that to a 1 in 2^64 chance..

    - Version 4.0 adds support for base32, creating names more suitable for
    case-insensitive filesystems (eg Mac).
 */
Interface BlockNameIO::CurrentInterface(bool caseSensitive)
{
  // implement major version 4 plus support for two prior versions
  if (caseSensitive)
    return makeInterface("nameio/block32", 4, 0, 2);
  else
    return makeInterface("nameio/block", 4, 0, 2);
}

BlockNameIO::BlockNameIO( const Interface &iface,
    const shared_ptr<CipherV1> &cipher, 
    bool caseSensitiveEncoding )
    : _interface( iface.major() )
    , _bs( cipher->cipherBlockSize() )
    , _cipher( cipher )
    , _caseSensitive( caseSensitiveEncoding )
{
  rAssert( _bs < 128 );
}

BlockNameIO::~BlockNameIO()
{
}

Interface BlockNameIO::interface() const
{
  return CurrentInterface(_caseSensitive);
}

int BlockNameIO::maxEncodedNameLen( int plaintextNameLen ) const
{
  // number of blocks, rounded up.. Only an estimate at this point, err on
  // the size of too much space rather then too little.
  int numBlocks = ( plaintextNameLen + _bs ) / _bs;
  int encodedNameLen = numBlocks * _bs + 2; // 2 checksum bytes
  if (_caseSensitive)
    return B256ToB32Bytes( encodedNameLen );
  else
    return B256ToB64Bytes( encodedNameLen );
}

int BlockNameIO::maxDecodedNameLen( int encodedNameLen ) const
{
  int decLen256 = _caseSensitive ? 
    B32ToB256Bytes( encodedNameLen ) :
    B64ToB256Bytes( encodedNameLen );
  return decLen256 - 2; // 2 checksum bytes removed..
}

int BlockNameIO::encodeName( const char *plaintextName, int length,
    uint64_t *iv, char *encodedName ) const
{
  // copy the data into the encoding buffer..
  memcpy( encodedName+2, plaintextName, length );

  // Pad encryption buffer to block boundary..
  int padding = _bs - length % _bs;
  if(padding == 0)
    padding = _bs; // padding a full extra block!

  memset( encodedName+length+2, (unsigned char)padding, padding );

  // store the IV before it is modified by the MAC call.
  uint64_t tmpIV = 0;
  if( iv && _interface >= 3 )
    tmpIV = *iv;

  // include padding in MAC computation
  unsigned int mac = _cipher->reduceMac16(
      _cipher->MAC_64( (unsigned char *)encodedName+2,
      length+padding, iv ));

  // add checksum bytes
  encodedName[0] = (mac >> 8) & 0xff;
  encodedName[1] = (mac     ) & 0xff;

  _cipher->blockEncode( (unsigned char *)encodedName+2, length+padding,
      (uint64_t)mac ^ tmpIV );

  // convert to base 64 ascii
  int encodedStreamLen = length + 2 + padding;
  int encLen;

  if (_caseSensitive) 
  {
    encLen = B256ToB32Bytes( encodedStreamLen );

    changeBase2Inline( (unsigned char *)encodedName, encodedStreamLen,
        8, 5, true );
    B32ToAscii( (unsigned char *)encodedName, encLen );
  } else 
  {
    encLen = B256ToB64Bytes( encodedStreamLen );

    changeBase2Inline( (unsigned char *)encodedName, encodedStreamLen,
        8, 6, true );
    B64ToAscii( (unsigned char *)encodedName, encLen );
  }

  return encLen;
}

int BlockNameIO::decodeName( const char *encodedName, int length,
    uint64_t *iv, char *plaintextName ) const
{
  int decLen256 = _caseSensitive ?
    B32ToB256Bytes( length ) :
    B64ToB256Bytes( length );
  int decodedStreamLen = decLen256 - 2;

  // don't bother trying to decode files which are too small
  if(decodedStreamLen < _bs)
    throw Error("Filename too small to decode");

  BUFFER_INIT( tmpBuf, 32, (unsigned int)length );

  // decode into tmpBuf,
  if (_caseSensitive) 
  {
    AsciiToB32((unsigned char *)tmpBuf, (unsigned char *)encodedName, length);
    changeBase2Inline((unsigned char *)tmpBuf, length, 5, 8, false);
  } else 
  {
    AsciiToB64((unsigned char *)tmpBuf, (unsigned char *)encodedName, length);
    changeBase2Inline((unsigned char *)tmpBuf, length, 6, 8, false);
  }

  // pull out the header information
  unsigned int mac = ((unsigned int)((unsigned char)tmpBuf[0])) << 8
    | ((unsigned int)((unsigned char)tmpBuf[1]));

  uint64_t tmpIV = 0;
  if( iv && _interface >= 3 )
    tmpIV = *iv;

  _cipher->blockDecode( (unsigned char *)tmpBuf+2, decodedStreamLen,
      (uint64_t)mac ^ tmpIV );

  // find out true string length
  int padding = (unsigned char)tmpBuf[2+decodedStreamLen-1];
  int finalSize = decodedStreamLen - padding;

  // might happen if there is an error decoding..
  if(padding > _bs || finalSize < 0)
  {
    VLOG(1) << "padding, _bx, finalSize = " << padding
      << ", " << _bs << ", " << finalSize;
    throw Error( "invalid padding size" );
  }

  // copy out the result..
  memcpy(plaintextName, tmpBuf+2, finalSize);
  plaintextName[finalSize] = '\0';

  // check the mac
  unsigned int mac2 = _cipher->reduceMac16(
      _cipher->MAC_64((const unsigned char *)tmpBuf+2,
      decodedStreamLen, iv));

  BUFFER_RESET( tmpBuf );

  if(mac2 != mac)
  {
    LOG(INFO) << "checksum mismatch: expected " << mac << ", got "
      << mac2 << " on decode of " << finalSize << " bytes";
    throw Error( "checksum mismatch in filename decode" );
  }

  return finalSize;
}

bool BlockNameIO::Enabled()
{
  return true;
}

}  // namespace encfs