encfs/encfs/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 "BlockNameIO.h"

#include <cstring>
#include <memory>

#include "Cipher.h"
#include "CipherKey.h"
#include "Error.h"
#include "Interface.h"
#include "NameIO.h"
#include "base64.h"
#include "internal/easylogging++.h"
#include "intl/gettext.h"

namespace encfs {

static std::shared_ptr<NameIO> NewBlockNameIO(
    const Interface &iface, const std::shared_ptr<Cipher> &cipher,
    const CipherKey &key) {
  int blockSize = 8;
  if (cipher) blockSize = cipher->cipherBlockSize();

  return std::shared_ptr<NameIO>(
      new BlockNameIO(iface, cipher, key, blockSize, false));
}

static std::shared_ptr<NameIO> NewBlockNameIO32(
    const Interface &iface, const std::shared_ptr<Cipher> &cipher,
    const CipherKey &key) {
  int blockSize = 8;
  if (cipher) blockSize = cipher->cipherBlockSize();

  return std::shared_ptr<NameIO>(
      new BlockNameIO(iface, cipher, key, blockSize, 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);

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

/*
    - 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 caseInsensitive) {
  // implement major version 4 plus support for two prior versions
  if (caseInsensitive)
    return Interface("nameio/block32", 4, 0, 2);
  else
    return Interface("nameio/block", 4, 0, 2);
}

BlockNameIO::BlockNameIO(const Interface &iface,
                         const std::shared_ptr<Cipher> &cipher,
                         const CipherKey &key, int blockSize,
                         bool caseInsensitiveEncoding)
    : _interface(iface.current()),
      _bs(blockSize),
      _cipher(cipher),
      _key(key),
      _caseInsensitive(caseInsensitiveEncoding) {
  // just to be safe..
  rAssert(blockSize < 128);
}

BlockNameIO::~BlockNameIO() {}

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

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 (_caseInsensitive)
    return B256ToB32Bytes(encodedNameLen);
  else
    return B256ToB64Bytes(encodedNameLen);
}

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

int BlockNameIO::encodeName(const char *plaintextName, int length, uint64_t *iv,
                            char *encodedName, int bufferLength) const {

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

  rAssert(bufferLength >= length + 2 + padding);
  memset(encodedName + length + 2, (unsigned char)padding, padding);

  // copy the data into the encoding buffer..
  memcpy(encodedName + 2, plaintextName, length);

  // 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->MAC_16((unsigned char *)encodedName + 2,
                                     length + padding, _key, 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, _key);

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

  if (_caseInsensitive) {
    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, int bufferLength) const {
  int decLen256 =
      _caseInsensitive ? B32ToB256Bytes(length) : B64ToB256Bytes(length);
  int decodedStreamLen = decLen256 - 2;

  // don't bother trying to decode files which are too small
  if (decodedStreamLen < _bs) {
    VLOG(1) << "Rejecting filename " << encodedName;
    throw Error("Filename too small to decode");
  }

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

  // decode into tmpBuf,
  if (_caseInsensitive) {
    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, _key);

  // 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..
  rAssert(finalSize < bufferLength);
  memcpy(plaintextName, tmpBuf + 2, finalSize);
  plaintextName[finalSize] = '\0';

  // check the mac
  unsigned int mac2 = _cipher->MAC_16((const unsigned char *)tmpBuf + 2,
                                      decodedStreamLen, _key, iv);

  BUFFER_RESET(tmpBuf);

  if (mac2 != mac) {
    VLOG(1) << "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