Android Open Source - conceal Native Mac Layered Input Stream

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License

The source code is released under:

BSD License For Conceal software Copyright (c) 2014, Facebook, Inc. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that...

Java Source Code

/*
 *  Copyright (c) 2014, Facebook, Inc./*from  ww  w  .  j av  a  2  s  .  c  om*/
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in the
 *  LICENSE file in the root directory of this source tree. An additional grant
 *  of patent rights can be found in the PATENTS file in the same directory.
 *
 */

package com.facebook.crypto.streams;

import com.facebook.crypto.mac.NativeMac;

import java.io.IOException;
import java.io.InputStream;

public class NativeMacLayeredInputStream extends InputStream {

  private final NativeMac mMac;
  private final TailInputStream mInputDelegate;

  private boolean mMacChecked = false;

  private static final String MAC_DOES_NOT_MATCH = "Mac does not match";

  /**
   * Creates a new input stream to read from.
   *
   * @param mac The object used to compute the mac.
   * @param inputDelegate The stream to read the data from.
   */
  public NativeMacLayeredInputStream(NativeMac mac, InputStream inputDelegate) {
    mMac = mac;
    mInputDelegate = new TailInputStream(inputDelegate, mac.getMacLength());
  }

  @Override
  public int available() throws IOException {
    return mInputDelegate.available();
  }

  @Override
  public void close() throws IOException {
    try {
      ensureMacValid();
    } finally {
      mInputDelegate.close();
    }
  }

  @Override
  public void mark(int readlimit) {
    throw new UnsupportedOperationException();
  }

  @Override
  public boolean markSupported() {
    return false;
  }

  @Override
  public int read() throws IOException {
    byte[] buffer = new byte[1];
    int read = read(buffer, 0, 1);
    while (read == 0) {
      read = read(buffer, 0, 1);
    }

    if (read == -1) {
      return -1;
    } else {
      return buffer[0] & 0xFF;
    }
  }

  @Override
  public int read(byte[] buffer) throws IOException {
    return read(buffer, 0, buffer.length);
  }

  @Override
  public int read(byte[] buffer, int offset, int length) throws IOException {
    int read = mInputDelegate.read(buffer, offset, length);
    if (read == -1) {
      ensureMacValid();
      return -1;
    }

    if (read > 0) {
      mMac.update(buffer, offset, read);
    }

    return read;
  }

  private void ensureMacValid() throws IOException {
    if (mMacChecked) {
      return;
    }

    mMacChecked = true;
    try {
      byte[] mac = mMac.doFinal();
      if (!constantTimeEquals(mInputDelegate.getTail(), mac)) {
        throw new IOException(MAC_DOES_NOT_MATCH);
      }
    } finally {
      mMac.destroy();
    }
  }

  @Override
  public synchronized void reset() throws IOException {
    throw new UnsupportedOperationException();
  }

  @Override
  public long skip(long byteCount) throws IOException {
    throw new UnsupportedOperationException();
  }

  private boolean constantTimeEquals(byte[] a, byte[] b) {
    if (a.length != b.length) {
      return false;
    }
    int compare = 0;
    for (int i = 0; i < a.length; ++i) {
      compare |= a[i] ^ b[i];
    }
    if (compare == 0) {
      return true;
    }
    return false;
  }
}

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