encryptedoutputstream.java

pastry的java实现的2.0b版

/*************************************************************************

"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

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This software is provided by RICE and the contributors on an "as is"
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********************************************************************************/

package rice.p2p.util;

import java.io.*;
import java.security.*;
import java.util.*;

/**
 * @(#) EncryptedOutputStream.java Class which serves as an output stream and
 * transparently encrypted the stream data with the given public key. It does
 * this by generating a symmetric key, k, and then encrypting k under the public
 * key. The header sent over the stream therefore looks like 4 bytes -
 * length(e(k)) e(k) chunks of upper-level data where each chunk is length(data)
 * [4 bytes] followed by data
 *
 * @version $Id: EncryptedOutputStream.java 2605 2005-06-24 22:49:20Z jeffh $
 * @author Alan Mislove
 */
public class EncryptedOutputStream extends OutputStream {

  // the maximal amount of data to buffer
  /**
   * DESCRIBE THE FIELD
   */
  public final int BUFFER_SIZE;
  // = 32678;

  // the public key
    /**
   * DESCRIBE THE FIELD
   */
  protected PublicKey publicKey;

  // the symmetric key
  /**
   * DESCRIBE THE FIELD
   */
  protected byte[] key;

  // the actual underlying stream
  /**
   * DESCRIBE THE FIELD
   */
  protected DataOutputStream stream;

  // the temporary array of bytes waiting to be sent out
  /**
   * DESCRIBE THE FIELD
   */
  protected byte[] buffer;

  // the amount of the buffer which is currently used
  /**
   * DESCRIBE THE FIELD
   */
  protected int bufferLength;

  /**
   * Builds an encrypted outputstream given a public key to encrypt thing under
   *
   * @param stream The underlying stream
   * @param publicKey DESCRIBE THE PARAMETER
   * @param bufferSize DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public EncryptedOutputStream(PublicKey publicKey, OutputStream stream, int bufferSize) throws IOException {
    BUFFER_SIZE = bufferSize;
    this.publicKey = publicKey;
    this.stream = new DataOutputStream(stream);
    this.key = SecurityUtils.generateKeySymmetric();
    this.buffer = new byte[BUFFER_SIZE];
    this.bufferLength = 0;

    writeHeader();
  }

  /**
   * Utility method which writes out the header information
   *
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  private void writeHeader() throws IOException {
    byte[] enckey = SecurityUtils.encryptAsymmetric(key, publicKey);

    stream.writeInt(enckey.length);
    stream.write(enckey);
  }

  /**
   * Writes the specified byte to this output stream.
   *
   * @param b the byte
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public void write(int b) throws IOException {
    write(new byte[]{(byte) (b & 0xff)});
  }

  /**
   * Writes the given bytes to the output
   *
   * @param b the data.
   * @param off the start offset in the data.
   * @param len the number of bytes to write.
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public void write(byte b[], int off, int len) throws IOException {
    if (b == null) {
      throw new NullPointerException();
    } else if ((off < 0) || (off > b.length) || (len < 0) ||
      ((off + len) > b.length) || ((off + len) < 0)) {
      throw new IndexOutOfBoundsException();
    } else if (len == 0) {
      return;
    }

    // if it will fit in the buffer, just fill it up
    // otherwise, write what we can and recur
    if (len <= BUFFER_SIZE - bufferLength) {
      System.arraycopy(b, off, buffer, bufferLength, len);
      bufferLength += len;
    } else {
      int l = BUFFER_SIZE - bufferLength;

      System.arraycopy(b, off, buffer, bufferLength, l);
      bufferLength += l;
      writeBuffer();

      write(b, off + l, len - l);
    }
  }

  /**
   * Internal method which writes out the buffered data
   *
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  protected void writeBuffer() throws IOException {
    byte[] encdata = SecurityUtils.encryptSymmetric(buffer, key, 0, bufferLength);
    stream.writeInt(encdata.length);
    stream.write(encdata);

    this.bufferLength = 0;
  }

  /**
   * Flushes this output stream and forces any buffered output bytes to be
   * written out.
   *
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public void flush() throws IOException {
    writeBuffer();
    stream.flush();
  }

  /**
   * Closes this output stream and releases any system resources associated with
   * this stream.
   *
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public void close() throws IOException {
    flush();
    stream.close();
  }
}