encryptedinputstream.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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********************************************************************************/

package rice.p2p.util;

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

/**
 * @(#) EncryptedInputStream.java Class which serves as an input stream and
 * transparently dencrypts the stream data with the given private key. It does
 * this by reading a symmetric key, k, and then decrypting k under the public
 * key. The header read from 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: EncryptedInputStream.java 2302 2005-03-11 00:58:26Z jeffh $
 * @author Alan Mislove
 */
public class EncryptedInputStream extends InputStream {

  // the public key
  /**
   * DESCRIBE THE FIELD
   */
  protected PrivateKey privateKey;

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

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

  // any buffered data from the stream
  /**
   * DESCRIBE THE FIELD
   */
  protected byte[] buffer;

  // the amount of buffered data which has been returned
  /**
   * DESCRIBE THE FIELD
   */
  protected int bufferLength;

  /**
   * Builds an encrypted inputstream given a private key to decrypt thing under
   *
   * @param stream The underlying stream
   * @param privateKey DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public EncryptedInputStream(PrivateKey privateKey, InputStream stream) throws IOException {
    this.privateKey = privateKey;
    this.stream = new DataInputStream(stream);

    readHeader();
  }

  /**
   * Utility method which reads the header information
   *
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  private void readHeader() throws IOException {
    byte[] enckey = new byte[stream.readInt()];
    stream.readFully(enckey);

    this.key = SecurityUtils.decryptAsymmetric(enckey, privateKey);
  }

  /**
   * Reads the next byte of data from the input stream. T
   *
   * @return the next byte of data, or <code>-1</code> if the end of the stream
   *      is reached.
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public int read() throws IOException {
    if ((buffer != null) && (bufferLength < buffer.length)) {
      bufferLength++;

      return buffer[bufferLength - 1] & 0xff;
    } else {
      readBuffer();
      return read();
    }
  }

  /**
   * Reads up to <code>len</code> bytes of data from the input stream into an
   * array of bytes. An attempt is made to read as many as <code>len</code>
   * bytes, but a smaller number may be read, possibly zero. The number of bytes
   * actually read is returned as an integer.
   *
   * @param b the buffer into which the data is read.
   * @param off the start offset in array <code>b</code> at which the data is
   *      written.
   * @param len the maximum number of bytes to read.
   * @return the total number of bytes read into the buffer, or <code>-1</code>
   *      if there is no more data because the end of the stream has been
   *      reached.
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public int read(byte b[], int off, int len) throws IOException {
    if ((buffer != null) && (bufferLength < buffer.length)) {
      int l = (len > available() ? available() : len);
      System.arraycopy(buffer, bufferLength, b, off, l);
      bufferLength += l;

      return l;
    } else {
      readBuffer();
      return read(b, off, len);
    }
  }

  /**
   * Internal method which reads in the next chunk of buffered data
   *
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  protected void readBuffer() throws IOException {
    byte[] encdata = new byte[stream.readInt()];
    stream.readFully(encdata);

    this.buffer = SecurityUtils.decryptSymmetric(encdata, key);
    this.bufferLength = 0;
  }

  /**
   * Returns the number of bytes that can be read (or skipped over) from this
   * input stream without blocking by the next caller of a method for this input
   * stream. The next caller might be the same thread or or another thread.
   *
   * @return the number of bytes that can be read from this input stream without
   *      blocking.
   * @exception IOException if an I/O error occurs.
   */
  public int available() throws IOException {
    if (buffer == null) {
      return 0;
    } else {
      return buffer.length - bufferLength;
    }
  }

  /**
   * Closes this input stream and releases any system resources associated with
   * the stream.
   *
   * @exception IOException if an I/O error occurs.
   */
  public void close() throws IOException {
    stream.close();
  }
}