gcc/libjava/classpath/gnu/javax/crypto/pad/IPad.java

/* IPad.java -- 
   Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

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it under the terms of the GNU General Public License as published by
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package gnu.javax.crypto.pad;

/**
 * <p>The basic visible methods of any padding algorithm.</p>
 *
 * <p>Padding algorithms serve to <i>pad</i> and <i>unpad</i> byte arrays usually
 * as the last step in an <i>encryption</i> or respectively a <i>decryption</i>
 * operation. Their input buffers are usually those processed by instances of
 * {@link gnu.crypto.mode.IMode} and/or {@link gnu.crypto.cipher.IBlockCipher}.</p>
 */
public interface IPad
{

  // Constants
  // -------------------------------------------------------------------------

  // Methods
  // -------------------------------------------------------------------------

  /** @return the canonical name of this instance. */
  String name();

  /**
   * Initialises the padding scheme with a designated block size.
   *
   * @param bs the designated block size.
   * @exception IllegalStateException if the instance is already initialised.
   * @exception IllegalArgumentException if the block size value is invalid.
   */
  void init(int bs) throws IllegalStateException;

  /**
   * Returns the byte sequence that should be appended to the designated input.
   *
   * @param in the input buffer containing the bytes to pad.
   * @param offset the starting index of meaningful data in <i>in</i>.
   * @param length the number of meaningful bytes in <i>in</i>.
   * @return the possibly 0-byte long sequence to be appended to the designated
   * input.
   */
  byte[] pad(byte[] in, int offset, int length);

  /**
   * Returns the number of bytes to discard from a designated input buffer.
   *
   * @param in the input buffer containing the bytes to unpad.
   * @param offset the starting index of meaningful data in <i>in</i>.
   * @param length the number of meaningful bytes in <i>in</i>.
   * @return the number of bytes to discard, to the left of index position
   * <tt>offset + length</tt> in <i>in</i>. In other words, if the return
   * value of a successful invocation of this method is <tt>result</tt>, then
   * the unpadded byte sequence will be <tt>offset + length - result</tt> bytes
   * in <i>in</i>, starting from index position <tt>offset</tt>.
   * @exception WrongPaddingException if the data is not terminated with the
   * expected padding bytes.
   */
  int unpad(byte[] in, int offset, int length) throws WrongPaddingException;

  /**
   * Resets the scheme instance for re-initialisation and use with other
   * characteristics. This method always succeeds.
   */
  void reset();

  /**
   * A basic symmetric pad/unpad test.
   *
   * @return <tt>true</tt> if the implementation passes a basic symmetric
   * self-test. Returns <tt>false</tt> otherwise.
   */
  boolean selfTest();
}