/* EAX.java --
   Copyright (C) 2004, 2006, 2014 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

GNU Classpath 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
General Public License for more details.

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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package gnu.javax.crypto.mode;

import gnu.java.security.Registry;
import gnu.javax.crypto.cipher.IBlockCipher;
import gnu.javax.crypto.mac.IMac;
import gnu.javax.crypto.mac.MacFactory;

import java.security.InvalidKeyException;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

/**
 * A conventional two-pass authenticated-encrypted mode, EAX. EAX is a
 * <i>Authenticated Encryption with Additional Data</i> (<b>AEAD</b>) scheme,
 * which provides protection and authentication for the message, and provides
 * authentication of an (optional) header. EAX is composed of the counter mode
 * (CTR) and the one-key CBC MAC (OMAC).
 * <p>
 * This class makes full use of the {@link IAuthenticatedMode} interface, that
 * is, all methods of both {@link IMode} and {@link IMac} can be used as
 * specified in the {@link IAuthenticatedMode} interface.
 * <p>
 * References:
 * <ol>
 * <li>M. Bellare, P. Rogaway, and D. Wagner; <a
 * href="http://www.cs.berkeley.edu/~daw/papers/eprint-short-ae.pdf">A
 * Conventional Authenticated-Encryption Mode</a>.</li>
 * </ol>
 */
public class EAX
    implements IAuthenticatedMode
{
  /** The tag size, in bytes. */
  private int tagSize;
  /** The nonce OMAC instance. */
  private IMac nonceOmac;
  /** The header OMAC instance. */
  private IMac headerOmac;
  /** The message OMAC instance. */
  private IMac msgOmac;
  /** The CTR instance. */
  private IMode ctr;
  /** The direction state (encrypting or decrypting). */
  private int state;
  /** Whether we're initialized or not. */
  private boolean init;
  /** The cipher block size. */
  private int cipherBlockSize;
  /** The cipher. */
  private IBlockCipher cipher;
  /** The [t]_n array. */
  private byte[] t_n;
  private static boolean valid = false;

  public EAX(IBlockCipher cipher, int cipherBlockSize)
  {
    this.cipher = cipher;
    this.cipherBlockSize = cipherBlockSize;
    String name = cipher.name();
    int i = name.indexOf('-');
    if (i >= 0)
      name = name.substring(0, i);
    String omacname = Registry.OMAC_PREFIX + name;
    nonceOmac = MacFactory.getInstance(omacname);
    headerOmac = MacFactory.getInstance(omacname);
    msgOmac = MacFactory.getInstance(omacname);
    ctr = ModeFactory.getInstance(Registry.CTR_MODE, cipher, cipherBlockSize);
    t_n = new byte[cipherBlockSize];
    init = false;
  }

  @Override
  public Object clone()
  {
    return new EAX((IBlockCipher) cipher.clone(), cipherBlockSize);
  }

  @Override
  public String name()
  {
    return Registry.EAX_MODE + "(" + cipher.name() + ")";
  }

  @Override
  public int defaultBlockSize()
  {
    return ctr.defaultBlockSize();
  }

  @Override
  public int defaultKeySize()
  {
    return ctr.defaultKeySize();
  }

  @Override
  public Iterator<Integer> blockSizes()
  {
    return ctr.blockSizes();
  }

  @Override
  public Iterator<Integer> keySizes()
  {
    return ctr.keySizes();
  }

  @Override
  public void init(Map<String,Object> attrib) throws InvalidKeyException
  {
    byte[] nonce = (byte[]) attrib.get(IV);
    if (nonce == null)
      throw new IllegalArgumentException("no nonce provided");
    byte[] key = (byte[]) attrib.get(KEY_MATERIAL);
    if (key == null)
      throw new IllegalArgumentException("no key provided");

    Arrays.fill(t_n, (byte) 0);
    nonceOmac.reset();
    nonceOmac.init(Collections.singletonMap(MAC_KEY_MATERIAL, (Object) key));
    nonceOmac.update(t_n, 0, t_n.length);
    nonceOmac.update(nonce, 0, nonce.length);
    byte[] N = nonceOmac.digest();
    nonceOmac.reset();
    nonceOmac.update(t_n, 0, t_n.length);
    nonceOmac.update(nonce, 0, nonce.length);
    t_n[t_n.length - 1] = 1;
    headerOmac.reset();
    headerOmac.init(Collections.singletonMap(MAC_KEY_MATERIAL, (Object) key));
    headerOmac.update(t_n, 0, t_n.length);
    t_n[t_n.length - 1] = 2;
    msgOmac.reset();
    msgOmac.init(Collections.singletonMap(MAC_KEY_MATERIAL, (Object) key));
    msgOmac.update(t_n, 0, t_n.length);
    Integer modeSize = (Integer) attrib.get(MODE_BLOCK_SIZE);
    if (modeSize == null)
      modeSize = Integer.valueOf(cipherBlockSize);
    HashMap<String,Object> ctrAttr = new HashMap<String,Object>();
    ctrAttr.put(KEY_MATERIAL, key);
    ctrAttr.put(IV, N);
    ctrAttr.put(STATE, Integer.valueOf(ENCRYPTION));
    ctrAttr.put(MODE_BLOCK_SIZE, modeSize);
    ctr.reset();
    ctr.init(ctrAttr);
    Integer st = (Integer) attrib.get(STATE);
    if (st != null)
      {
        state = st.intValue();
        if (state != ENCRYPTION && state != DECRYPTION)
          throw new IllegalArgumentException("invalid state");
      }
    else
      state = ENCRYPTION;

    Integer ts = (Integer) attrib.get(TRUNCATED_SIZE);
    if (ts != null)
      tagSize = ts.intValue();
    else
      tagSize = cipherBlockSize;
    if (tagSize < 0 || tagSize > cipherBlockSize)
      throw new IllegalArgumentException("tag size out of range");
    init = true;
  }

  @Override
  public int currentBlockSize()
  {
    return ctr.currentBlockSize();
  }

  @Override
  public void encryptBlock(byte[] in, int inOff, byte[] out, int outOff)
  {
    if (! init)
      throw new IllegalStateException("not initialized");
    if (state != ENCRYPTION)
      throw new IllegalStateException("not encrypting");
    ctr.update(in, inOff, out, outOff);
    msgOmac.update(out, outOff, ctr.currentBlockSize());
  }

  @Override
  public void decryptBlock(byte[] in, int inOff, byte[] out, int outOff)
  {
    if (! init)
      throw new IllegalStateException("not initialized");
    if (state != DECRYPTION)
      throw new IllegalStateException("not decrypting");
    msgOmac.update(in, inOff, ctr.currentBlockSize());
    ctr.update(in, inOff, out, outOff);
  }

  public void update(byte[] in, int inOff, byte[] out, int outOff)
  {
    switch (state)
      {
      case ENCRYPTION:
        encryptBlock(in, inOff, out, outOff);
        break;
      case DECRYPTION:
        decryptBlock(in, inOff, out, outOff);
        break;
      default:
        throw new IllegalStateException("impossible state " + state);
      }
  }

  @Override
  public void reset()
  {
    nonceOmac.reset();
    headerOmac.reset();
    msgOmac.reset();
    ctr.reset();
  }

  @Override
  public boolean selfTest()
  {
    return true; // XXX
  }

  @Override
  public int macSize()
  {
    return tagSize;
  }

  @Override
  public byte[] digest()
  {
    byte[] tag = new byte[tagSize];
    digest(tag, 0);
    return tag;
  }

  public void digest(byte[] out, int outOffset)
  {
    if (outOffset < 0 || outOffset + tagSize > out.length)
      throw new IndexOutOfBoundsException();
    byte[] N = nonceOmac.digest();
    byte[] H = headerOmac.digest();
    byte[] M = msgOmac.digest();
    for (int i = 0; i < tagSize; i++)
      out[outOffset + i] = (byte)(N[i] ^ H[i] ^ M[i]);
    reset();
  }

  @Override
  public void update(byte b)
  {
    if (! init)
      throw new IllegalStateException("not initialized");
    headerOmac.update(b);
  }

  @Override
  public void update(byte[] buf, int off, int len)
  {
    if (! init)
      throw new IllegalStateException("not initialized");
    headerOmac.update(buf, off, len);
  }
}