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/* TLSHMac.java -- HMAC used in TLS.

   Copyright (C) 2001, 2002, 2003, 2006  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.

You should have received a copy of the GNU General Public License

along with GNU Classpath; if not, write to the Free Software

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

conditions of the GNU General Public License cover the whole

combination.

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

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version.  */

package gnu.javax.net.ssl.provider;

import java.security.InvalidKeyException;

import java.util.Map;

import gnu.java.security.hash.IMessageDigest;

import gnu.javax.crypto.mac.HMac;

/**

 * The operation of this HMac is identical to normal HMacs, but this one

 * allows keys with short lengths (including zero).

 */

class TLSHMac extends HMac

{

  // Constants.

  // -------------------------------------------------------------------------

  private static final byte IPAD_BYTE = 0x36;

  private static final byte OPAD_BYTE = 0x5C;

  // Constructor.

  // -------------------------------------------------------------------------

  TLSHMac(IMessageDigest hash)

  {

    super(hash);

  }

  // Instance methods.

  // -------------------------------------------------------------------------

  public void init(Map attributes)

    throws InvalidKeyException, IllegalStateException

  {

    Integer ts = (Integer) attributes.get(TRUNCATED_SIZE);

    truncatedSize = (ts == null ? macSize : ts.intValue());

    if (truncatedSize < (macSize / 2)) {

      throw new IllegalArgumentException("Truncated size too small");

    } else if (truncatedSize < 10) {

      throw new IllegalArgumentException("Truncated size less than 80 bits");

    }

    // we dont use/save the key outside this method

    byte[] K = (byte[]) attributes.get(MAC_KEY_MATERIAL);

    if (K == null) { // take it as an indication to re-use previous key if set

      if (ipadHash == null)

        {

          throw new InvalidKeyException("Null key");

        }

      // we already went through the motions; ie. up to step #4.  re-use

      underlyingHash = (IMessageDigest) ipadHash.clone();

      return;

    }

    if (K.length > blockSize)

      {

        // (0) replace K with HASH(K) if K is larger than the hash's

        //     block size. Then pad with zeros until it is the correct

        //     size (the next `if').

        underlyingHash.update(K, 0, K.length);

        K = underlyingHash.digest();

      }

    if (K.length < blockSize)

      {

        // (1) append zeros to the end of K to create a B byte string

        //     (e.g., if K is of length 20 bytes and B=64, then K will be

        //     appended with 44 zero bytes 0x00)

        int limit = (K.length > blockSize) ? blockSize : K.length;

        byte[] newK = new byte[blockSize];

        System.arraycopy(K, 0, newK, 0, limit);

        K = newK;

      }

    underlyingHash.reset();

    opadHash = (IMessageDigest) underlyingHash.clone();

    if (ipad == null)

      {

        ipad = new byte[blockSize];

      }

    // (2) XOR (bitwise exclusive-OR) the B byte string computed in step

    //     (1) with ipad

    // (3) append the stream of data 'text' to the B byte string resulting

    //     from step (2)

    // (4) apply H to the stream generated in step (3)

    for (int i = 0; i < blockSize; i++)

      {

        ipad[i] = (byte)(K[i] ^ IPAD_BYTE);

      }

    for (int i = 0; i < blockSize; i++)

      {

        opadHash.update((byte)(K[i] ^ OPAD_BYTE));

      }

    underlyingHash.update(ipad, 0, blockSize);

    ipadHash = (IMessageDigest) underlyingHash.clone();

    K = null;

  }

}