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/* HMac.java --
   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.crypto.mac;
 
import gnu.java.security.Registry;
import gnu.java.security.hash.IMessageDigest;
import gnu.java.security.hash.MD5;
import gnu.java.security.util.Util;
 
import java.security.InvalidKeyException;
import java.util.HashMap;
import java.util.Map;
 
/**
 * The implementation of the <i>HMAC</i> (Keyed-Hash Message Authentication
 * Code).
 * <p>
 * <i>HMAC</i> can be used in combination with any iterated cryptographic hash
 * function. <i>HMAC</i> also uses a <i>secret key</i> for calculation and
 * verification of the message authentication values. The main goals behind this
 * construction are:
 * <ul>
 * <li>To use, without modifications, available hash functions. In particular,
 * hash functions that perform well in software, and for which code is freely
 * and widely available.</li>
 * <li>To preserve the original performance of the hash function without
 * incurring a significant degradation.</li>
 * <li>To use and handle keys in a simple way.</li>
 * <li>To have a well understood cryptographic analysis of the strength of the
 * authentication mechanism based on reasonable assumptions on the underlying
 * hash function.</li>
 * <li>To allow for easy replaceability of the underlying hash function in case
 * that faster or more secure hash functions are found or required.</li>
 * </ul>
 * <p>
 * References:
 * <ol>
 * <li><a href="http://www.ietf.org/rfc/rfc-2104.txt">RFC 2104</a>HMAC:
 * Keyed-Hashing for Message Authentication.<br>
 * H. Krawczyk, M. Bellare, and R. Canetti.</li>
 * </ol>
 */
public class HMac
    extends BaseMac
    implements Cloneable
{
  public static final String USE_WITH_PKCS5_V2 = "gnu.crypto.hmac.pkcs5";
  private static final byte IPAD_BYTE = 0x36;
  private static final byte OPAD_BYTE = 0x5C;
  /** caches the result of the correctness test, once executed. */
  private static Boolean valid;
  protected int macSize;
  protected int blockSize;
  protected IMessageDigest ipadHash;
  protected IMessageDigest opadHash;
  protected byte[] ipad;
 
  /**
   * Trivial constructor for use by concrete subclasses.
   *
   * @param underlyingHash the underlying hash algorithm instance.
   */
  protected HMac(IMessageDigest underlyingHash)
  {
    super(Registry.HMAC_NAME_PREFIX + underlyingHash.name(), underlyingHash);
 
    this.blockSize = underlyingHash.blockSize();
    this.macSize = underlyingHash.hashSize();
    ipadHash = opadHash = null;
  }
 
  public Object clone() throws CloneNotSupportedException
  {
    HMac result = (HMac) super.clone();
    if (this.ipadHash != null)
      result.ipadHash = (IMessageDigest) this.ipadHash.clone();
    if (this.opadHash != null)
      result.opadHash = (IMessageDigest) this.opadHash.clone();
    if (this.ipad != null)
      result.ipad = (byte[]) this.ipad.clone();
 
    return result;
  }
 
  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;
      }
 
    // for HMACs used in key-derivation functions (e.g. PBKDF2) the key material
    // need not be >= the (output) block size of the underlying algorithm
    Boolean pkcs5 = (Boolean) attributes.get(USE_WITH_PKCS5_V2);
    if (pkcs5 == null)
      pkcs5 = Boolean.FALSE;
    if (K.length < macSize && ! pkcs5.booleanValue())
      throw new InvalidKeyException("Key too short");
 
    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;
  }
 
  public void reset()
  {
    super.reset();
    if (ipad != null)
      {
        underlyingHash.update(ipad, 0, blockSize);
        ipadHash = (IMessageDigest) underlyingHash.clone();
      }
  }
 
  public byte[] digest()
  {
    if (ipadHash == null)
      throw new IllegalStateException("HMAC not initialised");
    byte[] out = underlyingHash.digest();
    // (5) XOR (bitwise exclusive-OR) the B byte string computed in step (1)
    //     with opad
    underlyingHash = (IMessageDigest) opadHash.clone();
    // (6) append the H result from step (4) to the B byte string resulting from
    //     step (5)
    underlyingHash.update(out, 0, macSize);
    // (7) apply H to the stream generated in step (6) and output the result
    out = underlyingHash.digest(); // which also resets the underlying hash
    // truncate and return
    if (truncatedSize == macSize)
      return out;
    byte[] result = new byte[truncatedSize];
    System.arraycopy(out, 0, result, 0, truncatedSize);
    return result;
  }
 
  public boolean selfTest()
  {
    if (valid == null)
      {
        try
          {
            IMac mac = new HMac(new MD5()); // use rfc-2104 test vectors
            String tv1 = "9294727A3638BB1C13F48EF8158BFC9D";
            String tv3 = "56BE34521D144C88DBB8C733F0E8B3F6";
            byte[] k1 = new byte[] {
                0x0B, 0x0B, 0x0B, 0x0B, 0x0B, 0x0B, 0x0B, 0x0B,
                0x0B, 0x0B, 0x0B, 0x0B, 0x0B, 0x0B, 0x0B, 0x0B };
            byte[] k3 = new byte[] {
                (byte) 0xAA, (byte) 0xAA, (byte) 0xAA, (byte) 0xAA,
                (byte) 0xAA, (byte) 0xAA, (byte) 0xAA, (byte) 0xAA,
                (byte) 0xAA, (byte) 0xAA, (byte) 0xAA, (byte) 0xAA,
                (byte) 0xAA, (byte) 0xAA, (byte) 0xAA, (byte) 0xAA };
            byte[] data = new byte[50];
            for (int i = 0; i < 50;)
              data[i++] = (byte) 0xDD;
 
            HashMap map = new HashMap();
            // test vector #1
            map.put(MAC_KEY_MATERIAL, k1);
            mac.init(map);
            mac.update("Hi There".getBytes("ASCII"), 0, 8);
            if (! tv1.equals(Util.toString(mac.digest())))
              valid = Boolean.FALSE;
 
            // test #2 is not used since it causes a "Key too short" exception
 
            // test vector #3
            map.put(MAC_KEY_MATERIAL, k3);
            mac.init(map);
            mac.update(data, 0, 50);
            if (! tv3.equals(Util.toString(mac.digest())))
              valid = Boolean.FALSE;
            valid = Boolean.TRUE;
          }
        catch (Exception x)
          {
            x.printStackTrace(System.err);
            valid = Boolean.FALSE;
          }
      }
    return valid.booleanValue();
  }
}