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diff --git a/libjava/classpath/gnu/javax/crypto/key/dh/DHKeyPairX509Codec.java b/libjava/classpath/gnu/javax/crypto/key/dh/DHKeyPairX509Codec.java
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+/* DHKeyPairX509Codec.java -- X.509 DER encoder/decoder for DH keys
+   Copyright (C) 2006 Free Software Foundation, Inc.
+
+This file is 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, 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; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, 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.key.dh;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.math.BigInteger;
+import java.security.InvalidParameterException;
+import java.security.PrivateKey;
+import java.security.PublicKey;
+import java.util.ArrayList;
+
+import gnu.java.security.OID;
+import gnu.java.security.Registry;
+import gnu.java.security.der.BitString;
+import gnu.java.security.der.DER;
+import gnu.java.security.der.DERReader;
+import gnu.java.security.der.DERValue;
+import gnu.java.security.der.DERWriter;
+import gnu.java.security.key.IKeyPairCodec;
+import gnu.java.security.util.DerUtil;
+
+public class DHKeyPairX509Codec
+    implements IKeyPairCodec
+{
+  private static final OID DH_ALG_OID = new OID(Registry.DH_OID_STRING);
+
+  // implicit 0-arguments constructor
+
+  public int getFormatID()
+  {
+    return X509_FORMAT;
+  }
+
+  /**
+   * Returns the DER-encoded form of the X.509 ASN.1 <i>SubjectPublicKeyInfo</i>
+   * representation of a DH public key. The ASN.1 specification, as defined in
+   * RFC-3280, and RFC-2459, is as follows:
+   *
+   * <pre>
+   *   SubjectPublicKeyInfo ::= SEQUENCE {
+   *     algorithm         AlgorithmIdentifier,
+   *     subjectPublicKey  BIT STRING
+   *   }
+   *
+   *   AlgorithmIdentifier ::= SEQUENCE {
+   *     algorithm   OBJECT IDENTIFIER,
+   *     parameters  ANY DEFINED BY algorithm OPTIONAL
+   *   }
+   *
+   *   DhParams ::= SEQUENCE {
+   *     p  INTEGER, -- odd prime, p=jq +1
+   *     g  INTEGER, -- generator, g
+   *     q  INTEGER  -- factor of p-1
+   *   }
+   * </pre>
+   *
+   * <p>The <i>subjectPublicKey</i> field, which is a BIT STRING, contains the
+   * DER-encoded form of the DH public key as an INTEGER.</p>
+   *
+   * <pre>
+   *       DHPublicKey ::= INTEGER -- public key, y = g^x mod p
+   * </pre>
+   * <p>
+   * <b>IMPORTANT</b>: with RI's {@link javax.crypto.spec.DHGenParameterSpec}
+   * and {@link javax.crypto.spec.DHParameterSpec} classes, we may end up with
+   * Diffie-Hellman keys that have a <code>null</code> for the <code>q</code>
+   * parameter. RFC-2631 DOES NOT allow for an <i>optional</i> value for that
+   * parameter, hence we replace such null values with <code>0</code>, and do
+   * the reverse in the corresponding decode method.
+   *
+   * @param key the {@link PublicKey} instance to encode. MUST be an instance of
+   *          {@link GnuDHPublicKey}.
+   * @return the DER-encoded form of the ASN.1 representation of the
+   *         <i>SubjectPublicKeyInfo</i> in an X.509 certificate.
+   * @throw InvalidParameterException if <code>key</code> is not an instance
+   *        of {@link GnuDHPublicKey} or if an exception occurs during the
+   *        marshalling process.
+   */
+  public byte[] encodePublicKey(PublicKey key)
+  {
+    if (! (key instanceof GnuDHPublicKey))
+      throw new InvalidParameterException("Wrong key type");
+
+    DERValue derOID = new DERValue(DER.OBJECT_IDENTIFIER, DH_ALG_OID);
+
+    GnuDHPublicKey dhKey = (GnuDHPublicKey) key;
+    BigInteger p = dhKey.getParams().getP();
+    BigInteger g = dhKey.getParams().getG();
+    BigInteger q = dhKey.getQ();
+    if (q == null)
+      q = BigInteger.ZERO;
+    BigInteger y = dhKey.getY();
+
+    DERValue derP = new DERValue(DER.INTEGER, p);
+    DERValue derG = new DERValue(DER.INTEGER, g);
+    DERValue derQ = new DERValue(DER.INTEGER, q);
+
+    ArrayList params = new ArrayList(3);
+    params.add(derP);
+    params.add(derG);
+    params.add(derQ);
+    DERValue derParams = new DERValue(DER.CONSTRUCTED | DER.SEQUENCE, params);
+
+    ArrayList algorithmID = new ArrayList(2);
+    algorithmID.add(derOID);
+    algorithmID.add(derParams);
+    DERValue derAlgorithmID = new DERValue(DER.CONSTRUCTED | DER.SEQUENCE,
+                                           algorithmID);
+
+    DERValue derDHPublicKey = new DERValue(DER.INTEGER, y);
+    byte[] yBytes = derDHPublicKey.getEncoded();
+    DERValue derSPK = new DERValue(DER.BIT_STRING, new BitString(yBytes));
+
+    ArrayList spki = new ArrayList(2);
+    spki.add(derAlgorithmID);
+    spki.add(derSPK);
+    DERValue derSPKI = new DERValue(DER.CONSTRUCTED | DER.SEQUENCE, spki);
+
+    byte[] result;
+    ByteArrayOutputStream baos = new ByteArrayOutputStream();
+    try
+      {
+        DERWriter.write(baos, derSPKI);
+        result = baos.toByteArray();
+      }
+    catch (IOException x)
+      {
+        InvalidParameterException e = new InvalidParameterException();
+        e.initCause(x);
+        throw e;
+      }
+
+    return result;
+  }
+
+  /**
+   * @throws InvalidParameterException ALWAYS.
+   */
+  public byte[] encodePrivateKey(PrivateKey key)
+  {
+    throw new InvalidParameterException("Wrong format for private keys");
+  }
+
+  /**
+   * @param input the byte array to unmarshall into a valid DH
+   *          {@link PublicKey} instance. MUST NOT be null.
+   * @return a new instance of a {@link GnuDHPublicKey} decoded from the
+   *         <i>SubjectPublicKeyInfo</i> material in an X.509 certificate.
+   * @throw InvalidParameterException if an exception occurs during the
+   *        unmarshalling process.
+   */
+  public PublicKey decodePublicKey(byte[] input)
+  {
+    if (input == null)
+      throw new InvalidParameterException("Input bytes MUST NOT be null");
+
+    BigInteger p, g, q, y;
+    DERReader der = new DERReader(input);
+    try
+      {
+        DERValue derSPKI = der.read();
+        DerUtil.checkIsConstructed(derSPKI, "Wrong SubjectPublicKeyInfo field");
+
+        DERValue derAlgorithmID = der.read();
+        DerUtil.checkIsConstructed(derAlgorithmID, "Wrong AlgorithmIdentifier field");
+
+        DERValue derOID = der.read();
+        if (! (derOID.getValue() instanceof OID))
+          throw new InvalidParameterException("Wrong Algorithm field");
+
+        OID algOID = (OID) derOID.getValue();
+        if (! algOID.equals(DH_ALG_OID))
+          throw new InvalidParameterException("Unexpected OID: " + algOID);
+
+        DERValue derParams = der.read();
+        DerUtil.checkIsConstructed(derParams, "Wrong DH Parameters field");
+
+        DERValue val = der.read();
+        DerUtil.checkIsBigInteger(val, "Wrong P field");
+        p = (BigInteger) val.getValue();
+        val = der.read();
+        DerUtil.checkIsBigInteger(val, "Wrong G field");
+        g = (BigInteger) val.getValue();
+        val = der.read();
+        DerUtil.checkIsBigInteger(val, "Wrong Q field");
+        q = (BigInteger) val.getValue();
+        if (q.compareTo(BigInteger.ZERO) == 0)
+          q = null;
+
+        val = der.read();
+        if (! (val.getValue() instanceof BitString))
+          throw new InvalidParameterException("Wrong SubjectPublicKey field");
+
+        byte[] yBytes = ((BitString) val.getValue()).toByteArray();
+
+        DERReader dhPub = new DERReader(yBytes);
+        val = dhPub.read();
+        DerUtil.checkIsBigInteger(val, "Wrong Y field");
+        y = (BigInteger) val.getValue();
+      }
+    catch (IOException x)
+      {
+        InvalidParameterException e = new InvalidParameterException();
+        e.initCause(x);
+        throw e;
+      }
+
+    return new GnuDHPublicKey(Registry.X509_ENCODING_ID, q, p, g, y);
+  }
+
+  /**
+   * @throws InvalidParameterException ALWAYS.
+   */
+  public PrivateKey decodePrivateKey(byte[] input)
+  {
+    throw new InvalidParameterException("Wrong format for private keys");
+  }
+}