/* DSSKeyPairX509Codec.java -- X.509 Encoding/Decoding handler
   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.java.security.key.dss;

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;

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;

/**
 * An implementation of an {@link IKeyPairCodec} that knows how to encode /
 * decode X.509 ASN.1 external representation of DSS public keys.
 */
public class DSSKeyPairX509Codec
    implements IKeyPairCodec
{
  private static final OID DSA_ALG_OID = new OID(Registry.DSA_OID_STRING);

  // implicit 0-arguments constructor

  public int getFormatID()
  {
    return X509_FORMAT;
  }

  /**
   * Returns the X.509 ASN.1 <i>SubjectPublicKeyInfo</i> representation of a
   * DSA 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
   *   }
   *
   *   DssParams ::= SEQUENCE {
   *     p   INTEGER,
   *     q   INTEGER,
   *     g   INTEGER
   *   }
   * </pre>
   * <p>
   * Note that RFC-3280 (page 79) implies that some certificates MAY have an
   * absent, or NULL, parameters field in their AlgorithmIdentifier element,
   * implying that those parameters MUST be <i>inherited</i> from another
   * certificate. This implementation, encodes a <i>NULL</i> element as the DER
   * value of the parameters field when such is the case.
   * <p>
   * The <i>subjectPublicKey</i> field, which is a BIT STRING, contains the
   * DER-encoded form of the DSA public key as an INTEGER.
   * 
   * <pre>
   *       DSAPublicKey ::= INTEGER -- public key, Y
   * </pre>
   * 
   * @param key the {@link PublicKey} instance to encode. MUST be an instance of
   *          {@link DSSPublicKey}.
   * @return 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 DSSPublicKey} or if an exception occurs during the
   *        marshalling process.
   */
  public byte[] encodePublicKey(PublicKey key)
  {
    if (! (key instanceof DSSPublicKey))
      throw new InvalidParameterException("key");

    DERValue derOID = new DERValue(DER.OBJECT_IDENTIFIER, DSA_ALG_OID);

    DSSPublicKey dssKey = (DSSPublicKey) key;
    DERValue derParams;
    if (dssKey.hasInheritedParameters())
      derParams = new DERValue(DER.NULL, null);
    else
      {
        BigInteger p = dssKey.getParams().getP();
        BigInteger q = dssKey.getParams().getQ();
        BigInteger g = dssKey.getParams().getG();

        DERValue derP = new DERValue(DER.INTEGER, p);
        DERValue derQ = new DERValue(DER.INTEGER, q);
        DERValue derG = new DERValue(DER.INTEGER, g);

        ArrayList params = new ArrayList(3);
        params.add(derP);
        params.add(derQ);
        params.add(derG);
        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);

    BigInteger y = dssKey.getY();
    DERValue derDSAPublicKey = new DERValue(DER.INTEGER, y);
    byte[] yBytes = derDSAPublicKey.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(x.getMessage());
        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 DSS
   *          {@link PublicKey} instance. MUST NOT be null.
   * @return a new instance of a {@link DSSPublicKey} 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 = null;
    BigInteger g = null;
    BigInteger q = null;
    BigInteger 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(DSA_ALG_OID))
          throw new InvalidParameterException("Unexpected OID: " + algOID);

        DERValue val = der.read();
        // RFC-3280, page 79 states: "If the subjectPublicKeyInfo field of the
        // certificate contains an algorithm field with null parameters or
        // parameters are omitted, compare the certificate subjectPublicKey
        // algorithm to the working_public_key_algorithm.  If the certificate
        // subjectPublicKey algorithm and the working_public_key_algorithm are
        // different, set the working_public_key_parameters to null."
        // in other words, the parameters field of an AlgorithmIdentifier
        // element MAY NOT be present at all, or if present MAY be NULL!
        // the Mauve test ValidDSAParameterInheritenceTest5, in
        // gnu.testlet.java.security.cert.pkix.pkits, is/was failing because
        // of this.
        if (val.getTag() == DER.NULL)
          val = der.read();
        else if (val.isConstructed())
          {
            val = der.read();
            DerUtil.checkIsBigInteger(val, "Wrong P field");
            p = (BigInteger) val.getValue();
            val = der.read();
            DerUtil.checkIsBigInteger(val, "Wrong Q field");
            q = (BigInteger) val.getValue();
            val = der.read();
            DerUtil.checkIsBigInteger(val, "Wrong G field");
            g = (BigInteger) val.getValue();

            val = der.read();
          }

        if (! (val.getValue() instanceof BitString))
          throw new InvalidParameterException("Wrong SubjectPublicKey field");

        byte[] yBytes = ((BitString) val.getValue()).toByteArray();

        DERReader dsaPub = new DERReader(yBytes);
        val = dsaPub.read();
        DerUtil.checkIsBigInteger(val, "Wrong Y field");
        y = (BigInteger) val.getValue();
      }
    catch (IOException x)
      {
        InvalidParameterException e = new InvalidParameterException(x.getMessage());
        e.initCause(x);
        throw e;
      }
    return new DSSPublicKey(Registry.X509_ENCODING_ID, p, q, g, y);
  }

  /**
   * @throws InvalidParameterException ALWAYS.
   */
  public PrivateKey decodePrivateKey(byte[] input)
  {
    throw new InvalidParameterException("Wrong format for private keys");
  }
}