/* DSSKey.java -- 
   Copyright 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
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General Public License for more details.

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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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permission to link this library with independent modules to produce an
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package gnu.java.security.key.dss;

import gnu.java.security.Registry;
import gnu.java.security.action.GetPropertyAction;
import gnu.java.security.util.FormatUtil;

import java.math.BigInteger;
import java.security.AccessController;
import java.security.Key;
import java.security.interfaces.DSAKey;
import java.security.interfaces.DSAParams;
import java.security.spec.DSAParameterSpec;

/**
 * A base asbtract class for both public and private DSS (Digital Signature
 * Standard) keys. It encapsulates the three DSS numbers: <code>p</code>,
 * <code>q</code> and <code>g</code>.
 * <p>
 * According to the JDK, cryptographic <i>Keys</i> all have a <i>format</i>.
 * The format used in this implementation is called <i>Raw</i>, and basically
 * consists of the raw byte sequences of algorithm parameters. The exact order
 * of the byte sequences and the implementation details are given in each of the
 * relevant <code>getEncoded()</code> methods of each of the private and
 * public keys.
 * <p>
 * <b>IMPORTANT</b>: Under certain circumstances (e.g. in an X.509 certificate
 * with inherited AlgorithmIdentifier's parameters of a SubjectPublicKeyInfo
 * element) these three MPIs may be <code>null</code>.
 * 
 * @see DSSPrivateKey#getEncoded
 * @see DSSPublicKey#getEncoded
 */
public abstract class DSSKey
    implements Key, DSAKey
{
  /**
   * A prime modulus, where
   * <code>2<sup>L-1</sup> &lt; p &lt; 2<sup>L</sup></code> for
   * <code>512 &lt;= L &lt;= 1024</code> and <code>L</code> a multiple of
   * <code>64</code>.
   */
  protected final BigInteger p;

  /**
   * A prime divisor of <code>p - 1</code>, where
   * <code>2<sup>159</sup> &lt; q
   * &lt; 2<sup>160</sup></code>.
   */
  protected final BigInteger q;

  /**
   * <code>g = h<sup>(p-1)</sup>/q mod p</code>, where <code>h</code> is
   * any integer with <code>1 &lt; h &lt; p - 1</code> such that <code>h<sup>
   * (p-1)</sup>/q mod p > 1</code> (<code>g</code>
   * has order <code>q mod p
   * </code>).
   */
  protected final BigInteger g;

  /**
   * Identifier of the default encoding format to use when externalizing the key
   * material.
   */
  protected final int defaultFormat;

  /** String representation of this key. Cached for speed. */
  private transient String str;

  /**
   * Trivial protected constructor.
   * 
   * @param defaultFormat the identifier of the encoding format to use by
   *          default when externalizing the key.
   * @param p the DSS parameter <code>p</code>.
   * @param q the DSS parameter <code>q</code>.
   * @param g the DSS parameter <code>g</code>.
   */
  protected DSSKey(int defaultFormat, BigInteger p, BigInteger q, BigInteger g)
  {
    super();

    this.defaultFormat = defaultFormat <= 0 ? Registry.RAW_ENCODING_ID
                                            : defaultFormat;
    this.p = p;
    this.q = q;
    this.g = g;
  }

  public DSAParams getParams()
  {
    return new DSAParameterSpec(p, q, g);
  }

  public String getAlgorithm()
  {
    return Registry.DSS_KPG;
  }

  /** @deprecated see getEncoded(int). */
  public byte[] getEncoded()
  {
    return getEncoded(defaultFormat);
  }

  public String getFormat()
  {
    return FormatUtil.getEncodingShortName(defaultFormat);
  }

  /**
   * Returns <code>true</code> if the designated object is an instance of
   * {@link DSAKey} and has the same DSS (Digital Signature Standard) parameter
   * values as this one.
   * <p>
   * Always returns <code>false</code> if the MPIs of this key are
   * <i>inherited</i>. This may be the case when the key is re-constructed from
   * an X.509 certificate with absent or NULL AlgorithmIdentifier's parameters
   * field.
   * 
   * @param obj the other non-null DSS key to compare to.
   * @return <code>true</code> if the designated object is of the same type
   *         and value as this one.
   */
  public boolean equals(Object obj)
  {
    if (hasInheritedParameters())
      return false;

    if (obj == null)
      return false;

    if (! (obj instanceof DSAKey))
      return false;

    DSAKey that = (DSAKey) obj;
    return p.equals(that.getParams().getP())
           && q.equals(that.getParams().getQ())
           && g.equals(that.getParams().getG());
  }

  public String toString()
  {
    if (str == null)
      {
        String ls = (String) AccessController.doPrivileged(new GetPropertyAction("line.separator"));
        StringBuilder sb = new StringBuilder(ls)
            .append("defaultFormat=").append(defaultFormat).append(",")
            .append(ls);
        if (hasInheritedParameters())
          sb.append("p=inherited,").append(ls)
              .append("q=inherited,").append(ls)
              .append("g=inherited");
        else
          sb.append("p=0x").append(p.toString(16)).append(",").append(ls)
              .append("q=0x").append(q.toString(16)).append(",").append(ls)
              .append("g=0x").append(g.toString(16));
        str = sb.toString();
      }
    return str;
  }

  public abstract byte[] getEncoded(int format);

  /**
   * @return <code>true</code> if <code>p</code>, <code>q</code> and
   *         <code>g</code> are all <code>null</code>. Returns
   *         <code>false</code> otherwise.
   */
  public boolean hasInheritedParameters()
  {
    return p == null && q == null && g == null;
  }
}