/* DSSKeyPairGenerator.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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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.hash.Sha160;
import gnu.java.security.key.IKeyPairGenerator;
import gnu.java.security.util.PRNG;

import java.io.PrintWriter;
import java.math.BigInteger;
import java.security.KeyPair;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.spec.DSAParameterSpec;
import java.util.Map;

/**
 * <p>A key-pair generator for asymetric keys to use in conjunction with the DSS
 * (Digital Signature Standard).</p>
 *
 * References:<br>
 * <a href="http://www.itl.nist.gov/fipspubs/fip186.htm">Digital Signature
 * Standard (DSS)</a>, Federal Information Processing Standards Publication 186.
 * National Institute of Standards and Technology.
 */
public class DSSKeyPairGenerator implements IKeyPairGenerator
{

  // Debugging methods and variables
  // -------------------------------------------------------------------------

  private static final String NAME = "dss";

  private static final boolean DEBUG = false;

  private static final int debuglevel = 5;

  private static final PrintWriter err = new PrintWriter(System.out, true);

  private static void debug(String s)
  {
    err.println(">>> " + NAME + ": " + s);
  }

  // Constants and variables
  // -------------------------------------------------------------------------

  /** The BigInteger constant 2. */
  private static final BigInteger TWO = new BigInteger("2");

  /** Property name of the length (Integer) of the modulus (p) of a DSS key. */
  public static final String MODULUS_LENGTH = "gnu.crypto.dss.L";

  /**
   * Property name of the Boolean indicating wether or not to use default pre-
   * computed values of <code>p</code>, <code>q</code> and <code>g</code> for
   * a given modulus length. The ultimate behaviour of this generator with
   * regard to using pre-computed parameter sets will depend on the value of
   * this property and of the following one {@link #STRICT_DEFAULTS}:
   * 
   * <ol>
   *   <li>If this property is {@link Boolean#FALSE} then this generator
   *   will accept being setup for generating parameters for any modulus length
   *   provided the modulus length is between <code>512</code> and
   *   <code>1024</code>, and is of the form <code>512 + 64 * n</code>. In
   *   addition, a new paramter set will always be generated; i.e. no pre-
   *   computed values are used.</li>
   *   
   *   <li>If this property is {@link Boolean#TRUE} and the value of
   *   {@link #STRICT_DEFAULTS} is also {@link Boolean#TRUE} then this generator
   *   will only accept being setup for generating parameters for modulus
   *   lengths of <code>512</code>, <code>768</code> and <code>1024</code>. Any
   *   other value, of the modulus length, even if between <code>512</code> and
   *   <code>1024</code>, and of the form <code>512 + 64 * n</code>, will cause
   *   an {@link IllegalArgumentException} to be thrown. When those modulus
   *   length (<code>512</code>, <code>768</code>, and <code>1024</code>) are
   *   specified, the paramter set is always the same.</li>
   *   
   *   <li>Finally, if this property is {@link Boolean#TRUE} and the value of
   *   {@link #STRICT_DEFAULTS} is {@link Boolean#FALSE} then this generator
   *   will behave as in point 1 above, except that it will use pre-computed
   *   values when possible; i.e. the modulus length is one of <code>512</code>,
   *   <code>768</code>, or <code>1024</code>.</li>
   * </ol>
   * 
   * The default value of this property is {@link Boolean#TRUE}.
   */
  public static final String USE_DEFAULTS = "gnu.crypto.dss.use.defaults";

  /**
   * Property name of the Boolean indicating wether or not to generate new
   * parameters, even if the modulus length <i>L</i> is not one of the pre-
   * computed defaults (value {@link Boolean#FALSE}), or throw an exception
   * (value {@link Boolean#TRUE}) -- the exception in this case is an
   * {@link IllegalArgumentException}. The default value for this property is
   * {@link Boolean#FALSE}. The ultimate behaviour of this generator will
   * depend on the values of this and {@link #USE_DEFAULTS} properties -- see
   * {@link #USE_DEFAULTS} for more information.
   */
  public static final String STRICT_DEFAULTS = "gnu.crypto.dss.strict.defaults";

  /**
   * Property name of an optional {@link SecureRandom} instance to use. The
   * default is to use a classloader singleton from {@link PRNG}.
   */
  public static final String SOURCE_OF_RANDOMNESS = "gnu.crypto.dss.prng";

  /**
   * Property name of an optional {@link DSAParameterSpec} instance to use for
   * this generator's <code>p</code>, <code>q</code>, and <code>g</code> values.
   * The default is to generate these values or use pre-computed ones,
   * depending on the value of the <code>USE_DEFAULTS</code> attribute.
   */
  public static final String DSS_PARAMETERS = "gnu.crypto.dss.params";

  /**
   * Property name of the preferred encoding format to use when externalizing
   * generated instance of key-pairs from this generator. The property is taken
   * to be an {@link Integer} that encapsulates an encoding format identifier.
   */
  public static final String PREFERRED_ENCODING_FORMAT = "gnu.crypto.dss.encoding";

  /** Default value for the modulus length. */
  public static final int DEFAULT_MODULUS_LENGTH = 1024;

  /** Default encoding format to use when none was specified. */
  private static final int DEFAULT_ENCODING_FORMAT = Registry.RAW_ENCODING_ID;

  /** Initial SHS context. */
  private static final int[] T_SHS = new int[] { 0x67452301, 0xEFCDAB89,
                                                0x98BADCFE, 0x10325476,
                                                0xC3D2E1F0 };

  // from jdk1.3.1/docs/guide/security/CryptoSpec.html#AppB
  public static final DSAParameterSpec KEY_PARAMS_512 = new DSAParameterSpec(
                                                                             new BigInteger(
                                                                                            "fca682ce8e12caba26efccf7110e526db078b05edecbcd1eb4a208f3ae1617ae"
                                                                                                + "01f35b91a47e6df63413c5e12ed0899bcd132acd50d99151bdc43ee737592e17",
                                                                                            16),
                                                                             new BigInteger(
                                                                                            "962eddcc369cba8ebb260ee6b6a126d9346e38c5",
                                                                                            16),
                                                                             new BigInteger(
                                                                                            "678471b27a9cf44ee91a49c5147db1a9aaf244f05a434d6486931d2d14271b9e"
                                                                                                + "35030b71fd73da179069b32e2935630e1c2062354d0da20a6c416e50be794ca4",
                                                                                            16));

  public static final DSAParameterSpec KEY_PARAMS_768 = new DSAParameterSpec(
                                                                             new BigInteger(
                                                                                            "e9e642599d355f37c97ffd3567120b8e25c9cd43e927b3a9670fbec5d8901419"
                                                                                                + "22d2c3b3ad2480093799869d1e846aab49fab0ad26d2ce6a22219d470bce7d77"
                                                                                                + "7d4a21fbe9c270b57f607002f3cef8393694cf45ee3688c11a8c56ab127a3daf",
                                                                                            16),
                                                                             new BigInteger(
                                                                                            "9cdbd84c9f1ac2f38d0f80f42ab952e7338bf511",
                                                                                            16),
                                                                             new BigInteger(
                                                                                            "30470ad5a005fb14ce2d9dcd87e38bc7d1b1c5facbaecbe95f190aa7a31d23c4"
                                                                                                + "dbbcbe06174544401a5b2c020965d8c2bd2171d3668445771f74ba084d2029d8"
                                                                                                + "3c1c158547f3a9f1a2715be23d51ae4d3e5a1f6a7064f316933a346d3f529252",
                                                                                            16));

  public static final DSAParameterSpec KEY_PARAMS_1024 = new DSAParameterSpec(
                                                                              new BigInteger(
                                                                                             "fd7f53811d75122952df4a9c2eece4e7f611b7523cef4400c31e3f80b6512669"
                                                                                                 + "455d402251fb593d8d58fabfc5f5ba30f6cb9b556cd7813b801d346ff26660b7"
                                                                                                 + "6b9950a5a49f9fe8047b1022c24fbba9d7feb7c61bf83b57e7c6a8a6150f04fb"
                                                                                                 + "83f6d3c51ec3023554135a169132f675f3ae2b61d72aeff22203199dd14801c7",
                                                                                             16),
                                                                              new BigInteger(
                                                                                             "9760508f15230bccb292b982a2eb840bf0581cf5",
                                                                                             16),
                                                                              new BigInteger(
                                                                                             "f7e1a085d69b3ddecbbcab5c36b857b97994afbbfa3aea82f9574c0b3d078267"
                                                                                                 + "5159578ebad4594fe67107108180b449167123e84c281613b7cf09328cc8a6e1"
                                                                                                 + "3c167a8b547c8d28e0a3ae1e2bb3a675916ea37f0bfa213562f1fb627a01243b"
                                                                                                 + "cca4f1bea8519089a883dfe15ae59f06928b665e807b552564014c3bfecf492a",
                                                                                             16));

  private static final BigInteger TWO_POW_160 = TWO.pow(160);

  /** The length of the modulus of DSS keys generated by this instance. */
  private int L;

  /** The optional {@link SecureRandom} instance to use. */
  private SecureRandom rnd = null;

  private BigInteger seed;

  private BigInteger counter;

  private BigInteger p;

  private BigInteger q;

  private BigInteger e;

  private BigInteger g;

  private BigInteger XKEY;

  /** Our default source of randomness. */
  private PRNG prng = null;

  /** Preferred encoding format of generated keys. */
  private int preferredFormat;

  // Constructor(s)
  // -------------------------------------------------------------------------

  // implicit 0-arguments constructor

  // Class methods
  // -------------------------------------------------------------------------

  // Instance methods
  // -------------------------------------------------------------------------

  // gnu.crypto.key.IKeyPairGenerator interface implementation ---------------

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

  /**
   * <p>Configures this instance.</p>
   *
   * @param attributes the map of name/value pairs to use.
   * @exception IllegalArgumentException if the designated MODULUS_LENGTH
   * value is not greater than 512, less than 1024 and not of the form
   * <code>512 + 64j</code>.
   */
  public void setup(Map attributes)
  {
    // find out the modulus length
    Integer l = (Integer) attributes.get(MODULUS_LENGTH);
    L = (l == null ? DEFAULT_MODULUS_LENGTH : l.intValue());
    if ((L % 64) != 0 || L < 512 || L > 1024)
      throw new IllegalArgumentException(MODULUS_LENGTH);

    // should we use the default pre-computed params?
    Boolean useDefaults = (Boolean) attributes.get(USE_DEFAULTS);
    if (useDefaults == null)
      {
        useDefaults = Boolean.TRUE;
      }

    Boolean strictDefaults = (Boolean) attributes.get(STRICT_DEFAULTS);
    if (strictDefaults == null)
      strictDefaults = Boolean.FALSE;

    // are we given a set of DSA params or we shall use/generate our own?
    DSAParameterSpec params = (DSAParameterSpec) attributes.get(DSS_PARAMETERS);
    if (params != null)
      {
        p = params.getP();
        q = params.getQ();
        g = params.getG();
      }
    else if (useDefaults.equals(Boolean.TRUE))
      {
        switch (L)
          {
          case 512:
            p = KEY_PARAMS_512.getP();
            q = KEY_PARAMS_512.getQ();
            g = KEY_PARAMS_512.getG();
            break;
          case 768:
            p = KEY_PARAMS_768.getP();
            q = KEY_PARAMS_768.getQ();
            g = KEY_PARAMS_768.getG();
            break;
          case 1024:
            p = KEY_PARAMS_1024.getP();
            q = KEY_PARAMS_1024.getQ();
            g = KEY_PARAMS_1024.getG();
            break;
          default:
            if (strictDefaults.equals(Boolean.TRUE))
              throw new IllegalArgumentException(
                  "Does not provide default parameters for " + L
                  + "-bit modulus length");
            else
              {
                p = null;
                q = null;
                g = null;
              }
          }
      }
    else
      {
        p = null;
        q = null;
        g = null;
      }

    // do we have a SecureRandom, or should we use our own?
    rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);

    // what is the preferred encoding format
    Integer formatID = (Integer) attributes.get(PREFERRED_ENCODING_FORMAT);
    preferredFormat = formatID == null
        ? DEFAULT_ENCODING_FORMAT
        : formatID.intValue();

    // set the seed-key
    byte[] kb = new byte[20]; // we need 160 bits of randomness
    nextRandomBytes(kb);
    XKEY = new BigInteger(1, kb).setBit(159).setBit(0);
  }

  public KeyPair generate()
  {
    if (p == null)
      {
        BigInteger[] params = new FIPS186(L, rnd).generateParameters();
        seed = params[FIPS186.DSA_PARAMS_SEED];
        counter = params[FIPS186.DSA_PARAMS_COUNTER];
        q = params[FIPS186.DSA_PARAMS_Q];
        p = params[FIPS186.DSA_PARAMS_P];
        e = params[FIPS186.DSA_PARAMS_E];
        g = params[FIPS186.DSA_PARAMS_G];
        if (DEBUG && debuglevel > 0)
          {
            debug("seed: " + seed.toString(16));
            debug("counter: " + counter.intValue());
            debug("q: " + q.toString(16));
            debug("p: " + p.toString(16));
            debug("e: " + e.toString(16));
            debug("g: " + g.toString(16));
          }
      }

    BigInteger x = nextX();
    BigInteger y = g.modPow(x, p);

    PublicKey pubK = new DSSPublicKey(preferredFormat, p, q, g, y);
    PrivateKey secK = new DSSPrivateKey(preferredFormat, p, q, g, x);

    return new KeyPair(pubK, secK);
  }

  // Other instance methods --------------------------------------------------

  /**
   * <p>This method applies the following algorithm described in 3.1 of
   * FIPS-186:</p>
   *
   * <ol>
   *    <li>XSEED = optional user input.</li>
   *    <li>XVAL = (XKEY + XSEED) mod 2<sup>b</sup>.</li>
   *    <li>x = G(t, XVAL) mod q.</li>
   *    <li>XKEY = (1 + XKEY + x) mod 2<sup>b</sup>.</li>
   * </ol>
   *
   * <p>Where <code>b</code> is the length of a secret b-bit seed-key (XKEY).</p>
   *
   * <p>Note that in this implementation, XSEED, the optional user input, is
   * always zero.</p>
   */
  private synchronized BigInteger nextX()
  {
    byte[] xk = XKEY.toByteArray();
    byte[] in = new byte[64]; // 512-bit block for SHS
    System.arraycopy(xk, 0, in, 0, xk.length);

    int[] H = Sha160.G(T_SHS[0], T_SHS[1], T_SHS[2], T_SHS[3], T_SHS[4], in, 0);
    byte[] h = new byte[20];
    for (int i = 0, j = 0; i < 5; i++)
      {
        h[j++] = (byte) (H[i] >>> 24);
        h[j++] = (byte) (H[i] >>> 16);
        h[j++] = (byte) (H[i] >>> 8);
        h[j++] = (byte) H[i];
      }
    BigInteger result = new BigInteger(1, h).mod(q);
    XKEY = XKEY.add(result).add(BigInteger.ONE).mod(TWO_POW_160);

    return result;
  }

  /**
   * <p>Fills the designated byte array with random data.</p>
   *
   * @param buffer the byte array to fill with random data.
   */
  private void nextRandomBytes(byte[] buffer)
  {
    if (rnd != null)
      {
        rnd.nextBytes(buffer);
      }
    else
      getDefaultPRNG().nextBytes(buffer);
  }

  private PRNG getDefaultPRNG()
  {
    if (prng == null)
      prng = PRNG.getInstance();

    return prng;
  }
}
