/* RSAPSSSignature.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
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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.

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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA

Linking this library statically or dynamically with other modules is
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permission to link this library with independent modules to produce an
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package gnu.java.security.sig.rsa;

import gnu.java.security.Configuration;
import gnu.java.security.Registry;
import gnu.java.security.hash.HashFactory;
import gnu.java.security.hash.IMessageDigest;
import gnu.java.security.sig.BaseSignature;
import gnu.java.security.util.Util;

import java.math.BigInteger;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.util.logging.Logger;

/**
 * The RSA-PSS signature scheme is a public-key encryption scheme combining the
 * RSA algorithm with the Probabilistic Signature Scheme (PSS) encoding method.
 * <p>
 * The inventors of RSA are Ronald L. Rivest, Adi Shamir, and Leonard Adleman,
 * while the inventors of the PSS encoding method are Mihir Bellare and Phillip
 * Rogaway. During efforts to adopt RSA-PSS into the P1363a standards effort,
 * certain adaptations to the original version of RSA-PSS were made by Mihir
 * Bellare and Phillip Rogaway and also by Burt Kaliski (the editor of IEEE
 * P1363a) to facilitate implementation and integration into existing protocols.
 * <p>
 * References:
 * <ol>
 * <li><a
 * href="http://www.cosic.esat.kuleuven.ac.be/nessie/workshop/submissions/rsa-pss.zip">
 * RSA-PSS Signature Scheme with Appendix, part B.</a><br>
 * Primitive specification and supporting documentation.<br>
 * Jakob Jonsson and Burt Kaliski.</li>
 * </ol>
 */
public class RSAPSSSignature
    extends BaseSignature
{
  private static final Logger log = Logger.getLogger(RSAPSSSignature.class.getName());

  /** The underlying EMSA-PSS instance for this object. */
  private EMSA_PSS pss;

  /** The desired length in octets of the EMSA-PSS salt. */
  private int sLen;

  /**
   * Default 0-arguments constructor. Uses SHA-1 as the default hash and a
   * 0-octet <i>salt</i>.
   */
  public RSAPSSSignature()
  {
    this(Registry.SHA160_HASH, 0);
  }

  /**
   * Constructs an instance of this object using the designated message digest
   * algorithm as its underlying hash function, and having 0-octet <i>salt</i>.
   *
   * @param mdName the canonical name of the underlying hash function.
   */
  public RSAPSSSignature(String mdName)
  {
    this(mdName, 0);
  }

  /**
   * Constructs an instance of this object using the designated message digest
   * algorithm as its underlying hash function.
   *
   * @param mdName the canonical name of the underlying hash function.
   * @param sLen the desired length in octets of the salt to use for encoding /
   *          decoding signatures.
   */
  public RSAPSSSignature(String mdName, int sLen)
  {
    this(HashFactory.getInstance(mdName), sLen);
  }

  public RSAPSSSignature(IMessageDigest md, int sLen)
  {
    super(Registry.RSA_PSS_SIG, md);

    pss = EMSA_PSS.getInstance(md.name());
    this.sLen = sLen;
  }

  /** Private constructor for cloning purposes. */
  private RSAPSSSignature(RSAPSSSignature that)
  {
    this(that.md.name(), that.sLen);

    this.publicKey = that.publicKey;
    this.privateKey = that.privateKey;
    this.md = (IMessageDigest) that.md.clone();
    this.pss = (EMSA_PSS) that.pss.clone();
  }

  public Object clone()
  {
    return new RSAPSSSignature(this);
  }

  protected void setupForVerification(PublicKey k)
      throws IllegalArgumentException
  {
    if (! (k instanceof RSAPublicKey))
      throw new IllegalArgumentException();

    publicKey = (RSAPublicKey) k;
  }

  protected void setupForSigning(PrivateKey k) throws IllegalArgumentException
  {
    if (! (k instanceof RSAPrivateKey))
      throw new IllegalArgumentException();

    privateKey = (RSAPrivateKey) k;
  }

  protected Object generateSignature() throws IllegalStateException
  {
    // 1. Apply the EMSA-PSS encoding operation to the message M to produce an
    // encoded message EM of length CEILING((modBits ? 1)/8) octets such
    // that the bit length of the integer OS2IP(EM) is at most modBits ? 1:
    // EM = EMSA-PSS-Encode(M,modBits ? 1).
    // Note that the octet length of EM will be one less than k if
    // modBits ? 1 is divisible by 8. If the encoding operation outputs
    // 'message too long' or 'encoding error,' then output 'message too
    // long' or 'encoding error' and stop.
    int modBits = ((RSAPrivateKey) privateKey).getModulus().bitLength();
    byte[] salt = new byte[sLen];
    this.nextRandomBytes(salt);
    byte[] EM = pss.encode(md.digest(), modBits - 1, salt);
    if (Configuration.DEBUG)
      log.fine("EM (sign): " + Util.toString(EM));
    // 2. Convert the encoded message EM to an integer message representative
    // m (see Section 1.2.2): m = OS2IP(EM).
    BigInteger m = new BigInteger(1, EM);
    // 3. Apply the RSASP signature primitive to the public key K and the
    // message representative m to produce an integer signature
    // representative s: s = RSASP(K,m).
    BigInteger s = RSA.sign(privateKey, m);
    // 4. Convert the signature representative s to a signature S of length k
    // octets (see Section 1.2.1): S = I2OSP(s, k).
    // 5. Output the signature S.
    int k = (modBits + 7) / 8;
    // return encodeSignature(s, k);
    return RSA.I2OSP(s, k);
  }

  protected boolean verifySignature(Object sig) throws IllegalStateException
  {
    if (publicKey == null)
      throw new IllegalStateException();
    // byte[] S = decodeSignature(sig);
    byte[] S = (byte[]) sig;
    // 1. If the length of the signature S is not k octets, output 'signature
    // invalid' and stop.
    int modBits = ((RSAPublicKey) publicKey).getModulus().bitLength();
    int k = (modBits + 7) / 8;
    if (S.length != k)
      return false;
    // 2. Convert the signature S to an integer signature representative s:
    // s = OS2IP(S).
    BigInteger s = new BigInteger(1, S);
    // 3. Apply the RSAVP verification primitive to the public key (n, e) and
    // the signature representative s to produce an integer message
    // representative m: m = RSAVP((n, e), s).
    // If RSAVP outputs 'signature representative out of range,' then
    // output 'signature invalid' and stop.
    BigInteger m = null;
    try
      {
        m = RSA.verify(publicKey, s);
      }
    catch (IllegalArgumentException x)
      {
        return false;
      }
    // 4. Convert the message representative m to an encoded message EM of
    // length emLen = CEILING((modBits - 1)/8) octets, where modBits is
    // equal to the bit length of the modulus: EM = I2OSP(m, emLen).
    // Note that emLen will be one less than k if modBits - 1 is divisible
    // by 8. If I2OSP outputs 'integer too large,' then output 'signature
    // invalid' and stop.
    int emBits = modBits - 1;
    int emLen = (emBits + 7) / 8;
    byte[] EM = m.toByteArray();
    if (Configuration.DEBUG)
      log.fine("EM (verify): " + Util.toString(EM));
    if (EM.length > emLen)
      return false;
    else if (EM.length < emLen)
      {
        byte[] newEM = new byte[emLen];
        System.arraycopy(EM, 0, newEM, emLen - EM.length, EM.length);
        EM = newEM;
      }
    // 5. Apply the EMSA-PSS decoding operation to the message M and the
    // encoded message EM: Result = EMSA-PSS-Decode(M, EM, emBits). If
    // Result = 'consistent,' output 'signature verified.' Otherwise,
    // output 'signature invalid.'
    byte[] mHash = md.digest();
    boolean result = false;
    try
      {
        result = pss.decode(mHash, EM, emBits, sLen);
      }
    catch (IllegalArgumentException x)
      {
        result = false;
      }
    return result;
  }
}