/* RSAPKCS1V1_5Signature.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
the Free Software Foundation; either version 2 of the License, 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.

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along with GNU Classpath; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, 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
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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
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package gnu.java.security.sig.rsa;

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

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.Arrays;

/**
 * The RSA-PKCS1-V1.5 signature scheme is a digital signature scheme with
 * appendix (SSA) combining the RSA algorithm with the EMSA-PKCS1-v1_5 encoding
 * method.
 * <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>
 * <li><a href="http://www.ietf.org/rfc/rfc3447.txt">Public-Key Cryptography
 * Standards (PKCS) #1:</a><br>
 * RSA Cryptography Specifications Version 2.1.<br>
 * Jakob Jonsson and Burt Kaliski.</li>
 * </ol>
 */
public class RSAPKCS1V1_5Signature
    extends BaseSignature
{
  /** The underlying EMSA-PKCS1-v1.5 instance for this object. */
  private EMSA_PKCS1_V1_5 pkcs1;

  /**
   * Default 0-arguments constructor. Uses SHA-1 as the default hash.
   */
  public RSAPKCS1V1_5Signature()
  {
    this(Registry.SHA160_HASH);
  }

  /**
   * 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.
   */
  public RSAPKCS1V1_5Signature(final String mdName)
  {
    this(HashFactory.getInstance(mdName));
  }

  public RSAPKCS1V1_5Signature(IMessageDigest md)
  {
    super(Registry.RSA_PKCS1_V1_5_SIG, md);

    pkcs1 = EMSA_PKCS1_V1_5.getInstance(md.name());
  }

  /** Private constructor for cloning purposes. */
  private RSAPKCS1V1_5Signature(final RSAPKCS1V1_5Signature that)
  {
    this(that.md.name());

    this.publicKey = that.publicKey;
    this.privateKey = that.privateKey;
    this.md = (IMessageDigest) that.md.clone();
    this.pkcs1 = (EMSA_PKCS1_V1_5) that.pkcs1.clone();
  }

  public Object clone()
  {
    return new RSAPKCS1V1_5Signature(this);
  }

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

    publicKey = k;
  }

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

    privateKey = k;
  }

  protected Object generateSignature() throws IllegalStateException
  {
    // 1. EMSA-PKCS1-v1_5 encoding: Apply the EMSA-PKCS1-v1_5 encoding
    // operation (Section 9.2) to the message M to produce an encoded
    // message EM of length k octets:
    //
    // EM = EMSA-PKCS1-V1_5-ENCODE (M, k).
    //
    // If the encoding operation outputs "message too long," output
    // "message too long" and stop. If the encoding operation outputs
    // "intended encoded message length too short," output "RSA modulus
    // too short" and stop.
    final int modBits = ((RSAPrivateKey) privateKey).getModulus().bitLength();
    final int k = (modBits + 7) / 8;
    final byte[] EM = pkcs1.encode(md.digest(), k);
    // 2. RSA signature:
    // a. Convert the encoded message EM to an integer message epresentative
    // m (see Section 4.2): m = OS2IP (EM).
    final BigInteger m = new BigInteger(1, EM);
    // b. Apply the RSASP1 signature primitive (Section 5.2.1) to the RSA
    // private key K and the message representative m to produce an
    // integer signature representative s: s = RSASP1 (K, m).
    final BigInteger s = RSA.sign(privateKey, m);
    // c. Convert the signature representative s to a signature S of length
    // k octets (see Section 4.1): S = I2OSP (s, k).
    // 3. Output the signature S.
    return RSA.I2OSP(s, k);
  }

  protected boolean verifySignature(final Object sig)
      throws IllegalStateException
  {
    if (publicKey == null)
      throw new IllegalStateException();
    final byte[] S = (byte[]) sig;
    // 1. Length checking: If the length of the signature S is not k octets,
    // output "invalid signature" and stop.
    final int modBits = ((RSAPublicKey) publicKey).getModulus().bitLength();
    final int k = (modBits + 7) / 8;
    if (S.length != k)
      return false;
    // 2. RSA verification:
    // a. Convert the signature S to an integer signature representative
    // s (see Section 4.2): s = OS2IP (S).
    final BigInteger s = new BigInteger(1, S);
    // b. Apply the RSAVP1 verification primitive (Section 5.2.2) to the
    // RSA public key (n, e) and the signature representative s to
    // produce an integer message representative m:
    // m = RSAVP1 ((n, e), s).
    // If RSAVP1 outputs "signature representative out of range,"
    // output "invalid signature" and stop.
    final BigInteger m;
    try
      {
        m = RSA.verify(publicKey, s);
      }
    catch (IllegalArgumentException x)
      {
        return false;
      }
    // c. Convert the message representative m to an encoded message EM
    // of length k octets (see Section 4.1): EM = I2OSP (m, k).
    // If I2OSP outputs "integer too large," output "invalid signature"
    // and stop.
    final byte[] EM;
    try
      {
        EM = RSA.I2OSP(m, k);
      }
    catch (IllegalArgumentException x)
      {
        return false;
      }
    // 3. EMSA-PKCS1-v1_5 encoding: Apply the EMSA-PKCS1-v1_5 encoding
    // operation (Section 9.2) to the message M to produce a second
    // encoded message EM' of length k octets:
    // EM' = EMSA-PKCS1-V1_5-ENCODE (M, k).
    // If the encoding operation outputs "message too long," output
    // "message too long" and stop. If the encoding operation outputs
    // "intended encoded message length too short," output "RSA modulus
    // too short" and stop.
    final byte[] EMp = pkcs1.encode(md.digest(), k);
    // 4. Compare the encoded message EM and the second encoded message EM'.
    // If they are the same, output "valid signature"; otherwise, output
    // "invalid signature."
    return Arrays.equals(EM, EMp);
  }
}