/* RSACipherImpl.java --
   Copyright (C) 2005, 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.javax.crypto;

import gnu.classpath.debug.Component;
import gnu.classpath.debug.SystemLogger;
import gnu.java.security.util.ByteArray;

import java.math.BigInteger;
import java.security.AlgorithmParameters;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.interfaces.RSAKey;
import java.security.interfaces.RSAPrivateCrtKey;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.AlgorithmParameterSpec;
import java.util.logging.Logger;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.CipherSpi;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.ShortBufferException;

public class RSACipherImpl
    extends CipherSpi
{
  private static final Logger logger = SystemLogger.SYSTEM;
  private static final byte[] EMPTY = new byte[0];
  private int opmode = -1;
  private RSAPrivateKey decipherKey = null;
  private RSAPublicKey blindingKey = null;
  private RSAPublicKey encipherKey = null;
  private SecureRandom random = null;
  private byte[] dataBuffer = null;
  private int pos = 0;

  protected void engineSetMode(String mode) throws NoSuchAlgorithmException
  {
    throw new NoSuchAlgorithmException("only one mode available");
  }

  protected void engineSetPadding(String pad) throws NoSuchPaddingException
  {
    throw new NoSuchPaddingException("only one padding available");
  }

  protected int engineGetBlockSize()
  {
    return 1;
  }

  protected int engineGetOutputSize(int inputLen)
  {
    int outputLen = 0;
    if (decipherKey != null)
      outputLen = (decipherKey.getModulus().bitLength() + 7) / 8;
    else if (encipherKey != null)
      outputLen = (encipherKey.getModulus().bitLength() + 7) / 8;
    else
      throw new IllegalStateException("not initialized");
    if (inputLen > outputLen)
      throw new IllegalArgumentException("not configured to encode " + inputLen
                                         + "bytes; at most " + outputLen);
    return outputLen;
  }

  protected int engineGetKeySize(final Key key) throws InvalidKeyException
  {
    if (! (key instanceof RSAKey))
      throw new InvalidKeyException("not an RSA key");
    return ((RSAKey) key).getModulus().bitLength();
  }

  protected byte[] engineGetIV()
  {
    return null;
  }

  protected AlgorithmParameters engineGetParameters()
  {
    return null;
  }

  protected void engineInit(int opmode, Key key, SecureRandom random)
      throws InvalidKeyException
  {
    int outputLen = 0;
    if (opmode == Cipher.ENCRYPT_MODE)
      {
        if (! (key instanceof RSAPublicKey))
          throw new InvalidKeyException("expecting a RSAPublicKey");
        encipherKey = (RSAPublicKey) key;
        decipherKey = null;
        blindingKey = null;
        outputLen = (encipherKey.getModulus().bitLength() + 7) / 8;
      }
    else if (opmode == Cipher.DECRYPT_MODE)
      {
        if (key instanceof RSAPrivateKey)
          {
            decipherKey = (RSAPrivateKey) key;
            encipherKey = null;
            blindingKey = null;
            outputLen = (decipherKey.getModulus().bitLength() + 7) / 8;
          }
        else if (key instanceof RSAPublicKey)
          {
            if (decipherKey == null)
              throw new IllegalStateException("must configure decryption key first");
            if (! decipherKey.getModulus().equals(((RSAPublicKey) key).getModulus()))
              throw new InvalidKeyException("blinding key is not compatible");
            blindingKey = (RSAPublicKey) key;
            return;
          }
        else
          throw new InvalidKeyException(
              "expecting either an RSAPrivateKey or an RSAPublicKey (for blinding)");
      }
    else
      throw new IllegalArgumentException("only encryption and decryption supported");
    this.random = random;
    this.opmode = opmode;
    pos = 0;
    dataBuffer = new byte[outputLen];
  }

  protected void engineInit(int opmode, Key key, AlgorithmParameterSpec spec,
                            SecureRandom random) throws InvalidKeyException
  {
    engineInit(opmode, key, random);
  }

  protected void engineInit(int opmode, Key key, AlgorithmParameters params,
                            SecureRandom random) throws InvalidKeyException
  {
    engineInit(opmode, key, random);
  }

  protected byte[] engineUpdate(byte[] in, int offset, int length)
  {
    if (opmode != Cipher.ENCRYPT_MODE && opmode != Cipher.DECRYPT_MODE)
      throw new IllegalStateException("not initialized");
    System.arraycopy(in, offset, dataBuffer, pos, length);
    pos += length;
    return EMPTY;
  }

  protected int engineUpdate(byte[] in, int offset, int length, byte[] out,
                             int outOffset)
  {
    engineUpdate(in, offset, length);
    return 0;
  }

  protected byte[] engineDoFinal(byte[] in, int offset, int length)
      throws IllegalBlockSizeException, BadPaddingException
  {
    engineUpdate(in, offset, length);
    if (opmode == Cipher.DECRYPT_MODE)
      {
        if (pos < dataBuffer.length)
          throw new IllegalBlockSizeException("expecting exactly "
                                              + dataBuffer.length + " bytes");
        BigInteger enc = new BigInteger(1, dataBuffer);
        byte[] dec = rsaDecrypt(enc);
        logger.log(Component.CRYPTO, "RSA: decryption produced\n{0}",
                   new ByteArray(dec));
        if (dec[0] != 0x02)
          throw new BadPaddingException("expected padding type 2");
        int i;
        for (i = 1; i < dec.length && dec[i] != 0x00; i++)
          ; // keep incrementing i
        int len = dec.length - i - 1; // skip the 0x00 byte
        byte[] result = new byte[len];
        System.arraycopy(dec, i + 1, result, 0, len);
        pos = 0;
        return result;
      }
    else
      {
        offset = dataBuffer.length - pos;
        if (offset < 3)
          throw new IllegalBlockSizeException("input is too large to encrypt");
        byte[] dec = new byte[dataBuffer.length];
        dec[0] = 0x02;
        if (random == null)
          random = new SecureRandom();
        byte[] pad = new byte[offset - 2];
        random.nextBytes(pad);
        for (int i = 0; i < pad.length; i++)
          if (pad[i] == 0)
            pad[i] = 1;
        System.arraycopy(pad, 0, dec, 1, pad.length);
        dec[dec.length - pos] = 0x00;
        System.arraycopy(dataBuffer, 0, dec, offset, pos);
        logger.log(Component.CRYPTO, "RSA: produced padded plaintext\n{0}",
                   new ByteArray(dec));
        BigInteger x = new BigInteger(1, dec);
        BigInteger y = x.modPow(encipherKey.getPublicExponent(),
                                encipherKey.getModulus());
        byte[] enc = y.toByteArray();
        if (enc[0] == 0x00)
          {
            byte[] tmp = new byte[enc.length - 1];
            System.arraycopy(enc, 1, tmp, 0, tmp.length);
            enc = tmp;
          }
        pos = 0;
        return enc;
      }
  }

  protected int engineDoFinal(byte[] out, int offset)
      throws ShortBufferException, IllegalBlockSizeException,
      BadPaddingException
  {
    byte[] result = engineDoFinal(EMPTY, 0, 0);
    if (out.length - offset < result.length)
      throw new ShortBufferException("need " + result.length + ", have "
                                     + (out.length - offset));
    System.arraycopy(result, 0, out, offset, result.length);
    return result.length;
  }

  protected int engineDoFinal(final byte[] input, final int offset,
                              final int length, final byte[] output,
                              final int outputOffset)
      throws ShortBufferException, IllegalBlockSizeException,
      BadPaddingException
  {
    byte[] result = engineDoFinal(input, offset, length);
    if (output.length - outputOffset < result.length)
      throw new ShortBufferException("need " + result.length + ", have "
                                     + (output.length - outputOffset));
    System.arraycopy(result, 0, output, outputOffset, result.length);
    return result.length;
  }

  /**
   * Decrypts the ciphertext, employing RSA blinding if possible.
   */
  private byte[] rsaDecrypt(BigInteger enc)
  {
    if (random == null)
      random = new SecureRandom();
    BigInteger n = decipherKey.getModulus();
    BigInteger r = null;
    BigInteger pubExp = null;
    if (blindingKey != null)
      pubExp = blindingKey.getPublicExponent();
    if (pubExp != null && (decipherKey instanceof RSAPrivateCrtKey))
      pubExp = ((RSAPrivateCrtKey) decipherKey).getPublicExponent();
    if (pubExp != null)
      {
        r = new BigInteger(n.bitLength() - 1, random);
        enc = r.modPow(pubExp, n).multiply(enc).mod(n);
      }
    BigInteger dec = enc.modPow(decipherKey.getPrivateExponent(), n);
    if (pubExp != null)
      dec = dec.multiply(r.modInverse(n)).mod(n);
    return dec.toByteArray();
  }
}