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/* RSASignatureFactory.java -- A Factory class to instantiate RSA Signatures

   Copyright (C) 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.java.security.sig.rsa;

import java.util.Collections;

import java.util.HashSet;

import java.util.Iterator;

import java.util.Set;

import gnu.java.security.Registry;

import gnu.java.security.hash.HashFactory;

import gnu.java.security.hash.IMessageDigest;

import gnu.java.security.sig.ISignature;

/**

 * A Factory class to instantiate RSA Signature classes.

 */

public class RSASignatureFactory

{

  private static Set names;

  /**

   * Private constructor to enforce usage through Factory (class) methods.

   */

  private RSASignatureFactory()

  {

    super();

  }

  /**

   * Returns a new instance of an RSA Signature given its name. The name of an

   * RSA Signature always starts with <code>rsa-</code>, followed by either

   * <code>pss</code> or <code>pkcs1_v1.5</code>. An optional message digest

   * name, to be used with the RSA signature may be specified by appending the

   * hyphen chanaracter <code>-</code> followed by the canonical message digest

   * algorithm name. When no message digest algorithm name is given, SHA-160 is

   * used.

   *

   * @param name the composite RSA signature name.

   * @return a new instance of an RSA Signature algorithm implementation.

   * Returns <code>null</code> if the given name does not correspond to any

   * supported RSA Signature encoding and message digest combination.

   */

  public static final ISignature getInstance(String name)

  {

    if (name == null)

      return null;

    name = name.trim();

    if (name.length() == 0)

      return null;

    name = name.toLowerCase();

    if (! name.startsWith(Registry.RSA_SIG_PREFIX))

      return null;

    name = name.substring(Registry.RSA_SIG_PREFIX.length()).trim();

    if (name.startsWith(Registry.RSA_PSS_ENCODING))

      return getPSSSignature(name);

    else if (name.startsWith(Registry.RSA_PKCS1_V1_5_ENCODING))

      return getPKCS1Signature(name);

    else

      return null;

  }

  /**

   * Returns a {@link Set} of names of <i>RSA</i> signatures supported by this

   * <i>Factory</i>.

   *

   * @return a {@link Set} of RSA Signature algorithm names (Strings).

   */

  public static synchronized final Set getNames()

  {

    if (names == null)

      {

        Set hashNames = HashFactory.getNames();

        HashSet hs = new HashSet();

        for (Iterator it = hashNames.iterator(); it.hasNext();)

          {

            String mdName = (String) it.next();

            hs.add(Registry.RSA_PSS_SIG + "-" + mdName);

          }

        hs.add(Registry.RSA_PKCS1_V1_5_SIG + "-" + Registry.MD2_HASH);

        hs.add(Registry.RSA_PKCS1_V1_5_SIG + "-" + Registry.MD5_HASH);

        hs.add(Registry.RSA_PKCS1_V1_5_SIG + "-" + Registry.SHA160_HASH);

        hs.add(Registry.RSA_PKCS1_V1_5_SIG + "-" + Registry.SHA256_HASH);

        hs.add(Registry.RSA_PKCS1_V1_5_SIG + "-" + Registry.SHA384_HASH);

        hs.add(Registry.RSA_PKCS1_V1_5_SIG + "-" + Registry.SHA512_HASH);

        names = Collections.unmodifiableSet(hs);

      }

    return names;

  }

  private static final ISignature getPSSSignature(String name)

  {

    name = name.substring(Registry.RSA_PSS_ENCODING.length()).trim();

    // remove the hyphen if found at the beginning

    if (name.startsWith("-"))

      name = name.substring(1).trim();

    IMessageDigest md;

    if (name.length() == 0)

      md = HashFactory.getInstance(Registry.SHA160_HASH);

    else

      {

        // check if there is such a hash

        md = HashFactory.getInstance(name);

        if (md == null)

          return null;

      }

    ISignature result = new RSAPSSSignature(md, 0);

    return result;

  }

  private static final ISignature getPKCS1Signature(String name)

  {

    name = name.substring(Registry.RSA_PKCS1_V1_5_ENCODING.length()).trim();

    // remove the hyphen if found at the beginning

    if (name.startsWith("-"))

      name = name.substring(1).trim();

    IMessageDigest md;

    if (name.length() == 0)

      md = HashFactory.getInstance(Registry.SHA160_HASH);

    else

      {

        // check if there is such a hash

        md = HashFactory.getInstance(name);

        if (md == null)

          return null;

      }

    ISignature result = new RSAPKCS1V1_5Signature(md);

    return result;

  }

}