gnu.java.security.sig.rsa

Class EMSA_PSS

Implemented Interfaces:
Cloneable

public class EMSA_PSS
extends Object
implements Cloneable

An implementation of the EMSA-PSS encoding/decoding scheme.

EMSA-PSS coincides with EMSA4 in IEEE P1363a D5 except that EMSA-PSS acts on octet strings and not on bit strings. In particular, the bit lengths of the hash and the salt must be multiples of 8 in EMSA-PSS. Moreover, EMSA4 outputs an integer of a desired bit length rather than an octet string.

EMSA-PSS is parameterized by the choice of hash function Hash and mask generation function MGF. In this submission, MGF is based on a Hash definition that coincides with the corresponding definitions in IEEE Std 1363-2000, PKCS #1 v2.0, and the draft ANSI X9.44. In PKCS #1 v2.0 and the draft ANSI X9.44, the recommended hash function is SHA-1, while IEEE Std 1363-2000 recommends SHA-1 and RIPEMD-160.

References:

  1. RSA-PSS Signature Scheme with Appendix, part B.
    Primitive specification and supporting documentation.
    Jakob Jonsson and Burt Kaliski.

Method Summary

Object
clone()
This method may be called to create a new copy of the Object.
boolean
decode(byte[] mHash, byte[] EM, int emBits, int sLen)
The decoding operation EMSA-PSS-Decode recovers the message hash from an encoded message EM and compares it to the hash of M.
byte[]
encode(byte[] mHash, int emBits, byte[] salt)
The encoding operation EMSA-PSS-Encode computes the hash of a message M using a hash function and maps the result to an encoded message EM of a specified length using a mask generation function.
static EMSA_PSS
getInstance(String mdName)
Returns an instance of this object given a designated name of a hash function.

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

clone

public Object clone()
This method may be called to create a new copy of the Object. The typical behavior is as follows:
  • o == o.clone() is false
  • o.getClass() == o.clone().getClass() is true
  • o.equals(o) is true

However, these are not strict requirements, and may be violated if necessary. Of the three requirements, the last is the most commonly violated, particularly if the subclass does not override Object.equals(Object).

If the Object you call clone() on does not implement Cloneable (which is a placeholder interface), then a CloneNotSupportedException is thrown. Notice that Object does not implement Cloneable; this method exists as a convenience for subclasses that do.

Object's implementation of clone allocates space for the new Object using the correct class, without calling any constructors, and then fills in all of the new field values with the old field values. Thus, it is a shallow copy. However, subclasses are permitted to make a deep copy.

All array types implement Cloneable, and override this method as follows (it should never fail):

 public Object clone()
 {
   try
     {
       super.clone();
     }
   catch (CloneNotSupportedException e)
     {
       throw new InternalError(e.getMessage());
     }
 }
 
Overrides:
clone in interface Object
Returns:
a copy of the Object
See Also:
Cloneable

decode

public boolean decode(byte[] mHash,
                      byte[] EM,
                      int emBits,
                      int sLen)
The decoding operation EMSA-PSS-Decode recovers the message hash from an encoded message EM and compares it to the hash of M.
Parameters:
mHash - the byte sequence resulting from applying the message digest algorithm Hash to the message M.
EM - the encoded message, an octet string of length emLen = CEILING(emBits/8).
emBits - the maximal bit length of the integer OS2IP(EM), at least 8.hLen + 8.sLen + 9.
sLen - the length, in octets, of the expected salt.
Returns:
true if the result of the verification was consistent with the expected reseult; and false if the result was inconsistent.
Throws:
IllegalArgumentException - if an exception occurs.

encode

public byte[] encode(byte[] mHash,
                     int emBits,
                     byte[] salt)
The encoding operation EMSA-PSS-Encode computes the hash of a message M using a hash function and maps the result to an encoded message EM of a specified length using a mask generation function.
Parameters:
mHash - the byte sequence resulting from applying the message digest algorithm Hash to the message M.
emBits - the maximal bit length of the integer OS2IP(EM), at least 8.hLen + 8.sLen + 9.
salt - the salt to use when encoding the output.
Returns:
the encoded message EM, an octet string of length emLen = CEILING(emBits / 8).
Throws:
IllegalArgumentException - if an exception occurs.

getInstance

public static EMSA_PSS getInstance(String mdName)
Returns an instance of this object given a designated name of a hash function.
Parameters:
mdName - the canonical name of a hash function.
Returns:
an instance of this object configured for use with the designated options.

EMSA_PSS.java -- Copyright (C) 2001, 2002, 2003, 2006, 2010 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. You should have received a copy of the GNU General Public License 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 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.