Mega Code Archive
SHA_Interleave algorithm as described in section 3 1 of RFC2945
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/*
* JBoss, Home of Professional Open Source.
* Copyright 2008, Red Hat Middleware LLC, and individual contributors
* as indicated by the @author tags. See the copyright.txt file in the
* distribution for a full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
import java.io.ByteArrayOutputStream;
import java.security.MessageDigest;
import java.security.MessageDigestSpi;
import java.security.NoSuchAlgorithmException;
import java.security.ProviderException;
/** The SHA_Interleave algorithm as described in section 3.1 of RFC2945. This
needs an SHA MessageDigest provider to function.
@author Scott.Stark@jboss.org
@version $Revision: 85945 $
*/
public class SHAInterleave extends MessageDigestSpi
{
private static final int SHA_HASH_LEN = 20;
private ByteArrayOutputStream evenBytes;
private ByteArrayOutputStream oddBytes;
private int count;
private boolean skipLeadingZeros;
private MessageDigest sha;
/** Creates a new instance of SHAInterleave
@exception ProviderException thrown if MessageDigest.getInstance("SHA")
throws a NoSuchAlgorithmException.
*/
public SHAInterleave()
{
try
{
sha = MessageDigest.getInstance("SHA");
}
catch(NoSuchAlgorithmException e)
{
throw new ProviderException("Failed to obtain SHA MessageDigest");
}
evenBytes = new ByteArrayOutputStream();
oddBytes = new ByteArrayOutputStream();
engineReset();
}
protected int engineGetDigestLength()
{
return 2 * SHA_HASH_LEN;
}
/**
* Completes the digest computation by performing final
* operations such as padding. Once <code>engineDigest</code> has
* been called, the engine should be reset (see
* {@link #engineReset() engineReset}).
* Resetting is the responsibility of the
* engine implementor.
*
* @return the array of bytes for the resulting digest value.
*/
protected byte[] engineDigest()
{
byte[] E = evenBytes.toByteArray();
byte[] G = sha.digest(E);
// If the count is odd, drop the first byte
byte[] F = oddBytes.toByteArray();
int offset = 0;
if( count % 2 == 1 )
offset = 1;
sha.reset();
sha.update(F, offset, F.length-offset);
byte[] H = sha.digest();
int length = G.length + H.length;
byte[] digest = new byte[length];
for(int i = 0; i < G.length; ++i)
digest[2 * i] = G[i];
for(int i = 0; i < H.length; ++i)
digest[2 * i + 1] = H[i];
engineReset();
return digest;
}
/**
* Resets the digest for further use.
*/
protected void engineReset()
{
skipLeadingZeros = true;
count = 0;
evenBytes.reset();
oddBytes.reset();
sha.reset();
}
/**
* Updates the digest using the specified byte.
*
* @param input the byte to use for the update.
*/
protected void engineUpdate(byte input)
{
if( skipLeadingZeros == true && input == 0 )
return;
skipLeadingZeros = false;
if( count % 2 == 0 )
evenBytes.write(input);
else
oddBytes.write(input);
count ++;
}
/**
* Updates the digest using the specified array of bytes,
* starting at the specified offset.
*
* @param input the array of bytes to use for the update.
* @param offset the offset to start from in the array of bytes.
* @param len the input of bytes to use, starting at
* <code>offset</code>.
*/
protected void engineUpdate(byte[] input, int offset, int len)
{
for(int i = offset; i < offset+len; i ++)
engineUpdate(input[i]);
}
}
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