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The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. This jar contains APIs for JDK 1.5 and up. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.

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package org.bouncycastle.crypto.digests;

import org.bouncycastle.crypto.ExtendedDigest;
import org.bouncycastle.crypto.engines.ThreefishEngine;
import org.bouncycastle.crypto.params.SkeinParameters;
import org.bouncycastle.util.Memoable;

/**
 * Implementation of the Skein parameterised hash function in 256, 512 and 1024 bit block sizes,
 * based on the {@link ThreefishEngine Threefish} tweakable block cipher.
 * 
 * This is the 1.3 version of Skein defined in the Skein hash function submission to the NIST SHA-3
 * competition in October 2010.
 * 
 * Skein was designed by Niels Ferguson - Stefan Lucks - Bruce Schneier - Doug Whiting - Mihir
 * Bellare - Tadayoshi Kohno - Jon Callas - Jesse Walker.
 *
 * @see SkeinEngine
 * @see SkeinParameters
 */
public class SkeinDigest
    implements ExtendedDigest, Memoable
{
    /**
     * 256 bit block size - Skein-256
     */
    public static final int SKEIN_256 = SkeinEngine.SKEIN_256;
    /**
     * 512 bit block size - Skein-512
     */
    public static final int SKEIN_512 = SkeinEngine.SKEIN_512;
    /**
     * 1024 bit block size - Skein-1024
     */
    public static final int SKEIN_1024 = SkeinEngine.SKEIN_1024;

    private SkeinEngine engine;

    /**
     * Constructs a Skein digest with an internal state size and output size.
     *
     * @param stateSizeBits  the internal state size in bits - one of {@link #SKEIN_256}, {@link #SKEIN_512} or
     *                       {@link #SKEIN_1024}.
     * @param digestSizeBits the output/digest size to produce in bits, which must be an integral number of
     *                       bytes.
     */
    public SkeinDigest(int stateSizeBits, int digestSizeBits)
    {
        this.engine = new SkeinEngine(stateSizeBits, digestSizeBits);
        init(null);
    }

    public SkeinDigest(SkeinDigest digest)
    {
        this.engine = new SkeinEngine(digest.engine);
    }

    public void reset(Memoable other)
    {
        SkeinDigest d = (SkeinDigest)other;
        engine.reset(d.engine);
    }

    public Memoable copy()
    {
        return new SkeinDigest(this);
    }

    public String getAlgorithmName()
    {
        return "Skein-" + (engine.getBlockSize() * 8) + "-" + (engine.getOutputSize() * 8);
    }

    public int getDigestSize()
    {
        return engine.getOutputSize();
    }

    public int getByteLength()
    {
        return engine.getBlockSize();
    }

    /**
     * Optionally initialises the Skein digest with the provided parameters.

     * See {@link SkeinParameters} for details on the parameterisation of the Skein hash function.
     *
     * @param params the parameters to apply to this engine, or null to use no parameters.
     */
    public void init(SkeinParameters params)
    {
        engine.init(params);
    }

    public void reset()
    {
        engine.reset();
    }

    public void update(byte in)
    {
        engine.update(in);
    }

    public void update(byte[] in, int inOff, int len)
    {
        engine.update(in, inOff, len);
    }

    public int doFinal(byte[] out, int outOff)
    {
        return engine.doFinal(out, outOff);
    }

}