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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 and up.

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package org.bouncycastle.crypto.digests;


/**
 * implementation of SHA-3 based on following KeccakNISTInterface.c from https://keccak.noekeon.org/
 * 
 * Following the naming conventions used in the C source code to enable easy review of the implementation.
 */
public class SHA3Digest
    extends KeccakDigest
{
    private static int checkBitLength(int bitLength)
    {
        switch (bitLength)
        {
        case 224:
        case 256:
        case 384:
        case 512:
            return bitLength;
        default:
            throw new IllegalArgumentException("'bitLength' " + bitLength + " not supported for SHA-3");
        }
    }

    public SHA3Digest()
    {
        this(256);
    }

    public SHA3Digest(int bitLength)
    {
        super(checkBitLength(bitLength));
    }

    public SHA3Digest(SHA3Digest source)
    {
        super(source);
    }

    public String getAlgorithmName()
    {
        return "SHA3-" + fixedOutputLength;
    }

    public int doFinal(byte[] out, int outOff)
    {
        absorbBits(0x02, 2);
        
        return super.doFinal(out,  outOff);
    }

    /*
     * TODO Possible API change to support partial-byte suffixes.
     */
    protected int doFinal(byte[] out, int outOff, byte partialByte, int partialBits)
    {
        if (partialBits < 0 || partialBits > 7)
        {
            throw new IllegalArgumentException("'partialBits' must be in the range [0,7]");
        }

        int finalInput = (partialByte & ((1 << partialBits) - 1)) | (0x02 << partialBits);
        int finalBits = partialBits + 2;

        if (finalBits >= 8)
        {
            absorb((byte)finalInput);
            finalBits -= 8;
            finalInput >>>= 8;
        }

        return super.doFinal(out, outOff, (byte)finalInput, finalBits);
    }
}