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/*
 * Copyright (c) 2000 - 2006 The Legion Of The Bouncy Castle (http://www.bouncycastle.org)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files 
 * (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, 
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is 
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES 
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE 
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR 
 * IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. 
 */
 
package com.amazonaws.crypto;

import java.util.Hashtable;

/**
 * HMAC implementation based on RFC2104
 *
 * H(K XOR opad, H(K XOR ipad, text))
 */
public class HMac
    implements Mac
{
    private final static byte IPAD = (byte)0x36;
    private final static byte OPAD = (byte)0x5C;

    private Digest digest;
    private int digestSize;
    private int blockLength = 64;
    private byte[] inputPad;
    private byte[] outputPad;

    private static Hashtable blockLengths;
    
    static
    {
        blockLengths = new Hashtable();
        blockLengths.put("SHA-1", new Integer(64));
    }
    
    public HMac(
        Digest digest)
    {
        this.digest = digest;
        digestSize = digest.getDigestSize();
        
        Integer  b = (Integer)blockLengths.get(digest.getAlgorithmName());
        
        if (b == null)
        {
            throw new IllegalArgumentException("unknown digest passed");
        }

        blockLength = b.intValue();

        inputPad = new byte[blockLength];
        outputPad = new byte[blockLength];
    }

    public String getAlgorithmName()
    {
        return digest.getAlgorithmName() + "/HMAC";
    }

    public Digest getUnderlyingDigest()
    {
        return digest;
    }

    public void init(byte[] key)
    {
        digest.reset();

        if (key.length > blockLength)
        {
            digest.update(key, 0, key.length);
            digest.doFinal(inputPad, 0);
            for (int i = digestSize; i < inputPad.length; i++)
            {
                inputPad[i] = 0;
            }
        }
        else
        {
            System.arraycopy(key, 0, inputPad, 0, key.length);
            for (int i = key.length; i < inputPad.length; i++)
            {
                inputPad[i] = 0;
            }
        }

        outputPad = new byte[inputPad.length];
        System.arraycopy(inputPad, 0, outputPad, 0, inputPad.length);

        for (int i = 0; i < inputPad.length; i++)
        {
            inputPad[i] ^= IPAD;
        }

        for (int i = 0; i < outputPad.length; i++)
        {
            outputPad[i] ^= OPAD;
        }

        digest.update(inputPad, 0, inputPad.length);
    }

    public int getMacSize()
    {
        return digestSize;
    }

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

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

    public int doFinal(
        byte[] out,
        int outOff)
    {
        byte[] tmp = new byte[digestSize];
        digest.doFinal(tmp, 0);

        digest.update(outputPad, 0, outputPad.length);
        digest.update(tmp, 0, tmp.length);

        int     len = digest.doFinal(out, outOff);

        reset();

        return len;
    }

    /**
     * Reset the mac generator.
     */
    public void reset()
    {
        /*
         * reset the underlying digest.
         */
        digest.reset();

        /*
         * reinitialize the digest.
         */
        digest.update(inputPad, 0, inputPad.length);
    }
}




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