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	/*
	* Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code 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
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package com.sun.crypto.provider;

	import java.nio.ByteBuffer;
	import java.security.Key;
	import java.security.InvalidKeyException;
	import java.security.spec.AlgorithmParameterSpec;
	import java.util.Arrays;
	import java.util.Objects;

	import sun.security.util.math.*;
	import sun.security.util.math.intpoly.*;

	/**
	* This class represents the Poly1305 function defined in RFC 7539.
	*
	* This function is used in the implementation of ChaCha20/Poly1305
	* AEAD mode.
	*/
	final class Poly1305 {

	private static final int KEY_LENGTH = 32;
	private static final int RS_LENGTH = KEY_LENGTH / 2;
	private static final int BLOCK_LENGTH = 16;
	private static final int TAG_LENGTH = 16;

	private static final IntegerFieldModuloP ipl1305 =
	new IntegerPolynomial1305();

	private byte[] keyBytes;
	private final byte[] block = new byte[BLOCK_LENGTH];
	private int blockOffset;

	private IntegerModuloP r;
	private IntegerModuloP s;
	private MutableIntegerModuloP a;
	private final MutableIntegerModuloP n = ipl1305.get1().mutable();

	Poly1305() { }

	/**
	* Initialize the Poly1305 object
	*
	* @param newKey the {@code Key} which will be used for the authentication.
	* @param params this parameter is unused.
	*
	* @throws InvalidKeyException if {@code newKey} is {@code null} or is
	* not 32 bytes in length.
	*/
	void engineInit(Key newKey, AlgorithmParameterSpec params)
	throws InvalidKeyException {
	Objects.requireNonNull(newKey, "Null key provided during init");
	keyBytes = newKey.getEncoded();
	if (keyBytes == null) {
	throw new InvalidKeyException("Key does not support encoding");
	} else if (keyBytes.length != KEY_LENGTH) {
	throw new InvalidKeyException("Incorrect length for key: " +
	keyBytes.length);
	}

	engineReset();
	setRSVals();
	}

	/**
	* Returns the length of the MAC (authentication tag).
	*
	* @return the length of the auth tag, which is always 16 bytes.
	*/
	int engineGetMacLength() {
	return TAG_LENGTH;
	}

	/**
	* Reset the Poly1305 object, discarding any current operation but
	* maintaining the same key.
	*/
	void engineReset() {
	// Clear the block and reset the offset
	Arrays.fill(block, (byte)0);
	blockOffset = 0;
	// Discard any previous accumulator and start at zero
	a = ipl1305.get0().mutable();
	}

	/**
	* Update the MAC with bytes from a {@code ByteBuffer}
	*
	* @param buf the {@code ByteBuffer} containing the data to be consumed.
	* Upon return the buffer's position will be equal to its limit.
	*/
	void engineUpdate(ByteBuffer buf) {
	int remaining = buf.remaining();
	while (remaining > 0) {
	int bytesToWrite = Integer.min(remaining,
	BLOCK_LENGTH - blockOffset);

	if (bytesToWrite >= BLOCK_LENGTH) {
	// If bytes to write == BLOCK_LENGTH, then we have no
	// left-over data from previous updates and we can create
	// the IntegerModuloP directly from the input buffer.
	processBlock(buf, bytesToWrite);
	} else {
	// We have some left-over data from previous updates, so
	// copy that into the holding block until we get a full block.
	buf.get(block, blockOffset, bytesToWrite);
	blockOffset += bytesToWrite;

	if (blockOffset >= BLOCK_LENGTH) {
	processBlock(block, 0, BLOCK_LENGTH);
	blockOffset = 0;
	}
	}

	remaining -= bytesToWrite;
	}
	}

	/**
	* Update the MAC with bytes from an array.
	*
	* @param input the input bytes.
	* @param offset the starting index from which to update the MAC.
	* @param len the number of bytes to process.
	*/
	void engineUpdate(byte[] input, int offset, int len) {
	Objects.checkFromIndexSize(offset, len, input.length);
	if (blockOffset > 0) {
	// We have some left-over data from previous updates
	int blockSpaceLeft = BLOCK_LENGTH - blockOffset;
	if (len < blockSpaceLeft) {
	System.arraycopy(input, offset, block, blockOffset, len);
	blockOffset += len;
	return; // block wasn't filled
	} else {
	System.arraycopy(input, offset, block, blockOffset,
	blockSpaceLeft);
	offset += blockSpaceLeft;
	len -= blockSpaceLeft;
	processBlock(block, 0, BLOCK_LENGTH);
	blockOffset = 0;
	}
	}
	while (len >= BLOCK_LENGTH) {
	processBlock(input, offset, BLOCK_LENGTH);
	offset += BLOCK_LENGTH;
	len -= BLOCK_LENGTH;
	}
	if (len > 0) { // and len < BLOCK_LENGTH
	System.arraycopy(input, offset, block, 0, len);
	blockOffset = len;
	}
	}

	/**
	* Update the MAC with a single byte of input
	*
	* @param input the byte to update the MAC with.
	*/
	void engineUpdate(byte input) {
	assert (blockOffset < BLOCK_LENGTH);
	// we can't hold fully filled unprocessed block
	block[blockOffset++] = input;

	if (blockOffset == BLOCK_LENGTH) {
	processBlock(block, 0, BLOCK_LENGTH);
	blockOffset = 0;
	}
	}


	/**
	* Finish the authentication operation and reset the MAC for a new
	* authentication operation.
	*
	* @return the authentication tag as a byte array.
	*/
	byte[] engineDoFinal() {
	byte[] tag = new byte[BLOCK_LENGTH];

	// Finish up: process any remaining data < BLOCK_SIZE, then
	// create the tag from the resulting little-endian integer.
	if (blockOffset > 0) {
	processBlock(block, 0, blockOffset);
	blockOffset = 0;
	}

	// Add in the s-half of the key to the accumulator
	a.addModPowerTwo(s, tag);

	// Reset for the next auth
	engineReset();
	return tag;
	}

	/**
	* Process a single block of data. This should only be called
	* when the block array is complete. That may not necessarily
	* be a full 16 bytes if the last block has less than 16 bytes.
	*/
	private void processBlock(ByteBuffer buf, int len) {
	n.setValue(buf, len, (byte)0x01);
	a.setSum(n); // a += (n \| 0x01)
	a.setProduct(r); // a = (a * r) % p
	}

	private void processBlock(byte[] block, int offset, int length) {
	Objects.checkFromIndexSize(offset, length, block.length);
	n.setValue(block, offset, length, (byte)0x01);
	a.setSum(n); // a += (n \| 0x01)
	a.setProduct(r); // a = (a * r) % p
	}

	/**
	* Partition the authentication key into the R and S components, clamp
	* the R value, and instantiate IntegerModuloP objects to R and S's
	* numeric values.
	*/
	private void setRSVals() {
	// Clamp the bytes in the "r" half of the key.
	keyBytes[3] &= 15;
	keyBytes[7] &= 15;
	keyBytes[11] &= 15;
	keyBytes[15] &= 15;
	keyBytes[4] &= 252;
	keyBytes[8] &= 252;
	keyBytes[12] &= 252;

	// Create IntegerModuloP elements from the r and s values
	r = ipl1305.getElement(keyBytes, 0, RS_LENGTH, (byte)0);
	s = ipl1305.getElement(keyBytes, RS_LENGTH, RS_LENGTH, (byte)0);
	}
	}

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