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	/*
	* Copyright (c) 2016, 2021, 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 sun.security.provider;

	import java.math.BigInteger;
	import java.security.DigestException;
	import java.security.MessageDigest;
	import java.security.NoSuchAlgorithmException;
	import java.security.NoSuchProviderException;
	import java.security.SecureRandomParameters;
	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.HexFormat;
	import java.util.List;

	public class HashDrbg extends AbstractHashDrbg {

	private static final byte[] ZERO = new byte[1];
	private static final byte[] ONE = new byte[]{1};

	private MessageDigest digest;

	private byte[] v;
	private byte[] c;

	public HashDrbg(SecureRandomParameters params) {
	mechName = "Hash_DRBG";
	configure(params);
	}

	/**
	* This call, used by the constructors, instantiates the digest.
	*/
	@Override
	protected void initEngine() {
	try {
	/*
	* Use the local SUN implementation to avoid native
	* performance overhead.
	*/
	digest = MessageDigest.getInstance(algorithm, "SUN");
	} catch (NoSuchProviderException \| NoSuchAlgorithmException e) {
	// Fallback to any available.
	try {
	digest = MessageDigest.getInstance(algorithm);
	} catch (NoSuchAlgorithmException exc) {
	throw new InternalError(
	"internal error: " + algorithm + " not available.", exc);
	}
	}
	}

	private byte[] hashDf(int requested, List<byte[]> inputs) {
	return hashDf(digest, outLen, requested, inputs);
	}

	/**
	* A hash-based derivation function defined in NIST SP 800-90Ar1 10.3.1.
	* The function is used inside Hash_DRBG, and can also be used as an
	* approved conditioning function as described in 800-90B 6.4.2.2.
	*
	* Note: In each current call, requested is seedLen, therefore small,
	* no need to worry about overflow.
	*
	* @param digest a {@code MessageDigest} object in reset state
	* @param outLen {@link MessageDigest#getDigestLength} of {@code digest}
	* @param requested requested output length, in bytes
	* @param inputs input data
	* @return the condensed/expanded output
	*/
	public static byte[] hashDf(MessageDigest digest, int outLen,
	int requested, List<byte[]> inputs) {
	// 1. temp = the Null string.
	// 2. len = upper_int(no_of_bits_to_return / outLen)
	int len = (requested + outLen - 1) / outLen;
	byte[] temp = new byte[len * outLen];
	// 3. counter = 0x01
	int counter = 1;

	// 4. For i = 1 to len do
	for (int i=0; i<len; i++) {
	// 4.1 temp = temp
	// \|\| Hash (counter \|\| no_of_bits_to_return \|\| input_string).
	digest.update((byte) counter);
	digest.update((byte)(requested >> 21)); // requested*8 as int32
	digest.update((byte)(requested >> 13));
	digest.update((byte)(requested >> 5));
	digest.update((byte)(requested << 3));
	for (byte[] input : inputs) {
	digest.update(input);
	}
	try {
	digest.digest(temp, i * outLen, outLen);
	} catch (DigestException e) {
	throw new AssertionError("will not happen", e);
	}
	// 4.2 counter = counter + 1
	counter++;
	}
	// 5. requested_bits = leftmost (temp, no_of_bits_to_return).
	return temp.length == requested? temp: Arrays.copyOf(temp, requested);
	// 6. Return
	}

	// This method is used by both instantiation and reseeding.
	@Override
	protected final synchronized void hashReseedInternal(List<byte[]> inputs) {

	// 800-90Ar1 10.1.1.2: Instantiate Process.
	// 800-90Ar1 10.1.1.3: Reseed Process.
	byte[] seed;

	// Step 2: seed = Hash_df (seed_material, seedlen).
	if (v != null) {
	// Step 1 of 10.1.1.3: Prepend 0x01 \|\| V
	inputs.add(0, ONE);
	inputs.add(1, v);
	seed = hashDf(seedLen, inputs);
	} else {
	seed = hashDf(seedLen, inputs);
	}

	// Step 3. V = seed.
	v = seed;

	// Step 4. C = Hash_df ((0x00 \|\| V), seedlen).
	inputs = new ArrayList<>(2);
	inputs.add(ZERO);
	inputs.add(v);
	c = hashDf(seedLen, inputs);

	// Step 5. reseed_counter = 1.
	reseedCounter = 1;

	//status();

	// Step 6: Return
	}

	private void status() {
	if (debug != null) {
	debug.println(this, "V = " + HexFormat.of().formatHex(v));
	debug.println(this, "C = " + HexFormat.of().formatHex(c));
	debug.println(this, "reseed counter = " + reseedCounter);
	}
	}

	/**
	* Adds byte arrays into an existing one.
	*
	* @param out existing array
	* @param data more arrays, can be of different length
	*/
	private static void addBytes(byte[] out, int len, byte[]... data) {
	for (byte[] d: data) {
	int dlen = d.length;
	int carry = 0;
	for (int i = 0; i < len; i++) {
	int sum = (out[len - i - 1] & 0xff) + carry;
	if (i < dlen) {
	sum += (d[dlen - i - 1] & 0xff);
	}
	out[len - i - 1] = (byte) sum;
	carry = sum >> 8;
	if (i >= dlen - 1 && carry == 0) break;
	}
	}
	}

	/**
	* Generates a user-specified number of random bytes.
	*
	* @param result the array to be filled in with random bytes.
	*/
	@Override
	public final synchronized void generateAlgorithm(
	byte[] result, byte[] additionalInput) {

	if (debug != null) {
	debug.println(this, "generateAlgorithm");
	}

	// 800-90Ar1 10.1.1.4: Hash_DRBG_Generate Process

	// Step 1: Check reseed_counter. Will not fail. Already checked in
	// AbstractDrbg#engineNextBytes.

	// Step 2: additional_input
	if (additionalInput != null) {
	digest.update((byte)2);
	digest.update(v);
	digest.update(additionalInput);
	addBytes(v, seedLen, digest.digest());
	}

	// Step 3. Hashgen (requested_number_of_bits, V).
	hashGen(result, v);

	// Step 4. H = Hash (0x03 \|\| V).
	digest.update((byte)3);
	digest.update(v);
	byte[] h = digest.digest();

	// Step 5. V = (V + H + C + reseed_counter) mod 2seedlen.
	byte[] rcBytes;
	if (reseedCounter < 256) {
	rcBytes = new byte[]{(byte)reseedCounter};
	} else {
	rcBytes = BigInteger.valueOf(reseedCounter).toByteArray();
	}
	addBytes(v, seedLen, h, c, rcBytes);

	// Step 6. reseed_counter = reseed_counter + 1.
	reseedCounter++;

	//status();

	// Step 7: Return.
	}

	// 800-90Ar1 10.1.1.4: Hashgen
	private void hashGen(byte[] output, byte[] v) {

	// Step 2. data = V
	byte[] data = v;

	// Step 3: W is output not filled

	// Step 4: For i = 1 to m
	int pos = 0;
	int len = output.length;

	while (len > 0) {
	// Step 4.1 w = Hash (data).
	digest.update(data);
	if (len < outLen) {
	// Step 4.2 W = W \|\| w.
	byte[] out = digest.digest();
	System.arraycopy(out, 0, output, pos, len);
	Arrays.fill(out, (byte)0);
	} else {
	try {
	// Step 4.2 digest into right position, no need to cat
	digest.digest(output, pos, outLen);
	} catch (DigestException e) {
	throw new AssertionError("will not happen", e);
	}
	}
	len -= outLen;
	if (len <= 0) {
	// shortcut, so that data and pos needn't be updated
	break;
	}
	// Step 4.3 data = (data + 1) mod 2^seedlen.
	if (data == v) {
	data = Arrays.copyOf(v, v.length);
	}
	addBytes(data, seedLen, ONE);
	pos += outLen;
	}

	// Step 5: No need to truncate
	// Step 6: Return
	}
	}

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