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	/*
	* Copyright (c) 1998, 2020, 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.io.IOException;
	import java.security.MessageDigest;
	import java.security.SecureRandomSpi;
	import java.security.NoSuchAlgorithmException;
	import java.security.NoSuchProviderException;

	/**
	* <p>This class provides a crytpographically strong pseudo-random number
	* generator based on the SHA-1 hash algorithm.
	*
	* <p>Note that if a seed is not provided, we attempt to provide sufficient
	* seed bytes to completely randomize the internal state of the generator
	* (20 bytes). However, our seed generation algorithm has not been thoroughly
	* studied or widely deployed.
	*
	* <p>Also note that when a random object is deserialized,
	* <a href="#engineNextBytes(byte[])">engineNextBytes</a> invoked on the
	* restored random object will yield the exact same (random) bytes as the
	* original object. If this behaviour is not desired, the restored random
	* object should be seeded, using
	* <a href="#engineSetSeed(byte[])">engineSetSeed</a>.
	*
	* @author Benjamin Renaud
	* @author Josh Bloch
	* @author Gadi Guy
	*/

	public final class SecureRandom extends SecureRandomSpi
	implements java.io.Serializable {

	@java.io.Serial
	private static final long serialVersionUID = 3581829991155417889L;

	private static final int DIGEST_SIZE = 20;
	private transient MessageDigest digest;
	private byte[] state;
	private byte[] remainder;
	private int remCount;

	/**
	* An empty constructor that creates an unseeded SecureRandom object.
	* <p>
	* Unless the user calls setSeed(), the first call to engineGetBytes()
	* will have the SeedGenerator provide sufficient seed bytes to
	* completely randomize the internal state of the generator (20 bytes).
	* Note that the old threaded seed generation algorithm is provided
	* only as a fallback, and has not been thoroughly studied or widely
	* deployed.
	* <p>
	* The SeedGenerator relies on a VM-wide entropy pool to generate
	* seed bytes for these objects. The first time the SeedGenerator is
	* called, it may take several seconds of CPU time to initialize,
	* depending on the underlying hardware. Successive calls run
	* quickly because they rely on the same (internal) pseudo-random
	* number generator for their seed bits.
	*/
	public SecureRandom() {
	init(null);
	}

	/**
	* This constructor is used to instantiate the private seeder object
	* with a given seed from the SeedGenerator.
	*
	* @param seed the seed.
	*/
	private SecureRandom(byte[] seed) {
	init(seed);
	}

	/**
	* This call, used by the constructors, instantiates the SHA digest
	* and sets the seed, if given.
	*/
	private void init(byte[] seed) {
	try {
	/*
	* Use the local SUN implementation to avoid native
	* performance overhead.
	*/
	digest = MessageDigest.getInstance("SHA", "SUN");
	} catch (NoSuchProviderException \| NoSuchAlgorithmException e) {
	// Fallback to any available.
	try {
	digest = MessageDigest.getInstance("SHA");
	} catch (NoSuchAlgorithmException exc) {
	throw new InternalError(
	"internal error: SHA-1 not available.", exc);
	}
	}

	if (seed != null) {
	engineSetSeed(seed);
	}
	}

	/**
	* Returns the given number of seed bytes, computed using the seed
	* generation algorithm that this class uses to seed itself. This
	* call may be used to seed other random number generators. While
	* we attempt to return a "truly random" sequence of bytes, we do not
	* know exactly how random the bytes returned by this call are. (See
	* the empty constructor <a href = "#SecureRandom">SecureRandom</a>
	* for a brief description of the underlying algorithm.)
	* The prudent user will err on the side of caution and get extra
	* seed bytes, although it should be noted that seed generation is
	* somewhat costly.
	*
	* @param numBytes the number of seed bytes to generate.
	*
	* @return the seed bytes.
	*/
	@Override
	public byte[] engineGenerateSeed(int numBytes) {
	// Neither of the SeedGenerator implementations require
	// locking, so no sync needed here.
	byte[] b = new byte[numBytes];
	SeedGenerator.generateSeed(b);
	return b;
	}

	/**
	* Reseeds this random object. The given seed supplements, rather than
	* replaces, the existing seed. Thus, repeated calls are guaranteed
	* never to reduce randomness.
	*
	* @param seed the seed.
	*/
	@Override
	public synchronized void engineSetSeed(byte[] seed) {
	if (state != null) {
	digest.update(state);
	for (int i = 0; i < state.length; i++) {
	state[i] = 0;
	}
	}
	state = digest.digest(seed);
	remCount = 0;
	}

	private static void updateState(byte[] state, byte[] output) {
	int last = 1;
	int v;
	byte t;
	boolean zf = false;

	// state(n + 1) = (state(n) + output(n) + 1) % 2^160;
	for (int i = 0; i < state.length; i++) {
	// Add two bytes
	v = (int)state[i] + (int)output[i] + last;
	// Result is lower 8 bits
	t = (byte)v;
	// Store result. Check for state collision.
	zf = zf \| (state[i] != t);
	state[i] = t;
	// High 8 bits are carry. Store for next iteration.
	last = v >> 8;
	}

	// Make sure at least one bit changes!
	if (!zf) {
	state[0]++;
	}
	}

	/**
	* This static object will be seeded by SeedGenerator, and used
	* to seed future instances of SHA1PRNG SecureRandoms.
	*
	* Bloch, Effective Java Second Edition: Item 71
	*/
	private static class SeederHolder {

	private static final SecureRandom seeder;

	static {
	/*
	* Call to SeedGenerator.generateSeed() to add additional
	* seed material (likely from the Native implementation).
	*/
	seeder = new SecureRandom(SeedGenerator.getSystemEntropy());
	byte [] b = new byte[DIGEST_SIZE];
	SeedGenerator.generateSeed(b);
	seeder.engineSetSeed(b);
	}
	}

	/**
	* Generates a user-specified number of random bytes.
	*
	* @param result the array to be filled in with random bytes.
	*/
	@Override
	public synchronized void engineNextBytes(byte[] result) {
	int index = 0;
	int todo;
	byte[] output = remainder;

	if (state == null) {
	byte[] seed = new byte[DIGEST_SIZE];
	SeederHolder.seeder.engineNextBytes(seed);
	state = digest.digest(seed);
	}

	// Use remainder from last time
	int r = remCount;
	if (r > 0) {
	// How many bytes?
	todo = (result.length - index) < (DIGEST_SIZE - r) ?
	(result.length - index) : (DIGEST_SIZE - r);
	// Copy the bytes, zero the buffer
	for (int i = 0; i < todo; i++) {
	result[i] = output[r];
	output[r++] = 0;
	}
	remCount += todo;
	index += todo;
	}

	// If we need more bytes, make them.
	while (index < result.length) {
	// Step the state
	digest.update(state);
	output = digest.digest();
	updateState(state, output);

	// How many bytes?
	todo = (result.length - index) > DIGEST_SIZE ?
	DIGEST_SIZE : result.length - index;
	// Copy the bytes, zero the buffer
	for (int i = 0; i < todo; i++) {
	result[index++] = output[i];
	output[i] = 0;
	}
	remCount += todo;
	}

	// Store remainder for next time
	remainder = output;
	remCount %= DIGEST_SIZE;
	}

	/*
	* readObject is called to restore the state of the random object from
	* a stream. We have to create a new instance of MessageDigest, because
	* it is not included in the stream (it is marked "transient").
	*
	* Note that the engineNextBytes() method invoked on the restored random
	* object will yield the exact same (random) bytes as the original.
	* If you do not want this behaviour, you should re-seed the restored
	* random object, using engineSetSeed().
	*/
	@java.io.Serial
	private void readObject(java.io.ObjectInputStream s)
	throws IOException, ClassNotFoundException {

	s.defaultReadObject ();

	try {
	/*
	* Use the local SUN implementation to avoid native
	* performance overhead.
	*/
	digest = MessageDigest.getInstance("SHA", "SUN");
	} catch (NoSuchProviderException \| NoSuchAlgorithmException e) {
	// Fallback to any available.
	try {
	digest = MessageDigest.getInstance("SHA");
	} catch (NoSuchAlgorithmException exc) {
	throw new InternalError(
	"internal error: SHA-1 not available.", exc);
	}
	}
	}
	}

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