/*
 * Copyright (c) 1996, 2016, 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
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 */

package sun.security.provider;

/**
 * This class generates seeds for the SHA1PRNG cryptographically strong
 * random number generator.
 * <p>
 * The seed is produced using one of two techniques, via a computation
 * of current system activity or from an entropy gathering device.
 * <p>
 * In the default technique the seed is produced by counting the
 * number of times the VM manages to loop in a given period. This number
 * roughly reflects the machine load at that point in time.
 * The samples are translated using a permutation (s-box)
 * and then XORed together. This process is non linear and
 * should prevent the samples from "averaging out". The s-box
 * was designed to have even statistical distribution; it's specific
 * values are not crucial for the security of the seed.
 * We also create a number of sleeper threads which add entropy
 * to the system by keeping the scheduler busy.
 * Twenty such samples should give us roughly 160 bits of randomness.
 * <p>
 * These values are gathered in the background by a daemon thread
 * thus allowing the system to continue performing it's different
 * activites, which in turn add entropy to the random seed.
 * <p>
 * The class also gathers miscellaneous system information, some
 * machine dependent, some not. This information is then hashed together
 * with the 20 seed bytes.
 * <p>
 * The alternative to the above approach is to acquire seed material
 * from an entropy gathering device, such as /dev/random. This can be
 * accomplished by setting the value of the {@code securerandom.source}
 * Security property to a URL specifying the location of the entropy
 * gathering device, or by setting the {@code java.security.egd} System
 * property.
 * <p>
 * In the event the specified URL cannot be accessed the default
 * threading mechanism is used.
 *
 * @author Joshua Bloch
 * @author Gadi Guy
 */

import java.security.*;
import java.io.*;
import java.util.Properties;
import java.util.Enumeration;
import java.net.*;
import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Random;
import sun.security.util.Debug;

abstract class SeedGenerator {

    // Static instance is created at link time
    private static SeedGenerator instance;

    private static final Debug debug = Debug.getInstance("provider");

    // Static initializer to hook in selected or best performing generator
    static {
        String egdSource = SunEntries.getSeedSource();

        /*
         * Try the URL specifying the source (e.g. file:/dev/random)
         *
         * The URLs "file:/dev/random" or "file:/dev/urandom" are used to
         * indicate the SeedGenerator should use OS support, if available.
         *
         * On Windows, this causes the MS CryptoAPI seeder to be used.
         *
         * On Solaris/Linux/MacOS, this is identical to using
         * URLSeedGenerator to read from /dev/[u]random
         */
        if (egdSource.equals(SunEntries.URL_DEV_RANDOM) ||
                egdSource.equals(SunEntries.URL_DEV_URANDOM)) {
            try {
                instance = new NativeSeedGenerator(egdSource);
                if (debug != null) {
                    debug.println(
                        "Using operating system seed generator" + egdSource);
                }
            } catch (IOException e) {
                if (debug != null) {
                    debug.println("Failed to use operating system seed "
                                  + "generator: " + e.toString());
                }
            }
        } else if (!egdSource.isEmpty()) {
            try {
                instance = new URLSeedGenerator(egdSource);
                if (debug != null) {
                    debug.println("Using URL seed generator reading from "
                                  + egdSource);
                }
            } catch (IOException e) {
                if (debug != null) {
                    debug.println("Failed to create seed generator with "
                                  + egdSource + ": " + e.toString());
                }
            }
        }

        // Fall back to ThreadedSeedGenerator
        if (instance == null) {
            if (debug != null) {
                debug.println("Using default threaded seed generator");
            }
            instance = new ThreadedSeedGenerator();
        }
    }

    /**
     * Fill result with bytes from the queue. Wait for it if it isn't ready.
     */
    public static void generateSeed(byte[] result) {
        instance.getSeedBytes(result);
    }

    abstract void getSeedBytes(byte[] result);

    /**
     * Retrieve some system information, hashed.
     */
    static byte[] getSystemEntropy() {
        final MessageDigest md;

        try {
            md = MessageDigest.getInstance("SHA");
        } catch (NoSuchAlgorithmException nsae) {
            throw new InternalError("internal error: SHA-1 not available.",
                    nsae);
        }

        // The current time in millis
        byte b =(byte)System.currentTimeMillis();
        md.update(b);

        java.security.AccessController.doPrivileged
            (new java.security.PrivilegedAction<>() {
                @Override
                public Void run() {
                    try {
                        // System properties can change from machine to machine
                        Properties p = System.getProperties();
                        for (String s: p.stringPropertyNames()) {
                            md.update(s.getBytes());
                            md.update(p.getProperty(s).getBytes());
                        }

                        // Include network adapter names (and a Mac address)
                        addNetworkAdapterInfo(md);

                        // The temporary dir
                        File f = new File(p.getProperty("java.io.tmpdir"));
                        int count = 0;
                        try (
                            DirectoryStream<Path> stream =
                                Files.newDirectoryStream(f.toPath())) {
                            // We use a Random object to choose what file names
                            // should be used. Otherwise on a machine with too
                            // many files, the same first 1024 files always get
                            // used. Any, We make sure the first 512 files are
                            // always used.
                            Random r = new Random();
                            for (Path entry: stream) {
                                if (count < 512 || r.nextBoolean()) {
                                    md.update(entry.getFileName()
                                        .toString().getBytes());
                                }
                                if (count++ > 1024) {
                                    break;
                                }
                            }
                        }
                    } catch (Exception ex) {
                        md.update((byte)ex.hashCode());
                    }

                    // get Runtime memory stats
                    Runtime rt = Runtime.getRuntime();
                    byte[] memBytes = longToByteArray(rt.totalMemory());
                    md.update(memBytes, 0, memBytes.length);
                    memBytes = longToByteArray(rt.freeMemory());
                    md.update(memBytes, 0, memBytes.length);

                    return null;
                }
            });
        return md.digest();
    }

    /*
     * Include network adapter names and, if available, a Mac address
     *
     * See also java.util.concurrent.ThreadLocalRandom.initialSeed()
     */
    private static void addNetworkAdapterInfo(MessageDigest md) {

        try {
            Enumeration<NetworkInterface> ifcs =
                NetworkInterface.getNetworkInterfaces();
            while (ifcs.hasMoreElements()) {
                NetworkInterface ifc = ifcs.nextElement();
                md.update(ifc.toString().getBytes());
                if (!ifc.isVirtual()) { // skip fake addresses
                    byte[] bs = ifc.getHardwareAddress();
                    if (bs != null) {
                        md.update(bs);
                        break;
                    }
                }
            }
        } catch (Exception ignore) {
        }
    }

    /**
     * Helper function to convert a long into a byte array (least significant
     * byte first).
     */
    private static byte[] longToByteArray(long l) {
        byte[] retVal = new byte[8];

        for (int i=0; i<8; i++) {
            retVal[i] = (byte) l;
            l >>= 8;
        }

        return retVal;
    }

    /*
    // This method helps the test utility receive unprocessed seed bytes.
    public static int genTestSeed() {
        return myself.getByte();
    }
    */


    private static class ThreadedSeedGenerator extends SeedGenerator
            implements Runnable {
        // Queue is used to collect seed bytes
        private byte[] pool;
        private int start, end, count;

        // Thread group for our threads
        ThreadGroup seedGroup;

        /**
         * The constructor is only called once to construct the one
         * instance we actually use. It instantiates the message digest
         * and starts the thread going.
         */
        ThreadedSeedGenerator() {
            pool = new byte[20];
            start = end = 0;

            MessageDigest digest;

            try {
                digest = MessageDigest.getInstance("SHA");
            } catch (NoSuchAlgorithmException e) {
                throw new InternalError("internal error: SHA-1 not available."
                        , e);
            }

            final ThreadGroup[] finalsg = new ThreadGroup[1];
            Thread t = java.security.AccessController.doPrivileged
                (new java.security.PrivilegedAction<>() {
                        @Override
                        public Thread run() {
                            ThreadGroup parent, group =
                                Thread.currentThread().getThreadGroup();
                            while ((parent = group.getParent()) != null) {
                                group = parent;
                            }
                            finalsg[0] = new ThreadGroup
                                (group, "SeedGenerator ThreadGroup");
                            Thread newT = new Thread(finalsg[0],
                                ThreadedSeedGenerator.this,
                                "SeedGenerator Thread",
                                0,
                                false);
                            newT.setPriority(Thread.MIN_PRIORITY);
                            newT.setDaemon(true);
                            return newT;
                        }
                    });
            seedGroup = finalsg[0];
            t.start();
        }

        /**
         * This method does the actual work. It collects random bytes and
         * pushes them into the queue.
         */
        @Override
        public final void run() {
            try {
                while (true) {
                    // Queue full? Wait till there's room.
                    synchronized(this) {
                        while (count >= pool.length) {
                            wait();
                        }
                    }

                    int counter, quanta;
                    byte v = 0;

                    // Spin count must not be under 64000
                    for (counter = quanta = 0;
                            (counter < 64000) && (quanta < 6); quanta++) {

                        // Start some noisy threads
                        try {
                            BogusThread bt = new BogusThread();
                            Thread t = new Thread
                                (seedGroup, bt, "SeedGenerator Thread", 0,
                                        false);
                            t.start();
                        } catch (Exception e) {
                            throw new InternalError("internal error: " +
                                "SeedGenerator thread creation error.", e);
                        }

                        // We wait 250milli quanta, so the minimum wait time
                        // cannot be under 250milli.
                        int latch = 0;
                        long startTime = System.nanoTime();
                        while (System.nanoTime() - startTime < 250000000) {
                            synchronized(this){};
                            // Mask the sign bit and keep latch non-negative
                            latch = (latch + 1) & 0x1FFFFFFF;
                        }

                        // Translate the value using the permutation, and xor
                        // it with previous values gathered.
                        v ^= rndTab[latch % 255];
                        counter += latch;
                    }

                    // Push it into the queue and notify anybody who might
                    // be waiting for it.
                    synchronized(this) {
                        pool[end] = v;
                        end++;
                        count++;
                        if (end >= pool.length) {
                            end = 0;
                        }

                        notifyAll();
                    }
                }
            } catch (Exception e) {
                throw new InternalError("internal error: " +
                    "SeedGenerator thread generated an exception.", e);
            }
        }

        @Override
        void getSeedBytes(byte[] result) {
            for (int i = 0; i < result.length; i++) {
                result[i] = getSeedByte();
            }
        }

        byte getSeedByte() {
            byte b;

            try {
                // Wait for it...
                synchronized(this) {
                    while (count <= 0) {
                        wait();
                    }
                }
            } catch (Exception e) {
                if (count <= 0) {
                    throw new InternalError("internal error: " +
                        "SeedGenerator thread generated an exception.", e);
                }
            }

            synchronized(this) {
                // Get it from the queue
                b = pool[start];
                pool[start] = 0;
                start++;
                count--;
                if (start == pool.length) {
                    start = 0;
                }

                // Notify the daemon thread, just in case it is
                // waiting for us to make room in the queue.
                notifyAll();
            }

            return b;
        }

        // The permutation was calculated by generating 64k of random
        // data and using it to mix the trivial permutation.
        // It should be evenly distributed. The specific values
        // are not crucial to the security of this class.
        private static final byte[] rndTab = {
            56, 30, -107, -6, -86, 25, -83, 75, -12, -64,
            5, -128, 78, 21, 16, 32, 70, -81, 37, -51,
            -43, -46, -108, 87, 29, 17, -55, 22, -11, -111,
            -115, 84, -100, 108, -45, -15, -98, 72, -33, -28,
            31, -52, -37, -117, -97, -27, 93, -123, 47, 126,
            -80, -62, -93, -79, 61, -96, -65, -5, -47, -119,
            14, 89, 81, -118, -88, 20, 67, -126, -113, 60,
            -102, 55, 110, 28, 85, 121, 122, -58, 2, 45,
            43, 24, -9, 103, -13, 102, -68, -54, -101, -104,
            19, 13, -39, -26, -103, 62, 77, 51, 44, 111,
            73, 18, -127, -82, 4, -30, 11, -99, -74, 40,
            -89, 42, -76, -77, -94, -35, -69, 35, 120, 76,
            33, -73, -7, 82, -25, -10, 88, 125, -112, 58,
            83, 95, 6, 10, 98, -34, 80, 15, -91, 86,
            -19, 52, -17, 117, 49, -63, 118, -90, 36, -116,
            -40, -71, 97, -53, -109, -85, 109, -16, -3, 104,
            -95, 68, 54, 34, 26, 114, -1, 106, -121, 3,
            66, 0, 100, -84, 57, 107, 119, -42, 112, -61,
            1, 48, 38, 12, -56, -57, 39, -106, -72, 41,
            7, 71, -29, -59, -8, -38, 79, -31, 124, -124,
            8, 91, 116, 99, -4, 9, -36, -78, 63, -49,
            -67, -87, 59, 101, -32, 92, 94, 53, -41, 115,
            -66, -70, -122, 50, -50, -22, -20, -18, -21, 23,
            -2, -48, 96, 65, -105, 123, -14, -110, 69, -24,
            -120, -75, 74, 127, -60, 113, 90, -114, 105, 46,
            27, -125, -23, -44, 64
        };

        /**
         * This inner thread causes the thread scheduler to become 'noisy',
         * thus adding entropy to the system load.
         * At least one instance of this class is generated for every seed byte.
         */
        private static class BogusThread implements Runnable {
            @Override
            public final void run() {
                try {
                    for (int i = 0; i < 5; i++) {
                        Thread.sleep(50);
                    }
                    // System.gc();
                } catch (Exception e) {
                }
            }
        }
    }

    static class URLSeedGenerator extends SeedGenerator {

        private String deviceName;
        private InputStream seedStream;

        /**
         * The constructor is only called once to construct the one
         * instance we actually use. It opens the entropy gathering device
         * which will supply the randomness.
         */

        URLSeedGenerator(String egdurl) throws IOException {
        if (egdurl == null) {
                throw new IOException("No random source specified");
            }
            deviceName = egdurl;
            init();
        }

        private void init() throws IOException {
            final URL device = new URL(deviceName);
            try {
                seedStream = java.security.AccessController.doPrivileged
                    (new java.security.PrivilegedExceptionAction<>() {
                        @Override
                        public InputStream run() throws IOException {
                            /*
                             * return a shared InputStream for file URLs and
                             * avoid buffering.
                             * The URL.openStream() call wraps InputStream in a
                             * BufferedInputStream which
                             * can buffer up to 8K bytes. This read is a
                             * performance issue for entropy sources which
                             * can be slow to replenish.
                             */
                            if (device.getProtocol().equalsIgnoreCase("file")) {
                                File deviceFile =
                                    SunEntries.getDeviceFile(device);
                                return FileInputStreamPool
                                    .getInputStream(deviceFile);
                            } else {
                                return device.openStream();
                            }
                        }
                    });
            } catch (Exception e) {
                throw new IOException(
                    "Failed to open " + deviceName, e.getCause());
            }
        }

        @Override
        void getSeedBytes(byte[] result) {
            int len = result.length;
            int read = 0;
            try {
                while (read < len) {
                    int count = seedStream.read(result, read, len - read);
                    // /dev/random blocks - should never have EOF
                    if (count < 0) {
                        throw new InternalError(
                            "URLSeedGenerator " + deviceName +
                            " reached end of file");
                    }
                    read += count;
                }
            } catch (IOException ioe) {
                throw new InternalError("URLSeedGenerator " + deviceName +
                    " generated exception: " + ioe.getMessage(), ioe);
            }
        }
    }
}