| 1 | /******************************************************************************
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| 2 | *
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| 3 | * Copyright (C) 1998 Logi Ragnarsson
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| 4 | *
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| 5 | * Adapted 1999 for use in MindTerm by Mats Andersson ([email protected])
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| 6 | * This class is the Spinner class of the Cryptonite library found at:
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| 7 | * <http://www.hi.is/~logir/cryptonite/>
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| 8 | *
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| 9 | * This program is free software; you can redistribute it and/or modify
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| 10 | * it under the terms of the GNU General Public License as published by
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| 11 | * the Free Software Foundation; either version 2 of the License, or
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| 12 | * (at your option) any later version.
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| 13 | *
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| 14 | * This program is distributed in the hope that it will be useful,
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| 15 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 16 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 17 | * GNU General Public License for more details.
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| 18 | *
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| 19 | *****************************************************************************
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| 20 | * $Author: mats $
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| 21 | * $Date: 1999/07/19 17:13:50 $
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| 22 | * $Name: rel1-2-1 $
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| 23 | *****************************************************************************/
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| 24 | package mindbright.security;
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| 25 |
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| 26 | /** Helper class for the RandomSpinner (SecureRandom) class. */
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| 27 | public class Spinner extends Thread {
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| 28 |
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| 29 | /** Return the number of spins performed in t milliseconds. */
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| 30 | public static int spin(long t) {
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| 31 | int counter = 0;
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| 32 | Thread s = new Spinner(t);
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| 33 | s.start();
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| 34 | do {
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| 35 | ++counter;
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| 36 | Thread.yield();
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| 37 | } while (s.isAlive());
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| 38 | return counter;
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| 39 | }
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| 40 |
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| 41 | /* This one is completely bogus, but after the initial seeding we trust the
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| 42 | milliseconds to be "random-enough"...
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| 43 | */
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| 44 | public static int bogusSpin() {
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| 45 | Runtime rt = Runtime.getRuntime();
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| 46 | int bogus;
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| 47 | Thread.yield();
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| 48 | rt.gc();
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| 49 | bogus = (int)System.currentTimeMillis();
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| 50 | bogus = ((bogus & 0xff) + ((bogus & 0xff00) >>> 8)) & 0xff;
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| 51 | return bogus;
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| 52 | }
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| 53 |
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| 54 | private long t;
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| 55 |
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| 56 | private Spinner(long t) {
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| 57 | this.t=t;
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| 58 | }
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| 59 |
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| 60 | public void run() {
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| 61 | try {
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| 62 | Thread.sleep(t);
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| 63 | } catch (InterruptedException ex) {
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| 64 | }
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| 65 | }
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| 66 |
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| 67 | /**
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| 68 | * Returns t such that spin(t) is larger than n. This value may change as
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| 69 | * the load of the system changes.
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| 70 | */
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| 71 | public static int guessTime(int n) {
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| 72 | int t=5;
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| 73 | while(spin(t)<n)
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| 74 | t=(t*3)/2;
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| 75 | return t;
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| 76 | }
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| 77 |
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| 78 | }
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