author | robm |
Thu, 24 Jul 2014 22:22:43 +0100 | |
changeset 25749 | a556ba0ff94d |
parent 16915 | 675d1569af3e |
permissions | -rw-r--r-- |
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/* |
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* Copyright (c) 1998, 2014, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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package sun.security.provider; |
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import java.io.IOException; |
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import java.security.MessageDigest; |
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import java.security.SecureRandomSpi; |
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import java.security.NoSuchAlgorithmException; |
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import java.security.NoSuchProviderException; |
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/** |
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* <p>This class provides a crytpographically strong pseudo-random number |
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* generator based on the SHA-1 hash algorithm. |
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* |
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* <p>Note that if a seed is not provided, we attempt to provide sufficient |
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* seed bytes to completely randomize the internal state of the generator |
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* (20 bytes). However, our seed generation algorithm has not been thoroughly |
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* studied or widely deployed. |
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* |
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* <p>Also note that when a random object is deserialized, |
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* <a href="#engineNextBytes(byte[])">engineNextBytes</a> invoked on the |
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* restored random object will yield the exact same (random) bytes as the |
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* original object. If this behaviour is not desired, the restored random |
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* object should be seeded, using |
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* <a href="#engineSetSeed(byte[])">engineSetSeed</a>. |
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* |
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* @author Benjamin Renaud |
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* @author Josh Bloch |
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* @author Gadi Guy |
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*/ |
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public final class SecureRandom extends SecureRandomSpi |
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implements java.io.Serializable { |
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private static final long serialVersionUID = 3581829991155417889L; |
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private static final int DIGEST_SIZE = 20; |
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private transient MessageDigest digest; |
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private byte[] state; |
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private byte[] remainder; |
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private int remCount; |
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/** |
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* This empty constructor automatically seeds the generator. We attempt |
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* to provide sufficient seed bytes to completely randomize the internal |
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* state of the generator (20 bytes). Note, however, that our seed |
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* generation algorithm has not been thoroughly studied or widely deployed. |
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* |
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* <p>The first time this constructor is called in a given Virtual Machine, |
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* it may take several seconds of CPU time to seed the generator, depending |
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* on the underlying hardware. Successive calls run quickly because they |
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* rely on the same (internal) pseudo-random number generator for their |
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* seed bits. |
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*/ |
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public SecureRandom() { |
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init(null); |
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} |
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/** |
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* This constructor is used to instantiate the private seeder object |
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* with a given seed from the SeedGenerator. |
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* |
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* @param seed the seed. |
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*/ |
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private SecureRandom(byte seed[]) { |
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init(seed); |
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} |
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/** |
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* This call, used by the constructors, instantiates the SHA digest |
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* and sets the seed, if given. |
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*/ |
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private void init(byte[] seed) { |
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try { |
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/* |
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* Use the local SUN implementation to avoid native |
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* performance overhead. |
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*/ |
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digest = MessageDigest.getInstance("SHA", "SUN"); |
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} catch (NoSuchProviderException | NoSuchAlgorithmException e) { |
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// Fallback to any available. |
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try { |
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digest = MessageDigest.getInstance("SHA"); |
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} catch (NoSuchAlgorithmException exc) { |
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throw new InternalError( |
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"internal error: SHA-1 not available.", exc); |
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} |
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} |
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if (seed != null) { |
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engineSetSeed(seed); |
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} |
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} |
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/** |
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* Returns the given number of seed bytes, computed using the seed |
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* generation algorithm that this class uses to seed itself. This |
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* call may be used to seed other random number generators. While |
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* we attempt to return a "truly random" sequence of bytes, we do not |
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* know exactly how random the bytes returned by this call are. (See |
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* the empty constructor <a href = "#SecureRandom">SecureRandom</a> |
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* for a brief description of the underlying algorithm.) |
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* The prudent user will err on the side of caution and get extra |
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* seed bytes, although it should be noted that seed generation is |
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* somewhat costly. |
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* |
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* @param numBytes the number of seed bytes to generate. |
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* |
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* @return the seed bytes. |
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*/ |
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@Override |
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public byte[] engineGenerateSeed(int numBytes) { |
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// Neither of the SeedGenerator implementations require |
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// locking, so no sync needed here. |
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byte[] b = new byte[numBytes]; |
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SeedGenerator.generateSeed(b); |
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return b; |
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} |
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/** |
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* Reseeds this random object. The given seed supplements, rather than |
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* replaces, the existing seed. Thus, repeated calls are guaranteed |
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* never to reduce randomness. |
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* |
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* @param seed the seed. |
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*/ |
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@Override |
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synchronized public void engineSetSeed(byte[] seed) { |
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if (state != null) { |
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digest.update(state); |
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for (int i = 0; i < state.length; i++) { |
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state[i] = 0; |
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} |
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} |
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state = digest.digest(seed); |
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} |
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private static void updateState(byte[] state, byte[] output) { |
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int last = 1; |
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int v; |
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byte t; |
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boolean zf = false; |
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// state(n + 1) = (state(n) + output(n) + 1) % 2^160; |
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for (int i = 0; i < state.length; i++) { |
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// Add two bytes |
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v = (int)state[i] + (int)output[i] + last; |
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// Result is lower 8 bits |
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t = (byte)v; |
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// Store result. Check for state collision. |
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zf = zf | (state[i] != t); |
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state[i] = t; |
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// High 8 bits are carry. Store for next iteration. |
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last = v >> 8; |
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} |
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// Make sure at least one bit changes! |
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if (!zf) { |
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state[0]++; |
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} |
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} |
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/** |
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* This static object will be seeded by SeedGenerator, and used |
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* to seed future instances of SHA1PRNG SecureRandoms. |
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* |
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* Bloch, Effective Java Second Edition: Item 71 |
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*/ |
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private static class SeederHolder { |
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private static final SecureRandom seeder; |
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static { |
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/* |
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* Call to SeedGenerator.generateSeed() to add additional |
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* seed material (likely from the Native implementation). |
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*/ |
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seeder = new SecureRandom(SeedGenerator.getSystemEntropy()); |
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byte [] b = new byte[DIGEST_SIZE]; |
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SeedGenerator.generateSeed(b); |
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seeder.engineSetSeed(b); |
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} |
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} |
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/** |
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* Generates a user-specified number of random bytes. |
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* |
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* @param bytes the array to be filled in with random bytes. |
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*/ |
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@Override |
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public synchronized void engineNextBytes(byte[] result) { |
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int index = 0; |
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int todo; |
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byte[] output = remainder; |
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if (state == null) { |
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byte[] seed = new byte[DIGEST_SIZE]; |
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SeederHolder.seeder.engineNextBytes(seed); |
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state = digest.digest(seed); |
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} |
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// Use remainder from last time |
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int r = remCount; |
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if (r > 0) { |
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// How many bytes? |
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todo = (result.length - index) < (DIGEST_SIZE - r) ? |
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(result.length - index) : (DIGEST_SIZE - r); |
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// Copy the bytes, zero the buffer |
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for (int i = 0; i < todo; i++) { |
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result[i] = output[r]; |
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output[r++] = 0; |
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} |
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remCount += todo; |
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index += todo; |
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} |
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// If we need more bytes, make them. |
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while (index < result.length) { |
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// Step the state |
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digest.update(state); |
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output = digest.digest(); |
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updateState(state, output); |
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// How many bytes? |
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todo = (result.length - index) > DIGEST_SIZE ? |
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DIGEST_SIZE : result.length - index; |
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// Copy the bytes, zero the buffer |
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for (int i = 0; i < todo; i++) { |
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result[index++] = output[i]; |
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output[i] = 0; |
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} |
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remCount += todo; |
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} |
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// Store remainder for next time |
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remainder = output; |
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remCount %= DIGEST_SIZE; |
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} |
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/* |
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* readObject is called to restore the state of the random object from |
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* a stream. We have to create a new instance of MessageDigest, because |
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* it is not included in the stream (it is marked "transient"). |
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* |
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* Note that the engineNextBytes() method invoked on the restored random |
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* object will yield the exact same (random) bytes as the original. |
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* If you do not want this behaviour, you should re-seed the restored |
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* random object, using engineSetSeed(). |
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*/ |
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private void readObject(java.io.ObjectInputStream s) |
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throws IOException, ClassNotFoundException { |
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s.defaultReadObject (); |
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try { |
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/* |
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* Use the local SUN implementation to avoid native |
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* performance overhead. |
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*/ |
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digest = MessageDigest.getInstance("SHA", "SUN"); |
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} catch (NoSuchProviderException | NoSuchAlgorithmException e) { |
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// Fallback to any available. |
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try { |
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digest = MessageDigest.getInstance("SHA"); |
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} catch (NoSuchAlgorithmException exc) { |
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throw new InternalError( |
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"internal error: SHA-1 not available.", exc); |
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} |
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} |
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} |
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} |