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/*
* Copyright 2016 gitblit.com
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.gitblit.utils;
/**
* Wrapper class for java.security.SecureRandom, which will periodically reseed
* the PRNG in case an instance of the class has been running for a long time.
*
* @author Florian Zschocke
*/
public class SecureRandom {
/** Period (in ms) after which a new SecureRandom will be created in order to get a fresh random seed. */
private static final long RESEED_PERIOD = 24 * 60 * 60 * 1000; /* 24 hours */
private long last;
private java.security.SecureRandom random;
public SecureRandom() {
// Make sure the SecureRandom is seeded right from the start.
// This also lets any blocks during seeding occur at creation
// and prevents it from happening when getting next random bytes.
seed();
}
public byte[] randomBytes(int num) {
byte[] bytes = new byte[num];
nextBytes(bytes);
return bytes;
}
public void nextBytes(byte[] bytes) {
random.nextBytes(bytes);
reseed(false);
}
void reseed(boolean forced) {
long ts = System.currentTimeMillis();
if (forced || (ts - last) > RESEED_PERIOD) {
last = ts;
runReseed();
}
}
private void seed() {
random = new java.security.SecureRandom();
random.nextBytes(new byte[0]);
last = System.currentTimeMillis();
}
private void runReseed() {
// Have some other thread hit the penalty potentially incurred by reseeding,
// so that we can immediately return and not block the operation in progress.
new Thread() {
public void run() {
seed();
}
}.start();
}
}
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