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Interleave samples to get a better estimate of PBKDF2 running time.

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akwizgran
2013-12-28 13:44:26 +00:00
parent a9c46e6ed1
commit 7a57375438
1 changed files with 10 additions and 8 deletions
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18
briar-core/src/net/sf/briar/crypto/CryptoComponentImpl.java
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@@ -61,6 +61,7 @@ class CryptoComponentImpl implements CryptoComponent {
private static final int STORAGE_IV_BYTES = 16; // 128 bits
private static final int PBKDF_SALT_BYTES = 16; // 128 bits
private static final int PBKDF_TARGET_MILLIS = 500;
private static final int PBKDF_SAMPLES = 30;
// Labels for secret derivation
private static final byte[] MASTER = { 'M', 'A', 'S', 'T', 'E', 'R', '\0' };
@@ -463,18 +464,19 @@ class CryptoComponentImpl implements CryptoComponent {
// Package access for testing
int chooseIterationCount(int targetMillis) {
List<Long> quickSamples = new ArrayList<Long>();
List<Long> slowSamples = new ArrayList<Long>();
List<Long> quickSamples = new ArrayList<Long>(PBKDF_SAMPLES);
List<Long> slowSamples = new ArrayList<Long>(PBKDF_SAMPLES);
long iterationNanos = 0, initNanos = 0;
while(iterationNanos <= 0 || initNanos <= 0) {
// Take ten samples of the running time with one iteration
for(int i = 0; i < 10; i++) quickSamples.add(sampleRunningTime(1));
// Take ten samples of the running time with eleven iterations
for(int i = 0; i < 10; i++) slowSamples.add(sampleRunningTime(11));
// Sample the running time with one iteration and two iterations
for(int i = 0; i < PBKDF_SAMPLES; i++) {
quickSamples.add(sampleRunningTime(1));
slowSamples.add(sampleRunningTime(2));
}
// Calculate the iteration time and the initialisation time
long quickMedian = median(quickSamples);
long slowMedian = median(slowSamples);
iterationNanos = (slowMedian - quickMedian) / 10;
iterationNanos = slowMedian - quickMedian;
initNanos = quickMedian - iterationNanos;
if(LOG.isLoggable(INFO)) {
LOG.info("Init: " + initNanos + ", iteration: "
@@ -483,7 +485,7 @@ class CryptoComponentImpl implements CryptoComponent {
}
long targetNanos = targetMillis * 1000L * 1000L;
long iterations = (targetNanos - initNanos) / iterationNanos;
if(LOG.isLoggable(INFO)) LOG.info("Raw iterations: " + iterations);
if(LOG.isLoggable(INFO)) LOG.info("Target iterations: " + iterations);
if(iterations < 1) return 1;
if(iterations > Integer.MAX_VALUE) return Integer.MAX_VALUE;
return (int) iterations;