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HHH-18947 Changed UUID v 7 implementation for better entropy #9436

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Dec 17, 2024
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HHH-18947 Changed UUID v 7 implementation for better entropy #9436

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53 changes: 24 additions & 29 deletions hibernate-core/src/main/java/org/hibernate/id/uuid/UuidVersion7Strategy.java
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,6 @@
import org.hibernate.engine.spi.SharedSessionContractImplementor;
import org.hibernate.id.UUIDGenerationStrategy;

import static java.time.temporal.ChronoUnit.MILLIS;

/**
* Implements UUID Version 7 generation strategy as defined by the <a href="https://datatracker.ietf.org/doc/html/rfc9562#name-uuid-version-7">RFC 9562</a>.
Expand All @@ -26,8 +25,7 @@
* to guarantee additional monotonicity.
* </li>
* <li>2 bits - variant field, set to 0b10.</li>
* <li>14 bits - counter to guarantee additional monotonicity, resets to 0 when timestamp changes. </li>
* <li>48 bits - pseudorandom data to provide uniqueness.</li>
* <li>62 bits - pseudorandom counter to guarantee additional monotonicity, uniqueness, and good entropy.</li>
* </ul>
*
* @author Cedomir Igaly
Expand All @@ -37,55 +35,58 @@
*/
public class UuidVersion7Strategy implements UUIDGenerationStrategy, UuidValueGenerator {

private static final long MAX_RANDOM_SEQUENCE = 0x3FFF_FFFF_FFFF_FFFFL;

public static final UuidVersion7Strategy INSTANCE = new UuidVersion7Strategy();

private static class Holder {
private static final SecureRandom numberGenerator = new SecureRandom();

}

public record State(Instant lastTimestamp, int lastSequence) {
public record State(Instant lastTimestamp, long lastSequence, long nanos) {

State(Instant lastTimestamp, long lastSequence) {
this( lastTimestamp, lastSequence, nanos( lastTimestamp ) );
}

public long millis() {
return lastTimestamp.toEpochMilli();
}

public long nanos() {
return (long) ( ( lastTimestamp.getNano() % 1_000_000L ) * 0.004096 );
private static long nanos(Instant timestamp) {
return (long) ((timestamp.getNano() % 1_000_000L) * 0.004096);
}

public State getNextState() {
final Instant now = Instant.now();
if ( lastTimestamp.toEpochMilli() < now.toEpochMilli() ) {
return new State(
now.truncatedTo( MILLIS ),
randomSequence()
);
if ( lastTimestamp.toEpochMilli() < now.toEpochMilli() ||
lastTimestamp.toEpochMilli() == now.toEpochMilli() && nanos < nanos( now ) ) {
return new State( now, randomSequence() );
}
else if ( lastSequence == 0x3FFF ) {
return new State(
lastTimestamp.plusMillis( 1 ),
Holder.numberGenerator.nextInt( 1 << 14 )
);
final long nextSequence = lastSequence + Holder.numberGenerator.nextLong( 0xFFFF_FFFFL );
if ( nextSequence > MAX_RANDOM_SEQUENCE ) {
return new State( lastTimestamp.plusNanos( 250 ), randomSequence() );
}
else {
return new State( lastTimestamp, lastSequence + 1 );
return new State( lastTimestamp, nextSequence );
}
}

private static int randomSequence() {
return Holder.numberGenerator.nextInt( 1 << 14 );
private static long randomSequence() {
return Holder.numberGenerator.nextLong( MAX_RANDOM_SEQUENCE );
}
}

private final AtomicReference<State> lastState;

@Internal
public UuidVersion7Strategy() {
this( Instant.EPOCH, Integer.MIN_VALUE );
this( Instant.EPOCH, Holder.numberGenerator.nextLong( MAX_RANDOM_SEQUENCE ) );
}

@Internal
public UuidVersion7Strategy(final Instant initialTimestamp, final int initialSequence) {
public UuidVersion7Strategy(final Instant initialTimestamp, final long initialSequence) {
this.lastState = new AtomicReference<>( new State( initialTimestamp, initialSequence ) );
}

Expand Down Expand Up @@ -115,14 +116,8 @@ public UUID generateUuid(final SharedSessionContractImplementor session) {
| state.nanos() & 0xFFFL,
// LSB bits 0-1 - variant = 4
0x8000_0000_0000_0000L
// LSB bits 2-15 - counter
| (long) state.lastSequence << 48
// LSB bits 16-63 - pseudorandom data
| randomNode()
// LSB bits 2-15 - pseudorandom counter
| state.lastSequence
);
}

private static long randomNode() {
return Holder.numberGenerator.nextLong( 0x1_0000_0000_0000L ) | 0x1000_0000_0000L;
}
}
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