org.whispersystems.libsignal.kdf.HKDF Maven / Gradle / Ivy
/**
* Copyright (C) 2013-2016 Open Whisper Systems
*
* Licensed according to the LICENSE file in this repository.
*/
package org.whispersystems.libsignal.kdf;
import java.io.ByteArrayOutputStream;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
public abstract class HKDF {
private static final int HASH_OUTPUT_SIZE = 32;
public static HKDF createFor(int messageVersion) {
switch (messageVersion) {
case 2: return new HKDFv2();
case 3: return new HKDFv3();
default: throw new AssertionError("Unknown version: " + messageVersion);
}
}
public byte[] deriveSecrets(byte[] inputKeyMaterial, byte[] info, int outputLength) {
byte[] salt = new byte[HASH_OUTPUT_SIZE];
return deriveSecrets(inputKeyMaterial, salt, info, outputLength);
}
public byte[] deriveSecrets(byte[] inputKeyMaterial, byte[] salt, byte[] info, int outputLength) {
byte[] prk = extract(salt, inputKeyMaterial);
return expand(prk, info, outputLength);
}
private byte[] extract(byte[] salt, byte[] inputKeyMaterial) {
try {
Mac mac = Mac.getInstance("HmacSHA256");
mac.init(new SecretKeySpec(salt, "HmacSHA256"));
return mac.doFinal(inputKeyMaterial);
} catch (NoSuchAlgorithmException | InvalidKeyException e) {
throw new AssertionError(e);
}
}
private byte[] expand(byte[] prk, byte[] info, int outputSize) {
try {
int iterations = (int) Math.ceil((double) outputSize / (double) HASH_OUTPUT_SIZE);
byte[] mixin = new byte[0];
ByteArrayOutputStream results = new ByteArrayOutputStream();
int remainingBytes = outputSize;
for (int i= getIterationStartOffset();i