HomekitUtils.java

package com.beowulfe.hap.impl;

import java.math.BigInteger;
import java.security.InvalidAlgorithmParameterException;
import java.security.SecureRandom;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import net.i2p.crypto.eddsa.spec.EdDSANamedCurveTable;
import net.i2p.crypto.eddsa.spec.EdDSAParameterSpec;

import com.nimbusds.srp6.SRP6Routines;

public class HomekitUtils {
	
	private static volatile SecureRandom secureRandom;

	public static BigInteger generateSalt() {
		return new BigInteger(SRP6Routines.generateRandomSalt(16));
	}
	
	public static byte[] generateKey() throws InvalidAlgorithmParameterException {
		EdDSAParameterSpec spec = EdDSANamedCurveTable.getByName("ed25519-sha-512");
		byte[] seed = new byte[spec.getCurve().getField().getb()/8];
		getSecureRandom().nextBytes(seed);
		return seed;
	}
	
	public static String generateMac() {
		int byte1 = ((getSecureRandom().nextInt(255) + 1) | 2) & 0xFE; //Unicast locally administered MAC;
		return Integer.toHexString(byte1) + ":" + Stream.generate(() -> getSecureRandom().nextInt(255) + 1)
			.limit(5)
			.map(i -> Integer.toHexString(i))
			.collect(Collectors.joining(":"));
	}
	
	private static SecureRandom getSecureRandom() {
		if (secureRandom == null) {
			synchronized(HomekitUtils.class) {
				if (secureRandom == null) {
					secureRandom = new SecureRandom();
				}
			}
		}
		return secureRandom;
	}
}