bcprov/src/main/java/org/bouncycastle/pqc/crypto/xmss/KeyedHashFunctions.java

package org.bouncycastle.pqc.crypto.xmss;

import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.Xof;

/**
 * Crypto functions for XMSS.
 *
 */
public final class KeyedHashFunctions {

	private final Digest digest;
	private final int digestSize;

	protected KeyedHashFunctions(Digest digest, int digestSize) {
		super();
		if (digest == null) {
			throw new NullPointerException("digest == null");
		}
		this.digest = digest;
		this.digestSize = digestSize;
	}

	private byte[] coreDigest(int fixedValue, byte[] key, byte[] index) {
		byte[] buffer = new byte[digestSize + key.length + index.length];
		byte[] in = XMSSUtil.toBytesBigEndian(fixedValue, digestSize);
		/* fill first n byte of out buffer */
		for (int i = 0; i < in.length; i++) {
			buffer[i] = in[i];
		}
		/* add key */
		for (int i = 0; i < key.length; i++) {
			buffer[in.length + i] = key[i];
		}
		/* add index */
		for (int i = 0; i < index.length; i++) {
			buffer[in.length + key.length + i] = index[i];
		}
		digest.update(buffer, 0, buffer.length);
		byte[] out = new byte[digestSize];
		if (digest instanceof Xof) {
			((Xof) digest).doFinal(out, 0, digestSize);
		} else {
			digest.doFinal(out, 0);
		}
		return out;
	}

	protected byte[] F(byte[] key, byte[] in) {
		if (key.length != digestSize) {
			throw new IllegalArgumentException("wrong key length");
		}
		if (in.length != digestSize) {
			throw new IllegalArgumentException("wrong in length");
		}
		return coreDigest(0, key, in);
	}

	protected byte[] H(byte[] key, byte[] in) {
		if (key.length != digestSize) {
			throw new IllegalArgumentException("wrong key length");
		}
		if (in.length != (2 * digestSize)) {
			throw new IllegalArgumentException("wrong in length");
		}
		return coreDigest(1, key, in);
	}

	protected byte[] HMsg(byte[] key, byte[] in) {
		if (key.length != (3 * digestSize)) {
			throw new IllegalArgumentException("wrong key length");
		}
		return coreDigest(2, key, in);
	}

	protected byte[] PRF(byte[] key, byte[] address) {
		if (key.length != digestSize) {
			throw new IllegalArgumentException("wrong key length");
		}
		if (address.length != 32) {
			throw new IllegalArgumentException("wrong address length");
		}
		return coreDigest(3, key, address);
	}
}