/*
 * This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that
 * it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If
 * not, see <http://www.gnu.org/licenses/>.
 */
package silentium.commons.crypt;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.math.BigInteger;
import java.security.KeyPair;
import java.security.interfaces.RSAPublicKey;

/**
 *
 */
public class ScrambledKeyPair {
	private static final Logger log = LoggerFactory.getLogger(ScrambledKeyPair.class.getName());

	public final KeyPair _pair;
	public final byte[] _scrambledModulus;

	public ScrambledKeyPair(final KeyPair pPair) {
		_pair = pPair;
		_scrambledModulus = scrambleModulus(((RSAPublicKey) _pair.getPublic()).getModulus());
	}

	private static byte[] scrambleModulus(final BigInteger modulus) {
		byte[] scrambledMod = modulus.toByteArray();

		if (scrambledMod.length == 0x81 && scrambledMod[0] == 0x00) {
			final byte[] temp = new byte[0x80];
			System.arraycopy(scrambledMod, 1, temp, 0, 0x80);
			scrambledMod = temp;
		}
		// step 1 : 0x4d-0x50 <-> 0x00-0x04
		for (int i = 0; i < 4; i++) {
			final byte temp = scrambledMod[0x00 + i];
			scrambledMod[0x00 + i] = scrambledMod[0x4d + i];
			scrambledMod[0x4d + i] = temp;
		}
		// step 2 : xor first 0x40 bytes with last 0x40 bytes
		for (int i = 0; i < 0x40; i++) {
			scrambledMod[i] = (byte) (scrambledMod[i] ^ scrambledMod[0x40 + i]);
		}
		// step 3 : xor bytes 0x0d-0x10 with bytes 0x34-0x38
		for (int i = 0; i < 4; i++) {
			scrambledMod[0x0d + i] = (byte) (scrambledMod[0x0d + i] ^ scrambledMod[0x34 + i]);
		}
		// step 4 : xor last 0x40 bytes with first 0x40 bytes
		for (int i = 0; i < 0x40; i++) {
			scrambledMod[0x40 + i] = (byte) (scrambledMod[0x40 + i] ^ scrambledMod[i]);
		}
		log.debug("Modulus was scrambled.");

		return scrambledMod;
	}
}