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/*
This file is part of GNUnet.
Copyright (C) 2012, 2013 Christian Grothoff (and other contributing authors)
GNUnet 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, or (at your
option) any later version.
GNUnet 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 GNUnet; see the file COPYING. If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA.
*/
package org.gnunet.util.crypto;
import org.gnunet.construct.FixedSizeIntegerArray;
import org.gnunet.construct.Message;
import org.gnunet.util.HashCode;
import java.math.BigInteger;
import java.security.SecureRandom;
/**
* Private key for elliptic curve Diffie Hellman exchange.
* Note that (in contrast to NaCl) the key is encoded
* as big endian.
*/
public class EcdhePrivateKey implements Message {
/**
* Private key byte string, in big endian form.
*/
@FixedSizeIntegerArray(bitSize = 8, signed = false, length = 32)
public byte[] d;
/**
* Create an ecdh private key without allocating the key data.
*/
public EcdhePrivateKey() {
// empty constructor for org.gnunet.construct.*
}
/**
* Get the public key for this private key.
*
* @return the public key for this private key
*/
public EcdhePublicKey getPublicKey() {
BigInteger dCoeff = this.asCoefficient();
Ed25519 A = Ed25519.B.scalarmult(dCoeff);
return new EcdhePublicKey(A);
}
/*
* Derive key material from the give public key and a this private ECDHE key.
*
* @param publicKey public key to use for the ECDH
* @return key material
*/
public HashCode ecdh(EcdhePublicKey publicKey) {
BigInteger dCoeff = this.asCoefficient();
Ed25519 Q = publicKey.asPoint().scalarmult(dCoeff);
// hash big endian representation of the x-coordinate.
return HashCode.hash(Q.P0.toByteArray());
}
/**
* Create a random private key.
*
* @return a random private key
*/
public static EcdhePrivateKey createRandom() {
SecureRandom sr = new SecureRandom();
EcdhePrivateKey privateKey = new EcdhePrivateKey();
privateKey.d = new byte[32];
sr.nextBytes(privateKey.d);
// clear bits so that d mod 8 = 0
privateKey.d[31] &= (byte) 248;
// make sure the key fits in 255 bits
privateKey.d[0] &= (byte) 127;
// make sure key does not have lots of leading zeros
privateKey.d[0] |= (byte) 64;
return privateKey;
}
public BigInteger asCoefficient() {
/* We have a big endian value here ... */
return new BigInteger(1, d);
}
}
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