/* ====================================================================
* Copyright (c) 1999, 2000 Ben Laurie. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. All advertising materials mentioning features or use of this
* software must display the following acknowledgment:
* "This product includes software developed by Ben Laurie
* for use in the Lucre project."
*
* 4. The name "Lucre" must not be used to
* endorse or promote products derived from this software without
* prior written permission.
*
* 5. Redistributions of any form whatsoever must retain the following
* acknowledgment:
* "This product includes software developed by Ben Laurie
* for use in the Lucre project."
*
* THIS SOFTWARE IS PROVIDED BY BEN LAURIE ``AS IS'' AND ANY
* EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL BEN LAURIE OR
* HIS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
* ====================================================================
*
* For more information on Lucre see http://anoncvs.aldigital.co.uk/lucre/.
*
*/
package uk.co.aldigital.ben.lucre;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.PrintStream;
import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
class DoubleCoinRequest extends PublicCoinRequest {
private BigInteger m_biBlindingFactorY;
private BigInteger m_biBlindingFactorG;
private UnsignedCoin m_coin=new UnsignedCoin();
DoubleCoinRequest(PublicBank bank)
throws NoSuchAlgorithmException {
BigInteger y;
m_coin.random(bank);
y=m_coin.generateCoinNumber(bank);
// choose b_y
BigInteger p1=bank.getPrime().subtract(Util.ONE);
for( ; ; )
{
m_biBlindingFactorY=Util.random(1,bank.getPrime()
.subtract(Util.ONE));
Util.dumpNumber("by= ",m_biBlindingFactorY);
// y has to be an invertible exponent, so ensure it has an inverse
// mod p-1.
if(m_biBlindingFactorY.gcd(p1).equals(Util.ONE))
break;
}
// choose b_g
m_biBlindingFactorG=Util.random(1,bank.getPrime().subtract(Util.ONE));
Util.dumpNumber("bg= ",m_biBlindingFactorG);
// calculate A->B: y^b_y g^b_g
m_biCoinRequest=bank.getGenerator().modPow(m_biBlindingFactorG,
bank.getPrime());
y=y.modPow(m_biBlindingFactorY,bank.getPrime());
m_biCoinRequest=m_biCoinRequest.multiply(y).mod(bank.getPrime());
Util.dumpNumber("A->B= ",m_biCoinRequest);
}
DoubleCoinRequest(BufferedReader rdr)
throws IOException {
read(rdr);
}
DoubleCoinRequest(String szFile)
throws IOException {
this(Util.newBufferedFileReader(szFile));
}
void write(PrintStream str) {
super.write(str);
m_coin.write(str);
Util.dumpNumber(str,"blindingY=",m_biBlindingFactorY);
Util.dumpNumber(str,"blindingG=",m_biBlindingFactorG);
}
void read(BufferedReader rdr)
throws IOException {
super.read(rdr);
m_coin.read(rdr);
m_biBlindingFactorY=Util.readNumber(rdr,"blindingY=");
m_biBlindingFactorG=Util.readNumber(rdr,"blindingG=");
}
BigInteger unblind(BigInteger biSignedCoin,PublicBank bank) {
BigInteger z=bank.getPublicKey().modPow(m_biBlindingFactorG,
bank.getPrime());
z=z.modInverse(bank.getPrime());
z=z.multiply(biSignedCoin);
z=z.mod(bank.getPrime());
BigInteger p1=bank.getPrime().subtract(Util.ONE);
BigInteger byinv=m_biBlindingFactorY.modInverse(p1);
z=z.modPow(byinv,bank.getPrime());
return z;
}
Coin processResponse(PublicBank bank,
BigInteger biSignedCoinRequest) {
BigInteger biCoinSignature=unblind(biSignedCoinRequest,bank);
Util.dumpNumber("z= ",biCoinSignature);
return new Coin(m_coin,biCoinSignature);
}
}