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Java SDK for Hyperledger fabric project
/*
*
* Copyright 2017, 2018 IBM Corp. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package org.hyperledger.fabric.sdk.idemix;
import com.google.protobuf.ByteString;
import org.apache.milagro.amcl.FP256BN.BIG;
import org.apache.milagro.amcl.FP256BN.ECP;
import org.apache.milagro.amcl.FP256BN.ECP2;
import org.apache.milagro.amcl.FP256BN.PAIR;
import org.apache.milagro.amcl.RAND;
import org.hyperledger.fabric.protos.idemix.Idemix;
/**
* IdemixCredential represents a user's idemix credential,
* which is a BBS+ signature (see "Constant-Size Dynamic k-TAA" by Man Ho Au, Willy Susilo, Yi Mu)
* on the user's secret key and attribute values.
*/
public class IdemixCredential {
private final ECP A;
private final ECP B;
private final BIG E;
private final BIG S;
private final byte[][] Attrs;
/**
* Constructor creating a new credential
*
* @param key the issuer key pair
* @param m a credential request
* @param attrs an array of attribute values as BIG
*/
IdemixCredential(IdemixIssuerKey key, IdemixCredRequest m, BIG[] attrs) {
if (key == null || key.getIpk() == null || m == null || attrs == null) {
throw new IllegalArgumentException("Cannot create idemix credential from null input");
}
if (attrs.length != key.getIpk().getAttributeNames().length) {
throw new IllegalArgumentException("Amount of attribute values does not match amount of attributes in issuer public key");
}
final RAND rng = IdemixUtils.getRand();
// Place a BBS+ signature on the user key and the attribute values
// (For BBS+, see "Constant-Size Dynamic k-TAA" by Man Ho Au, Willy Susilo, Yi Mu)
E = IdemixUtils.randModOrder(rng);
S = IdemixUtils.randModOrder(rng);
B = new ECP();
B.copy(IdemixUtils.genG1);
B.add(m.getNym());
B.add(key.getIpk().getHRand().mul(S));
for (int i = 0; i < attrs.length / 2; i++) {
B.add(key.getIpk().getHAttrs()[2 * i].mul2(attrs[2 * i], key.getIpk().getHAttrs()[2 * i + 1], attrs[2 * i + 1]));
}
if (attrs.length % 2 != 0) {
B.add(key.getIpk().getHAttrs()[attrs.length - 1].mul(attrs[attrs.length - 1]));
}
BIG exp = new BIG(key.getIsk()).plus(E);
exp.mod(IdemixUtils.GROUP_ORDER);
exp.invmodp(IdemixUtils.GROUP_ORDER);
A = B.mul(exp);
Attrs = new byte[attrs.length][IdemixUtils.FIELD_BYTES];
byte[] b = new byte[IdemixUtils.FIELD_BYTES];
for (int i = 0; i < attrs.length; i++) {
attrs[i].toBytes(b);
System.arraycopy(b, 0, Attrs[i], 0, IdemixUtils.FIELD_BYTES);
}
}
/**
* Construct an IdemixCredential from a serialized credential
*
* @param proto a protobuf representation of a credential
*/
public IdemixCredential(Idemix.Credential proto) {
if (proto == null) {
throw new IllegalArgumentException("Cannot create idemix credential from null input");
}
A = IdemixUtils.transformFromProto(proto.getA());
B = IdemixUtils.transformFromProto(proto.getB());
E = BIG.fromBytes(proto.getE().toByteArray());
S = BIG.fromBytes(proto.getS().toByteArray());
Attrs = new byte[proto.getAttrsCount()][];
for (int i = 0; i < proto.getAttrsCount(); i++) {
Attrs[i] = proto.getAttrs(i).toByteArray();
}
}
ECP getA() {
return A;
}
ECP getB() {
return B;
}
BIG getE() {
return E;
}
BIG getS() {
return S;
}
public byte[][] getAttrs() {
return Attrs;
}
/**
* verify cryptographically verifies the credential
*
* @param sk the secret key of the user
* @param ipk the public key of the issuer
* @return true iff valid
*/
public boolean verify(BIG sk, IdemixIssuerPublicKey ipk) {
if (ipk == null || Attrs.length != ipk.getAttributeNames().length) {
return false;
}
for (byte[] attr : Attrs) {
if (attr == null) {
return false;
}
}
ECP bPrime = new ECP();
bPrime.copy(IdemixUtils.genG1);
bPrime.add(ipk.getHsk().mul2(sk, ipk.getHRand(), S));
for (int i = 0; i < Attrs.length / 2; i++) {
bPrime.add(ipk.getHAttrs()[2 * i].mul2(BIG.fromBytes(Attrs[2 * i]), ipk.getHAttrs()[2 * i + 1], BIG.fromBytes(Attrs[2 * i + 1])));
}
if (Attrs.length % 2 != 0) {
bPrime.add(ipk.getHAttrs()[Attrs.length - 1].mul(BIG.fromBytes(Attrs[Attrs.length - 1])));
}
if (!B.equals(bPrime)) {
return false;
}
ECP2 a = IdemixUtils.genG2.mul(E);
a.add(ipk.getW());
a.affine();
return PAIR.fexp(PAIR.ate(a, A)).equals(PAIR.fexp(PAIR.ate(IdemixUtils.genG2, B)));
}
/**
* @return A proto representation of this credential
*/
Idemix.Credential toProto() {
Idemix.Credential.Builder builder = Idemix.Credential.newBuilder()
.setA(IdemixUtils.transformToProto(A))
.setB(IdemixUtils.transformToProto(B))
.setE(ByteString.copyFrom(IdemixUtils.bigToBytes(E)))
.setS(ByteString.copyFrom(IdemixUtils.bigToBytes(S)));
for (byte[] attr : Attrs) {
builder.addAttrs(ByteString.copyFrom(attr));
}
return builder.build();
}
}