Collapse RatchetingSessionV2 and RatchetingSessionV3.
Moxie Marlinspike
10 years ago
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/**
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* Copyright (C) 2014 Open Whisper Systems
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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package org.whispersystems.libaxolotl.ratchet;
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import org.whispersystems.libaxolotl.IdentityKey;
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import org.whispersystems.libaxolotl.IdentityKeyPair;
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import org.whispersystems.libaxolotl.InvalidKeyException;
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import org.whispersystems.libaxolotl.state.SessionState;
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import org.whispersystems.libaxolotl.ecc.Curve;
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import org.whispersystems.libaxolotl.ecc.ECKeyPair;
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import org.whispersystems.libaxolotl.ecc.ECPublicKey;
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import org.whispersystems.libaxolotl.kdf.DerivedSecrets;
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import org.whispersystems.libaxolotl.kdf.HKDF;
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import org.whispersystems.libaxolotl.util.Pair;
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import java.io.ByteArrayOutputStream;
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import java.io.IOException;
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public class RatchetingSessionV2 {
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public static void initializeSession(SessionState sessionState,
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ECKeyPair ourBaseKey,
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ECPublicKey theirBaseKey,
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ECKeyPair ourEphemeralKey,
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ECPublicKey theirEphemeralKey,
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IdentityKeyPair ourIdentityKey,
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IdentityKey theirIdentityKey)
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throws InvalidKeyException
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{
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if (isAlice(ourBaseKey.getPublicKey(), theirBaseKey, ourEphemeralKey.getPublicKey(), theirEphemeralKey)) {
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initializeSessionAsAlice(sessionState, ourBaseKey, theirBaseKey, theirEphemeralKey,
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ourIdentityKey, theirIdentityKey);
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} else {
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initializeSessionAsBob(sessionState, ourBaseKey, theirBaseKey,
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ourEphemeralKey, ourIdentityKey, theirIdentityKey);
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}
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sessionState.setSessionVersion(2);
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}
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private static void initializeSessionAsAlice(SessionState sessionState,
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ECKeyPair ourBaseKey, ECPublicKey theirBaseKey,
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ECPublicKey theirEphemeralKey,
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IdentityKeyPair ourIdentityKey,
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IdentityKey theirIdentityKey)
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throws InvalidKeyException
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{
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sessionState.setRemoteIdentityKey(theirIdentityKey);
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sessionState.setLocalIdentityKey(ourIdentityKey.getPublicKey());
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ECKeyPair sendingKey = Curve.generateKeyPair(true);
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Pair<RootKey, ChainKey> receivingChain = calculate3DHE(true, ourBaseKey, theirBaseKey, ourIdentityKey, theirIdentityKey);
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Pair<RootKey, ChainKey> sendingChain = receivingChain.first().createChain(theirEphemeralKey, sendingKey);
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sessionState.addReceiverChain(theirEphemeralKey, receivingChain.second());
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sessionState.setSenderChain(sendingKey, sendingChain.second());
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sessionState.setRootKey(sendingChain.first());
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}
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private static void initializeSessionAsBob(SessionState sessionState,
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ECKeyPair ourBaseKey, ECPublicKey theirBaseKey,
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ECKeyPair ourEphemeralKey,
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IdentityKeyPair ourIdentityKey,
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IdentityKey theirIdentityKey)
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throws InvalidKeyException
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{
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sessionState.setRemoteIdentityKey(theirIdentityKey);
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sessionState.setLocalIdentityKey(ourIdentityKey.getPublicKey());
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Pair<RootKey, ChainKey> sendingChain = calculate3DHE(false, ourBaseKey, theirBaseKey,
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ourIdentityKey, theirIdentityKey);
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sessionState.setSenderChain(ourEphemeralKey, sendingChain.second());
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sessionState.setRootKey(sendingChain.first());
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}
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private static Pair<RootKey, ChainKey> calculate3DHE(boolean isAlice,
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ECKeyPair ourEphemeral, ECPublicKey theirEphemeral,
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IdentityKeyPair ourIdentity, IdentityKey theirIdentity)
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throws InvalidKeyException
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{
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try {
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ByteArrayOutputStream secrets = new ByteArrayOutputStream();
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if (isAlice) {
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secrets.write(Curve.calculateAgreement(theirEphemeral, ourIdentity.getPrivateKey()));
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secrets.write(Curve.calculateAgreement(theirIdentity.getPublicKey(), ourEphemeral.getPrivateKey()));
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} else {
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secrets.write(Curve.calculateAgreement(theirIdentity.getPublicKey(), ourEphemeral.getPrivateKey()));
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secrets.write(Curve.calculateAgreement(theirEphemeral, ourIdentity.getPrivateKey()));
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}
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secrets.write(Curve.calculateAgreement(theirEphemeral, ourEphemeral.getPrivateKey()));
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DerivedSecrets derivedSecrets = new HKDF().deriveSecrets(secrets.toByteArray(),
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"WhisperText".getBytes());
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return new Pair<RootKey, ChainKey>(new RootKey(derivedSecrets.getCipherKey().getEncoded()),
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new ChainKey(derivedSecrets.getMacKey().getEncoded(), 0));
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} catch (IOException e) {
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throw new AssertionError(e);
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}
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}
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private static boolean isAlice(ECPublicKey ourBaseKey, ECPublicKey theirBaseKey,
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ECPublicKey ourEphemeralKey, ECPublicKey theirEphemeralKey)
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{
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if (ourEphemeralKey.equals(ourBaseKey)) {
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return false;
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}
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if (theirEphemeralKey.equals(theirBaseKey)) {
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return true;
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}
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return isLowEnd(ourBaseKey, theirBaseKey);
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}
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private static boolean isLowEnd(ECPublicKey ourKey, ECPublicKey theirKey) {
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return ourKey.compareTo(theirKey) < 0;
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}
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}
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