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/**
* Copyright (C) 2014 Open Whisper Systems
*
* 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 org.whispersystems.libaxolotl.ratchet;
import org.whispersystems.libaxolotl.kdf.DerivedMessageSecrets;
import org.whispersystems.libaxolotl.kdf.HKDF;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
public class ChainKey {
private static final byte[] MESSAGE_KEY_SEED = {0x01};
private static final byte[] CHAIN_KEY_SEED = {0x02};
private final HKDF kdf;
private final byte[] key;
private final int index;
public ChainKey(HKDF kdf, byte[] key, int index) {
this.kdf = kdf;
this.key = key;
this.index = index;
}
public byte[] getKey() {
return key;
}
public int getIndex() {
return index;
}
public ChainKey getNextChainKey() {
byte[] nextKey = getBaseMaterial(CHAIN_KEY_SEED);
return new ChainKey(kdf, nextKey, index + 1);
}
public MessageKeys getMessageKeys() {
byte[] inputKeyMaterial = getBaseMaterial(MESSAGE_KEY_SEED);
byte[] keyMaterialBytes = kdf.deriveSecrets(inputKeyMaterial, "WhisperMessageKeys".getBytes(), DerivedMessageSecrets.SIZE);
DerivedMessageSecrets keyMaterial = new DerivedMessageSecrets(keyMaterialBytes);
return new MessageKeys(keyMaterial.getCipherKey(), keyMaterial.getMacKey(), keyMaterial.getIv(), index);
}
private byte[] getBaseMaterial(byte[] seed) {
try {
Mac mac = Mac.getInstance("HmacSHA256");
mac.init(new SecretKeySpec(key, "HmacSHA256"));
return mac.doFinal(seed);
} catch (NoSuchAlgorithmException | InvalidKeyException e) {
throw new AssertionError(e);
}
}
}
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