content: /**
   * Copyright (C) 2014-2016 Open Whisper Systems
   *
   * Licensed according to the LICENSE file in this repository.
   */
  package org.whispersystems.libsignal.ratchet;
  
  
  import org.whispersystems.libsignal.kdf.DerivedMessageSecrets;
  import org.whispersystems.libsignal.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);
      }
    }
  }
  