CheckedKeyChain.java

/*
 *  Copyright (c) 2014, Facebook, Inc.
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in the
 *  LICENSE file in the root directory of this source tree. An additional grant
 *  of patent rights can be found in the PATENTS file in the same directory.
 *
 */

package com.facebook.crypto;

import com.facebook.crypto.exception.KeyChainException;
import com.facebook.crypto.keychain.KeyChain;
import com.facebook.crypto.mac.NativeMac;

/**
 * Wrapper implementation of KeyChain.
 * Checks that returned arrays match the length specified by the config.
 * If there's a mismatch an IllegalStateArgument exception is thrown.
 */
class CheckedKeyChain implements KeyChain {

  private final KeyChain mDelegate;
  private final CryptoConfig mConfig;

  /**
   * @param mDelegate the keychain to be checked
   * @param mConfig the configuration to be used
   */
  public CheckedKeyChain(KeyChain mDelegate, CryptoConfig mConfig) {
    this.mDelegate = mDelegate;
    this.mConfig = mConfig;
  }

  @Override
  public byte[] getCipherKey() throws KeyChainException {
    byte[] result = mDelegate.getCipherKey();
    checkLength(result, mConfig.keyLength, "Key");
    return result;
  }

  @Override
  public byte[] getMacKey() throws KeyChainException {
    byte[] result = mDelegate.getMacKey();
    checkLength(result, NativeMac.KEY_LENGTH, "Mac");
    return result;
  }

  @Override
  public byte[] getNewIV() throws KeyChainException {
    byte[] result = mDelegate.getNewIV();
    checkLength(result, mConfig.ivLength, "IV");
    return result;
  }

  @Override
  public void destroyKeys() {
    mDelegate.destroyKeys();
  }

  private void checkLength(byte[] key, int lengthInBytes, String name) {
    if (key.length != lengthInBytes) {
      throw new IllegalStateException(
              name + " should be " + lengthInBytes + " bytes long but is " + key.length);
    }
  }
}