content: /*
   * Copyright (C) 2018 The Android Open Source Project
   *
   * 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 com.android.ike.ikev2.message;
  
  import com.android.ike.ikev2.exceptions.IkeException;
  import com.android.ike.ikev2.exceptions.InvalidSyntaxException;
  
  import java.nio.ByteBuffer;
  import java.security.SecureRandom;
  
  /**
   * IkeNoncePayload represents a Nonce payload.
   *
   * <p>Length of nonce data must be at least half the key size of negotiated PRF. It must be between
   * 16 and 256 octets. IKE library always generates nonce of GENERATED_NONCE_LEN octets which is long
   * enough for all currently known PRFs.
   *
   * <p>Critical bit must be ignored when doing decoding and must not be set when doing encoding for
   * this payload.
   *
   * @see <a href="https://tools.ietf.org/html/rfc7296">RFC 7296, Internet Key Exchange Protocol
   *     Version 2 (IKEv2).
   */
  public final class IkeNoncePayload extends IkePayload {
      // The longest key size of all currently known PRFs is 512 bits (64 bytes). Since we are
      // required to generate nonce that is long enough for all proposed PRFs, it is simple that we
      // always generate 32 bytes nonce, which is enough for all known PRFs.
      private static final int GENERATED_NONCE_LEN = 32;
  
      private static final int MIN_NONCE_LEN = 16;
      private static final int MAX_NONCE_LEN = 256;
  
      public final byte[] nonceData;
  
      /**
       * Construct an instance of IkeNoncePayload in the context of {@link IkePayloadFactory}.
       *
       * @param critical indicates if it is a critical payload.
       * @param payloadBody the nonce data
       */
      IkeNoncePayload(boolean critical, byte[] payloadBody) throws IkeException {
          super(PAYLOAD_TYPE_NONCE, critical);
          if (payloadBody.length < MIN_NONCE_LEN || payloadBody.length > MAX_NONCE_LEN) {
              throw new InvalidSyntaxException(
                      "Invalid nonce data with length of: " + payloadBody.length);
          }
          // Check that the length of payloadBody satisfies the "half the key size of negotiated PRF"
          // condition when processing IKE Message in upper layer. Cannot do this check here for
          // lacking PRF information.
          nonceData = payloadBody;
      }
  
      /** Generate Nonce data and construct an instance of IkeNoncePayload. */
      public IkeNoncePayload() {
          super(PAYLOAD_TYPE_NONCE, false);
          nonceData = new byte[GENERATED_NONCE_LEN];
          new SecureRandom().nextBytes(nonceData);
      }
  
      /**
       * Encode Nonce payload to ByteBuffer.
       *
       * @param nextPayload type of payload that follows this payload.
       * @param byteBuffer destination ByteBuffer that stores encoded payload.
       */
      @Override
      protected void encodeToByteBuffer(@PayloadType int nextPayload, ByteBuffer byteBuffer) {
          int payloadLength = GENERIC_HEADER_LENGTH + nonceData.length;
  
          encodePayloadHeaderToByteBuffer(nextPayload, payloadLength, byteBuffer);
          byteBuffer.put(nonceData);
      }
  
      /**
       * Get entire payload length.
       *
       * @return entire payload length.
       */
      @Override
      protected int getPayloadLength() {
          return GENERIC_HEADER_LENGTH + nonceData.length;
      }
  
      /**
       * Return the payload type as a String.
       *
       * @return the payload type as a String.
       */
      @Override
      public String getTypeString() {
          return "Nonce Payload";
      }
  }
  