content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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 org.apache.shiro.crypto.cipher;
  
  /**
   * A cipher <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation">mode of operation</a>
   * directs a cipher algorithm how to convert data during the encryption or decryption process.  This enum represents
   * all JDK-standard Cipher operation mode names as defined in
   * <a href="http://java.sun.com/javase/6/docs/technotes/guides/security/StandardNames.html">JDK Security Standard
   * Names</a>, as well as a few more that are well-known and supported by other JCA Providers.
   * <p/>
   * This {@code enum} exists to provide Shiro end-users type-safety when declaring an operation mode.  This helps reduce
   * error by providing a compile-time mechanism to specify a mode and guarantees a valid name that will be
   * recognized by an underlying JCA Provider.
   * <h2>Standard or Non-Standard?</h2>
   * All modes listed specify whether they are a JDK standard mode or a non-standard mode.  Standard modes are included
   * in all JDK distributions.  Non-standard modes can
   * sometimes result in better performance or more secure output, but may not be available on the target JDK
   * platform and rely on an external JCA Provider to be installed.  Some providers
   * (like <a href="http://www.bouncycastle.org">Bouncy Castle</a>) may support these modes however.
   *
   * @see <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation">Block Cipher Modes of Operation<a/>
   * @since 1.0
   */
  public enum OperationMode {
  
      /**
       * <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Cipher-block_chaining_.28CBC.29">
       * Cipher-block Chaining</a> mode, defined in <a href="http://csrc.nist.gov/publications/fips/index.html">FIPS
       * PUB 81</a>.
       * <p/>
       * This is a standard JDK operation mode and should be supported by all JDK environments.
       */
      CBC,
  
      /**
       * <a href="http://en.wikipedia.org/wiki/CCM_mode">Counter with CBC-MAC</a> mode<b>*</b> - for block ciphers with
       * 128 bit block-size only. See <a href="http://www.ietf.org/rfc/rfc3610.txt">RFC 3610</a> for AES Ciphers.
       * This mode has essentially been replaced by the more-capable {@link #EAX EAX} mode.
       * <p/>
       * <b>*THIS IS A NON-STANDARD MODE</b>. It is not guaranteed to be supported across JDK installations.  You must
       * ensure you have a JCA Provider that can support this cipher operation mode.
       * <a href="http://www.bouncycastle.org">Bouncy Castle</a> <em>may</em> be one such provider.
       */
      CCM,
  
      /**
       * <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Cipher_feedback_.28CFB.29">Cipher
       * Feedback<a/> mode, defined in <a href="http://csrc.nist.gov/publications/fips/index.html">FIPS PUB 81</a>.
       * <p/>
       * This is a standard JDK operation mode and should be supported by all JDK environments.
       */
      CFB,
  
      /**
       * <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Counter_.28CTR.29">Counter Mode</a>, aka
       * Integer Counter Mode (ICM) and Segmented Integer Counter (SIC).  Counter is a simplification of {@link #OFB OFB}
       * and updates the input block as a counter.
       * <p/>
       * This is a standard JDK operation mode and should be supported by all JDK environments.
       */
      CTR,
  
      /**
       * <a href="http://en.wikipedia.org/wiki/EAX_mode">EAX Mode</a><b>*</b>.  This is a patent-free but less-efficient
       * alternative to {@link #OCB OCB} and has capabilities beyond what {@link #CCM CCM} can provide.
       * <p/>
       * <b>*THIS IS A NON-STANDARD MODE</b>. It is not guaranteed to be supported across JDK installations.  You must
       * ensure you have a JCA Provider that can support this cipher operation mode.
       * <a href="http://www.bouncycastle.org">Bouncy Castle</a> <em>may</em> be one such provider.
       */
      EAX,
  
      /**
       * <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Electronic_codebook_.28ECB.29">Electronic
       * Codebook</a> mode, defined in <a href="http://csrc.nist.gov/publications/fips/index.html">FIPS PUB 81</a>.
       * ECB is the only mode that does <em>not</em> require an Initialization Vector, but because of this, can be seen
       * as less secure than operation modes that require an IV.
       * <p/>
       * This is a standard JDK operation mode and should be supported by all JDK environments.
       */
      ECB,
  
      /**
       * <a href="http://en.wikipedia.org/wiki/GCM_mode">Galois/Counter</a> mode<b>*</b> - for block ciphers with 128
       * bit block-size only.
       * <p/>
       * <b>*THIS IS A NON-STANDARD MODE</b>. It is not guaranteed to be supported across JDK installations.  You must
       * ensure you have a JCA Provider that can support this cipher operation mode.
       * <a href="http://www.bouncycastle.org">Bouncy Castle</a> <em>may</em> be one such provider.
       */
      GCM,
  
      /**
       * No mode.
       * <p/>
       * This is a standard JDK operation mode and should be supported by all JDK environments.
       */
      NONE,
  
      /**
       * <a href="http://en.wikipedia.org/wiki/OCB_mode">Offset Codebook</a> mode<b>*</b>.  Parallel mode that provides
       * both message privacy and authenticity in a single pass.  This is a very efficient mode, but is patent-encumbered.
       * A less-efficient (two pass) alternative is available by using {@link #EAX EAX} mode.
       * <p/>
       * <b>*THIS IS A NON-STANDARD MODE</b>. It is not guaranteed to be supported across JDK installations.  You must
       * ensure you have a JCA Provider that can support this cipher operation mode.
       * <a href="http://www.bouncycastle.org">Bouncy Castle</a> <em>may</em> be one such provider.
       */
      OCB,
  
      /**
       * <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Output_feedback_.28OFB.29">Output
       * Feedback</a> mode, defined in <a href="http://csrc.nist.gov/publications/fips/index.html">FIPS PUB 81</a>.
       * <p/>
       * This is a standard JDK operation mode and should be supported by all JDK environments.
       */
      OFB,
  
      /**
       * <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Propagating_cipher-block_chaining_.28PCBC.29">
       * Propagating Cipher Block Chaining</a> mode, defined in <a href="http://web.mit.edu/kerberos/">Kerberos version 4<a/>.
       * <p/>
       * This is a standard JDK operation mode and should be supported by all JDK environments.
       */
      PCBC
  }
  