/*

  * 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;

 import org.apache.shiro.util.ByteSource;

 import java.io.InputStream;

 import java.io.OutputStream;

 /**

  * A {@code CipherService} uses a cryptographic algorithm called a

  * <a href="http://en.wikipedia.org/wiki/Cipher">Cipher</a> to convert an original input source using a {@code key} to

  * an uninterpretable format.  The resulting encrypted output is only able to be converted back to original form with

  * a {@code key} as well.  {@code CipherService}s can perform both encryption and decryption.

  * <h2>Cipher Basics</h2>

  * For what is known as <em>Symmetric</em> {@code Cipher}s, the {@code Key} used to encrypt the source is the same

  * as (or trivially similar to) the {@code Key} used to decrypt it.

  * <p/>

  * For <em>Asymmetric</em> {@code Cipher}s, the encryption {@code Key} is not the same as the decryption {@code Key}.

  * The most common type of Asymmetric Ciphers are based on what is called public/private key pairs:

  * <p/>

  * A <em>private</em> key is known only to a single party, and as its name implies, is supposed be kept very private

  * and secure.  A <em>public</em> key that is associated with the private key can be disseminated freely to anyone.

  * Then data encrypted by the public key can only be decrypted by the private key and vice versa, but neither party

  * need share their private key with anyone else.  By not sharing a private key, you can guarantee no 3rd party can

  * intercept the key and therefore use it to decrypt a message.

  * <p/>

  * This asymmetric key technology was created as a

  * more secure alternative to symmetric ciphers that sometimes suffer from man-in-the-middle attacks since, for

  * data shared between two parties, the same Key must also be shared and may be compromised.

  * <p/>

  * Note that a symmetric cipher is perfectly fine to use if you just want to encode data in a format no one else

  * can understand and you never give away the key.  Shiro uses a symmetric cipher when creating certain

  * HTTP Cookies for example - because it is often undesirable to have user's identity stored in a plain-text cookie,

  * that identity can be converted via a symmetric cipher.  Since the the same exact Shiro application will receive

  * the cookie, it can decrypt it via the same {@code Key} and there is no potential for discovery since that Key

  * is never shared with anyone.

  * <h2>{@code CipherService}s vs JDK {@link javax.crypto.Cipher Cipher}s</h2>

  * Shiro {@code CipherService}s essentially do the same things as JDK {@link javax.crypto.Cipher Cipher}s, but in

  * simpler and easier-to-use ways for most application developers.  When thinking about encrypting and decrypting data

  * in an application, most app developers want what a {@code CipherService} provides, rather than having to manage the

  * lower-level intricacies of the JDK's {@code Cipher} API.  Here are a few reasons why most people prefer

  * {@code CipherService}s:

  * <ul>

  * <li><b>Stateless Methods</b> - {@code CipherService} method calls do not retain state between method invocations.

  * JDK {@code Cipher} instances do retain state across invocations, requiring its end-users to manage the instance

  * and its state themselves.</li>

  * <li><b>Thread Safety</b> - {@code CipherService} instances are thread-safe inherently because no state is

  * retained across method invocations.  JDK {@code Cipher} instances retain state and cannot be used by multiple

  * threads concurrently.</li>

  * <li><b>Single Operation</b> - {@code CipherService} method calls are single operation methods: encryption or

  * decryption in their entirety are done as a single method call.  This is ideal for the large majority of developer

  * needs where you have something unencrypted and just want it decrypted (or vice versa) in a single method call.  In

  * contrast, JDK {@code Cipher} instances can support encrypting/decrypting data in chunks over time (because it

  * retains state), but this often introduces API clutter and confusion for most application developers.</li>

  * <li><b>Type Safe</b> - There are {@code CipherService} implementations for different Cipher algorithms

  * ({@code AesCipherService}, {@code BlowfishCipherService}, etc).  There is only one JDK {@code Cipher} class to

  * represent all cipher algorithms/instances.

  * <li><b>Simple Construction</b> - Because {@code CipherService} instances are type-safe, instantiating and using

  * one is often as simple as calling the default constructor, for example, <code>new AesCipherService();</code>.  The

  * JDK {@code Cipher} class however requires using a procedural factory method with String arguments to indicate how

  * the instance should be created.  The String arguments themselves are somewhat cryptic and hard to

  * understand unless you're a security expert.  Shiro hides these details from you, but allows you to configure them

  * if you want.</li>

  * </ul>

  *

  * @see BlowfishCipherService

  * @see AesCipherService

  * @since 1.0

  */

 public interface CipherService {

     /**

      * Decrypts encrypted data via the specified cipher key and returns the original (pre-encrypted) data.

      * Note that the key must be in a format understood by the CipherService implementation.

      *

      * @param encrypted     the previously encrypted data to decrypt

      * @param decryptionKey the cipher key used during decryption.

      * @return a byte source representing the original form of the specified encrypted data.

      * @throws CryptoException if there is an error during decryption

      */

     ByteSource decrypt(byte[] encrypted, byte[] decryptionKey) throws CryptoException;

     /**

      * Receives encrypted data from the given {@code InputStream}, decrypts it, and sends the resulting decrypted data

      * to the given {@code OutputStream}.

      * <p/>

      * <b>NOTE:</b> This method <em>does NOT</em> flush or close either stream prior to returning - the caller must

      * do so when they are finished with the streams.  For example:

      * <pre>

      * try {

      *     InputStream in = ...

      *     OutputStream out = ...

      *     cipherService.decrypt(in, out, decryptionKey);

      * } finally {

      *     if (in != null) {

      *         try {

      *             in.close();

      *         } catch (IOException ioe1) { ... log, trigger event, etc }

      *     }

      *     if (out != null) {

      *         try {

      *             out.close();

      *         } catch (IOException ioe2) { ... log, trigger event, etc }

      *     }

      * }

      * </pre>

      *

      * @param in            the stream supplying the data to decrypt

      * @param out           the stream to send the decrypted data

      * @param decryptionKey the cipher key to use for decryption

      * @throws CryptoException if there is any problem during decryption.

      */

     void decrypt(InputStream in, OutputStream out, byte[] decryptionKey) throws CryptoException;

     /**

      * Encrypts data via the specified cipher key.  Note that the key must be in a format understood by

      * the {@code CipherService} implementation.

      *

      * @param raw           the data to encrypt

      * @param encryptionKey the cipher key used during encryption.

      * @return a byte source with the encrypted representation of the specified raw data.

      * @throws CryptoException if there is an error during encryption

      */

     ByteSource encrypt(byte[] raw, byte[] encryptionKey) throws CryptoException;

     /**

      * Receives the data from the given {@code InputStream}, encrypts it, and sends the resulting encrypted data to the

      * given {@code OutputStream}.

      * <p/>

      * <b>NOTE:</b> This method <em>does NOT</em> flush or close either stream prior to returning - the caller must

      * do so when they are finished with the streams.  For example:

      * <pre>

      * try {

      *     InputStream in = ...

      *     OutputStream out = ...

      *     cipherService.encrypt(in, out, encryptionKey);

      * } finally {

      *     if (in != null) {

      *         try {

      *             in.close();

      *         } catch (IOException ioe1) { ... log, trigger event, etc }

      *     }

      *     if (out != null) {

      *         try {

      *             out.close();

      *         } catch (IOException ioe2) { ... log, trigger event, etc }

      *     }

      * }

      * </pre>

      *

      * @param in            the stream supplying the data to encrypt

      * @param out           the stream to send the encrypted data

      * @param encryptionKey the cipher key to use for encryption

      * @throws CryptoException if there is any problem during encryption.

      */

     void encrypt(InputStream in, OutputStream out, byte[] encryptionKey) throws CryptoException;

 }