src/org/jsecurity/crypto/Cipher.java

/*
 * 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.jsecurity.crypto;

/**
 * A <tt>Cipher</tt> is an algorithm used in cryptography that converts an original input source using a <tt>Key</tt> to
 * an uninterpretable format.  The resulting encrypted output is only able to be converted back to original form with
 * a <tt>Key</tt> as well.
 *
 * <p>In what is known as <em>Symmetric</em> <tt>Cipher</tt>s, the <tt>Key</tt> used to encrypt the source is the same
 * as (or trivially similar to) the <tt>Key</tt> used to decrypt it.
 *
 * <p>In <em>Assymetric</em> <tt>Cipher</tt>s, the encryption <tt>Key</tt> is not the same as the decryption <tt>Key</tt>.
 * The most common type of Assymetric 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 assymetric 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.  JSecurity uses a symmetric cipher when using certain
 * HTTP Cookies for example - because it is often undesireable 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 JSecurity application will receive
 * the cookie, it can decrypt it via the same <tt>Key</tt> and there is no potential for discovery since that Key
 * is never shared with anyone.
 *
 * @author Les Hazlewood
 * @see BlowfishCipher
 * @since 0.9
 */
public interface Cipher {

    /**
     * Encrypts data via the specified Cipher key.  Note that the key must be in a format understood by
     * the Cipher implementation.
     *
     * @param raw           the data to encrypt
     * @param encryptionKey the Cipher key used during encryption.
     * @return an encrypted representation of the specified raw data.
     */
    byte[] encrypt(byte[] raw, byte[] encryptionKey);

    /**
     * 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 Cipher implementation.
     *
     * @param encrypted     the previously encrypted data to decrypt
     * @param decryptionKey the Cipher key used during decryption.
     * @return the original form of the specified encrypted data.
     */
    byte[] decrypt(byte[] encrypted, byte[] decryptionKey);

}