/*
 * =============================================================================
 * 
 *   Copyright (c) 2007-2010, The JASYPT team (http://www.jasypt.org)
 * 
 *   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 org.jasypt.digest;

import java.security.Provider;

import org.jasypt.commons.CommonUtils;
import org.jasypt.contrib.org.apache.commons.codec_1_3.binary.Base64;
import org.jasypt.digest.config.DigesterConfig;
import org.jasypt.digest.config.StringDigesterConfig;
import org.jasypt.exceptions.AlreadyInitializedException;
import org.jasypt.exceptions.EncryptionInitializationException;
import org.jasypt.exceptions.EncryptionOperationNotPossibleException;
import org.jasypt.normalization.Normalizer;
import org.jasypt.salt.SaltGenerator;


 Standard implementation of the StringDigester interface. This class lets the user specify the algorithm (and provider) to be used for creating digests, the size of the salt to be applied, the number of times the hash function will be applied (iterations) and the salt generator to be used. 

This class avoids byte-conversion problems related to the fact of 
different platforms having different default charsets, and returns 
digests in the form of BASE64-encoded or HEXADECIMAL ASCII Strings.


This class is thread-safe.



Configuration


The algorithm, provider, salt size, iterations and salt generator can take values 
in any of these ways:

  
Using its default values.
  
Setting a DigesterConfig 
      object which provides new 
      configuration values.
  
Calling the corresponding setX(...) methods.

And the actual values to be used for initialization will be established
by applying the following priorities:

  
First, the default values are considered.
  
Then, if a DigesterConfig 
      object has been set with
      setConfig, the non-null values returned by its
      getX methods override the default values.
  
Finally, if the corresponding setX method has been called
      on the digester itself for any of the configuration parameters, the 
      values set by these calls override all of the above.




Initialization


Before it is ready to create digests, an object of this class has to be
initialized. Initialization happens:

  
When initialize is called.
  
When digest or matches are called for the
      first time, if initialize has not been called before.

Once a digester has been initialized, trying to
change its configuration
will result in an AlreadyInitializedException being thrown.



Usage


A digester may be used in two different ways:

  
For creating digests, by calling the digest method.
  
For matching digests, this is, checking whether a digest
      corresponds adequately to a digest (as in password checking) or not, by
      calling the matches method.
 

The steps taken for creating digests are:

  
The String message is converted to a byte array.
  
A salt of the specified size is generated (see SaltGenerator).
  
The salt bytes are added to the message.
  
The hash function is applied to the salt and message altogether, 
      and then to the
      results of the function itself, as many times as specified
      (iterations).
  
If specified by the salt generator (see SaltGenerator.includePlainSaltInEncryptionResults()), the undigested salt and the final result of the hash
      function are concatenated and returned as a result.
  
The result of the concatenation is encoded in BASE64 or HEXADECIMAL
      and returned as an ASCII String.

Put schematically in bytes:

  

    DIGEST = |S|..(ssb)..|S|X|X|X|...|X|
      

        
S: salt bytes (plain, not digested). (OPTIONAL).
        
ssb: salt size in bytes.
        
X: bytes resulting from hashing (see below).
      
  
  

    |X|X|X|...|X| = 
    H(H(H(..(it)..H(Z|Z|Z|...|Z|))))
    

      
H: Hash function (algorithm).
      
it: Number of iterations.
      
Z: Input for hashing (see below).
 
    
  
  

    |Z|Z|Z|...|Z| =
    |S|..(ssb)..|S|M|M|M...|M|
    

        
S: salt bytes (plain, not digested).
        
ssb: salt size in bytes.
        
M: message bytes.
    
  

If a random salt generator is used, two digests created for the same 
message will always be different
(except in the case of random salt coincidence).
Because of this, in this case the result of the digest method 
will contain both the undigested salt and the digest of the 
(salt + message), so that another digest operation can be performed 
with the same salt on a different message to check if both messages 
match (all of which will be managed automatically by the 
matches method).

     
To learn more about the mechanisms involved in digest creation, read
PKCS #5: Password-Based Cryptography Standard.

Author:
Daniel Fernández
Since:
1.0/**
 * <p>
 * Standard implementation of the {@link StringDigester} interface.
 * This class lets the user specify the algorithm (and provider) to be used for 
 * creating digests, the size of the salt to be applied,
 * the number of times the hash function will be applied (iterations) and
 * the salt generator to be used.
 * </p>
 * <p>
 * This class avoids byte-conversion problems related to the fact of 
 * different platforms having different default charsets, and returns 
 * digests in the form of BASE64-encoded or HEXADECIMAL ASCII Strings.
 * </p>
 * <p>
 * This class is <i>thread-safe</i>.
 * </p>
 * <p>
 * <br/><b><u>Configuration</u></b>
 * </p>
 * <p>
 * The algorithm, provider, salt size, iterations and salt generator can take values 
 * in any of these ways:
 * <ul>
 *   <li>Using its default values.</li>
 *   <li>Setting a <tt>{@link org.jasypt.digest.config.DigesterConfig}</tt> 
 *       object which provides new 
 *       configuration values.</li>
 *   <li>Calling the corresponding <tt>setX(...)</tt> methods.</li>
 * </ul>
 * And the actual values to be used for initialization will be established
 * by applying the following priorities:
 * <ol>
 *   <li>First, the default values are considered.</li>
 *   <li>Then, if a <tt>{@link org.jasypt.digest.config.DigesterConfig}</tt> 
 *       object has been set with
 *       <tt>setConfig</tt>, the non-null values returned by its
 *       <tt>getX</tt> methods override the default values.</li>
 *   <li>Finally, if the corresponding <tt>setX</tt> method has been called
 *       on the digester itself for any of the configuration parameters, the 
 *       values set by these calls override all of the above.</li>
 * </ol>
 * </p>
 * 
 * <p>
 * <br/><b><u>Initialization</u></b>
 * </p>
 * <p>
 * Before it is ready to create digests, an object of this class has to be
 * <i>initialized</i>. Initialization happens:
 * <ul>
 *   <li>When <tt>initialize</tt> is called.</li>
 *   <li>When <tt>digest</tt> or <tt>matches</tt> are called for the
 *       first time, if <tt>initialize</tt> has not been called before.</li>
 * </ul>
 * Once a digester has been initialized, trying to
 * change its configuration
 * will result in an <tt>AlreadyInitializedException</tt> being thrown.
 * </p>
 * 
 * <p>
 * <br/><b><u>Usage</u></b>
 * </p>
 * <p>
 * A digester may be used in two different ways:
 * <ul>
 *   <li>For <i>creating digests</i>, by calling the <tt>digest</tt> method.</li>
 *   <li>For <i>matching digests</i>, this is, checking whether a digest
 *       corresponds adequately to a digest (as in password checking) or not, by
 *       calling the <tt>matches</tt> method.</li> 
 * </ul>
 * The steps taken for creating digests are:
 * <ol>
 *   <li>The String message is converted to a byte array.</li>
 *   <li>A salt of the specified size is generated (see 
 *       {@link org.jasypt.salt.SaltGenerator}).</li>
 *   <li>The salt bytes are added to the message.</li>
 *   <li>The hash function is applied to the salt and message altogether, 
 *       and then to the
 *       results of the function itself, as many times as specified
 *       (iterations).</li>
 *   <li>If specified by the salt generator (see 
 *       {@link org.jasypt.salt.SaltGenerator#includePlainSaltInEncryptionResults()}), 
 *       the <i>undigested</i> salt and the final result of the hash
 *       function are concatenated and returned as a result.</li>
 *   <li>The result of the concatenation is encoded in BASE64 or HEXADECIMAL
 *       and returned as an ASCII String.</li>
 * </ol>
 * Put schematically in bytes:
 * <ul>
 *   <li>
 *     DIGEST = <tt>|<b>S</b>|..(ssb)..|<b>S</b>|<b>X</b>|<b>X</b>|<b>X</b>|...|<b>X</b>|</tt>
 *       <ul>
 *         <li><tt><b>S</b></tt>: salt bytes (plain, not digested). <i>(OPTIONAL)</i>.</li>
 *         <li><tt>ssb</tt>: salt size in bytes.</li>
 *         <li><tt><b>X</b></tt>: bytes resulting from hashing (see below).</li>
 *       </ul>
 *   </li>
 *   <li>
 *     <tt>|<b>X</b>|<b>X</b>|<b>X</b>|...|<b>X</b>|</tt> = 
 *     <tt><i>H</i>(<i>H</i>(<i>H</i>(..(it)..<i>H</i>(<b>Z</b>|<b>Z</b>|<b>Z</b>|...|<b>Z</b>|))))</tt>
 *     <ul>
 *       <li><tt><i>H</i></tt>: Hash function (algorithm).</li>
 *       <li><tt>it</tt>: Number of iterations.</li>
 *       <li><tt><b>Z</b></tt>: Input for hashing (see below).</li> 
 *     </ul>
 *   </li>
 *   <li>
 *     <tt>|<b>Z</b>|<b>Z</b>|<b>Z</b>|...|<b>Z</b>|</tt> =
 *     <tt>|<b>S</b>|..(ssb)..|<b>S</b>|<b>M</b>|<b>M</b>|<b>M</b>...|<b>M</b>|</tt>
 *     <ul>
 *         <li><tt><b>S</b></tt>: salt bytes (plain, not digested).</li>
 *         <li><tt>ssb</tt>: salt size in bytes.</li>
 *         <li><tt><b>M</b></tt>: message bytes.</li>
 *     </ul>
 *   </li>
 * </ul>
 * <b>If a random salt generator is used, two digests created for the same 
 * message will always be different
 * (except in the case of random salt coincidence).</b>
 * Because of this, in this case the result of the <tt>digest</tt> method 
 * will contain both the <i>undigested</i> salt and the digest of the 
 * (salt + message), so that another digest operation can be performed 
 * with the same salt on a different message to check if both messages 
 * match (all of which will be managed automatically by the 
 * <tt>matches</tt> method).
 * </p>
 * <p>     
 * To learn more about the mechanisms involved in digest creation, read
 * <a href="http://www.rsasecurity.com/rsalabs/node.asp?id=2127" 
 * target="_blank">PKCS &#035;5: Password-Based Cryptography Standard</a>.
 * </p>
 * 
 * @since 1.0
 * 
 * @author Daniel Fern&aacute;ndez
 * 
 */
public final class StandardStringDigester implements StringDigester {


    

Charset to be used to obtain "digestable" byte arrays from input Strings.
Set to UTF-8.

 
This charset has to be fixed to some value so that we avoid problems 
with different platforms having different "default" charsets. 


It is set to UTF-8 because it covers the whole spectrum of characters
representable in Java (which internally uses UTF-16), and avoids the
size penalty of UTF-16 (which will always use two bytes for representing
each character, even if it is an ASCII one).


Setting this value to UTF-8 does not mean that Strings that originally
come for, for example, an ISO-8859-1 input, will not be correcly 
digested. It simply provides a way of "fixing" the way a String will
be converted into bytes for digesting.

/**
     * <p>
     * Charset to be used to obtain "digestable" byte arrays from input Strings.
     * Set to <b>UTF-8</b>.
     * </p>
     * <p> 
     * This charset has to be fixed to some value so that we avoid problems 
     * with different platforms having different "default" charsets. 
     * </p>
     * <p>
     * It is set to <b>UTF-8</b> because it covers the whole spectrum of characters
     * representable in Java (which internally uses UTF-16), and avoids the
     * size penalty of UTF-16 (which will always use two bytes for representing
     * each character, even if it is an ASCII one).
     * </p>
     * <p>
     * Setting this value to UTF-8 does not mean that Strings that originally
     * come for, for example, an ISO-8859-1 input, will not be correcly 
     * digested. It simply provides a way of "fixing" the way a String will
     * be converted into bytes for digesting.
     * </p>
     */
    public static final String MESSAGE_CHARSET = "UTF-8";
    
    

Charset to be used for encoding the resulting digests. 
Set to US-ASCII.


The result of digesting some bytes can be any other bytes, and so
the result of digesting, for example, some LATIN-1 valid String bytes, 
can be bytes that may not conform a "valid" LATIN-1 String.


Because of this, digests are always encoded in BASE64 or
HEXADECIMAL after 
being created, and this ensures that the 
digests will make perfectly representable, safe ASCII Strings. Because
of this, the charset used to convert the digest bytes to the returned 
String is set to US-ASCII.

/**
     * <p>
     * Charset to be used for encoding the resulting digests. 
     * Set to <b>US-ASCII</b>.
     * </p>
     * <p>
     * The result of digesting some bytes can be any other bytes, and so
     * the result of digesting, for example, some LATIN-1 valid String bytes, 
     * can be bytes that may not conform a "valid" LATIN-1 String.
     * </p>
     * <p>
     * Because of this, digests are always encoded in <i>BASE64</i> or
     * HEXADECIMAL after 
     * being created, and this ensures that the 
     * digests will make perfectly representable, safe ASCII Strings. Because
     * of this, the charset used to convert the digest bytes to the returned 
     * String is set to <b>US-ASCII</b>.
     * </p>
     */
    public static final String DIGEST_CHARSET = "US-ASCII";
    
    

Whether the Unicode normalization step should be ignored because of
legacy-compatibility issues. Defaults to FALSE (the normalization
step WILL be performed).

/**
     * <p>
     * Whether the Unicode normalization step should be ignored because of
     * legacy-compatibility issues. Defaults to <b>FALSE</b> (the normalization
     * step WILL be performed).
     * </p>
     */
    public static final boolean DEFAULT_UNICODE_NORMALIZATION_IGNORED = false;

    

Default type of String output. Set to BASE64. 
 
/**
     * <p>
     * Default type of String output. Set to <b>BASE64</b>. 
     * </p> 
     */
    public static final String DEFAULT_STRING_OUTPUT_TYPE = 
        CommonUtils.STRING_OUTPUT_TYPE_BASE64;

    
    // The StandardByteDigester that will be internally used.
    private final StandardByteDigester byteDigester;

    // If the config object set is a StringDigesterConfig, it must be referenced
    private StringDigesterConfig stringDigesterConfig = null;
    
    // This variable holds whether the unicode normalization step should
    // be ignored or not (default = DO NOT ignore).
    private boolean unicodeNormalizationIgnored = 
        DEFAULT_UNICODE_NORMALIZATION_IGNORED;
    
    // This variable holds the type of String output which will be done,
    // and also a boolean variable for faster comparison
    private String stringOutputType = DEFAULT_STRING_OUTPUT_TYPE;
    private boolean stringOutputTypeBase64 = true;
    

    // Prefix and suffix to be added to encryption results (if any)
    private String prefix = null;
    private String suffix = null;
    

    /*
     * Set of booleans which indicate whether the config or default values
     * have to be overriden because of the setX methods having been
     * called.
     */
    private boolean unicodeNormalizationIgnoredSet = false;
    private boolean stringOutputTypeSet = false;
    private boolean prefixSet = false;
    private boolean suffixSet = false;
    
    
    // BASE64 encoder which will make sure the returned digests are
    // valid US-ASCII strings (if the user chooses BASE64 output).
    // The Bsae64 encoder is THREAD-SAFE
    private final Base64 base64;


    
    
Creates a new instance of StandardStringDigester.
/**
     * Creates a new instance of <tt>StandardStringDigester</tt>.
     */
    public StandardStringDigester() {
        super();
        this.byteDigester = new StandardByteDigester();
        this.base64 = new Base64();
    }


    
    /*
     * Creates a new instance of <tt>StandardStringDigester</tt> using
     * the specified byte digester (constructor used for cloning)
     */
    private StandardStringDigester(final StandardByteDigester standardByteDigester) {
        super();
        this.byteDigester = standardByteDigester;
        this.base64 = new Base64();
    }

    
    

Sets a DigesterConfig or StringDigesterConfig object for the digester. If this config object is set, it will be asked values for: 

  
Algorithm
  
Security Provider (or provider name)
  
Salt size
  
Hashing iterations
  
Salt generator
  
Use of Unicode normalization mechanisms 
      (only StringDigesterConfig)
  
Output type (base64, hexadecimal) 
      (only StringDigesterConfig)


The non-null values it returns will override the default ones, 
and will be overriden by any values specified with a setX
method.

Params:
config – the DigesterConfig object to be used as the 
              source for configuration parameters./**
     * <p>
     * Sets a <tt>{@link org.jasypt.digest.config.DigesterConfig}</tt> 
     * or {@link StringDigesterConfig} object 
     * for the digester. If this config
     * object is set, it will be asked values for:
     * </p>
     * 
     * <ul>
     *   <li>Algorithm</li>
     *   <li>Security Provider (or provider name)</li>
     *   <li>Salt size</li>
     *   <li>Hashing iterations</li>
     *   <li>Salt generator</li>
     *   <li>Use of Unicode normalization mechanisms 
     *       (only <tt>StringDigesterConfig</tt>)</li>
     *   <li>Output type (base64, hexadecimal) 
     *       (only <tt>StringDigesterConfig</tt>)</li>
     * </ul>
     * 
     * <p>
     * The non-null values it returns will override the default ones, 
     * <i>and will be overriden by any values specified with a <tt>setX</tt>
     * method</i>.
     * </p>
     * 
     * @param config the <tt>DigesterConfig</tt> object to be used as the 
     *               source for configuration parameters.
     */
    public synchronized void setConfig(final DigesterConfig config) {
        this.byteDigester.setConfig(config);
        if ((config != null) && (config instanceof StringDigesterConfig)) {
            this.stringDigesterConfig = (StringDigesterConfig) config;
        }
    }

    
    

Sets the algorithm to be used for digesting, like MD5 
or SHA-1.


This algorithm has to be supported by your security infrastructure, and
it should be allowed as an algorithm for creating
java.security.MessageDigest instances.

 If you are specifying a security provider with setProvider(Provider) or setProviderName(String), this algorithm should be supported by your specified provider. 

If you are not specifying a provider, you will be able to use those
algorithms provided by the default security provider of your JVM vendor.
For valid names in the Sun JVM, see Java 
        Cryptography Architecture API Specification & 
        Reference.

Params:
algorithm – the name of the algorithm to be used./**
     * <p>
     * Sets the algorithm to be used for digesting, like <tt>MD5</tt> 
     * or <tt>SHA-1</tt>.
     * </p>
     * <p>
     * This algorithm has to be supported by your security infrastructure, and
     * it should be allowed as an algorithm for creating
     * java.security.MessageDigest instances.
     * </p>
     * <p>
     * If you are specifying a security provider with {@link #setProvider(Provider)} or
     * {@link #setProviderName(String)}, this algorithm should be
     * supported by your specified provider.
     * </p>
     * <p>
     * If you are not specifying a provider, you will be able to use those
     * algorithms provided by the default security provider of your JVM vendor.
     * For valid names in the Sun JVM, see <a target="_blank" 
     *         href="http://java.sun.com/j2se/1.5.0/docs/guide/security/CryptoSpec.html#AppA">Java 
     *         Cryptography Architecture API Specification & 
     *         Reference</a>.
     * </p>
     * 
     * @param algorithm the name of the algorithm to be used.
     */
    public void setAlgorithm(final String algorithm) {
        this.byteDigester.setAlgorithm(algorithm);
    }

    
    

Sets the size of the salt to be used to compute the digest.
This mechanism is explained in 
PKCS #5: Password-Based Cryptography Standard.


If salt size is set to zero, then no salt will be used.

Params:
saltSizeBytes – the size of the salt to be used, in bytes./**
     * <p>
     * Sets the size of the salt to be used to compute the digest.
     * This mechanism is explained in 
     * <a href="http://www.rsasecurity.com/rsalabs/node.asp?id=2127" 
     * target="_blank">PKCS &#035;5: Password-Based Cryptography Standard</a>.
     * </p>
     * 
     * <p>
     * If salt size is set to zero, then no salt will be used.
     * </p>
     * 
     * @param saltSizeBytes the size of the salt to be used, in bytes.
     */
    public void setSaltSizeBytes(final int saltSizeBytes) {
        this.byteDigester.setSaltSizeBytes(saltSizeBytes);
    }

    
    

Set the number of times the hash function will be applied recursively.


The hash function will be applied to its own results as many times as 
specified: h(h(...h(x)...))


This mechanism is explained in 
PKCS #5: Password-Based Cryptography Standard.

Params:
iterations – the number of iterations./**
     * <p>
     * Set the number of times the hash function will be applied recursively.
     * <br/>
     * The hash function will be applied to its own results as many times as 
     * specified: <i>h(h(...h(x)...))</i>
     * </p>
     * <p>
     * This mechanism is explained in 
     * <a href="http://www.rsasecurity.com/rsalabs/node.asp?id=2127" 
     * target="_blank">PKCS &#035;5: Password-Based Cryptography Standard</a>.
     * </p>
     * 
     * @param iterations the number of iterations.
     */
    public void setIterations(final int iterations) {
        this.byteDigester.setIterations(iterations);
    }

    
    
 Sets the salt generator to be used. If no salt generator is specified, an instance of RandomSaltGenerator will be used. 
Params:
saltGenerator – the salt generator to be used./**
     * <p>
     * Sets the salt generator to be used. If no salt generator is specified,
     * an instance of {@link org.jasypt.salt.RandomSaltGenerator} will be used. 
     * </p>
     * 
     * @param saltGenerator the salt generator to be used.
     */
    public void setSaltGenerator(final SaltGenerator saltGenerator) {
        this.byteDigester.setSaltGenerator(saltGenerator);
    }

    
    

Sets the name of the security provider to be asked for the
digest algorithm. This security provider has to be registered beforehand
at the JVM security framework. 

 The provider can also be set with the setProvider(Provider) method, in which case it will not be necessary neither registering the provider beforehand, nor calling this setProviderName(String) method to specify a provider name. 
 Note that a call to setProvider(Provider) overrides any value set by this method. 

If no provider name / provider is explicitly set, the default JVM
provider will be used.

Params:
providerName – the name of the security provider to be asked
                    for the digest algorithm.
Since:
1.3/**
     * <p>
     * Sets the name of the security provider to be asked for the
     * digest algorithm. This security provider has to be registered beforehand
     * at the JVM security framework. 
     * </p>
     * <p>
     * The provider can also be set with the {@link #setProvider(Provider)}
     * method, in which case it will not be necessary neither registering
     * the provider beforehand,
     * nor calling this {@link #setProviderName(String)} method to specify
     * a provider name.
     * </p>
     * <p>
     * Note that a call to {@link #setProvider(Provider)} overrides any value 
     * set by this method.
     * </p>
     * <p>
     * If no provider name / provider is explicitly set, the default JVM
     * provider will be used.
     * </p>
     * 
     * @since 1.3
     * 
     * @param providerName the name of the security provider to be asked
     *                     for the digest algorithm.
     */
    public void setProviderName(final String providerName) {
        this.byteDigester.setProviderName(providerName);
    }
    
    
    

Sets the security provider to be asked for the digest algorithm.
The provider does not have to be registered at the security 
infrastructure beforehand, and its being used here will not result in
its being registered.

 If this method is called, calling setProviderName(String) becomes unnecessary. 

If no provider name / provider is explicitly set, the default JVM
provider will be used.

Params:
provider – the provider to be asked for the chosen algorithm
Since:
1.3/**
     * <p>
     * Sets the security provider to be asked for the digest algorithm.
     * The provider does not have to be registered at the security 
     * infrastructure beforehand, and its being used here will not result in
     * its being registered.
     * </p>
     * <p>
     * If this method is called, calling {@link #setProviderName(String)}
     * becomes unnecessary.
     * </p>
     * <p>
     * If no provider name / provider is explicitly set, the default JVM
     * provider will be used.
     * </p>
     * 
     * @since 1.3
     * 
     * @param provider the provider to be asked for the chosen algorithm
     */
    public void setProvider(final Provider provider) {
        this.byteDigester.setProvider(provider);
    }
    
    
    

Whether the salt bytes are to be appended after the 
message ones before performing the digest operation on the whole. The 
default behaviour is to insert those bytes before the message bytes, but 
setting this configuration item to true allows compatibility 
with some external systems and specifications (e.g. LDAP {SSHA}).


If this parameter is not explicitly set, the default behaviour 
(insertion of salt before message) will be applied.

Params:
invertPositionOfSaltInMessageBeforeDigesting – 
       whether salt will be appended after the message before applying 
       the digest operation on the whole, instead of inserted before it
       (which is the default).
Since:
1.7/**
     * <p>
     * Whether the salt bytes are to be appended after the 
     * message ones before performing the digest operation on the whole. The 
     * default behaviour is to insert those bytes before the message bytes, but 
     * setting this configuration item to <tt>true</tt> allows compatibility 
     * with some external systems and specifications (e.g. LDAP {SSHA}).
     * </p>
     * <p>
     * If this parameter is not explicitly set, the default behaviour 
     * (insertion of salt before message) will be applied.
     * </p>
     * 
     * @since 1.7
     * 
     * @param invertPositionOfSaltInMessageBeforeDigesting
     *        whether salt will be appended after the message before applying 
     *        the digest operation on the whole, instead of inserted before it
     *        (which is the default).
     */
    public synchronized void setInvertPositionOfSaltInMessageBeforeDigesting(
            final boolean invertPositionOfSaltInMessageBeforeDigesting) {
        this.byteDigester.setInvertPositionOfSaltInMessageBeforeDigesting(invertPositionOfSaltInMessageBeforeDigesting);
    }
    
    
    

Whether the plain (not hashed) salt bytes are to 
be appended after the digest operation result bytes. The default behaviour is 
to insert them before the digest result, but setting this configuration 
item to true allows compatibility with some external systems
and specifications (e.g. LDAP {SSHA}).


If this parameter is not explicitly set, the default behaviour 
(insertion of plain salt before digest result) will be applied.

Params:
invertPositionOfPlainSaltInEncryptionResults – 
       whether plain salt will be appended after the digest operation 
       result instead of inserted before it (which is the 
       default).
Since:
1.7/**
     * <p>
     * Whether the plain (not hashed) salt bytes are to 
     * be appended after the digest operation result bytes. The default behaviour is 
     * to insert them before the digest result, but setting this configuration 
     * item to <tt>true</tt> allows compatibility with some external systems
     * and specifications (e.g. LDAP {SSHA}).
     * </p>
     * <p>
     * If this parameter is not explicitly set, the default behaviour 
     * (insertion of plain salt before digest result) will be applied.
     * </p>
     * 
     * @since 1.7
     * 
     * @param invertPositionOfPlainSaltInEncryptionResults
     *        whether plain salt will be appended after the digest operation 
     *        result instead of inserted before it (which is the 
     *        default).
     */
    public synchronized void setInvertPositionOfPlainSaltInEncryptionResults(
            final boolean invertPositionOfPlainSaltInEncryptionResults) {
        this.byteDigester.setInvertPositionOfPlainSaltInEncryptionResults(invertPositionOfPlainSaltInEncryptionResults);
    }
    
    
    

Whether digest matching operations will allow matching
digests with a salt size different to the one configured in the "saltSizeBytes"
property. This is possible because digest algorithms will produce a fixed-size 
result, so the remaining bytes from the hashed input will be considered salt.


This will allow the digester to match digests produced in environments which do not
establish a fixed salt size as standard (for example, SSHA password encryption
in LDAP systems).  


The value of this property will not affect the creation of digests, 
which will always have a salt of the size established by the "saltSizeBytes" 
property. It will only affect digest matching.  


Setting this property to true is not compatible with SaltGenerator implementations which return false for their SaltGenerator.includePlainSaltInEncryptionResults() property. 

Also, be aware that some algorithms or algorithm providers might not support
knowing the size of the digests beforehand, which is also incompatible with
a lenient behaviour.


If this parameter is not explicitly set, the default behaviour 
(NOT lenient) will be applied.

Params:
useLenientSaltSizeCheck – whether the digester will allow matching of 
       digests with different salt sizes than established or not (default 
       is false).
Since:
1.7/**
     * <p>
     * Whether digest matching operations will allow matching
     * digests with a salt size different to the one configured in the "saltSizeBytes"
     * property. This is possible because digest algorithms will produce a fixed-size 
     * result, so the remaining bytes from the hashed input will be considered salt.
     * </p>
     * <p>
     * This will allow the digester to match digests produced in environments which do not
     * establish a fixed salt size as standard (for example, SSHA password encryption
     * in LDAP systems).  
     * </p>
     * <p>
     * The value of this property will <b>not</b> affect the creation of digests, 
     * which will always have a salt of the size established by the "saltSizeBytes" 
     * property. It will only affect digest matching.  
     * </p>
     * <p>
     * Setting this property to <tt>true</tt> is not compatible with {@link SaltGenerator}
     * implementations which return false for their 
     * {@link SaltGenerator#includePlainSaltInEncryptionResults()} property. 
     * </p>
     * <p>
     * Also, be aware that some algorithms or algorithm providers might not support
     * knowing the size of the digests beforehand, which is also incompatible with
     * a lenient behaviour.
     * </p>
     * <p>
     * If this parameter is not explicitly set, the default behaviour 
     * (NOT lenient) will be applied.
     * </p>
     * 
     * @since 1.7
     * 
     * @param useLenientSaltSizeCheck whether the digester will allow matching of 
     *        digests with different salt sizes than established or not (default 
     *        is false).
     */
    public synchronized void setUseLenientSaltSizeCheck(final boolean useLenientSaltSizeCheck) {
        this.byteDigester.setUseLenientSaltSizeCheck(useLenientSaltSizeCheck);
    }
    
    
    

Sets whether the unicode text normalization step should be ignored.


The Java Virtual Machine internally handles all Strings as UNICODE. When
digesting or matching digests in jasypt, these Strings are first 
normalized to 
its NFC form so that digest matching is not affected by the specific
form in which the messages where input.


It is normally safe (and recommended) to leave this parameter set to 
its default FALSE value (and thus DO perform normalization 
operations). But in some specific cases in which issues with legacy
software could arise, it might be useful to set this to TRUE.


For more information on unicode text normalization, see this issue of 
Core Java Technologies Tech Tips.

Params:
unicodeNormalizationIgnored – whether the unicode text 
       normalization step should be ignored or not.
Since:
1.3/**
     * <p>
     * Sets whether the unicode text normalization step should be ignored.
     * </p>
     * <p>
     * The Java Virtual Machine internally handles all Strings as UNICODE. When
     * digesting or matching digests in jasypt, these Strings are first 
     * <b>normalized to 
     * its NFC form</b> so that digest matching is not affected by the specific
     * form in which the messages where input.
     * </p>
     * <p>
     * <b>It is normally safe (and recommended) to leave this parameter set to 
     * its default FALSE value (and thus DO perform normalization 
     * operations)</b>. But in some specific cases in which issues with legacy
     * software could arise, it might be useful to set this to TRUE.
     * </p>
     * <p>
     * For more information on unicode text normalization, see this issue of 
     * <a href="http://java.sun.com/mailers/techtips/corejava/2007/tt0207.html">Core Java Technologies Tech Tips</a>.
     * </p>
     * 
     * @since 1.3
     * 
     * @param unicodeNormalizationIgnored whether the unicode text 
     *        normalization step should be ignored or not.
     */
    public synchronized void setUnicodeNormalizationIgnored(final boolean unicodeNormalizationIgnored) {
        if (isInitialized()) {
            throw new AlreadyInitializedException();
        }
        this.unicodeNormalizationIgnored = unicodeNormalizationIgnored;
        this.unicodeNormalizationIgnoredSet = true;
    }
    
    
    

Sets the the form in which String output
will be encoded. Available encoding types are:


  
base64 (default)
  
hexadecimal


If not set, null will be returned.

Params:
stringOutputType – the string output type.
Since:
1.3/**
     * <p>
     * Sets the the form in which String output
     * will be encoded. Available encoding types are:
     * </p>
     * <ul>
     *   <li><tt><b>base64</b></tt> (default)</li>
     *   <li><tt><b>hexadecimal</b></tt></li>
     * </ul>
     * <p>
     * If not set, null will be returned.
     * </p>
     *
     * @since 1.3
     * 
     * @param stringOutputType the string output type.
     */
    public synchronized void setStringOutputType(final String stringOutputType) {
        CommonUtils.validateNotEmpty(stringOutputType, "String output type cannot be set empty");
        if (isInitialized()) {
            throw new AlreadyInitializedException();
        }
        this.stringOutputType = 
            CommonUtils.
                getStandardStringOutputType(stringOutputType);
        this.stringOutputTypeSet = true;
    }
    
    
    
 Sets the prefix to be added at the beginning of encryption results, and also to be expected at the beginning of plain messages provided for matching operations (raising an EncryptionOperationNotPossibleException if not). 

By default, no prefix will be added to encryption results.

Params:
prefix – the prefix to be set
Since:
1.7/**
     * <p>
     * Sets the prefix to be added at the beginning of encryption results, and also to
     * be expected at the beginning of plain messages provided for matching operations
     * (raising an {@link EncryptionOperationNotPossibleException} if not).
     * </p>
     * <p>
     * By default, no prefix will be added to encryption results.
     * </p>
     * 
     * @since 1.7
     * 
     * @param prefix the prefix to be set
     */
    public synchronized void setPrefix(final String prefix) {
        if (isInitialized()) {
            throw new AlreadyInitializedException();
        }
        this.prefix = prefix;
        this.prefixSet = true;
    }
    
    
    
 Sets the suffix to be added at the end of encryption results, and also to be expected at the end of plain messages provided for matching operations (raising an EncryptionOperationNotPossibleException if not). 

By default, no suffix will be added to encryption results.

Params:
suffix – the suffix to be set
Since:
1.7/**
     * <p>
     * Sets the suffix to be added at the end of encryption results, and also to
     * be expected at the end of plain messages provided for matching operations
     * (raising an {@link EncryptionOperationNotPossibleException} if not).
     * </p>
     * <p>
     * By default, no suffix will be added to encryption results.
     * </p>
     * 
     * @since 1.7
     * 
     * @param suffix the suffix to be set
     */
    public synchronized void setSuffix(final String suffix) {
        if (isInitialized()) {
            throw new AlreadyInitializedException();
        }
        this.suffix = suffix;
        this.suffixSet = true;
    }

    


    
    
    
    
    /*
     * Clone this digester.
     */
    StandardStringDigester cloneDigester() {
        
        // Check initialization
        if (!isInitialized()) {
            initialize();
        }
        
        final StandardStringDigester cloned = 
            new StandardStringDigester(this.byteDigester.cloneDigester());
        cloned.setPrefix(this.prefix);
        cloned.setSuffix(this.suffix);
        if (CommonUtils.isNotEmpty(this.stringOutputType)) {
            cloned.setStringOutputType(this.stringOutputType);
        }
        cloned.setUnicodeNormalizationIgnored(this.unicodeNormalizationIgnored);
        
        return cloned;
        
    }
    
    
    
    
    

  Returns true if the digester has already been initialized, false if
  not.
 
  Initialization happens:


  
When initialize is called.
  
When digest or matches are called for the
      first time, if initialize has not been called before.


  Once a digester has been initialized, trying to
  change its configuration will result in an 
  AlreadyInitializedException
  being thrown.

Returns:
true if the digester has already been initialized, false if
  not./**
     * <p>
     *   Returns true if the digester has already been initialized, false if
     *   not.<br/> 
     *   Initialization happens:
     * </p>
     * <ul>
     *   <li>When <tt>initialize</tt> is called.</li>
     *   <li>When <tt>digest</tt> or <tt>matches</tt> are called for the
     *       first time, if <tt>initialize</tt> has not been called before.</li>
     * </ul>
     * <p>
     *   Once a digester has been initialized, trying to
     *   change its configuration will result in an 
     *   <tt>AlreadyInitializedException</tt>
     *   being thrown.
     * </p>
     * 
     * @return true if the digester has already been initialized, false if
     *   not.
     */
    public boolean isInitialized() {
        return this.byteDigester.isInitialized();
    }

    
    

Initialize the digester.


This operation will consist in determining the actual configuration 
values to be used, and then initializing the digester with them.


These values are decided by applying the following priorities:


  
First, the default values are considered.
  
Then, if a 
      DigesterConfig object 
      has been set with
      setConfig, the non-null values returned by its
      getX methods override the default values.
  
Finally, if the corresponding setX method has been called
      on the digester itself for any of the configuration parameters, the 
      values set by these calls override all of the above.


  Once a digester has been initialized, trying to
  change its configuration will result in an 
  AlreadyInitializedException 
  being thrown.

Throws:
EncryptionInitializationException – if initialization could not
        be correctly done (for example, if the digest algorithm chosen
        cannot be used)./**
     * <p>
     * Initialize the digester.
     * </p>
     * <p>
     * This operation will consist in determining the actual configuration 
     * values to be used, and then initializing the digester with them.
     * <br/>
     * These values are decided by applying the following priorities:
     * </p>
     * <ol>
     *   <li>First, the default values are considered.</li>
     *   <li>Then, if a 
     *       <tt>{@link org.jasypt.digest.config.DigesterConfig}</tt> object 
     *       has been set with
     *       <tt>setConfig</tt>, the non-null values returned by its
     *       <tt>getX</tt> methods override the default values.</li>
     *   <li>Finally, if the corresponding <tt>setX</tt> method has been called
     *       on the digester itself for any of the configuration parameters, the 
     *       values set by these calls override all of the above.</li>
     * </ol>
     * <p>
     *   Once a digester has been initialized, trying to
     *   change its configuration will result in an 
     *   <tt>AlreadyInitializedException</tt> 
     *   being thrown.
     * </p>
     * 
     * @throws EncryptionInitializationException if initialization could not
     *         be correctly done (for example, if the digest algorithm chosen
     *         cannot be used).
     *
     */
    public synchronized void initialize() {
        
        // Double-check to avoid synchronization issues
        if (!this.isInitialized()) {

            /*
             * If a StringDigesterConfig object has been set, we need to 
             * consider the values it returns (if, for each value, the
             * corresponding "setX" method has not been called).
             */
            if (this.stringDigesterConfig != null) {
                
                final Boolean configUnicodeNormalizationIgnored = 
                    this.stringDigesterConfig.isUnicodeNormalizationIgnored();
                final String configStringOutputType = 
                    this.stringDigesterConfig.getStringOutputType();
                final String configPrefix = 
                    this.stringDigesterConfig.getPrefix();
                final String configSuffix =
                    this.stringDigesterConfig.getSuffix();

                this.unicodeNormalizationIgnored = 
                    ((this.unicodeNormalizationIgnoredSet) || (configUnicodeNormalizationIgnored == null))?
                            this.unicodeNormalizationIgnored : configUnicodeNormalizationIgnored.booleanValue();
                this.stringOutputType = 
                    ((this.stringOutputTypeSet) || (configStringOutputType == null))?
                            this.stringOutputType : configStringOutputType;
                this.prefix =
                    ((this.prefixSet) || (configPrefix == null))?
                            this.prefix : configPrefix;
                this.suffix =
                    ((this.suffixSet) || (configSuffix == null))?
                            this.suffix : configSuffix;
                
            }
            
            this.stringOutputTypeBase64 =
                (CommonUtils.STRING_OUTPUT_TYPE_BASE64.
                    equalsIgnoreCase(this.stringOutputType));
            
            this.byteDigester.initialize();
        
        }

    }
    

    

Performs a digest operation on a String message.


The steps taken for creating the digest are:

  
The String message is converted to a byte array.
  
A salt of the specified size is generated (see SaltGenerator).
  
The salt bytes are added to the message.
  
The hash function is applied to the salt and message altogether, 
      and then to the
      results of the function itself, as many times as specified
      (iterations).
  
If specified by the salt generator (see SaltGenerator.includePlainSaltInEncryptionResults()), the undigested salt and the final result of the hash
      function are concatenated and returned as a result.
  
The result of the concatenation is encoded in BASE64 (default) 
      or HEXADECIMAL
      and returned as an ASCII String.

Put schematically in bytes:

  

    DIGEST = |S|..(ssb)..|S|X|X|X|...|X|
      

        
S: salt bytes (plain, not digested). (OPTIONAL).
        
ssb: salt size in bytes.
        
X: bytes resulting from hashing (see below).
      
  
  

    |X|X|X|...|X| = 
    H(H(H(..(it)..H(Z|Z|Z|...|Z|))))
    

      
H: Hash function (algorithm).
      
it: Number of iterations.
      
Z: Input for hashing (see below).
 
    
  
  

    |Z|Z|Z|...|Z| =
    |S|..(ssb)..|S|M|M|M...|M|
    

        
S: salt bytes (plain, not digested).
        
ssb: salt size in bytes.
        
M: message bytes.
    
  



If a random salt generator is used, two digests created for the same 
message will always be different
(except in the case of random salt coincidence).
Because of this, in this case the result of the digest method 
will contain both the undigested salt and the digest of the 
(salt + message), so that another digest operation can be performed 
with the same salt on a different message to check if both messages 
match (all of which will be managed automatically by the 
matches method).

Params:
message – the String to be digested
Throws:
EncryptionOperationNotPossibleException – if the digest operation
        fails, ommitting any further information about the cause for
        security reasons.
EncryptionInitializationException – if initialization could not
        be correctly done (for example, if the digest algorithm chosen
        cannot be used).
Returns:
the digest result/**
     * <p>
     * Performs a digest operation on a String message.
     * </p>
     * <p>
     * The steps taken for creating the digest are:
     * <ol>
     *   <li>The String message is converted to a byte array.</li>
     *   <li>A salt of the specified size is generated (see 
     *       {@link org.jasypt.salt.SaltGenerator}).</li>
     *   <li>The salt bytes are added to the message.</li>
     *   <li>The hash function is applied to the salt and message altogether, 
     *       and then to the
     *       results of the function itself, as many times as specified
     *       (iterations).</li>
     *   <li>If specified by the salt generator (see 
     *       {@link org.jasypt.salt.SaltGenerator#includePlainSaltInEncryptionResults()}), 
     *       the <i>undigested</i> salt and the final result of the hash
     *       function are concatenated and returned as a result.</li>
     *   <li>The result of the concatenation is encoded in BASE64 (default) 
     *       or HEXADECIMAL
     *       and returned as an ASCII String.</li>
     * </ol>
     * Put schematically in bytes:
     * <ul>
     *   <li>
     *     DIGEST = <tt>|<b>S</b>|..(ssb)..|<b>S</b>|<b>X</b>|<b>X</b>|<b>X</b>|...|<b>X</b>|</tt>
     *       <ul>
     *         <li><tt><b>S</b></tt>: salt bytes (plain, not digested). <i>(OPTIONAL)</i>.</li>
     *         <li><tt>ssb</tt>: salt size in bytes.</li>
     *         <li><tt><b>X</b></tt>: bytes resulting from hashing (see below).</li>
     *       </ul>
     *   </li>
     *   <li>
     *     <tt>|<b>X</b>|<b>X</b>|<b>X</b>|...|<b>X</b>|</tt> = 
     *     <tt><i>H</i>(<i>H</i>(<i>H</i>(..(it)..<i>H</i>(<b>Z</b>|<b>Z</b>|<b>Z</b>|...|<b>Z</b>|))))</tt>
     *     <ul>
     *       <li><tt><i>H</i></tt>: Hash function (algorithm).</li>
     *       <li><tt>it</tt>: Number of iterations.</li>
     *       <li><tt><b>Z</b></tt>: Input for hashing (see below).</li> 
     *     </ul>
     *   </li>
     *   <li>
     *     <tt>|<b>Z</b>|<b>Z</b>|<b>Z</b>|...|<b>Z</b>|</tt> =
     *     <tt>|<b>S</b>|..(ssb)..|<b>S</b>|<b>M</b>|<b>M</b>|<b>M</b>...|<b>M</b>|</tt>
     *     <ul>
     *         <li><tt><b>S</b></tt>: salt bytes (plain, not digested).</li>
     *         <li><tt>ssb</tt>: salt size in bytes.</li>
     *         <li><tt><b>M</b></tt>: message bytes.</li>
     *     </ul>
     *   </li>
     * </ul>
     * </p>
     * <p>
     * <b>If a random salt generator is used, two digests created for the same 
     * message will always be different
     * (except in the case of random salt coincidence).</b>
     * Because of this, in this case the result of the <tt>digest</tt> method 
     * will contain both the <i>undigested</i> salt and the digest of the 
     * (salt + message), so that another digest operation can be performed 
     * with the same salt on a different message to check if both messages 
     * match (all of which will be managed automatically by the 
     * <tt>matches</tt> method).
     * </p>
     * 
     * @param message the String to be digested 
     * @return the digest result
     * @throws EncryptionOperationNotPossibleException if the digest operation
     *         fails, ommitting any further information about the cause for
     *         security reasons.
     * @throws EncryptionInitializationException if initialization could not
     *         be correctly done (for example, if the digest algorithm chosen
     *         cannot be used).
     */
    public String digest(final String message) {

        if (message == null) {
            return null;
        }

        // Check initialization
        if (!isInitialized()) {
            initialize();
        }
        
        try {

            // Normalize Unicode message to NFC form
            String normalizedMessage = null;
            if (! this.unicodeNormalizationIgnored) {
                normalizedMessage = Normalizer.normalizeToNfc(message);
            } else {
                normalizedMessage = message;
            }
            
            // The input String is converted into bytes using MESSAGE_CHARSET
            // as a fixed charset to avoid problems with different platforms
            // having different default charsets (see MESSAGE_CHARSET doc).
            final byte[] messageBytes = normalizedMessage.getBytes(MESSAGE_CHARSET);

            // The StandardByteDigester does its job.
            byte[] digest = this.byteDigester.digest(messageBytes);

            // We build the result variable
            final StringBuffer result = new StringBuffer();
            
            if (this.prefix != null) {
                // Prefix is added
                result.append(this.prefix);
            }
            
            // We encode the result in BASE64 or HEXADECIMAL so that we obtain
            // the safest result String possible.
            if (this.stringOutputTypeBase64) {
                digest = this.base64.encode(digest);
                result.append(new String(digest, DIGEST_CHARSET)); 
            } else {
                result.append(CommonUtils.toHexadecimal(digest));
            }
            
            if (this.suffix != null) {
                // Suffix is added
                result.append(this.suffix);
            }
            
            return result.toString(); 

        } catch (EncryptionInitializationException e) {
            throw e;
        } catch (EncryptionOperationNotPossibleException e) {
            throw e;
        } catch (Exception e) {
            // If digest fails, it is more secure not to return any information
            // about the cause in nested exceptions. Simply fail.
            throw new EncryptionOperationNotPossibleException();
        }
        
    }

    
    
    

Checks a message against a given digest.


This method tells whether a message corresponds to a specific digest
or not by getting the salt with which the digest was created and
applying it to a digest operation performed on the message. If 
new and existing digest match, the message is said to match the digest.


This method will be used, for instance, for password checking in
authentication processes.


A null message will only match a null digest.

Params:
message – the message to be compared to the digest.
digest – the digest.
Throws:
EncryptionOperationNotPossibleException – if the digest matching
        operation fails, ommitting any further information about the 
        cause for security reasons.
EncryptionInitializationException – if initialization could not
        be correctly done (for example, if the digest algorithm chosen
        cannot be used).
Returns:
true if the specified message matches the digest, false
        if not./**
     * <p>
     * Checks a message against a given digest.
     * </p>
     * <p>
     * This method tells whether a message corresponds to a specific digest
     * or not by getting the salt with which the digest was created and
     * applying it to a digest operation performed on the message. If 
     * new and existing digest match, the message is said to match the digest.
     * </p>
     * <p>
     * This method will be used, for instance, for password checking in
     * authentication processes.
     * </p>
     * <p>
     * A null message will only match a null digest.
     * </p>
     * 
     * @param message the message to be compared to the digest.
     * @param digest the digest. 
     * @return true if the specified message matches the digest, false
     *         if not.
     * @throws EncryptionOperationNotPossibleException if the digest matching
     *         operation fails, ommitting any further information about the 
     *         cause for security reasons.
     * @throws EncryptionInitializationException if initialization could not
     *         be correctly done (for example, if the digest algorithm chosen
     *         cannot be used).
     */
    public boolean matches(final String message, final String digest) {

        String processedDigest = digest;
        
        if (processedDigest != null) {
            if (this.prefix != null) {
                if (!processedDigest.startsWith(this.prefix)) {
                    throw new EncryptionOperationNotPossibleException(
                            "Digest does not start with required prefix \"" + this.prefix + "\"");
                }
                processedDigest = processedDigest.substring(this.prefix.length()); 
            }
            if (this.suffix != null) {
                if (!processedDigest.endsWith(this.suffix)) {
                    throw new EncryptionOperationNotPossibleException(
                            "Digest does not end with required suffix \"" + this.suffix + "\"");
                }
                processedDigest = processedDigest.substring(0, processedDigest.length() - this.suffix.length());
            }
        }
        

        if (message == null) {
            return (processedDigest == null);
        } else if (processedDigest == null) {
            return false;
        }

        
        // Check initialization
        if (!isInitialized()) {
            initialize();
        }
        
        try {

            // Normalize Unicode message to NFC form
            String normalizedMessage = null;
            if (! this.unicodeNormalizationIgnored) {
                normalizedMessage = Normalizer.normalizeToNfc(message);
            } else {
                normalizedMessage = message;
            }
            
            // We get a valid byte array from the message, in the 
            // fixed MESSAGE_CHARSET that the digest operations use.
            final byte[] messageBytes = normalizedMessage.getBytes(MESSAGE_CHARSET);
            

            // The BASE64 or HEXADECIMAL encoding is reversed and the digest
            // is converted into a byte array.
            byte[] digestBytes = null;
            if (this.stringOutputTypeBase64) {
                // The digest must be a US-ASCII String BASE64-encoded
                digestBytes = processedDigest.getBytes(DIGEST_CHARSET);
                digestBytes = this.base64.decode(digestBytes);
            } else {
                digestBytes = CommonUtils.fromHexadecimal(processedDigest);
            }
            
            // The StandardByteDigester is asked to match message to digest.
            return this.byteDigester.matches(messageBytes, digestBytes); 
        
        } catch (EncryptionInitializationException e) {
            throw e;
        } catch (EncryptionOperationNotPossibleException e) {
            throw e;
        } catch (Exception e) {
            // If digest fails, it is more secure not to return any information
            // about the cause in nested exceptions. Simply fail.
            throw new EncryptionOperationNotPossibleException();
        }

    }
    
    
}