/*

  * 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.StringUtils;

 /**

  * Base abstract class for block cipher algorithms.

  *

  * <h2>Usage</h2>

  * Note that this class exists mostly to simplify algorithm-specific subclasses.  Unless you understand the concepts of

  * cipher modes of operation, block sizes, and padding schemes, and you want direct control of these things, you should

  * typically not uses instances of this class directly.  Instead, algorithm-specific subclasses, such as

  * {@link AesCipherService}, {@link BlowfishCipherService}, and others are usually better suited for regular use.

  * <p/>

  * However, if you have the need to create a custom block cipher service where no sufficient algorithm-specific subclass

  * exists in Shiro, this class would be very useful.

  *

  * <h2>Configuration</h2>

  * Block ciphers can accept configuration parameters that direct how they operate.  These parameters concatenated

  * together in a single String comprise what the JDK JCA documentation calls a

  * <a href="http://java.sun.com/javase/6/docs/technotes/guides/security/crypto/CryptoSpec.html#trans">transformation

  * string</a>.  We think that it is better for Shiro to construct this transformation string automatically based on its

  * constituent parts instead of having the end-user construct the string manually, which may be error prone or

  * confusing.  To that end, Shiro {@link DefaultBlockCipherService}s have attributes that can be set individually in

  * a type-safe manner based on your configuration needs, and Shiro will build the transformation string for you.

  * <p/>

  * The following sections typically document the configuration options for block (byte array)

  * {@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])} method invocations.  Streaming configuration

  * for those same attributes are done via mirrored {@code streaming}* attributes, and their purpose is identical, but

  * they're only used during streaming {@link #encrypt(java.io.InputStream, java.io.OutputStream, byte[])} and

  * {@link #decrypt(java.io.InputStream, java.io.OutputStream, byte[])} methods.  See the "Streaming"

  * section below for more.

  *

  * <h3>Block Size</h3>

  * The block size specifies the number of bits (not bytes) that the cipher operates on when performing an operation.

  * It can be specified explicitly via the {@link #setBlockSize blockSize} attribute.  If not set, the JCA Provider

  * default will be used based on the cipher algorithm.  Block sizes are usually very algorithm specific, so set this

  * value only if you know you don't want the JCA Provider's default for the desired algorithm.  For example, the

  * AES algorithm's Rijndael implementation <em>only</em> supports a 128 bit block size and will not work with any other

  * size.

  * <p/>

  * Also note that the {@link #setInitializationVectorSize initializationVectorSize} is usually the same as the

  * {@link #setBlockSize blockSize} in block ciphers.  If you change either attribute, you should ensure that the other

  * attribute is correct for the target cipher algorithm.

  *

  * <h3>Operation Mode</h3>

  * You may set the block cipher's<a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation">mode of

  * operation</a> via the {@link #setMode(OperationMode) mode} attribute, which accepts a type-safe

  * {@link OperationMode OperationMode} enum instance.  This type safety helps avoid typos when specifying the mode and

  * guarantees that the mode name will be recognized by the underlying JCA Provider.

  * <p/>

  * <b>*</b>If no operation mode is specified, Shiro defaults all of its block {@code CipherService} instances to the

  * {@link OperationMode#CBC CBC} mode, specifically to support auto-generation of initialization vectors during

  * encryption.  This is different than the JDK's default {@link OperationMode#ECB ECB} mode because {@code ECB} does

  * not support initialization vectors, which are necessary for strong encryption.  See  the

  * {@link org.apache.shiro.crypto.JcaCipherService JcaCipherService parent class} class JavaDoc for an extensive

  * explanation on why we do this and why we do not use the Sun {@code ECB} default.  You also might also want read

  * the <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Electronic_codebook_.28ECB.29">Wikipedia

  * section on ECB<a/> and look at the encrypted image to see an example of why {@code ECB} should not be used in

  * security-sensitive environments.

  * <p/>

  * In the rare case that you need to override the default with a mode not represented

  * by the {@link OperationMode} enum, you may specify the raw mode name string that will be recognized by your JCA

  * provider via the {@link #setModeName modeName} attribute.  Because this is not type-safe, it is recommended only to

  * use this attribute if the {@link OperationMode} enum does not represent your desired mode.

  * <p/>

  * <b>NOTE:</b> If you change the mode to one that does not support initialization vectors (such as

  * {@link OperationMode#ECB ECB} or {@link OperationMode#NONE NONE}), you <em>must</em> turn off auto-generated

  * initialization vectors by setting {@link #setGenerateInitializationVectors(boolean) generateInitializationVectors}

  * to {@code false}.  Abandoning initialization vectors significantly weakens encryption, so think twice before

  * disabling this feature.

  *

  * <h3>Padding Scheme</h3>

  * Because block ciphers process messages in fixed-length blocks, if the final block in a message is not equal to the

  * block length, <a href="http://en.wikipedia.org/wiki/Padding_(cryptography)">padding</a> is applied to match that

  * size to maintain the total length of the message.  This is good because it protects data patterns from being

  * identified  - when all chunks look the same length, it is much harder to infer what that data might be.

  * <p/>

  * You may set a padding scheme via the {@link #setPaddingScheme(PaddingScheme) paddingScheme} attribute, which

  * accepts a type-safe {@link PaddingScheme PaddingScheme} enum instance.  Like the {@link OperationMode} enum,

  * this enum offers type safety to help avoid typos and guarantees that the mode will be recongized by the underlying

  * JCA provider.

  * <p/>

  * <b>*</b>If no padding scheme is specified, this class defaults to the {@link PaddingScheme#PKCS5} scheme, specifically

  * to be compliant with the default behavior of auto-generating initialization vectors during encryption (see the

  * {@link org.apache.shiro.crypto.JcaCipherService JcaCipherService parent class} class JavaDoc for why).

  * <p/>

  * In the rare case that you need to override the default with a scheme not represented by the {@link PaddingScheme}

  * enum, you may specify the raw padding scheme name string that will be recognized by your JCA provider via the

  * {@link #setPaddingScheme paddingSchemeName} attribute.  Because this is not type-safe, it is recommended only to

  * use this attribute if the {@link PaddingScheme} enum does not represent your desired scheme.

  *

  * <h2>Streaming</h2>

  * Most people don't think of using block ciphers as stream ciphers, since their name implies working

  * with block data (i.e. byte arrays) only.  However, block ciphers can be turned into byte-oriented stream ciphers by

  * using an appropriate {@link OperationMode operation mode} with a {@link #getStreamingBlockSize() streaming block size}

  * of 8 bits.  This is why the {@link CipherService} interface provides both block and streaming operations.

  * <p/>

  * Because this streaming 8-bit block size rarely changes across block-cipher algorithms, default values have been set

  * for all three streaming configuration parameters.  The defaults are:

  * <ul>

  * <li>{@link #setStreamingBlockSize(int) streamingBlockSize} = {@code 8} (bits)</li>

  * <li>{@link #setStreamingMode streamingMode} = {@link OperationMode#CBC CBC}</li>

  * <li>{@link #setStreamingPaddingScheme(PaddingScheme) streamingPaddingScheme} = {@link PaddingScheme#PKCS5 PKCS5}</li>

  * </ul>

  * <p/>

  * These attributes have the same meaning as the {@code mode}, {@code blockSize}, and {@code paddingScheme} attributes

  * described above, but they are applied during streaming method invocations only ({@link #encrypt(java.io.InputStream, java.io.OutputStream, byte[])}

  * and {@link #decrypt(java.io.InputStream, java.io.OutputStream, byte[])}).

  *

  * @see BlowfishCipherService

  * @see AesCipherService

  * @see <a href="http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation">Wikipedia: Block Cipher Modes of Operation</a>

  * @since 1.0

  */

 public class DefaultBlockCipherService extends AbstractSymmetricCipherService {

     private static final int DEFAULT_BLOCK_SIZE = 0;

     private static final String TRANSFORMATION_STRING_DELIMITER = "/";

     private static final int DEFAULT_STREAMING_BLOCK_SIZE = 8; //8 bits (1 byte)

     private String modeName;

     private int blockSize; //size in bits (not bytes) - i.e. a blockSize of 8 equals 1 byte. negative or zero value = use system default

     private String paddingSchemeName;

     private String streamingModeName;

     private int streamingBlockSize;

     private String streamingPaddingSchemeName;

     private String transformationString; //cached value - rebuilt whenever any of its constituent parts change

     private String streamingTransformationString; //cached value - rebuilt whenever any of its constituent parts change

     /**

      * Creates a new {@link DefaultBlockCipherService} using the specified block cipher {@code algorithmName}.  Per this

      * class's JavaDoc, this constructor also sets the following defaults:

      * <ul>

      * <li>{@code streamingMode} = {@link OperationMode#CBC CBC}</li>

      * <li>{@code streamingPaddingScheme} = {@link PaddingScheme#NONE none}</li>

      * <li>{@code streamingBlockSize} = 8</li>

      * </ul>

      * All other attributes are null/unset, indicating the JCA Provider defaults will be used.

      *

      * @param algorithmName the block cipher algorithm to use when encrypting and decrypting

      */

     public DefaultBlockCipherService(String algorithmName) {

         super(algorithmName);

         this.modeName = OperationMode.CBC.name();

         this.paddingSchemeName = PaddingScheme.PKCS5.getTransformationName();

         this.blockSize = DEFAULT_BLOCK_SIZE; //0 = use the JCA provider's default

         this.streamingModeName = OperationMode.CBC.name();

         this.streamingPaddingSchemeName = PaddingScheme.PKCS5.getTransformationName();

         this.streamingBlockSize = DEFAULT_STREAMING_BLOCK_SIZE;

     }

     /**

      * Returns the cipher operation mode name (as a String) to be used when constructing

      * {@link javax.crypto.Cipher Cipher} transformation string or {@code null} if the JCA Provider default mode for

      * the specified {@link #getAlgorithmName() algorithm} should be used.

      * <p/>

      * This attribute is used <em>only</em> when constructing the transformation string for block (byte array)

      * operations ({@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])}).  The

      * {@link #getStreamingModeName() streamingModeName} attribute is used when the block cipher is used for

      * streaming operations.

      * <p/>

      * The default value is {@code null} to retain the JCA Provider default.

      *

      * @return the cipher operation mode name (as a String) to be used when constructing the

      *         {@link javax.crypto.Cipher Cipher} transformation string, or {@code null} if the JCA Provider default

      *         mode for the specified {@link #getAlgorithmName() algorithm} should be used.

      */

     public String getModeName() {

         return modeName;

     }

     /**

      * Sets the cipher operation mode name to be used when constructing the

      * {@link javax.crypto.Cipher Cipher} transformation string.  A {@code null} value indicates that the JCA Provider

      * default mode for the specified {@link #getAlgorithmName() algorithm} should be used.

      * <p/>

      * This attribute is used <em>only</em> when constructing the transformation string for block (byte array)

      * operations ({@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])}).  The

      * {@link #getStreamingModeName() streamingModeName} attribute is used when the block cipher is used for

      * streaming operations.

      * <p/>

      * The default value is {@code null} to retain the JCA Provider default.

      * <p/>

      * <b>NOTE:</b> most standard mode names are represented by the {@link OperationMode OperationMode} enum.  That enum

      * should be used with the {@link #setMode mode} attribute when possible to retain type-safety and reduce the

      * possibility of errors.  This method is better used if the {@link OperationMode} enum does not represent the

      * necessary mode.

      *

      * @param modeName the cipher operation mode name to be used when constructing

      *                 {@link javax.crypto.Cipher Cipher} transformation string, or {@code null} if the JCA Provider

      *                 default mode for the specified {@link #getAlgorithmName() algorithm} should be used.

      * @see #setMode

      */

     public void setModeName(String modeName) {

         this.modeName = modeName;

         //clear out the transformation string so the next invocation will rebuild it with the new mode:

         this.transformationString = null;

     }

     /**

      * Sets the cipher operation mode of operation to be used when constructing the

      * {@link javax.crypto.Cipher Cipher} transformation string.  A {@code null} value indicates that the JCA Provider

      * default mode for the specified {@link #getAlgorithmName() algorithm} should be used.

      * <p/>

      * This attribute is used <em>only</em> when constructing the transformation string for block (byte array)

      * operations ({@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])}).  The

      * {@link #setStreamingMode streamingMode} attribute is used when the block cipher is used for

      * streaming operations.

      * <p/>

      * If the {@link OperationMode} enum cannot represent your desired mode, you can set the name explicitly

      * via the {@link #setModeName modeName} attribute directly.  However, because {@link OperationMode} represents all

      * standard JDK mode names already, ensure that your underlying JCA Provider supports the non-standard name first.

      *

      * @param mode the cipher operation mode to be used when constructing

      *             {@link javax.crypto.Cipher Cipher} transformation string, or {@code null} if the JCA Provider

      *             default mode for the specified {@link #getAlgorithmName() algorithm} should be used.

      */

     public void setMode(OperationMode mode) {

         setModeName(mode.name());

     }

     /**

      * Returns the cipher algorithm padding scheme name (as a String) to be used when constructing

      * {@link javax.crypto.Cipher Cipher} transformation string or {@code null} if the JCA Provider default mode for

      * the specified {@link #getAlgorithmName() algorithm} should be used.

      * <p/>

      * This attribute is used <em>only</em> when constructing the transformation string for block (byte array)

      * operations ({@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])}).  The

      * {@link #getStreamingPaddingSchemeName() streamingPaddingSchemeName} attribute is used when the block cipher is

      * used for streaming operations.

      * <p/>

      * The default value is {@code null} to retain the JCA Provider default.

      *

      * @return the padding scheme name (as a String) to be used when constructing the

      *         {@link javax.crypto.Cipher Cipher} transformation string, or {@code null} if the JCA Provider default

      *         padding scheme for the specified {@link #getAlgorithmName() algorithm} should be used.

      */

     public String getPaddingSchemeName() {

         return paddingSchemeName;

     }

     /**

      * Sets the padding scheme name to be used when constructing the

      * {@link javax.crypto.Cipher Cipher} transformation string, or {@code null} if the JCA Provider default mode for

      * the specified {@link #getAlgorithmName() algorithm} should be used.

      * <p/>

      * This attribute is used <em>only</em> when constructing the transformation string for block (byte array)

      * operations ({@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])}).  The

      * {@link #getStreamingPaddingSchemeName() streamingPaddingSchemeName} attribute is used when the block cipher is

      * used for streaming operations.

      * <p/>

      * The default value is {@code null} to retain the JCA Provider default.

      * <p/>

      * <b>NOTE:</b> most standard padding schemes are represented by the {@link PaddingScheme PaddingScheme} enum.

      * That enum should be used with the {@link #setPaddingScheme paddingScheme} attribute when possible to retain

      * type-safety and reduce the possibility of errors.  Calling this method however is suitable if the

      * {@code PaddingScheme} enum does not represent the desired scheme.

      *

      * @param paddingSchemeName the padding scheme name to be used when constructing

      *                          {@link javax.crypto.Cipher Cipher} transformation string, or {@code null} if the JCA

      *                          Provider default padding scheme for the specified {@link #getAlgorithmName() algorithm}

      *                          should be used.

      * @see #setPaddingScheme

      */

     public void setPaddingSchemeName(String paddingSchemeName) {

         this.paddingSchemeName = paddingSchemeName;

         //clear out the transformation string so the next invocation will rebuild it with the new padding scheme:

         this.transformationString = null;

     }

     /**

      * Sets the padding scheme to be used when constructing the

      * {@link javax.crypto.Cipher Cipher} transformation string. A {@code null} value indicates that the JCA Provider

      * default padding scheme for the specified {@link #getAlgorithmName() algorithm} should be used.

      * <p/>

      * This attribute is used <em>only</em> when constructing the transformation string for block (byte array)

      * operations ({@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])}).  The

      * {@link #setStreamingPaddingScheme streamingPaddingScheme} attribute is used when the block cipher is used for

      * streaming operations.

      * <p/>

      * If the {@link PaddingScheme PaddingScheme} enum does represent your desired scheme, you can set the name explicitly

      * via the {@link #setPaddingSchemeName paddingSchemeName} attribute directly.  However, because

      * {@code PaddingScheme} represents all standard JDK scheme names already, ensure that your underlying JCA Provider

      * supports the non-standard name first.

      *

      * @param paddingScheme the padding scheme to be used when constructing

      *                      {@link javax.crypto.Cipher Cipher} transformation string, or {@code null} if the JCA Provider

      *                      default padding scheme for the specified {@link #getAlgorithmName() algorithm} should be used.

      */

     public void setPaddingScheme(PaddingScheme paddingScheme) {

         setPaddingSchemeName(paddingScheme.getTransformationName());

     }

     /**

      * Returns the block cipher's block size to be used when constructing

      * {@link javax.crypto.Cipher Cipher} transformation string or {@code 0} if the JCA Provider default block size

      * for the specified {@link #getAlgorithmName() algorithm} should be used.

      * <p/>

      * This attribute is used <em>only</em> when constructing the transformation string for block (byte array)

      * operations ({@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])}).  The

      * {@link #getStreamingBlockSize() streamingBlockSize} attribute is used when the block cipher is used for

      * streaming operations.

      * <p/>

      * The default value is {@code 0} which retains the JCA Provider default.

      *

      * @return the block cipher block size to be used when constructing the

      *         {@link javax.crypto.Cipher Cipher} transformation string, or {@code 0} if the JCA Provider default

      *         block size for the specified {@link #getAlgorithmName() algorithm} should be used.

      */

     public int getBlockSize() {

         return blockSize;

     }

     /**

      * Sets the block cipher's block size to be used when constructing

      * {@link javax.crypto.Cipher Cipher} transformation string.  {@code 0} indicates that the JCA Provider default

      * block size for the specified {@link #getAlgorithmName() algorithm} should be used.

      * <p/>

      * This attribute is used <em>only</em> when constructing the transformation string for block (byte array)

      * operations ({@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])}).  The

      * {@link #getStreamingBlockSize() streamingBlockSize} attribute is used when the block cipher is used for

      * streaming operations.

      * <p/>

      * The default value is {@code 0} which retains the JCA Provider default.

      * <p/>

      * <b>NOTE:</b> block cipher block sizes are very algorithm-specific.  If you change this value, ensure that it

      * will work with the specified {@link #getAlgorithmName() algorithm}.

      *

      * @param blockSize the block cipher block size to be used when constructing the

      *                  {@link javax.crypto.Cipher Cipher} transformation string, or {@code 0} if the JCA Provider

      *                  default block size for the specified {@link #getAlgorithmName() algorithm} should be used.

      */

     public void setBlockSize(int blockSize) {

         this.blockSize = Math.max(DEFAULT_BLOCK_SIZE, blockSize);

         //clear out the transformation string so the next invocation will rebuild it with the new block size:

         this.transformationString = null;

     }

     /**

      * Same purpose as the {@link #getModeName modeName} attribute, but is used instead only for for streaming

      * operations ({@link #encrypt(java.io.InputStream, java.io.OutputStream, byte[])} and

      * {@link #decrypt(java.io.InputStream, java.io.OutputStream, byte[])}).

      * <p/>

      * Note that unlike the {@link #getModeName modeName} attribute, the default value of this attribute is not

      * {@code null} - it is {@link OperationMode#CBC CBC} for reasons described in the class-level JavaDoc in the

      * {@code Streaming} section.

      *

      * @return the transformation string mode name to be used for streaming operations only.

      */

     public String getStreamingModeName() {

         return streamingModeName;

     }

     private boolean isModeStreamingCompatible(String modeName) {

         return modeName != null &&

                 !modeName.equalsIgnoreCase(OperationMode.ECB.name()) &&

                 !modeName.equalsIgnoreCase(OperationMode.NONE.name());

     }

     /**

      * Sets the transformation string mode name to be used for streaming operations only.  The default value is

      * {@link OperationMode#CBC CBC} for reasons described in the class-level JavaDoc in the {@code Streaming} section.

      *

      * @param streamingModeName transformation string mode name to be used for streaming operations only

      */

     public void setStreamingModeName(String streamingModeName) {

         if (!isModeStreamingCompatible(streamingModeName)) {

             String msg = "mode [" + streamingModeName + "] is not a valid operation mode for block cipher streaming.";

             throw new IllegalArgumentException(msg);

         }

         this.streamingModeName = streamingModeName;

         //clear out the streaming transformation string so the next invocation will rebuild it with the new mode:

         this.streamingTransformationString = null;

     }

     /**

      * Sets the transformation string mode to be used for streaming operations only.  The default value is

      * {@link OperationMode#CBC CBC} for reasons described in the class-level JavaDoc in the {@code Streaming} section.

      *

      * @param mode the transformation string mode to be used for streaming operations only

      */

     public void setStreamingMode(OperationMode mode) {

         setStreamingModeName(mode.name());

     }

     public String getStreamingPaddingSchemeName() {

         return streamingPaddingSchemeName;

     }

     public void setStreamingPaddingSchemeName(String streamingPaddingSchemeName) {

         this.streamingPaddingSchemeName = streamingPaddingSchemeName;

         //clear out the streaming transformation string so the next invocation will rebuild it with the new scheme:

         this.streamingTransformationString = null;

     }

     public void setStreamingPaddingScheme(PaddingScheme scheme) {

         setStreamingPaddingSchemeName(scheme.getTransformationName());

     }

     public int getStreamingBlockSize() {

         return streamingBlockSize;

     }

     public void setStreamingBlockSize(int streamingBlockSize) {

         this.streamingBlockSize = Math.max(DEFAULT_BLOCK_SIZE, streamingBlockSize);

         //clear out the streaming transformation string so the next invocation will rebuild it with the new block size:

         this.streamingTransformationString = null;

     }

     /**

      * Returns the transformation string to use with the {@link javax.crypto.Cipher#getInstance} call.  If

      * {@code streaming} is {@code true}, a block-cipher transformation string compatible with streaming operations will

      * be constructed and cached for re-use later (see the class-level JavaDoc for more on using block ciphers

      * for streaming).  If {@code streaming} is {@code false} a normal block-cipher transformation string will

      * be constructed and cached for later re-use.

      *

      * @param streaming if the transformation string is going to be used for a Cipher performing stream-based encryption or not.

      * @return the transformation string

      */

     protected String getTransformationString(boolean streaming) {

         if (streaming) {

             if (this.streamingTransformationString == null) {

                 this.streamingTransformationString = buildStreamingTransformationString();

             }

             return this.streamingTransformationString;

         } else {

             if (this.transformationString == null) {

                 this.transformationString = buildTransformationString();

             }

             return this.transformationString;

         }

     }

     private String buildTransformationString() {

         return buildTransformationString(getModeName(), getPaddingSchemeName(), getBlockSize());

     }

     private String buildStreamingTransformationString() {

         return buildTransformationString(getStreamingModeName(), getStreamingPaddingSchemeName(), 0);

     }

     private String buildTransformationString(String modeName, String paddingSchemeName, int blockSize) {

         StringBuilder sb = new StringBuilder(getAlgorithmName());

         if (StringUtils.hasText(modeName)) {

             sb.append(TRANSFORMATION_STRING_DELIMITER).append(modeName);

         }

         if (blockSize > 0) {

             sb.append(blockSize);

         }

         if (StringUtils.hasText(paddingSchemeName)) {

             sb.append(TRANSFORMATION_STRING_DELIMITER).append(paddingSchemeName);

         }

         return sb.toString();

     }

     /**

      * Returns {@code true} if the specified cipher operation mode name supports initialization vectors,

      * {@code false} otherwise.

      *

      * @param modeName the raw text name of the mode of operation

      * @return {@code true} if the specified cipher operation mode name supports initialization vectors,

      *         {@code false} otherwise.

      */

     private boolean isModeInitializationVectorCompatible(String modeName) {

         return modeName != null &&

                 !modeName.equalsIgnoreCase(OperationMode.ECB.name()) &&

                 !modeName.equalsIgnoreCase(OperationMode.NONE.name());

     }

     /**

      * Overrides the parent implementation to ensure initialization vectors are always generated if streaming is

      * enabled (block ciphers <em>must</em> use initialization vectors if they are to be used as a stream cipher).  If

      * not being used as a stream cipher, then the value is computed based on whether or not the currently configured

      * {@link #getModeName modeName} is compatible with initialization vectors as well as the result of the configured

      * {@link #setGenerateInitializationVectors(boolean) generateInitializationVectors} value.

      *

      * @param streaming whether or not streaming is being performed

      * @return {@code true} if streaming or a value computed based on if the currently configured mode is compatible

      *         with initialization vectors.

      */

     @Override

     protected boolean isGenerateInitializationVectors(boolean streaming) {

         return streaming || super.isGenerateInitializationVectors() && isModeInitializationVectorCompatible(getModeName());

     }

     @Override

     protected byte[] generateInitializationVector(boolean streaming) {

         if (streaming) {

             String streamingModeName = getStreamingModeName();

             if (!isModeInitializationVectorCompatible(streamingModeName)) {

                 String msg = "streamingMode attribute value [" + streamingModeName + "] does not support " +

                         "Initialization Vectors.  Ensure the streamingMode value represents an operation mode " +

                         "that is compatible with initialization vectors.";

                 throw new IllegalStateException(msg);

             }

         } else {

             String modeName = getModeName();

             if (!isModeInitializationVectorCompatible(modeName)) {

                 String msg = "mode attribute value [" + modeName + "] does not support " +

                         "Initialization Vectors.  Ensure the mode value represents an operation mode " +

                         "that is compatible with initialization vectors.";

                 throw new IllegalStateException(msg);

             }

         }

         return super.generateInitializationVector(streaming);

     }

 }