hcrypto.cipher
Class BlockCipher

java.lang.Object
  |
  +--hcrypto.cipher.CipherEngine
        |
        +--hcrypto.cipher.BlockCipher

Direct Known Subclasses:

AffineEngine, CaesarEngine, PlayfairEngine, SubstitutionEngine, TranspositionEngine, VigenereEngine

public abstract class BlockCipher

extends CipherEngine

This abstract class represents a basic block cipher. It provides implementations of methods to encrypt and decrypt files and strings, for the entire range of cipher engines.

Subclasses of this class must implement three methods: engineInit(HistoricalKey), engineEncode(String) and engineDecode(String). Of course, each particular cipher algorithm will implement these methods in its own way.

Traditional character ciphers, such as Caesar, Simple Substitution, Vigenere, and Enigma, can be represented as special cases of a block cipher by setting the blocksize to 1. This should be done in the engineInit() method.

The engineEncrypt() and engineDecrypt() methods also handle padding of strings that are smaller than blocksize. Details on the padding scheme are provided in Alphabet.

The class contains algorithm-independent implementations of the following methods: engineEncrypt(String), engineDecrypt(String), engineEncryptFile(String, String), and engineDecryptFile(String,String).

Field Summary

protected Alphabet	alphabet Stores a reference to the alphabet used by the particular cipher.
protected int	blocksize Stores the block size for the particular cipher.

Fields inherited from class hcrypto.cipher.CipherEngine

alphabetRangeOptions

Constructor Summary

BlockCipher()

Method Summary

protected abstract java.lang.String	engineDecode(java.lang.String s) This abstract method must be implemented in the subclass to perform basic decrypting step for a given cipher algorithm.
protected java.lang.String	engineDecrypt(java.lang.String s) This method encrypts a String, returning a String.
protected void	engineDecryptFile(java.lang.String inFileName, java.lang.String outFileName) This method decrypts its input file storing the decrypted data in the output file.
protected abstract java.lang.String	engineEncode(java.lang.String s) This abstract method must be implemented in the subclass to perform basic encrypting step for a given cipher algorithm.
protected java.lang.String	engineEncrypt(java.lang.String s) This method encrypts a String, returning a String.
protected void	engineEncryptFile(java.lang.String inFileName, java.lang.String outFileName) This method encrypts its input file storing the encrypted text in the output file.
protected abstract void	engineInit(HistoricalKey key) This abstract method must be implemented in the subclass to perform initializations required by a given cipher algorithm.

Methods inherited from class hcrypto.cipher.CipherEngine

getAlphabetRangeOptions

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

blocksize

protected int blocksize

Stores the block size for the particular cipher. This variable should be initialized in the subclass.

alphabet

protected Alphabet alphabet

Stores a reference to the alphabet used by the particular cipher. The cipher alphabet is defined as part of a HistoricalKey. This variable should be initialized in engineInit().

Constructor Detail

BlockCipher

public BlockCipher()

Method Detail

engineInit

protected abstract void engineInit(HistoricalKey key)
                            throws java.lang.Exception

This abstract method must be implemented in the subclass to perform initializations required by a given cipher algorithm. Its parameter provides algorithm-specific information that is used to encrypt and decrypt. The key also provides a reference to the Alphabet that defines which plaintext characters are to be encrypted.

Overrides:

engineInit in class CipherEngine

Parameters:

key - an instance of a HistoricalKey subclass appropriate to the particular cipher algorithm

engineEncode

protected abstract java.lang.String engineEncode(java.lang.String s)
                                          throws java.lang.Exception

This abstract method must be implemented in the subclass to perform basic encrypting step for a given cipher algorithm.

engineDecode

protected abstract java.lang.String engineDecode(java.lang.String s)
                                          throws java.lang.Exception

This abstract method must be implemented in the subclass to perform basic decrypting step for a given cipher algorithm.

engineEncryptFile

protected final void engineEncryptFile(java.lang.String inFileName,
                                       java.lang.String outFileName)
                                throws java.lang.Exception

This method encrypts its input file storing the encrypted text in the output file. Note the use of InputStreamReader and OutputStreamReader. These classes perform automatic Unicode conversion to and from platform-dependent and locale-dependent encodings. This is an important internationalization feature.

Overrides:

engineEncryptFile in class CipherEngine

Parameters:

inFileName - a String giving the name of the input file

outFileName - a String giving the name of the output file

engineDecryptFile

protected final void engineDecryptFile(java.lang.String inFileName,
                                       java.lang.String outFileName)
                                throws java.lang.Exception

This method decrypts its input file storing the decrypted data in the output file.

Overrides:

engineDecryptFile in class CipherEngine

Parameters:

inFileName - a String giving the name of the input file

outFileName - a String giving the name of the output file

engineEncrypt

protected final java.lang.String engineEncrypt(java.lang.String s)
                                        throws java.lang.Exception

This method encrypts a String, returning a String. It invokes the abstract method encode(String) which is implemented in an algorithm-specific way in the subclass.

Overrides:

engineEncrypt in class CipherEngine

Parameters:

s - the String to be encrypted

engineDecrypt

protected final java.lang.String engineDecrypt(java.lang.String s)
                                        throws java.lang.Exception

This method encrypts a String, returning a String. It invokes the abstract method decode(String) which is implemented in an algorithm-specific way in the subclass.

Overrides:

engineDecrypt in class CipherEngine

Parameters:

s - the String to be encrypted