hcrypto.cipher
Class HistoricalKey

java.lang.Object
  |
  +--hcrypto.cipher.HistoricalKey

Direct Known Subclasses:

AffineKey, CaesarKey, PlayfairKey, PolySubstitutionKey, RailFenceKey, SubstitutionKey, TranspositionKey, VigenereKey

public abstract class HistoricalKey

extends java.lang.Object

This abstract class provides a partial implementation of the HistoricalKey interface by providing default implementations of the getKeyword(), getAlphabet(), and getBlocksize() methods.

The HistoricalKey() constructor should be invoked by the subclass. It extracts the keyspec, which provides algorithm-specific data as well as a specification of the Alphabet used by the particular key. These are stored in instance variables.

The key specification is comprised of two parts: keydata/alphabetspec, separated by a forward slash "/". The keydata provides material that used to construct an algorithm-specific key. Here are some examples.

Algorithm	Keydata	AlphabetSpec
Caesar	shift	azAZ09
Substitution	keyword	printable
Affine	a,b	az

Here are some examples of key instantiations:

      CaesarKey key = new CaesarKey("55/printable");
      SubstitutionKey sKey = new SubstitutionKey("76TrombonesLEDTHEPARADE/azAZ09");
      AffineKey aKey = new AffineKey("3,3/azAZ09");
 

Field Summary

protected Alphabet	alphabet This instance variable stores a reference to the particular plaintext characters for which this cipher is defined.
protected int	blocksize Stores the blocksize.
protected char[]	ciphAlphabet The ciphertext alphabet represented as a contiguous array of char.
protected Alphabet	cipherAlphabet This instance variable stores a reference to the particular ciphertext characters for which this cipher is defined.
protected java.lang.String	keyDescriptorPrompt Stores a prompt that can be used by the interface to describes the type of key that would be used for a particular cipher.
protected java.lang.String	keyspec A keyspec takes the form keydata/plainalphabetspec/cipheralphabetspec, where plainalphabetspec is a sepcification for the plaintext alphabet, and cipheralphabetspec is a specification for the ciphertext alphabet.
protected java.lang.String	keyword Many historical ciphers use a keyword as part (or all) of the key.
protected char[]	plainAlphabet The plaintext alphabet represented as a contiguous array of char.

Constructor Summary

HistoricalKey()

Method Summary

abstract java.lang.String	getAlgorithm() This abstract method should be implemented in the algorithm-specific subclass.
Alphabet	getAlphabet() Returns a reference to this key's alphabet.
int	getBlocksize() Returns this cipher's blocksize.
char[]	getCiphAlphabet() Returns the cipher alphabet.
Alphabet	getCTAlphabet() Returns a reference to this key's cipherAlphabet.
static HistoricalKey	getInstance(java.lang.String algorithm, java.lang.String provider) searches for the provider named in the second parameter for an implementation of the algorithm named in its first parameter.
java.lang.String	getKeyDescriptorPrompt() Returns an interface prompt describing the key
java.lang.String	getKeyword() Returns the keyword for this key.
char[]	getPlainAlphabet() Returns the plaintext alphabet.
abstract void	init(java.lang.String keyspec) This abstract method should be implemented in the algorithm-specific subclass.
protected void	initAlphabets() This method constructs char arrays consisting of the characters in the plaintext and ciphertext alphabets.
void	initKey(java.lang.String keyspec, boolean removeDuplicates) Initializes the keyspec, keyword and alphabet instance variables given a specification of the form keydata/plainspec/cipherspec.
void	printAlphabets() Prints both the cipher and plain alphabets to the System console.
static java.lang.String	removeDuplicateChars(java.lang.String key) A utility method to remove duplicate characters from a string.

Methods inherited from class java.lang.Object

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

Field Detail

keyspec

protected java.lang.String keyspec

A keyspec takes the form keydata/plainalphabetspec/cipheralphabetspec, where plainalphabetspec is a sepcification for the plaintext alphabet, and cipheralphabetspec is a specification for the ciphertext alphabet. The spec for the ciphertext alphabet may be omitted, in which case the spec for the plaintext alphabet will be used for both alphabets.

An example would be xylophone/az/AZ where the keydata in this case is the keyword "xylophone", the plaintext alphabet consists of the lowercase letters a..z, and the ciphertext alphabet consists of the uppercase letters A..Z. In this case, the encryption algorithm will map letters from a..z to A..Z, and the decryption algorithm will perform the reverse mapping.

Another example would be xylophone/az. In this case the keyword is "xylophone" and both the plaintext and ciphertext alphabets are the lowercase letters a..z. In this case both encryption and decryption are performed by mapping from the set of characters a..z onto itself.

keyword

protected java.lang.String keyword

Many historical ciphers use a keyword as part (or all) of the key. For example, substitution and Vigenere ciphers use the keyword to initialize the cipher alphabet.

alphabet

protected Alphabet alphabet

This instance variable stores a reference to the particular plaintext characters for which this cipher is defined.

cipherAlphabet

protected Alphabet cipherAlphabet

This instance variable stores a reference to the particular ciphertext characters for which this cipher is defined.

plainAlphabet

protected char[] plainAlphabet

The plaintext alphabet represented as a contiguous array of char.

ciphAlphabet

protected char[] ciphAlphabet

The ciphertext alphabet represented as a contiguous array of char.

blocksize

protected int blocksize

Stores the blocksize. Character ciphers (such as Vigenere, Caesar) have a blocksize of 1. Block ciphers (such as Playfair) have a blocksize that is greater than 1.

keyDescriptorPrompt

protected java.lang.String keyDescriptorPrompt

Stores a prompt that can be used by the interface to describes the type of key that would be used for a particular cipher. For example, Caesar cipher would prompt with "positive integer"

Constructor Detail

HistoricalKey

public HistoricalKey()

Method Detail

getInstance

public static final HistoricalKey getInstance(java.lang.String algorithm,
                                              java.lang.String provider)

searches for the provider named in the second parameter for an implementation of the algorithm named in its first parameter.

Parameters:

algorithm, - a String giving the algorithm name

provider, - a String giving the provider name

initKey

public void initKey(java.lang.String keyspec,
                    boolean removeDuplicates)
             throws java.lang.Exception

Initializes the keyspec, keyword and alphabet instance variables given a specification of the form keydata/plainspec/cipherspec. It also initializes the char arrays.

Parameters:

keyspec - is a String specifying algorithm-specific key data -- for example the shift value for a Caesar cipher -- and an specification of the set of characters used in encryption.

init

public abstract void init(java.lang.String keyspec)
                   throws java.lang.Exception

This abstract method should be implemented in the algorithm-specific subclass.

getAlgorithm

public abstract java.lang.String getAlgorithm()

This abstract method should be implemented in the algorithm-specific subclass.

getKeyword

public java.lang.String getKeyword()

Returns the keyword for this key.

getAlphabet

public Alphabet getAlphabet()

Returns a reference to this key's alphabet.

getCTAlphabet

public Alphabet getCTAlphabet()

Returns a reference to this key's cipherAlphabet.

getBlocksize

public int getBlocksize()

Returns this cipher's blocksize.

getKeyDescriptorPrompt

public java.lang.String getKeyDescriptorPrompt()

Returns an interface prompt describing the key

removeDuplicateChars

public static java.lang.String removeDuplicateChars(java.lang.String key)

A utility method to remove duplicate characters from a string. For example, it would convert the passphrase "hello" to the keyword "helo".

initAlphabets

protected void initAlphabets()
                      throws java.lang.Exception

This method constructs char arrays consisting of the characters in the plaintext and ciphertext alphabets. Note: This method won't work if the keyword has duplicate characters. It will throw and exception.

getCiphAlphabet

public char[] getCiphAlphabet()

Returns the cipher alphabet.

getPlainAlphabet

public char[] getPlainAlphabet()

Returns the plaintext alphabet.

printAlphabets

public void printAlphabets()

Prints both the cipher and plain alphabets to the System console.