hcrypto.engines
Class PlayfairKey

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

public class PlayfairKey

extends HistoricalKey

This class represents a key for a Playfair cipher. The key is entirely represented by a keyword. The key is inserted into a matrix of letters in the PlayfairEngine class for encrypting and decrypting.

For this implementation of the Playfair cipher the alphabet range is restricted to "az". In the ciphertext alphabet, the letter 'j' is omitted and j's in the plaintext message are changed to i's.

For example: If the keyword is "keyword", the matrix would look like this:

   
k e y w o 
r d a b c 
f g h i l
m n p q s
t u v x z

The following rules are used to perform the mapping:

1. If both letters happen to be in the same row, the letters immediately to the right of each letter are used. The letter to the "right" of the last letter in a row is the first letter in that same row. For example, given the above square, "ey" would be encrypted as "yw".

2. If both letters are in the same column, the letters immediately below each letter are used. The letter "below" a bottom letter is the top letter of the same column. For example, given the above square, "ed" would be encrypted by "dg".

3. If the two letters are in different rows and in different columns, each letter is replaced by the letter in the same row that is also in the column occupied by the other letter. For example, for the above square, "dh" would be encrypted by "ag".

See also:

PlayfairEngine
Alphabet

Field Summary

static java.lang.String	DEFAULT_KEY_DESCRIPTOR_PROMPT_STRING A keyword description.
static java.lang.String	DEFAULT_KEYWORD_STRING A default keyword.

Fields inherited from class hcrypto.cipher.HistoricalKey

alphabet, blocksize, ciphAlphabet, cipherAlphabet, keyDescriptorPrompt, keyspec, keyword, plainAlphabet

Constructor Summary

PlayfairKey()

Method Summary

int	findCharPosition(char ch) Returns the position of the specified character.
java.lang.String	getAlgorithm() Returns the algorithm name "Playfair".
char	getChar(int index) Returns the character at the specified index.
char	getChar(int row, int col) Returns the character at the specified row and column.
int	getColIndex(int index) Returns the column index for the specified index.
int	getLeftColIndex(int index) Returns the left column index for the specified index.
int	getRightColIndex(int index) Returns the right column index for the specified index.
int	getRowAboveIndex(int index) Returns the row above the index for the specified index.
int	getRowBelowIndex(int index) Returns the row below the index for the specified index.
int	getRowIndex(int index) Returns the row index for the specified index.
void	init(java.lang.String keyspec) Initializes the PlayfairKey with the specified keyspec.
void	printKeySquare() Prints the playfair key to the System console.
void	testMethods() Performs exhaustive tests of the methods that perform various indexing functions on the key.

Methods inherited from class hcrypto.cipher.HistoricalKey

getAlphabet, getBlocksize, getCiphAlphabet, getCTAlphabet, getInstance, getKeyDescriptorPrompt, getKeyword, getPlainAlphabet, initAlphabets, initKey, printAlphabets, removeDuplicateChars

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_KEY_DESCRIPTOR_PROMPT_STRING

public static final java.lang.String DEFAULT_KEY_DESCRIPTOR_PROMPT_STRING

A keyword description.

DEFAULT_KEYWORD_STRING

public static final java.lang.String DEFAULT_KEYWORD_STRING

A default keyword.

Constructor Detail

PlayfairKey

public PlayfairKey()

Method Detail

init

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

Initializes the PlayfairKey with the specified keyspec.

Overrides:

init in class HistoricalKey

Parameters:

keySpec - takes the form "keyword/alphabet", i.e. "ralph/az" for example, which would be mapped into the instance variables keyword as a String with the value of "ralph" and alphabet as a String with the value "az".

getAlgorithm

public java.lang.String getAlgorithm()

Returns the algorithm name "Playfair".

Overrides:

getAlgorithm in class HistoricalKey

findCharPosition

public int findCharPosition(char ch)
                     throws java.lang.Exception

Returns the position of the specified character. Called from PlayfairCipherSpi.

getChar

public char getChar(int index)

Returns the character at the specified index. Called from PlayfairCipherSpi.

getChar

public char getChar(int row,
                    int col)

Returns the character at the specified row and column. Called from PlayfairCipherSpi.

getRowIndex

public int getRowIndex(int index)

Returns the row index for the specified index. Called from PlayfairCipherSpi.

getColIndex

public int getColIndex(int index)

Returns the column index for the specified index. Called from PlayfairCipherSpi.

getRightColIndex

public int getRightColIndex(int index)

Returns the right column index for the specified index. Called from PlayfairCipherSpi.

getLeftColIndex

public int getLeftColIndex(int index)

Returns the left column index for the specified index. Called from PlayfairCipherSpi.

getRowBelowIndex

public int getRowBelowIndex(int index)

Returns the row below the index for the specified index. Called from PlayfairCipherSpi.

getRowAboveIndex

public int getRowAboveIndex(int index)

Returns the row above the index for the specified index. Called from PlayfairCipherSpi.

testMethods

public void testMethods()

Performs exhaustive tests of the methods that perform various indexing functions on the key.

printKeySquare

public void printKeySquare()

Prints the playfair key to the System console.