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Merge pull request #162 from freitzzz/master
Columnar Transposition Cipher with example usage
This commit is contained in:
Chetan Kaushik
169
ciphers/ColumnarTranspositionCipher.java
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169
ciphers/ColumnarTranspositionCipher.java
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/**
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* Columnar Transposition Cipher Encryption and Decryption.
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* @author <a href="https://github.com/freitzzz">freitzzz</a>
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*/
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public class ColumnarTranspositionCipher {
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private static String keyword;
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private static Object[][] table;
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private static String abecedarium;
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public static final String ABECEDARIUM="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789,.;:-@";
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private static final String ENCRYPTION_FIELD="≈";
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private static final char ENCRYPTION_FIELD_CHAR='≈';
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/**
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* Encrypts a certain String with the Columnar Transposition Cipher Rule
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* @param word Word being encrypted
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* @param keyword String with keyword being used
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* @return a String with the word encrypted by the Columnar Transposition Cipher Rule
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*/
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public static String encrpyter(String word,String keyword){
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ColumnarTranspositionCipher.keyword=keyword;
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abecedariumBuilder(500);
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table=tableBuilder(word);
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Object[][] sortedTable=sortTable(table);
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String wordEncrypted="";
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for(int i=0;i<sortedTable[0].length;i++){
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for(int j=1;j<sortedTable.length;j++){
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wordEncrypted+=sortedTable[j][i];
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}
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}
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return wordEncrypted;
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}
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/**
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* Encrypts a certain String with the Columnar Transposition Cipher Rule
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* @param word Word being encrypted
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* @param keyword String with keyword being used
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* @param abecedarium String with the abecedarium being used. null for default one
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* @return a String with the word encrypted by the Columnar Transposition Cipher Rule
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*/
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public static String encrpyter(String word,String keyword,String abecedarium){
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ColumnarTranspositionCipher.keyword=keyword;
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if(abecedarium!=null){
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ColumnarTranspositionCipher.abecedarium=abecedarium;
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}else{
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ColumnarTranspositionCipher.abecedarium=ABECEDARIUM;
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}
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table=tableBuilder(word);
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Object[][] sortedTable=sortTable(table);
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String wordEncrypted="";
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for(int i=0;i<sortedTable[0].length;i++){
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for(int j=1;j<sortedTable.length;j++){
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wordEncrypted+=sortedTable[j][i];
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}
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}
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return wordEncrypted;
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}
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/**
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* Decryps a certain encrypted String with the Columnar Transposition Cipher Rule
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* @return a String decrypted with the word ecrypted by the Columnar Transpositiion Cipher Rule
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*/
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public static String decrypter(){
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String wordDecrypted="";
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for(int i=1;i<table.length;i++){
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for(int j=0;j<table[i].length;j++){
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wordDecrypted+=table[i][j];
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}
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}
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return wordDecrypted.replaceAll(ENCRYPTION_FIELD,"");
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}
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/**
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* Builds a table with the word to be encrpyted in rows by the Columnar Transposition Cipher Rule
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* @return An Object[][] with the word to be encrypted filled in rows and columns
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*/
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private static Object[][] tableBuilder(String word){
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Object[][] table=new Object[rows(word)+1][keyword.length()];
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char[] wordInChards=word.toCharArray();
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//Fils in the respective numbers
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table[0]=findElements();
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int charElement=0;
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for(int i=1;i<table.length;i++){
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for(int j=0;j<table[i].length;j++){
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if(charElement<wordInChards.length){
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table[i][j]=(char)wordInChards[charElement];
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charElement++;
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}else{
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table[i][j]=ENCRYPTION_FIELD_CHAR;
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}
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}
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}
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return table;
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}
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/**
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* Determines the number of rows the table should have regarding the Columnar Transposition Cipher Rule
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* @return an int with the number of rows that the table should have in order to respect the Columnar Transposition Cipher Rule.
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*/
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private static int rows(String word){
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if((double)word.length()/keyword.length()>word.length()/keyword.length()){
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return (word.length()/keyword.length())+1;
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}else{
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return word.length()/keyword.length();
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}
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}
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private static Object[] findElements(){
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Object[] charValues=new Object[keyword.length()];
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for(int i=0;i<charValues.length;i++){
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for(int j=0;j<abecedarium.length();j++){
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if(keyword.charAt(i)==abecedarium.charAt(j))charValues[i]=j;
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}
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}
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return charValues;
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}
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private static Object[][] sortTable(Object[][] table){
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Object[][] tableSorted=new Object[table.length][table[0].length];
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for(int i=0;i<tableSorted.length;i++){
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for(int j=0;j<tableSorted[i].length;j++){
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tableSorted[i][j]=table[i][j];
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}
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}
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for(int i=0;i<tableSorted[0].length;i++){
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for(int j=i+1;j<tableSorted[0].length;j++){
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if((int)tableSorted[0][i]>(int)table[0][j]){
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Object[] column=getColumn(tableSorted,tableSorted.length,i);
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switchColumns(tableSorted,j,i,column);
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}
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}
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}
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return tableSorted;
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}
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private static Object[] getColumn(Object[][] table,int rows,int column){
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Object[] columnArray=new Object[rows];
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for(int i=0;i<rows;i++){
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columnArray[i]=table[i][column];
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}
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return columnArray;
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}
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private static void switchColumns(Object[][] table, int firstColumnIndex,int secondColumnIndex,Object[] columnToSwitch){
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for(int i=0;i<table.length;i++){
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table[i][secondColumnIndex]=table[i][firstColumnIndex];
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table[i][firstColumnIndex]=columnToSwitch[i];
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}
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}
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/**
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* Creates an abecedarium with a specified ascii inded
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* @param value Number of characters being used based on the ASCII Table
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*/
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private static void abecedariumBuilder(int value){
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abecedarium="";
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for(int i=0;i<value;i++){
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abecedarium+=(char)i;
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}
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}
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private static void showTable(){
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for(int i=0;i<table.length;i++){
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for(int j=0;j<table[i].length;j++){
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System.out.print(table[i][j]+" ");
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}
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System.out.println();
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}
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}
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public static void main(String[] args){
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String keywordForExample="asd215";
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String wordBeingEncrypted="This is a test of the Columnar Transposition Cipher";
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System.out.println("### Example of Columnar Transposition Cipher ###\n");
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System.out.println("Word being encryped ->>> "+wordBeingEncrypted);
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System.out.println("Word encrypted ->>> "+ColumnarTranspositionCipher.encrpyter(wordBeingEncrypted,keywordForExample));
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System.out.println("Word decryped ->>> "+ColumnarTranspositionCipher.decrypter());
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System.out.println("\n### Encrypted Table ###");
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showTable();
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}
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}
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