98 lines
3.0 KiB
Java
98 lines
3.0 KiB
Java
package ciphers;
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import java.util.*;
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/**
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*
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* The simple substitution cipher is a cipher that has been in use for many hundreds of years
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* (an excellent history is given in Simon Singhs 'the Code Book').
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* It basically consists of substituting every plaintext character for a different ciphertext character.
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* It differs from the Caesar cipher in that the cipher alphabet is not simply the alphabet shifted,
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* it is completely jumbled.
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*
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* @author Hassan Elseoudy
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*/
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public class SimpleSubstitutionCipher {
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/**
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* Encrypt text by replacing each element with its opposite character.
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*
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* @param message
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* @param cipherSmall
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* @return Encrypted message
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*/
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public static String encode(String message, String cipherSmall) {
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String encoded = "";
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// This map is used to encode
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Map<Character,Character> cipherMap = new HashMap<Character,Character>();
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char beginSmallLetter = 'a';
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char beginCapitalLetter = 'A';
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cipherSmall = cipherSmall.toLowerCase();
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String cipherCapital = cipherSmall.toUpperCase();
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// To handle Small and Capital letters
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for(int i = 0; i < cipherSmall.length(); i++){
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cipherMap.put(beginSmallLetter++,cipherSmall.charAt(i));
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cipherMap.put(beginCapitalLetter++,cipherCapital.charAt(i));
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}
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for(int i = 0; i < message.length(); i++){
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if(Character.isAlphabetic(message.charAt(i)))
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encoded += cipherMap.get(message.charAt(i));
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else
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encoded += message.charAt(i);
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}
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return encoded;
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}
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/**
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* Decrypt message by replacing each element with its opposite character in cipher.
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*
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* @param encryptedMessage
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* @param cipherSmall
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* @return message
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*/
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public static String decode(String encryptedMessage, String cipherSmall) {
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String decoded = "";
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Map<Character,Character> cipherMap = new HashMap<Character,Character>();
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char beginSmallLetter = 'a';
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char beginCapitalLetter = 'A';
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cipherSmall = cipherSmall.toLowerCase();
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String cipherCapital = cipherSmall.toUpperCase();
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for(int i = 0; i < cipherSmall.length(); i++){
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cipherMap.put(cipherSmall.charAt(i),beginSmallLetter++);
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cipherMap.put(cipherCapital.charAt(i),beginCapitalLetter++);
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}
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for(int i = 0; i < encryptedMessage.length(); i++){
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if(Character.isAlphabetic(encryptedMessage.charAt(i)))
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decoded += cipherMap.get(encryptedMessage.charAt(i));
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else
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decoded += encryptedMessage.charAt(i);
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}
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return decoded;
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}
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/**
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*
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* TODO remove main and make JUnit Testing
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*/
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public static void main(String[] args) {
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String a = encode("defend the east wall of the castle","phqgiumeaylnofdxjkrcvstzwb");
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String b = decode(a,"phqgiumeaylnofdxjkrcvstzwb");
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System.out.println(b);
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}
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}
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