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Merged
merged 2 commits into from
Jan 28, 2020
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Simple Substitution Cipher Algorithm added. #1218

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Simple Substitution Cipher Algorithm added.
Hassan-Elseoudy Jan 28, 2020
e21d0ef
Update SimpleSubstitutionCipher.java
nikhilkala Jan 28, 2020
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97 changes: 97 additions & 0 deletions ciphers/SimpleSubstitutionCipher.java
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package ciphers;

import java.util.*;

/**
*
* The simple substitution cipher is a cipher that has been in use for many hundreds of years
* (an excellent history is given in Simon Singhs 'the Code Book').
* It basically consists of substituting every plaintext character for a different ciphertext character.
* It differs from the Caesar cipher in that the cipher alphabet is not simply the alphabet shifted,
* it is completely jumbled.
*
* @author Hassan Elseoudy
*/

public class SimpleSubstitutionCipher {

/**
* Encrypt text by replacing each element with its opposite character.
*
* @param message
* @param cipherSmall
* @return Encrypted message
*/
public static String encode(String message, String cipherSmall) {
String encoded = "";

// This map is used to encode
Map<Character,Character> cipherMap = new HashMap<Character,Character>();

char beginSmallLetter = 'a';
char beginCapitalLetter = 'A';

cipherSmall = cipherSmall.toLowerCase();
String cipherCapital = cipherSmall.toUpperCase();

// To handle Small and Capital letters
for(int i = 0; i < cipherSmall.length(); i++){
cipherMap.put(beginSmallLetter++,cipherSmall.charAt(i));
cipherMap.put(beginCapitalLetter++,cipherCapital.charAt(i));
}

for(int i = 0; i < message.length(); i++){
if(Character.isAlphabetic(message.charAt(i)))
encoded += cipherMap.get(message.charAt(i));
else
encoded += message.charAt(i);
}

return encoded;
}

/**
* Decrypt message by replacing each element with its opposite character in cipher.
*
* @param encryptedMessage
* @param cipherSmall
* @return message
*/
public static String decode(String encryptedMessage, String cipherSmall) {
String decoded = "";


Map<Character,Character> cipherMap = new HashMap<Character,Character>();

char beginSmallLetter = 'a';
char beginCapitalLetter = 'A';

cipherSmall = cipherSmall.toLowerCase();
String cipherCapital = cipherSmall.toUpperCase();

for(int i = 0; i < cipherSmall.length(); i++){
cipherMap.put(cipherSmall.charAt(i),beginSmallLetter++);
cipherMap.put(cipherCapital.charAt(i),beginCapitalLetter++);
}

for(int i = 0; i < encryptedMessage.length(); i++){
if(Character.isAlphabetic(encryptedMessage.charAt(i)))
decoded += cipherMap.get(encryptedMessage.charAt(i));
else
decoded += encryptedMessage.charAt(i);
}

return decoded;
}

/**
*
* TODO remove main and make JUnit Testing
*/
public static void main(String[] args) {
String a = encode("defend the east wall of the castle","phqgiumeaylnofdxjkrcvstzwb");
String b = decode(a,"phqgiumeaylnofdxjkrcvstzwb");
System.out.println(b);
}

}