package com.decryption;

/**

* Decryption

* Decrypting messages based on a key.

*

* There is no input for this program.

* Given: A message that has to decoded based on a key.

*

* @author Harsh <girdharharsh@gmail.com>

* @since 11/26/2015 5:20PM

*/

public class Decryption {

/**

* decryptMessage

* Returns the decoded message based on the unique key.

* Apply a decrytion scheme for decoding the message.

*

* @param key Unique key to decode the message

* @param msg The message that is to be decoded

* @return String Final decoded string

*/

public String decryptMessage(String key, String msg) {

// Ascii value of CAPS A -> as the output is in CAPS

int asciiA = (int) new Character('A');

// Whatever is decoded is concatenated in this string.

String decoded = "";

// First level of decoding.

// Fetch 2 characters from message string at a time and search in english alphabets.

for (int i = 0, len = msg.length(); i < len; i += 2) {

char messageChar = msg.charAt(i);

if (messageChar == ' ') {

decoded += " ";

i--;

continue;

}

String index = "" + messageChar + msg.charAt(i + 1);

// Searching alphabet in english characters.

char alphabetPos[] = Character.toChars(asciiA + Integer.parseInt(index));

// value associated with that alphabet in given key.

int keyIndex = key.indexOf(alphabetPos[0]);

// Search for alphabet situated at position 'keyIndex'.

char decodedCharacter[] = Character.toChars(asciiA + keyIndex);

decoded += decodedCharacter[0];

}

return decoded;

}

public static void main(String[] args) {

Decryption decryption = new Decryption();

String key = "BHISOECRTMGWYVALUZDNFJKPQX";

String msg = "012222 1114142503 0313012513 03141418192102 0113 2419182119021713 06131715070119";

System.out.println(decryption.decryptMessage(key, msg));

}

}