133 lines
3.7 KiB
Java
133 lines
3.7 KiB
Java
package ciphers;
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import java.util.Scanner;
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/**
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*
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* A Java implementation of Caesar Cipher. /It is a type of substitution cipher
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* in which each letter in the plaintext is replaced by a letter some fixed
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* number of positions down the alphabet. /
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*
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* @author FAHRI YARDIMCI
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* @author khalil2535
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*/
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public class Caesar {
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/**
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* Encrypt text by shifting every Latin char by add number shift for ASCII
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* Example : A + 1 -> B
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*
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* @param message
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* @param shift
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* @return Encrypted message
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*/
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public static String encode(String message, int shift) {
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String encoded = "";
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shift %= 26;
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final int length = message.length();
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for (int i = 0; i < length; i++) {
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// int current = message.charAt(i); //using char to shift characters because ascii is in-order latin alphabet
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char current = message.charAt(i); // Java law : char + int = char
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if (IsCapitalLatinLetter(current)) {
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current += shift;
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encoded += (char) (current > 'Z' ? current - 26 : current); // 26 = number of latin letters
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} else if (IsSmallLatinLetter(current)) {
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current += shift;
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encoded += (char) (current > 'z' ? current - 26 : current); // 26 = number of latin letters
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} else {
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encoded += current;
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}
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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 shifting back every Latin char to previous the ASCII
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* Example : B - 1 -> A
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*
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* @param encryptedMessage
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* @param shift
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* @return message
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*/
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public static String decode(String encryptedMessage, int shift) {
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String decoded = "";
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shift %= 26;
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final int length = encryptedMessage.length();
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for (int i = 0; i < length; i++) {
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char current = encryptedMessage.charAt(i);
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if (IsCapitalLatinLetter(current)) {
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current -= shift;
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decoded += (char) (current < 'A' ? current + 26 : current);// 26 = number of latin letters
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} else if (IsSmallLatinLetter(current)) {
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current -= shift;
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decoded += (char) (current < 'a' ? current + 26 : current);// 26 = number of latin letters
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} else {
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decoded += current;
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}
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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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* @param c
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* @return true if character is capital Latin letter or false for others
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*/
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private static boolean IsCapitalLatinLetter(char c) {
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return c >= 'A' && c <= 'Z';
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}
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/**
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*
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* @param c
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* @return true if character is small Latin letter or false for others
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*/
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private static boolean IsSmallLatinLetter(char c) {
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return c >= 'a' && c <= 'z';
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}
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/**
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*
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* @deprecated 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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Scanner input = new Scanner(System.in);
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System.out.println("Please enter the message (Latin Alphabet)");
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String message = input.nextLine();
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System.out.println(message);
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System.out.println("Please enter the shift number");
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int shift = input.nextInt() % 26;
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System.out.println("(E)ncode or (D)ecode ?");
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char choice = input.next().charAt(0);
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switch (choice) {
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case 'E':
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case 'e':
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System.out.println("ENCODED MESSAGE IS \n" + encode(message, shift)); //send our function to handle
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break;
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case 'D':
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case 'd':
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System.out.println("DECODED MESSAGE IS \n" + decode(message, shift));
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}
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input.close();
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}
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}
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