84 lines
2.7 KiB
Java
84 lines
2.7 KiB
Java
package Ciphers;
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import java.util.*;
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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 (an
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* excellent history is given in Simon Singhs 'the Code Book'). It basically consists of
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* substituting every plaintext character for a different ciphertext character. It differs from the
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* Caesar cipher in that the cipher alphabet is not simply the alphabet shifted, it is completely
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* 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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* @return Encrypted message
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*/
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public static String encode(String message, String cipherSmall) {
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StringBuilder encoded = new StringBuilder();
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// This map is used to encode
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Map<Character, Character> cipherMap = new HashMap<>();
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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))) encoded.append(cipherMap.get(message.charAt(i)));
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else encoded.append(message.charAt(i));
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}
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return encoded.toString();
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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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* @return message
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*/
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public static String decode(String encryptedMessage, String cipherSmall) {
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StringBuilder decoded = new StringBuilder();
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Map<Character, Character> cipherMap = new HashMap<>();
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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.append(cipherMap.get(encryptedMessage.charAt(i)));
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else decoded.append(encryptedMessage.charAt(i));
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}
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return decoded.toString();
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}
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/** TODO remove main and make JUnit Testing */
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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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