92 lines
2.9 KiB
Java
92 lines
2.9 KiB
Java
package ciphers;
|
|
|
|
import java.util.HashMap;
|
|
import java.util.Map;
|
|
|
|
/**
|
|
* 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.
|
|
*/
|
|
|
|
public class SimpleSubCipher {
|
|
|
|
/**
|
|
* 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<>();
|
|
|
|
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;
|
|
}
|
|
|
|
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);
|
|
}
|
|
|
|
}
|