JavaAlgorithms/ciphers/SimpleSubstitutionCipher.java

88 lines
2.7 KiB
Java
Raw Normal View History

package ciphers;
import java.util.*;
/**
2020-10-24 18:23:28 +08:00
* 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 {
2020-10-24 18:23:28 +08:00
/**
* 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));
}
2020-10-24 18:23:28 +08:00
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);
}
2020-10-24 18:23:28 +08:00
return encoded;
}
2020-10-24 18:23:28 +08:00
/**
* 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 = "";
2020-10-24 18:23:28 +08:00
Map<Character, Character> cipherMap = new HashMap<Character, Character>();
2020-10-24 18:23:28 +08:00
char beginSmallLetter = 'a';
char beginCapitalLetter = 'A';
2020-10-24 18:23:28 +08:00
cipherSmall = cipherSmall.toLowerCase();
String cipherCapital = cipherSmall.toUpperCase();
2020-10-24 18:23:28 +08:00
for (int i = 0; i < cipherSmall.length(); i++) {
cipherMap.put(cipherSmall.charAt(i), beginSmallLetter++);
cipherMap.put(cipherCapital.charAt(i), beginCapitalLetter++);
}
2020-10-24 18:23:28 +08:00
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);
}
2020-10-24 18:23:28 +08:00
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);
}
2020-01-29 04:16:27 +08:00
}