SimpleSubCipher.java

packagecom.thealgorithms.ciphers;

importjava.util.HashMap;
importjava.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.
 */
publicclassSimpleSubCipher {

/**
 * Encrypt text by replacing each element with its opposite character.
 *
 * @param message
 * @param cipherSmall
 * @return Encrypted message
 */
publicStringencode(Stringmessage, StringcipherSmall) {
StringBuilderencoded = newStringBuilder();

// This map is used to encode
Map<Character, Character> cipherMap = newHashMap<>();

charbeginSmallLetter = 'a';
charbeginCapitalLetter = 'A';

cipherSmall = cipherSmall.toLowerCase();
StringcipherCapital = cipherSmall.toUpperCase();

// To handle Small and Capital letters
for (inti = 0; i < cipherSmall.length(); i++) {
cipherMap.put(beginSmallLetter++, cipherSmall.charAt(i));
cipherMap.put(beginCapitalLetter++, cipherCapital.charAt(i));
 }

for (inti = 0; i < message.length(); i++) {
if (Character.isAlphabetic(message.charAt(i))) {
encoded.append(cipherMap.get(message.charAt(i)));
 } else {
encoded.append(message.charAt(i));
 }
 }

returnencoded.toString();
 }

/**
 * Decrypt message by replacing each element with its opposite character in
 * cipher.
 *
 * @param encryptedMessage
 * @param cipherSmall
 * @return message
 */
publicStringdecode(StringencryptedMessage, StringcipherSmall) {
StringBuilderdecoded = newStringBuilder();

Map<Character, Character> cipherMap = newHashMap<>();

charbeginSmallLetter = 'a';
charbeginCapitalLetter = 'A';

cipherSmall = cipherSmall.toLowerCase();
StringcipherCapital = cipherSmall.toUpperCase();

for (inti = 0; i < cipherSmall.length(); i++) {
cipherMap.put(cipherSmall.charAt(i), beginSmallLetter++);
cipherMap.put(cipherCapital.charAt(i), beginCapitalLetter++);
 }

for (inti = 0; i < encryptedMessage.length(); i++) {
if (Character.isAlphabetic(encryptedMessage.charAt(i))) {
decoded.append(cipherMap.get(encryptedMessage.charAt(i)));
 } else {
decoded.append(encryptedMessage.charAt(i));
 }
 }

returndecoded.toString();
 }
}