mwYgbNu8

1/*
2 * Write a program that asks the user for an encrypted message 
3 * and Caesar cipher key, and decrypts the message.
4 *
5 * Use the function caesarEncrypt! What key value do you need to 
6 * pass this function to decrypt your message?
7 *
8 */
9 
10
11var ALPHABET = "abcdefghijklmnopqrstuvwxyz";
12
13function start(){
14    var originalMessage = readLine("Enter the message you would like to encrypt: ");
15    originalMessage = originalMessage.toLowerCase();
16    
17    var secretKey = readInt("Enter the number you'd like to shift each character by: ");
18    
19    var encryptedMessage = caesarEncrypt(originalMessage, secretKey);
20    println("");
21    println("Encrypted message: " + encryptedMessage);
22    
23    println("");
24    println("Decrypting message...");
25    println("");
26    
27    // You will need to write caesarDecrypt below
28    var decrypted = caesarDecrypt(encryptedMessage, secretKey);
29    println("Done:");
30    
31    println(decrypted);
32}
33
34
35function caesarDecrypt(encryptedMessage, key){
36    var decryptedResult = "";
37    for(var i = 0; i < encryptedMessage.length; i++){
38    var originalCharacter = encryptedMessage.charAt(i);
39    var alphabeticIndex = ALPHABET.indexOf(originalCharacter);
40    if(alphabeticIndex >=0) {
41        var newIndex = alphabeticIndex - key + ALPHABET.length; 
42    newIndex = newIndex % ALPHABET.length; 
43    var newCharacter = ALPHABET.charAt(newIndex);
44    decryptedResult +=newCharacter
45    
46    }
47    else{ 
48        decryptedResult +=originalCharacter;
49    }
50    return decryptedResult;
51
52}}
53
54function caesarEncrypt(message, key){
55    var encryptedResult = "";
56    
57    for(var i = 0; i < message.length; i++){
58        // Get the character in the original message
59        var originalCharacter = message.charAt(i);
60        var alphabeticIndex = ALPHABET.indexOf(originalCharacter);
61        if(alphabeticIndex >= 0){
62            var newIndex = alphabeticIndex + key + ALPHABET.length;
63            newIndex = newIndex % ALPHABET.length;
64            var newCharacter = ALPHABET.charAt(newIndex);
65            encryptedResult += newCharacter
66        }
67
68        else{
69            encryptedResult += originalCharacter;
70        }
71    }
72    
73    return encryptedResult;
74}