YkL3ZP1r

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    
30    println("Done:");
31    
32    println(decrypted);
33}
34
35
36function caesarDecrypt(encryptedMessage, key){
37    // Write a function that returns the decrypted message
38    // Hint--use the caesarEncrypt method!
39    // Decrypting is the same process as encrypting,
40    // the key just needs to shift the letters back instead of forward
41
42}
43
44function caesarEncrypt(message, key){
45    var encryptedResult = "";
46    
47    for(var i = 0; i < message.length; i++){
48        // Get the character in the original message
49        var originalCharacter = message.charAt(i);
50        
51        // If it's an alphabetical character, we'll compute the new
52        // shifted character and add it to the encrypted result
53        var alphabeticIndex = ALPHABET.indexOf(originalCharacter);
54        if(alphabeticIndex >= 0){
55            // Compute new index
56            var newIndex = alphabeticIndex + key + ALPHABET.length;
57            newIndex = newIndex % ALPHABET.length;
58            
59            // Get the new character
60            var newCharacter = ALPHABET.charAt(newIndex);
61            
62            // Add the new shifted character to the encrypted result
63            encryptedResult += newCharacter
64        }
65        
66        // Otherwise we'll keep the original character
67        else{
68            encryptedResult += originalCharacter;
69        }
70    }
71    
72    return encryptedResult;
73}