m56LVS5C

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