Eve and Mallory Sends A Secret Code Without Bob Seeing Them

Eve and Mallory Send A Secret Code Without Bob Seeing Them

Eve and Mallory are being watched by Victor for every message that they send to each other. So, how does Eve send a secret message to Mallory? Well, this can be done with a covert channel in the messages they send. One example of this is to use a cipher based on Scrabble letters:

Note that in the graphic, the letter ‘Q’ should have a score of 10. Let’s say that Eve wants to send a secret code to Mallory, and writes a message of:

Hello Mallory, I watched a terrible movie about clowns last night. 
I think I need to get over my clown phobia, as I have nightmares after 
watching these films. Regards, Eve

Bob doesn’t see anything in this message, but Mallory straight away sees that the secret code is 238. Why? Because if you could the Scrabble letter values they add up to 238. Here’s the code that Mallory could use:

namespace Scrabble
{

using System;
    class Program
    {
        
        static void Main(string[] args)
        {
           
           string word="Hello";


            if (args.Length >0) word=args[0];
            Console.WriteLine(scrabble(word));

} 

       public static string scrabble(string word)
        {
          // int[] letter = { a, b, c, d, e, f, g, h, i, j, k, l,m,n,o,p,q, r,s,t,u,v,w,x,y,z};
             int[] letters = { 1, 3, 3, 2, 1, 4, 2, 4, 1, 8, 5, 1,3,1,1,3,10,1,1,1,1,4,4,8,4,10};
            int val = 0;



        
            word = word.ToLower();
            for (int i = 0; i < word.Length; i++)
            {
               if (word[i]<'a' || word[i]>'z') continue;
                val =  val+letters[word[i] - 'a'];

            }
            return (val.ToString());
        }
}
}

If we run the program, we get:

> scrabble.exe "Hello Mallory, I watched a terrible movie about clowns last night. I think I need to get over my clown phobia, as I have nightmares after watching these films. Regards, Eve"
238

If you want to solve you own, try here:

https://asecuritysite.com/ctf/ctf_95

And there’s 95 ciphers to solve here:

https://asecuritysite.com/encryption/ctf