Using Dictionary to map byte to BitArray

Question

I am developing an application that implements Simple Substitution Cypher. Now for speed reasons (and because that was one of the conditions) I need to use BitArray for encryption and decryption. The user will enter "coded" alphabet and I would need to map it in some way so I chose Dictionary since it uses hash table and has O(1) complexity when the user access data. But now I found myself wondering how can I do this when I have "coded" alphabet initialized like this:

BitArray codedAlphabet = new BitArray(bytes);

This would make me use 2 for loops to achieve my goal. Does anyone have different idea? Hopefully you understood what I am trying to achieve. Thank you in advance.

Code:

namespace Harpokrat.EncryptionAlgorithms
{
// Simple substitution cypher algorithm
    public class SimpleSubstitutionStrategy : IEncryptionStrategy
    {
        private string alphabet;  // message to be encrypted
        private string coded;      // this will be the key (input from file or from UI)

        private ArrayList AlphabetBackUp = new ArrayList();
        private ArrayList CodedBackUp    = new ArrayList();

        #region Properties
        public string Alphabet
        {
            get
            {
                return this.alphabet;
            }
            set
            {
                this.alphabet = value;
                foreach (char c in this.alphabet.ToCharArray())
                {
                    this.AlphabetBackUp.Add(c);
                }
            }
        }

        public string Coded
        {
            get
            {
                return this.coded;
            }

            set
            {
                this.coded = "yqmnnsgwatkgetwtawuiqwemsg"; //for testing purposes
                foreach (char c in this.coded.ToCharArray())
            {
                this.CodedBackUp.Add(c);
            }
        }
    }

    #endregion

    public string Decrypt(string message)
    {
        message = message.ToLower();
        string result = "";
        for (int i = 0; i < message.Length; i++)
        {
            int indexOfSourceChar = CodedBackUp.IndexOf(message[i]);
            if (indexOfSourceChar < 0 || (indexOfSourceChar > alphabet.Length - 1))
            {
                result += "#";
            }
            else
            {
                result += alphabet[indexOfSourceChar].ToString();
            }
        }
        return result;
    }

    public string Encrypt(string message)
    {
        message = message.ToLower();
        string result = "";
        for(int i = 0; i < message.Length; i++)
        {
            int indexOfSourceChar = AlphabetBackUp.IndexOf(message[i]);
            if (indexOfSourceChar < 0 || (indexOfSourceChar > coded.Length - 1))
            {
                result += "#";
            }
            else
            {
                result += coded[indexOfSourceChar].ToString();
            }
        }

        return result;
    }
}
}

Answer 1

I'd recommend a single method to set alphabet and coded at the same time, that internally builds the two dictionaries you'd need to do Encryption and Decryption, and a helper method to do a get-or-return-default ('#' in your case) on them. That way you can implement a single function that does either Encryption or Decryption depending on the dictionary passed in (which could be implemented in a single line of code if you're comfortable using LINQ).