How to convert the C# code to a VB6 code

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VB6

Hi everyone, I need to create a vb6 codes contains the Caeser Cipher (the mathematical method)

C = E(p) = (p + k) mod (26)

My friend just created a code in C# but i need to convert it to vb6 (but without using a function, because i am not good in this)

appreciate if someone can assist me with this

{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.ComponentModel.Composition;

    public class Ceaser : SecurityAlgorithm
    {
        readonly int key;

        #region Constructor

        public Ceaser(int key)
        {
            this.key = key;
        }

        #endregion

        #region Public Methods

        public override string Encrypt(string plainText)
        {
            return Process(plainText, Mode.Encrypt);
        }

        public override string Decrypt(string cipher)
        {
            return Process(cipher, Mode.Decrypt);
        }

        #endregion

        #region Private Methods

        private string Process(string message, Mode mode)
        {
            string result = string.Empty;

            foreach (char c in message)
            {
                var charposition = alphabet[c];
                var res = Common.GetAlphabetPosition(charposition, key, mode);
                result += alphabet.Keys.ElementAt(res % 26);
            }

            return result;
        }

        #endregion
    }
}