Welcome to the Lounge

string input = "   2365    2365    ";
string output = Regex.Replace(input, @"(?<=\d+)\s+(?=\d+)", "");

private string Encrypt(string input, string key)
{
    List<uint> result = new List<uint>();
    
    //XOR encryption
    for (int c = 0; c < input.Length; c++)
        result.Add(((uint)input[c] ^ (uint)key[c % key.Length]));

    //Normally, the uint added to the list above is cast into a char and appended to a string builder.
    //However, the strange characters thus produced were not very browser or copy/paste friendly.
    //So instead I left them as numbers, with spaces in between them.

    string output = "";

    foreach (uint i in result)
        output += i.ToString() + " ";

    return output;
}
private string Decrypt(string input, string key)
{
    char[] splitter = new char[] { ' ' };
    string[] splits = input.Split(splitter, StringSplitOptions.RemoveEmptyEntries);

    string comp = "";

    foreach (string s in splits)
    {
        comp += (char)(uint.Parse(s));
    }

    //The code above took the numbers and finished the "incomplete" encryption process, so that
    //the XOR process can be repeated to decrypt the string.

    StringBuilder result = new StringBuilder();

    for (int c = 0; c < comp.Length; c++)
        result.Append((char)((uint)comp[c] ^ (uint)key[c % key.Length]));

    return result.ToString();
}