C＃Playfair Cipher

Question

我要做的是拿一把钥匙和信息并将两者结合起来。删除重复的字母并从组合字符串构造2d 5x5数组。 然后用2d数组中字母的反向位置替换消息字符。因此，如果字母A位于2,3位，我将用位置3,2处的字母替换该字母。

我不知道如何做到这一点。我一直在这里搜索和reddit和codeproject和一般谷歌查询。我走了很多路，没有什么成功。我只是不知道该怎么做。

    // array of the alphabet for replacing string letters
        string alphabetArray = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        //char[][] alphabetArray = new Char[5,5] {{"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"}};
        // "parse" user input from key textbox
        string userCipherKey = ChipherTextBox.Text;

        // "parse" user input from message textbox
        string messageForEncryption = InputRichTextBox.Text;

        // insert cipher key into alphabet string array begining at the 0 location
        string combinedStrings = alphabetArray.Insert(0, userCipherKey);

        // remove duplicate letters from newly created array
        string arrayWithDuplicateCharsRemoved = ""; // localized decleration of new array name

        foreach (char value in combinedStrings)
        {
            // See if character is in the result already.
            if (arrayWithDuplicateCharsRemoved.IndexOf(value) == -1)
            {
                // Append to the result.
                arrayWithDuplicateCharsRemoved += value;
            }
        }

        // convert char values back to a string
        string encryptionArray = arrayWithDuplicateCharsRemoved.ToString();


        // turn the new string into a 2d array
        //char[] encryptionArray = removedDuplicateCharsFromArray.ToCharArray();
        string encryptedMessage;


        for (int i = 0; i < encryptionArray.Length; i++)
        {
            encryptedMessage = messageForEncryption.Replace(messageForEncryption, encryptionArray);
        }

        string messageOutput = encryptedMessage.ToString();

        return OutputRichTextBox.Text = messageOutput.ToString();

    }