Ceasar Cipher in VB.NET

Ceasar Cipher 

Public Class frmCeasarCipher

Function EncryptDecrypt(ByVal text1 As String, ByVal key As String, ByVal isEncrypt As Boolean) As String

 Dim char1 As String

        Dim char2 As String

        Dim cKey As Byte

        Dim strLength As Integer

        Dim Result As String = ""

        Dim j As Integer = -1

        If text1 "" And IsNumeric(key) Then

            strLength = text1.Length

            For i As Integer = 0 To strLength - 1

                char1 = text1.Substring(i, 1)

                If j < key.Length - 1 Then

                    j = j + 1

                Else

                    j = 0

                End If

                cKey = Val(key.Substring(j, 1))

                If isEncrypt Then

                    char2 = Chr(Asc(char1) + cKey)

                Else

                    char2 = Chr(Asc(char1) - cKey)

                End If

                Result &= char2

            Next

        Else

            MsgBox("Enter text or key!")

        End If

        Return Result

    End Function

    Private Sub btCrypt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btCrypt.Click

        txtResult.Text = EncryptDecrypt(txtText.Text, txtKey.Text, True)

    End Sub

    Private Sub btDecrypt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btDecrypt.Click

        txtResult.Text = EncryptDecrypt(txtText.Text, txtKey.Text, False)

    End Sub

End Class

Executable file & Source Code