Como faço isso em C# ???

Olá Pessoal, faz pouco tempo que estou programando em C#...

entao estou migrando algumas coisas de VB6 para C#.... e gostaria de saber como faço

isso..

Function DeCripto(ByVal InputString As String) As String
   Dim OutputString As String
   Dim DecodeKey    As Variant
   Dim x            As Integer
  
   For x = 1 To Len(InputString)
      DecodeKey = x Mod 26
      OutputString = OutputString & Chr$(Asc(Mid$(InputString, x, 1)) - DecodeKey)
   Next
  
   DeCripto = OutputString
End Function

Function EmCripto(ByVal InputString As String) As String
   Dim OutputString As String
   Dim DecodeKey    As Variant
   Dim x            As Integer
  
   For x = 1 To Len(InputString)
      DecodeKey = x Mod 26
      If DecodeKey + Asc(Mid$(InputString, x, 1)) > 255 Then
         OutputString = OutputString & Chr$(255)
      Else
         OutputString = OutputString & Chr$(DecodeKey + Asc(Mid$(InputString, x, 1)))
      End If
     
     
   Next
  
   EmCripto = OutputString
End Function

Obrigado.