VBA - Le chiffre de César

Option Explicit

Sub Main_Caesar()
Dim Ch As String
    Ch = Chiffre_Cesar("Ave Caesar morituri te salutant", 7)
    Debug.Print Ch
    Debug.Print Chiffre_Cesar(Ch, -7)
End Sub

Function Chiffre_Cesar(sTe As String, Nbre As Long) As String
Dim vT, sG As String, sT As String, i As Long, bA As Byte
  Const MAJ As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    Const NL As Byte = 26
      Const DMA As Byte = 65 - NL
        Const DMI As Byte = 97 - NL
    
    sT = sTe
    If Nbre < NL And Nbre > NL * -1 Then
        sG = String(NL * 4, " ")
        LSet sG = MAJ & MAJ & MAJ
        vT = Split(StrConv(sG, vbUnicode), Chr(0))
        For i = 1 To Len(sT)
            If Mid(sT, i, 1) Like "[a-zA-Z]" Then
                bA = Asc(Mid(sT, i, 1))
                If Mid(sT, i, 1) = vT(bA - DMA) Then
                    Mid(sT, i) = vT(bA - DMA + Nbre)
                Else
                    Mid(sT, i) = LCase(vT(bA - DMI + Nbre))
                End If
            End If
        Next i
    End If
    Chiffre_Cesar = sT
End Function