Dim Shared As String encrypted, decrypted

Sub BifidEncode(Byref polybius As String, Byref mensaje As String)
    Dim As String filas, columas
    Dim As Integer c, i, j, k, longi

    encrypted = Ucase(mensaje)
    For i = 1 To Len(encrypted)
        If Mid(encrypted, i, 1) = Chr(10) Then Mid(encrypted, i, 1) = Chr(9)
    Next i


    i = 0 : j = 0
    While i < Len(encrypted)
        c = Asc(Mid(encrypted, i + 1, 1))
        i += 1
        k = Instr(polybius, Chr(c)) - 1
        If k >= 0 Then
            filas &= Chr(k \ 5 + Asc("0"))
            columas &= Chr(k Mod 5 + Asc("0"))
            j += 1
        End If
    Wend

    longi = j
    filas &= columas

    encrypted = ""
    For i = 0 To longi - 1
        k = (Asc(Mid(filas, i * 2 + 1, 1)) - Asc("0")) * 5 + (Asc(Mid(filas, i * 2 + 2, 1)) - Asc("0"))
        encrypted &= Mid(polybius, k + 1, 1)
    Next i
End Sub

Sub BifidDecode(Byref polybius As String, Byref mensaje As String)
    Dim As String filas, columas
    Dim As Integer c, k, i, j, longi

    i = 0 : j = 0
    While i < Len(mensaje)
        c = Asc(Mid(mensaje, i + 1, 1))
        i += 1
        k = Instr(polybius, Chr(c)) - 1
        filas &= Chr(k \ 5 + Asc("0"))
        filas &= Chr(k Mod 5 + Asc("0"))
        j += 2
    Wend

    longi = i
    columas = Right(filas, longi)
    filas = Left(filas, longi)

    decrypted = ""
    For i = 0 To longi - 1
        k = (Asc(Mid(filas, i + 1, 1)) - Asc("0")) * 5 + (Asc(Mid(columas, i + 1, 1)) - Asc("0"))
        decrypted &= Mid(polybius, k + 1, 1)
    Next i
End Sub

Dim As String polys(3), msgs(3)

polys(0) = "ABCDEFGHIKLMNOPQRSTUVWXYZ"
polys(1) = "BGWKZQPNDSIOAXEFCLUMTHYVR"
polys(2) = "BGWKZQPNDSIOAXEFCLUMTHYVR"
polys(3) = "PLAYFIREXMBCDGHKNOQSTUVWZ"

msgs(0) = "ATTACKATDAWN"
msgs(1) = "FLEEATONCE"
msgs(2) = "ATTACKATDAWN"
msgs(3) = "The invasion will start on the first of January"

For i As Integer = 0 To Ubound(msgs)
    BifidEncode(polys(i), msgs(i))
    BifidDecode(polys(i), encrypted)
    Print "Mensaje   : "; msgs(i)
    Print "Encrypted : "; encrypted
    Print "Decrypted : "; decrypted
    If i < Ubound(msgs) Then Print
Next i

Sleep