Te paso 2 funciones que emplean Cesar:
Function Cifrar (cad as string) as string
;Encriptacion HAL (HAL -> IBM: Cesar + 1)
Dim i as long
dim ret as string
ret = ""
for i = 1 to len(cad)
ret = ret + chr(asc(mid(cad,i,1)) + 1)
next i
Cifrar = ret
end function
Function DESCifrar (cad as string) as string
;DESEncriptacion HAL (IBM -> HAL: Cesar - 1)
Dim i as long
dim ret as string
ret = ""
for i = 1 to len(cad)
ret = ret + chr(asc(mid(cad,i,1)) - 1)
next i
DESCifrar = ret
end function
No tengo VB aca, pero deberian funcionar bien. Sólo es para que veas algo básico.
Saludos!