input "Gimme a ofset:";ofst       ' set any offset you like

a$ = "Pack my box with five dozen liquor jugs"
print " Original: ";a$
a$ = cipher$(a$,ofst)
print "Encrypted: ";a$
print "Decrypted: ";cipher$(a$,ofst+6)

FUNCTION cipher$(a$,ofst)
for i = 1 to len(a$)
  aa$   = mid$(a$,i,1)
  code$ = " "
  if aa$ <> " " then
    ua$   = upper$(aa$)
    a     = asc(ua$) - 64
    code$ = chr$((((a mod 26) + ofst) mod 26) + 65)
    if ua$ <> aa$ then code$ = lower$(code$)
  end if
  cipher$ = cipher$;code$
next i
END FUNCTION