DEFINITION MODULE SimpleCipher ;

(*
    Description: provides a simple Caesar cipher layer which
                 can be attached to any channel device.  This,
                 pedagogical, module is designed to show how
                 it is possible to add further layers underneath
                 the channel devices.
*)

FROM IOChan IMPORT ChanId ;


(*
   InsertCipherLayer - inserts a caesar cipher below channel, cid.
                       The encryption, key, is specified.
*)

PROCEDURE InsertCipherLayer (cid: ChanId; key: INTEGER) ;


(*
   RemoveCipherLayer - removes a Caesar cipher below channel, cid.
*)

PROCEDURE RemoveCipherLayer (cid: ChanId) ;


END SimpleCipher.