Basic HTML version of Foils prepared April 7 1998

Foil 59 Why is type checking important!

From Basic Principles of Java and Internet Security CPS616 Web Technologies -- Spring 98. by Geoffrey C. Fox


1 If one has either deliberately or accidentally a "wild object pointer" that should be to a user defined on/off object but has somehow been applied to a sensitive object.
2 Then turning userobject.onoff to true is uncontroversial but this applied to appletprivilege could turn on the ability to write files!
  • Note setting userobject.onoff = true is really "go to location of this object and set its start address plus some many bytes to value true"!
3 Thus normal computer programs often overwrite themselves when you screw-up with a software error.
4 Java applets can obviously have software bugs but such errors do not let them ever overwrite themselves or anybody else.
  • Otherwise the overwriting can radically change security
5 Thus Java must guarantee types of objects precisely so operations can be stupid but never violate security.

in Table To:


© Northeast Parallel Architectures Center, Syracuse University, npac@npac.syr.edu

If you have any comments about this server, send e-mail to webmaster@npac.syr.edu.

Page produced by wwwfoil on Mon Apr 6 1998