bamford@ihuxw.UUCP (Harold Bamford) (06/17/85)
Concerning making a secure "login" by changing the shell... > Solutions: > 1) ... to catch INT 21H and stop all CHDIR requests at the PCDOS level. > 2) ... Also trap all ERASE, CREATE, and OPEN (for write) requests. > 3) Perfect, but perhaps impossible. Make the shell unbreakable. > This would require use of trapping Ctrl-Break, error interrupts, > divide-by-0 and overflow interrupts, and ANY OTHER abnormal termination > calls. Shouldn't be a problem trapping normal exits. > > Alan Bishop > ...!{decvax,akgua}!mcnc!ecsvax!bishop Adding resident programs to trap unauthorized activities is fine, but be sure that a new shell cannot be executed which would not have those resident programs. That is, saying, "command" should not result in executing the standard commmand.com. This implies changing command.com, or removing it from the path. If it is merely removed from the PATH, then the PATH variable should not be changable. Making MS-DOS secure is not easy in either concept or application. -- Harold Bamford AT&T Bell Labs Naperville, Ill (cornet) 8-367-5744 (312) 979-5744 (work)
bc@cyb-eng.UUCP (Bill Crews) (06/20/85)
> Adding resident programs to trap unauthorized activities is fine, but be > sure that a new shell cannot be executed which would not have those > resident programs. That is, saying, "command" should not result in > executing the standard commmand.com. This implies changing command.com, > or removing it from the path. If it is merely removed from the PATH, then > the PATH variable should not be changable. The suggested method of "trapping" involves intercepting execution as DOS itself (the "kernel", if you will) is being accessed. Therefore, another COMMAND.COM or any other application will be a slave to its actions. Of course, it would still be possible for someone to write a program to seek out the new vectors and reinstall the DOS kernel vectors, but limits to security will always exist. -- / \ Bill Crews ( bc ) Cyb Systems, Inc \__/ Austin, Texas [ gatech | ihnp4 | nbires | seismo | ucb-vax ] ! ut-sally ! cyb-eng ! bc