Newsgroups: sci.crypt
Path: msuinfo!uchinews!linac!att!walter!qualcom.qualcomm.com!qualcom.qualcomm.com!karn
From: karn@qualcom.qualcomm.com (Phil Karn)
Subject: Re: Why public domain encryption software may not be good enough.
Message-ID: <1992Jan30.232349.3454@qualcomm.com>
Sender: news@qualcomm.com
Nntp-Posting-Host: qualcom.qualcomm.com
Reply-To: karn@chicago.qualcomm.com
Organization: Qualcomm, Inc
References:  <3269@wet.UUCP>
Distribution: na
Date: Thu, 30 Jan 1992 23:23:49 GMT
Lines: 53

In article <3269@wet.UUCP>, naga@wet.UUCP (Peter Davidson) writes:
|> 6.  Can floppy disks - as well as files - be encrypted?
|>  

Actually, there may be a serious point here, if by this you are
referring to software that automatically encrypts and decrypts files
as they are written and read by ordinary programs.

The latest versions of Norton Utilities for MS-DOS has a nifty feature
called DISKREET that does precisely this. It creates and manages
encrypted virtual disk drives within files on ordinary disks. A
"pseudo disk driver" makes this virtual disk look like another drive,
and you can do all of the things to it that you might do to any other
drive. When you "attach" the encrypted virtual disk you give the
system an encryption key. And there are various timeouts and "panic
buttons" that automatically destroy the in-memory key (as will
rebooting the system or turning power off).

Like most of Norton's products, DISKREET is reasonably well thought
out and it certainly carries a sexy user interface.  But it has some
definite problems.  First of all, the virtual disks are of fixed size;
you would really like your encrypted virtual disk to use only as much
"real" disk space as it really needs at any given moment, and you
don't want to have to be bothered by having to constantly change disk
allocations. Unfortunately, this is probably forced by the usual brain
damage in MS-DOS.

Second, like almost all software DES implementations, DISKREET in DES
mode is slower than you would really like. This is a a real problem
with a "transparent" system like DISKREET since things may get
repeatedly encrypted and decrypted more often than they might if the
user explicitly controlled the encryption operation. (On the other
hand, automatic full encryption of files is clearly more secure,
especially when you consider user forgetfulness and/or editor
temporaries on disk free lists).

DISKREET does come with a "fast, proprietary, non-DES" encryption
mode, but I think we don't need to say much more about that.

And last BUT NOT LEAST, there is no documentation on the format of the
DISKREET encrypted file system. I have no reason to doubt Norton's
technical competence and ability to implement a secure PC encryption
system (unlike some other potential vendors I could name).  But I'm
sure he was faced with the very strong temptation (or pressure from
his marketing department) to put in *something* to prepare for the
inevitable poor luser who calls up crying about lost keys despite all
the stern warnings in the manual. Who knows?  Not that I doubt his
integrity, of course, but do I REALLY want to take the chance that
there ISN'T a trapdoor in DISKREET (for whatever purpose) when I can
easily protect myself with public domain encryption code whose
complete source code can be freely examined and recompiled?

Phil
