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From: ifarqhar@sunc.mqcc.mq.oz.au (Ian Farquhar)
Newsgroups: comp.sys.amiga.tech
Subject: Re: How to LOCK your Amiga?
Message-ID: <1025@macuni.mqcc.mq.oz>
Date: 7 Jan 91 00:45:35 GMT
References: <1991Jan6.233133.1@csc.fi>
Sender: news@macuni.mqcc.mq.oz
Organization: Macquarie University, Sydney
Lines: 41

Actually, there may be a solution to this that would be reasonably
secure, though it isn't pretty.  Write a handler that sits between the
l:fastfilesystem handler and the dos.library (ie. handler entry in the
devs:mountlist points to your handler and your handler loads the
l:fastfilesystem handler), which encodes all data going to and coming
from the disk.

The hardest is encoding the data.  You have to decide two things:

1)  What to encode.  You could only encode the data going to and coming
    from the read and write packets, so that the directory structure
    looked fine, but the data in these files was encrypted.  Or you
    could encode everything, which is less safe (as recovering corrupted
    data would become a real pain) but more secure.

2)  How to encode.  The ideal method would be a one-time pad, but this
    is a little difficult to arrange :-)  DES is an option, but it is
    notoriously slow to implement in software.  I would tend to go for
    a multi-barrel 256-slot enigma machine, which is fast to implement
    in assembler (it's all tables and pointers), and reasonably secure.
    If you had an 8 character password, this would yield 56 usable bits
    (in 7 bit ASCII), which would mean that it could set up to seven
    256 slot barrels.  That is not going to stop the NSA, but it will
    put Joe Average right off.

The password, of course, is established when the handler is fired up.
This could be done by a floppy (not advised, as it would contain the
barrel tables which would not necessarily compromise the encryption, but
make it somewhat easier to break), or much better to have it on a hard
disk partition in the old filing system, from which the secure one
boots.

Comments, anyone?  A small point: the file comment field makes the ideal
place to store security information if you wanted to extend this
further.

--
Ian Farquhar                      Phone : 61 2 805-9400
Office of Computing Services      Fax   : 61 2 805-7433
Macquarie University  NSW  2109   Also  : 61 2 805-7420
Australia                         EMail : ifarqhar@suna.mqcc.mq.oz.au