NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/comp/dcom/fax/2433

Text File | 1993-01-12 | 2.7 KB | 59 lines

Newsgroups: comp.dcom.fax
Path: sparky!uunet!van-bc!tgivan!dean
From: [e-mail] (Dean Neumann)
Subject: Re: Fax with encryption?
Message-ID: <[e-mail]>
Organization: TGI Technologies Ltd.
References: <[e-mail]>
Date: Tue, 12 Jan 1993 21:09:55 GMT
Lines: 48

In article <[e-mail]> [e-mail] (Mathias Koerber) writes:
>Having bought a Fax-Modem recently (OAFax 9648), I started wondering whether
>it wouldn't be possible to encrypt faxes. Not only in Software but also
>in standard Fax machines. I guess for a good encryption scheme, one would
>have to scan in the page into internal memory, then enter a bignum as key,
>all lines get encrypted on the fly while sending, and the receiving station
>stores the encrypted pages in memory. Then a special function asks for the
>bignum, decrypts and prints.
>
>  [further text ommitted...]

Watch out.  Normal data encryption schemes don't work for fax.  First
of all, fax transmissions are not error-free (even if your fax machine
supports ECM, you're never guaranteed that the receiver's fax machine
does).  Therefore, if you encrypted the entire page and some of the
scanlines get hit during transmission, the decryption will fail.  If
you encrypt each scanline separately you get around that, because
line hits cause only the one scanline to be lost, so the remaining
scanlines will decrypt ok.  However, you must encrypt the data before
it gets run-length (T.4) encoded, so that you don't mess up the
compression.  However, if you do that, you'll get very very low run
length compression because your uncompressed data is pseudo-random.
The end result will be 10-15 minute transmission times per encrypted
page, and if the receiving fax machine stores the page in it's memory
(or PC disk) in compressed (T.4) format, which most do because it's
efficient, you'll be trying to store a couple hundred Kbytes rather
than a couple dozen Kbytes per page.

It turns out that there are a couple vendors that have fax products
on the market that have solved these problems.  (I refer explicitly
to fax-image encryption as opposed to fax-protocol encryptors, or
which there are several).  But these are still proprietary solutions.
To my knowledge none have been placed in the public domain.
(No commercial plug, but I'll admit to bias up front; TGI is one of
those vendors).

Good luck with your search!

Regards,
Dean Neumann                    [e-mail]
TGI Technologies.               !van-bc!tgivan!dean

TGI (Corporate)         TGI (Ottawa)
107 East 3rd Ave        #2, 634 Churchill Ave
Vancouver, B.C.         Ottawa, Ontario
Canada V5T-1C7          Canada K1Z-5E8
[phone]          [phone]