secure fax (Re: email Crypto- third party)

[Paul Leyland]

> I don't know how secure it was, but Windows for Workgroups 
> version of MS
> Mail offered encryption with a key of faxes.
> 
> I never used it, but it did seem potentially useful.
> 
> 
> >Try to persuade solicitors firms you communicate with to buy and
> >install the hardware or software.

If all you want is to keep nosy people out of your faxes, as opposed to the
true professionals who are capable of black-bag and chequebook
cryptanalysis, you could use Adi Shamir's technique of a random mask
overlay.

For those who haven't heard of this trick, Alice and Bob each have an
identical random matrix of black and transparent squares printed onto an
acetate sheet.  The transmitted fax is essentially the XOR of this mask and
the original image.  Bob places the transparency on top of the received
paper fax and jiggles the alignment until the image shows through in black
and grey.  Remarkably effective and remarkably easy to use.   Of course, the
acetate mask has to be snail-mailed or couriered to the recipient
beforehand.

If the transparency is truly random and used only once, it is a true
one-time-pad with all that entails.


Paul