Public Keys and the Web Page.

[Ross Anderson]

George writes:

> Where better than the Web Page to include the company's
> Public Key and to arrange that an encrypted message can be
> sent to the company via the medium of the Web Page while the
> Web Page is still visible ? 

Indeed. I've kept my own PGP key on my web page for years. So have
most people. Most companies who use SSL do the same kind of thing
(even if they have a cert, how much can you trust Verisign given the
disclaimers :-)

> A company may desire to change its Private Key
> frequently -- perhaps every day -- as a security precaution.
> A contentious practice perhaps but experience may support
> it:  Impractical ? Not if the "Key-of-the-Day" appears on
> the Web Page but entirely impossible otherwise. 

I agree completely - and for two years now I've set students a
standard project exercise to write an applet which when clicked will
open a mail composition window in the client browser, get the text,
encrypt it and send it back to the server. With such a mechanism
you can change keys as often as you want.

Once `decryption warrants' become law, I reckon this approach could
become very popular.

> But I am an advocate of business solutions which evolve from
> business experience with the aid of finely honed business
> skills -- leaving legislation to follow and not to forestall
> experience. 

In recent research we've been following the business experience of the
publishing industry. We started off by devising mechanisms that were
suitable for protecting online medical books - if you're a doctor you
want to make sure that an online drug dosage database you're relying
on is genuine (see <http://www.cl.cam.ac.uk/~fapp2/papers/ec98-erl/>
for details).

We're now going further: we want users to be able to put together more
or less arbitrary security tags and processes in just about any way
that makes sense. So any document - web page, letter, book, whatever -
should be able to contain not just links but also security metadata
such as hashes of cited articles, public encryption keys, public
signature verification keys, timestamps, and so on, in ways that will
be compatible with XML.

More at <http://www.cl.cam.ac.uk/~jhl21/jikzi-cpw/>

Ross