[dave at farber.net: [IP] more on AP Story Justice Dept. Probing Domestic Spyin

[J.A. Terranson]

On Sun, 1 Jan 2006, coderman wrote:

> > (4) For any form of time-destruction messaging to really work, the keying
> > information would have to be tied to a physical <something> that cannot be
> > reclaimed, and which decays at a fixed, known, and closely approximatable
> > rate (a radiodecay probably doesn't meet this criteria);
> >
> > Every time-sensitive auto-destructing system Ive seen discussed here fails
> > these weaknesses.
>
> this doesn't provide time destruction so i assume this is in reference
> to Tyler's description.  you could couple the user authentication with
> a physically hardened token of some sort for access to the pads but
> even this would require manual destruction.
>
> do they make physically hardened authentication tokens with timed self
> destruction built in?

Not that I am aware of, and if they did, I would by definition not trust
them.  I want my time-limited key to be some natural phenomenon that
cannot be recreated after it "dies", but which is "readable" (for keying)
and stable for a known time interval.

Is there radioactive material which has has a known property that can be
reliably and repetitively measured, that is useful as either a key or a
seed, and that is guaranteed to change on a known schedule in a
significant (i.e., keying data no longer relevant) way?

The idea being something like msg xor radioseed "keys" = plaintext, but
after 30 days, radioseed is different (and the original not knowable), and
therefore message is dead.

-- 
Yours,

J.A. Terranson
sysadmin at mfn.org
0xBD4A95BF


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