RE: Modems that variate speed

Sorry I can't attribute the quote properly; Microsloth Mail strikes
again...

> [modems that change speed in mid-transmission proposed as a
>  defense against wiretap]
>
> Aaron

This would probably thwart someone trying to tap the data stream
in real time, assuming that the speed changes caught the snooper
by surprise, but I don't think that real-time data traps are the
real problem. Someone who went to the effort of listening in on
your transmission would probably record the whole session on
tape; then, they could map the speed changes and pick up all the
data at their leisure later on. I would speculate that a really
good DAT deck could record the modem session well enough to give
your opponent all the time he needs to figure out the speed shifts
and pick up the data.

   -Philippe

On Tue, 12 Jul 1994, Philippe Nave wrote:

> This would probably thwart someone trying to tap the data stream
> in real time, assuming that the speed changes caught the snooper
> by surprise, but I don't think that real-time data traps are the
> real problem. Someone who went to the effort of listening in on
> your transmission would probably record the whole session on
> tape; then, they could map the speed changes and pick up all the
> data at their leisure later on. I would speculate that a really
> good DAT deck could record the modem session well enough to give
> your opponent all the time he needs to figure out the speed shifts
> and pick up the data.
> 
>    -Philippe

Then the efforts would be wasted. Hmmm... There has to be a way to keep 
people from snooping on our lines. I guess PGP and other methods like it 
will be the only way...

Aaron



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> Then the efforts would be wasted. Hmmm... There has to be a way to keep 
> people from snooping on our lines. I guess PGP and other methods like it 
> will be the only way...
> 
> Aaron


End-to-end security, such as with ciphers, is infinitely preferable to
kludges and half-hearted attempts at security through obscurity such
as making modem tapping every so slightly harder than it is now.

Tricks like modem speed varying would be cumbersome to implement,
would require pre-arrangement of the pattern to be used, etc. Just not
very strong. (A bit like frequency-hopping/spread-spectrum, which has
aspects of crypto systems, as I'm sure Phil Karn can tell us about.
But at best a one-time pad and at worst a weak cipher.)

End-to-end encryption is much cleaner, stronger, and allows the public
key methods of incalculable importance. 

--Tim May


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