[Cryptography] Measuring propagation times

[Stephan Neuhaus]

On 9/25/25 01:33, John Gilmore wrote:
> On 22 Sep 2025, at 17:54, Sampo Syreeni wrote:
>> My recent idea is perhaps even funkier: why not time at the nanosecond
>> level how non-contact chips communicate with each other, and build a
>> purposely chatty privacy amplification protocol between them, relying on
>> the upper bound on propagation guaranteed by relativity?
> 
> Steven M. Bellovin <smb at cs.columbia.edu> wrote:
>> I think that there are real-world protocols that do that. Or see [sec]5 of
>> https://www.cs.columbia.edu/~smb/papers/netmeas.pdf from 1992.
> 
> Ultrawideband communication devices use very carefully measured
> propagation delays of infrequent wideband pulses, for locating peer
> communicators in relative 3d space.  See:
> 
>    https://en.wikipedia.org/wiki/Ultra-wideband

Here is a more security-oriented talk by Srdjan Čapkun of ETH Zurich on 
this and similar topics: 
https://gaia.insait.ai/wp-content/uploads/2022/10/INSAIT_Srdjan-Capkun.pdf

Cheers

Stephan