5 ms·

Couldn't it exchange a few messages with the key and precisely measure the time? I'm not sure if such precise measurement is possible, but given that light trav

by comboy 12y ago

Couldn't it exchange a few messages with the key and precisely measure the time? I'm not sure if such precise measurement is possible, but given that light travels ~ 1 feet per second with 10Mhz clock you could theoretically test if it was more than 50 feet away (many approximations here, but I guess within an order of magnitude)

jffry 12y ago
You could attempt to time round-trip signal latency directly or via interference patterns, but it's a much shorter timescale. Light travels just shy of 1 billion feet per second, so we're talking differentiating in the 10s of nanoseconds, which requires nontrivial components.
- maxerickson 12y ago
  I already posted this link in the epic nope thread that is a sibling to this one, but the paper linked from Wikipedia speaks of an experimental implementation with a return time of 1 ns: https://en.wikipedia.org/wiki/Distance-bounding_protocol https://en.wikipedia.org/wiki/Distance-bounding_protocol
  - jffry 12y ago
    That's cool. I wonder how difficult it would be to implement in practice.
    - maxerickson 12y ago
      There are papers going back to at least 2005 (this one, a top search result, is cited 390 times: http://www.cl.cam.ac.uk/~mgk25/sc2005-distance.pdf http://www.cl.cam.ac.uk/~mgk25/sc2005-distance.pdf ), so it would not be all that surprising if there are some existing commercial implementations. The current rash of thefts seem to come down to the systems being completely naive to amplification attacks though.
jrockway 12y ago
HDMI already does this for DRM (it won't cough up device keys if it thinks the TV is too far away), so it's possible to measure with the right precision. That said, signals in twisted pairs propagate at about .6c whereas signals in air propagate at speeds very close to c, so this use case is a little more challenging.
comboy 12y ago
* per nanosecond of course
deleted 12y ago
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by comboy 12y ago

jffry 12y ago

You could attempt to time round-trip signal latency directly or via interference patterns, but it's a much shorter timescale. Light travels just shy of 1 billion feet per second, so we're talking differentiating in the 10s of nanoseconds, which requires nontrivial components.

maxerickson 12y ago
I already posted this link in the epic nope thread that is a sibling to this one, but the paper linked from Wikipedia speaks of an experimental implementation with a return time of 1 ns: https://en.wikipedia.org/wiki/Distance-bounding_protocol https://en.wikipedia.org/wiki/Distance-bounding_protocol
- jffry 12y ago
  That's cool. I wonder how difficult it would be to implement in practice.
  - maxerickson 12y ago
    There are papers going back to at least 2005 (this one, a top search result, is cited 390 times: http://www.cl.cam.ac.uk/~mgk25/sc2005-distance.pdf http://www.cl.cam.ac.uk/~mgk25/sc2005-distance.pdf ), so it would not be all that surprising if there are some existing commercial implementations. The current rash of thefts seem to come down to the systems being completely naive to amplification attacks though.

jrockway 12y ago

HDMI already does this for DRM (it won't cough up device keys if it thinks the TV is too far away), so it's possible to measure with the right precision. That said, signals in twisted pairs propagate at about .6c whereas signals in air propagate at speeds very close to c, so this use case is a little more challenging.

comboy 12y ago

* per nanosecond of course

deleted 12y ago

[deleted]