> But it does protect against the exact threat model you proposed.
Encryption doesn't protect against traffic analysis. Knowing someone is present or that some device is in use is significant information.
Does the device you are proposing authenticate the reader before transmitting anything? If not, it's not particularly difficult (probaly by modifying a reader) to test if people have a security device on them. That only requires a ping, no crypto needed.
> I'm a ham
I used to be, for many years. (I wish I had more time for such things these days)
> large, awkward, and expensive antenna
That depends entirely on what you want to do. If you want to read the entire crypto transaction from the next building, then yes, an expensive antenna[1] will be required. If I just want to detect who is carrying a security device, you won't need a particularly accurate antenna - it just needs to have a decent gain.
My point with that example is that it's never a good idea to underestimate how much time and effort people will put into an attack. If criminals can add a man-in-the-middle chip piggybacked onto a chip-and-pin smartcard[2], they can made a decent cantenna.
> So do you or don't you think RF communication in a security device is an inherent problem in and of itself?
RF is an extra risk that should be avoided whenever possible for security devices, especially when effective alternatives are available.
In your linked video about the hospital, the smart card was slotted into a reader. This would work well and has no need for RF. It's certainly a far better solution than memorizing bad passwords.
Encryption doesn't protect against traffic analysis. Knowing someone is present or that some device is in use is significant information.
Does the device you are proposing authenticate the reader before transmitting anything? If not, it's not particularly difficult (probaly by modifying a reader) to test if people have a security device on them. That only requires a ping, no crypto needed.
> I'm a ham
I used to be, for many years. (I wish I had more time for such things these days)
> large, awkward, and expensive antenna
That depends entirely on what you want to do. If you want to read the entire crypto transaction from the next building, then yes, an expensive antenna[1] will be required. If I just want to detect who is carrying a security device, you won't need a particularly accurate antenna - it just needs to have a decent gain.
My point with that example is that it's never a good idea to underestimate how much time and effort people will put into an attack. If criminals can add a man-in-the-middle chip piggybacked onto a chip-and-pin smartcard[2], they can made a decent cantenna.
> So do you or don't you think RF communication in a security device is an inherent problem in and of itself?
RF is an extra risk that should be avoided whenever possible for security devices, especially when effective alternatives are available.
In your linked video about the hospital, the smart card was slotted into a reader. This would work well and has no need for RF. It's certainly a far better solution than memorizing bad passwords.
[1] The $10k antenna used for TempestSDR that was mentioned yesterday should work. https://news.ycombinator.com/item?id=10685504
[2] http://hackaday.com/2015/10/21/smart-cards-used-to-hack-smar...