[Cryptography] Public-key auth as envisaged by first-year science students

[Dave Howe]

On 11/08/2016 21:10, Michael Kjörling wrote:
> If someone injects a MITM, call it Mallory, in between Alice and Bob,
> on a wireless network, then wouldn't Alice and Bob _still be able to
> communicate directly_? Unless Mallory is doubly active (not only
> functioning as a MITM attacker to intercept and handle communication
> supposedly being passed between Alice and Bob, but also disrupting
> attempts at direct communication between Alice and Bob), Alice should
> still hear Bob's transmissions and Bob should still hear Alice's. So
> if Alice sends a message to Bob, which Mallory is able to MITM and
> where Mallory responds back to Alice, then _at the very least_ Alice
> should also hear _Bob's_ response presumably with a slight delay
> compared to that from Mallory, _and_ it's possible that Bob would hear
> _Mallory's_ response.
Depends on how it is intercepted. Common scenarios for wifi MitM are a
fake AP or ARP poisoning; in both cases, the traffic goes to and from an
AP, and never directly between Alice and Bob; while sniffing could
*possibly* pick up the original packets in the latter case, you would
need to pull packets not addressed to your hw address (i.e. promiscuous
mode and you would need to be using  a PSK). A point to point link, by
contrast, could have this property, but only if Mallory's intercept dish
pair isn't sufficient to block the signal path.