Re: Safely proving device identity?

Also, if you do use the RSA-only scheme, be sure there's some evidence
of liveness before the device takes any action, to avoid replay
attacks. For example, the device could send a nonce to the client
which it expects to see again in the first (encrypted/MACd) message
from the client. Alternatively, you can include the device nonce into
the key agreement:

Client:
1. r = random floor(log2(n))-bit number
2. send s = r^e mod n to device

Device:
3. receive s
4. send c = random 256-bit nonce
5. Hash(s^d mod n || c) is the session key

Client:
6. Hash(r || c) is the session key

The device can pick and send the nonce as soon as it notices a client
wishes to establish a session (in some cases that may be sooner than
upon receiving s).

- xmath

.

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