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Add recommendations on minimum length of R1 and R2 #14

Closed rikard-sics closed 1 year ago

rikard-sics commented 2 years ago

It would be good to specify recommendations for the minimum length of R1 and R2. Similarly to how OSCORE does it in: https://datatracker.ietf.org/doc/html/rfc8613#page-72

rikard-sics commented 2 years ago

Comment by Christian during CoRE interim on October 13:

Might be good, but some devices may keep it shorter if sure of no reuse. Similar to what raised in the Echo-Request-Tag document.

So we can allow smaller values (if they can make sure it's safe) to not lock out embedded implementations.

rikard-sics commented 2 years ago

We have a brief mention of minimum lenghts: The length of the nonces N1 and N2 is application specific. The application needs to set the length of each nonce such that the probability of its value being repeated is negligible. To this end, each nonce is typically at least 8 bytes long.