Re: [core] Question about AEAD nonce uniqueness

[Jim Schaad <[e-mail]>]

There is not a problem with dealing with nonce uniqueness in this draft because each entity is going to be assigned to a unique key for transmissions.  The transport key is derived from the PSK and the sender ID.  Sender IDs will be unique based on the enrollment protocol in the group as each entity will have a unique identifier.

 

Jim

 

 

From: core [mailto:[e-mail]] On Behalf Of Mohit Sethi
Sent: Monday, April 10, 2017 4:51 AM
To: Core <[e-mail]>; [e-mail]
Subject: [core] Question about AEAD nonce uniqueness

 

Hi OSCoAP authors

I was trying to read the OSCoAP and 6tisch minimal security drafts. I have a question about the AEAD nonce uniqueness. RFC 5116 says that:

   When there are multiple devices performing encryption using a single
   key, those devices must coordinate to ensure that the nonces are
   unique.  A simple way to do this is to use a nonce format that
   contains a field that is distinct for each one of the devices

So my obvious question is how is the AEAD nonce uniqueness ensured. The PSK is known to at least two parties (more in case of some uses such as multicast OSCoAP https://tools.ietf.org/html/draft-tiloca-core-multicast-oscoap-01)?? 

The draft currently says that AEAD Nonce uniqueness is ensured with sequence numbers and sender context which is essentially the sender ID. But how do you ensure that the two parties have different sender ID. Especially since sender ID is not fixed length. I guess there will be other problems in case of sender ID collisions? 

--Mohit