[Roll] RPL secure messages

[Rahul Jadhav <[e-mail]>]

Hello All,

During the interim, Pascal raised this point as to whether it is necessary
to have a secure message counter-part for every new message that is defined
in new drafts?

To put it in context, currently we have:
Code 0x00 -> DIS, 0x80 -> Secure DIS
Code 0x01 -> DIO, 0x81 -> Secure DIO ... so on for all other messages we
have a secure equivalent. Inadvertently, the MSB is reserved as a secure
bit (without explicitly stating so).

Problem is, there is no one out there using secure messages at RPL layer
(would be very happy to be proved wrong here). Most deployments depend on
L2 security for RPL messaging.

So given the context, is it necessary for new drafts to work on secure
messaging for new messages drafted?

My take is that given that the work required to specify secure messages is
not much, we should do it anyways for all new msgs.  In terms of saving
some codes, I believe we may not be able to save much since the
implementations might check the MSB to find if the message is secure or
not, thus non-secure messages may not be able to use that bit.
Also adding a new message code is much rare as compared to adding new
control options. Almost every new draft is adding a new control option but
very few are adding new message code.

However, we currently have two drafts DAO-Projection and Capabilities
defining new message codes, and hence this discussion may be relevant now.

Thoughts welcome.

Regards,
Rahul