Optimize the kid context bytes from the message by relying on JP to add it as the Token value

[Mališa Vučinić]

Tag: WGLC

As per discussion at https://bitbucket.org/6tisch/draft-ietf-6tisch-minimal-security/issues/19/concerns-about-the-cojp-message-size-the

Mališa Vučinić wrote (https://mailarchive.ietf.org/arch/msg/6tisch/fWK4i3bs3r4VmFCkSoGzgtlWSuo):

This probably belongs to another thread, but let me bring it up here: The value that we carry in Stateless-Proxy/Token encodes the value that we carry as the OSCORE kid context, with some other info.

I am looking for a way to not transport OSCORE kid context, but to use OSCORE id context during key derivation and to retrieve the correct OSCORE context from the Stateless-Proxy/Token value. This would save us 8 bytes.

Looking at oscore-13, this seems to be feasible as in Section 5, there is a MAY on the transport of kid context, except that when it's carried it should be set to id_context. Do you see any problem with the solution that I outlined?

This was brought up in another review regarding message overhead (https://bitbucket.org/6tisch/draft-ietf-6tisch-minimal-security/issues/19/concerns-about-the-cojp-message-size-the)

[Mališa Vučinić]

This optimization would imply severe layer violation. To be discussed whether we should pursue it.