On Fri, 17 Apr 2026, at 10:23, [email protected] wrote:
> Internet-Draft draft-ietf-emu-eap-edhoc-09.txt is now available. It is a work
> item of the EAP Method Update (EMU) WG of the IETF.
>
>    Title:   Using the Extensible Authentication Protocol (EAP) with 
> Ephemeral Diffie-Hellman over COSE (EDHOC)
>    Authors: Dan Garcia-Carrillo
>             Rafael Marin-Lopez
>             Göran Selander
>             John Preuß Mattsson
>             Francisco Lopez-Gomez
>    Name:    draft-ietf-emu-eap-edhoc-09.txt
>    Pages:   33
>    Dates:   2026-04-17
>
> Abstract:
>
>    The Extensible Authentication Protocol (EAP), defined in RFC 3748,
>    provides a standard mechanism for support of multiple authentication
>    methods.  This document specifies the EAP authentication method EAP-
>    EDHOC, based on Ephemeral Diffie-Hellman Over COSE (EDHOC).  EDHOC is
>    a lightweight security handshake protocol, enabling authentication
>    and establishment of shared secret keys suitable in constrained
>    settings.  This document also provides guidance on authentication and
>    authorization for EAP-EDHOC.

Section 3.1.6. Fragmentation,

As this EAP method targets low MTU environments (<256 bytes), it would be 
helpful to explicitly have the supplicant and server send a preferred MTU.

TEAPv2 is proposing a *maximum* MTU as this is even a problem at 1500 bytes for 
all the existing common EAP methods.

If the MTU is actually lower for new EAP methods you still have an opportunity 
to negotiate a lower value, something akin to my proposal for TEAPv2:

https://github.com/InkbridgeNetworks/teapv2/pull/1

Maybe use a reserved bit to indicate there is an MTU preference is included and 
then scale that value by at least 4x to get up to an MTU of 1024; after that I 
maybe using EDHOC makes less and instead an operator would use EAP-TLS.

Security concern, a MitM could amend that value, but if you specify a minimum 
value (32 bytes?), hopefully that impact is lessened.

Cheers

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