[Emu] TEAP - RFC 7170 - Errata ID 5768

[Oleg Pekar <[e-mail]>]

Hi Jouni,
I propose the following fix for the issues described in this errata id:
1) In Section "4.2.13.  Crypto-Binding TLV" make "EMSK Compound MAC" and
"MSK Compound MAC" fields 32 octets long (currently 20 octets). The MAC
value is truncated at 32 octets if it is longer than 32 octets or padded to
a length of 32 octets with zeros to the right if it is less than 32 octets.
The length of the TLV should be changed to 100 bytes (currently 76).

The motivation is to keep collision-resistance strength of MAC on 128 bit.
Hash value truncation is described in "NIST Special Publication 800-107
Revision 1: Recommendation for Applications Using Approved Hash Algorithms"
<https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-107r1.pdf>


2) In Section "5.3.  Computing the Compound MAC" specify that "MAC is the
MAC function negotiated in TLS of TEAP Phase 1" (currently it says TLS 1.2)

The motivation is to support TLS 1.2, 1.3 and possibly later TLS versions.

3) In Section "5.3.  Computing the Compound MAC" when specifying the list
of field to be placed in the BUFFER" should say "...2  A single octet
contains TEAP EAP method type 0x37". Alternatively it could be "...2  A
single octet contains EAP Type of the inner EAP method related to the
calculation or 0 if no inner EAP method was executed" (currently "...2  The
EAP Type sent by the other party in the first TEAP message")

Please note that there's still a discussion on sending Crypto-Binding TLV
on "Authentication inner EAP method" or "Inner EAP method that exports MSK"
only.

Thanks
Oleg