Subject: Interim AH in MEGACO

From: J Ramachandra <[email-masked]>
Date: Thu, 30 Mar 2000 06:25:19 -0600

Hello,

I have a couple of questions on Interim AH Scheme.

The MEGACO V16 document (section 10.2) refers to RFC 2402
Section 5. This in turn refers to RFC 2403 (HMAC-MD5-96)
and RFC 2404 (HMAC-SHA-1-96)as two possible options. These
two algorithms produce 128 and 160 bits authenticator value,
but over the network only truncated 96 bits are transmitted
to reduce the attack.
Now, the question is, MEGACO/H.248 ABNF specifies authData
as 32 to 64 Hex digits. Why is it not from 24 to 64
hex digits?  Where one has to fit in the 24 hex digits(96 bits)
in this 32 Hex digit space? OR am I missing something?

Also, the same section specifies "synthesized IP header
consisting of a 32 bit source IP address, a 32 bit destination
address and an 16 bit UDP encoded as 10 hex digits". Which UDP
port number to be used  (Source or destination)?

- J.K.Ramachandra,
  AXES TECHNOLOGIES.