Subject: RE: CGA issues

From: "Tuomas Aura" <[email-masked]>
Date: Tue, 11 May 2004 00:29:32 -0700

Jari Arkko quoted Iljitsch van Beijnum:
> > Finally, the draft doesn't specify the value of the universal/local
and
> > group bits in the cryptographically generated interface identifier.
> > Obviously it's important that naive implementations don't adopt a
link
> > address that happens to have the group bit set, as will be the case
in
> > approximately 50% of all CGAs. Additionally, it is probably prudent
to
> > set the u/l bit to 1, as CGAs aren't "universal".
> 
> Tuomas, can you say something about this?

See step 6 of the GCA generation algorithm in section 4 of 
draft-ietf-send-cga. The "g" bit *is* set to 0. The "u" bit 
is set to 0 to indicate local scope. (1 would indicate 
universal scope.)

The CGA verification algorithm in section 5 of the same 
draft ignores the values of the "u" and "g" bits. This is
is an intentional design choice that was discussed on the list.
Checking the bit values during the verification would not 
buy any additional security but it would close some future 
design options. Thus, it is better not to check them.

Tuomas

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