Subject: MPPE and Multi-link

From: "Ian Moy." <[email-masked]>
Date: Wed, 8 Sep 1999 16:48:07 +0100 (BST)

Hi,

I have been looking at implementing MPPE over a multi-link and have come
up with a few questions.

I was planning to do the encryption at the bundle level, before the
multi-link stage. If I wanted to use a 128-bit key, you need to use the
CHAP challenge value to initialise the session key but, I believe, CHAP
will be used on each individual link.

Will a different challenge value be used on each link?

If so, does this mean that you cannot use MPPE with 128-bit key at the
bundle level?

I am presuming that MPPE with 40-bit key can be used as this only requires
the password, which will be the same for each link?

Any help on this matter will be greatly received.

Ian.

---

From: James Carlson <[email-masked]>
Date: 08 Sep 1999 17:42:45 -0400

> will be used on each individual link.

At least *some* security must be present on each individual link if it
is present on *any* link in the bundle.

> Will a different challenge value be used on each link?

Absolutely!  CHAP demands that the random numbers be, well, random.

> If so, does this mean that you cannot use MPPE with 128-bit key at the

I would say that MPPE isn't a standard, isn't an active subject of
this working group, and doesn't take some of the other relevant
standards, such as RFC 1990, into consideration in its design.  If it
doesn't work in that or other contexts, then that's just how it is.

-- 
James Carlson, System Architect                     <[email-masked]>
IronBridge Networks / 55 Hayden Avenue   71.246W   Vox:  +1 781 372 8132
Lexington MA  02421-7996 / USA           42.423N   Fax:  +1 781 372 8090
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp