Subject: Re: draft-ietf-pppext-mppe-00.txt

From: Archie Cobbs <[email-masked]>
Date: Sat, 21 Mar 1998 23:15:18 -0800 (PST)

A couple of minor comments on draft-ietf-pppext-mppe-00.txt..

1. The "Get_Start_Key" function is described in pseudo-code as:

    Get_Start_Key(Challenge, H) {
       SHAInit(Context)
       SHAUpdate(Context, H, 16)
       SHAUpdate(Context, H+Challenge, 24)
       SHAFinal(Context, Digest)
       memcpy(H, Digest, 16)
    }

  It would be clearer to write this as:

    Get_Start_Key(Challenge, H) {
       SHAInit(Context)
       SHAUpdate(Context, H, 16)
       SHAUpdate(Context, H, 16)
       SHAUpdate(Context, Challenge, 8)
       SHAFinal(Context, Digest)
       memcpy(H, Digest, 16)
    }

  if that's in fact what is meant (is it??).

2. Because Get_Start_Key() requires the MS-CHAP challenge value,
   MPPE may interact badly with Multi-link PPP.. because, which
   challenge do you use if there are multiple links?

   In pratice this is probably not likely to happen, but maybe
   it ought to be mentioned.

-Archie

___________________________________________________________________________
Archie Cobbs   *   Whistle Communications, Inc.  *   http://www.whistle.com