Subject: Padding when ECP On Bundle with DESE alg

From: sunilkrd <[email-masked]>
Date: Wed, 03 Dec 97 11:43:00 PST

Hello,
     The rfc on DESE (all of them ?) state that DESE implementations should 
pad the datagrams to a multiple of 8 octets. This can be done by negotiating 
the LCP Self describing padding option on every link on which ECP is to be 
negotiated.    
  However if ECP is to be negotiated on an MP bundle(80fd) with the DESE 
algorithm, there is no way to negotiate Padding on the bundle. How does the 
DESE algorithm work in such an implementation ?

Regards,
Sunil Kumar Reddy,
([email-masked])
Future Software Pvt. Ltd.

---

From: Gerry Meyer <[email-masked]>
Date: Wed, 3 Dec 1997 11:16:37 +0000 (GMT)

> DESE algorithm work in such an implementation ?

LCP Self Describing Padding is not negotiated when using any of the
encryption options (or not for any purpose related to encryption).

The padding scheme is NOT separately negotiated - it is implicitly
activated through the negotiation of the Encryption option itself
(through ECP negotiation).

draft-ietf-pppext-des-encrypt-v2-01.txt hopefully clarifies this in
Section 6.1:

6.1.  Padding Considerations

   Since the DES algorithm operates on blocks of 8 octets, plain text
   packets which are of length not a multiple of 8 octets must be
   padded.

......

                 Consequently, this specification requires that the
   unambiguous technique described below MUST be applied to ALL plain
   text packets.

   The method of padding is based on that described for the LCP Self-
   Describing-Padding (SDP) option (as defined in RFC 1570[4]), but
   differs in two respects: first, maximum-pad value is fixed to be 8,
   and second, the method is to be applied to ALL packets, not just
   "specifically identified protocols".

.....

   The padding operation described above is performed independently of
   whether or not the LCP Self-Describing-Padding (SDP) option has been
   negotiated.  If it has, SDP would be applied to the packet as a whole
   after it had been ciphered and after the Encryption Protocol
   Identifiers had been prepended.

	Gerry