The PPP Encryption Control Protocol (ECP)
RFC 1968

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Network Working Group                                           G. Meyer
Request for Comments: 1968                                Spider Systems
Category: Standards Track                                      June 1996

               The PPP Encryption Control Protocol (ECP)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   The Point-to-Point Protocol (PPP) [1] provides a standard method for
   transporting multi-protocol datagrams over point-to-point links.  PPP
   also defines an extensible Link Control Protocol.

   This document defines a method for negotiating data encryption over
   PPP links.

Conventions

   The following language conventions are used in the items of
   specification in this document:

   o  MUST -- the item is an absolute requirement of the specification.
      MUST is only used where it is actually required for interopera-
      tion, not to try to impose a particular method on implementors
      where not required for interoperability.

   o  SHOULD -- the item should be followed for all but exceptional cir-
      cumstances.

   o  MAY or optional -- the item is truly optional and may be followed
      or ignored according to the needs of the implementor.

      The words "should" and "may" are also used, in lower case, in
      their more ordinary senses.

Meyer                       Standards Track                     [Page 1]
RFC 1968                     PPP Encryption                    June 1996

Table of Contents

      1. Introduction ...........................................  2
      2. Encryption Control Protocol (ECP) ......................  2
          2.1 Sending Encrypted Datagrams .......................  3
      3. Additional Packets .....................................  4
          3.1 Reset-Request and Reset-Ack .......................  5
      4. ECP Configuration Options ..............................  6
          4.1 Proprietary Encryption OUI ........................  7
          4.2 Publicly Available Encryption Types ...............  8
          4.3 Negotiating an Encryption Algorithm ...............  9
      5. Security Considerations ................................ 10

1. Introduction

   In order to establish communications over a PPP link, each end of the
   link must first send LCP packets to configure and test the data link
   during Link Establishment phase.  After the link has been
   established, optional facilities may be negotiated as needed.

   One such facility is data encryption.  A wide variety of encryption
   methods may be negotiated, although typically only one method is used
   in each direction of the link.

   A different encryption algorithm may be negotiated in each direction,
   for speed, cost, memory or other considerations.

2. Encryption Control Protocol (ECP)

   The Encryption Control Protocol (ECP) is responsible for configuring
   and enabling data encryption algorithms on both ends of the point-
   to-point link.

   ECP uses the same packet exchange mechanism as the Link Control
   Protocol (LCP).  ECP packets may not be exchanged until PPP has
   reached the Network-Layer Protocol phase.  ECP packets received
   before this phase is reached should be silently discarded.

   The Encryption Control Protocol is exactly the same as LCP [1] with
   the following exceptions:

      Frame Modifications

         The packet may utilise any modifications to the basic frame
         format which have been negotiated during the Link Establishment
         phase.

Meyer                       Standards Track                     [Page 2]
RFC 1968                     PPP Encryption                    June 1996

      Data Link Layer Protocol Field

         Exactly one ECP packet is encapsulated in the PPP Information
         field, where the PPP Protocol field indicates type hex 8053
         (Encryption Control Protocol).

         When individual link data encryption is used in a multiple link
         connection to a single destination [2], the PPP Protocol field
         indicates type hex 8055 (Individual link Encryption Control
         Protocol).

      Code field

         ECP uses (decimal) codes 1 through 7 (Configure-Request,
         Configure-Ack, Configure-Nak, Configure-Reject, Terminate-
         Request, Terminate-Ack and Code-Reject); And may also use code
         14 (Reset-Request) and code 15 (Reset-Ack).  Other codes should
         be treated as unrecognised and should result in Code-Rejects.

      Negotiation

         ECP packets may not be exchanged until PPP has reached the
         Network-Layer Protocol phase.  An implementation should be
         prepared to wait for Authentication and Link Quality