Network File System Version 4                               T. Myklebust
Internet-Draft                                               Hammerspace
Updates: 5531 (if approved)                                C. Lever, Ed.
Intended status: Standards Track                                  Oracle
Expires: May 16, 2019                                  November 12, 2018

         Remote Procedure Call Version 2 Encryption By Default


   This document proposes a mechanism that makes it possible to enable
   in-transit encryption of Remote Procedure Call traffic with little
   administrative overhead and full compatibility with implementations
   that do not support it.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 16, 2019.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  RPC on TLS in Operation . . . . . . . . . . . . . . . . . . .   4
     3.1.  Discovering Server-side TLS Support . . . . . . . . . . .   4
     3.2.  Streams and Datagrams . . . . . . . . . . . . . . . . . .   5
     3.3.  Authentication  . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   In 2014, the IETF published [RFC7258] which recognized that
   unauthorized observation of network traffic had become widespread,
   and was a subversive threat to all who make use of the Internet at
   large.  It strongly recommended that newly defined Internet protocols
   make a real effort to mitigate monitoring attacks.  Typically this
   mitigation is done by encrypting data in transit.

   The Remote Procedure Call version 2 protocol has been around for more
   than a decade [RFC5531].  Support for in-transit encryption of RPC
   was introduced with RPCSEC GSS [RFC7861].  However, experience has
   shown that RPCSEC GSS is challenging to deploy, especially in
   environments where:

   o  Per-host administrative or deployment costs must be kept to a

   o  Parts of the RPC header that remain in clear-text are a security

   o  Host CPU resources are at a premium, or

   o  Host identity management is carried out in a security domain that
      is distinct from user identity management.

   However strong a privacy service is, it is not effective if it cannot
   be deployed in typical environments.

   An alternative approach is to employ a transport layer security
   mechanism that can protect the privacy of each RPC connection
   transparently to RPC and Upper Layer protocols.  The Transport Layer

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   Security protocol [RFC8446] (TLS) is a well-established Internet
   building block that protects many common Internet protocols such as
   https [RFC2818].

   Encrypting at the RPC transport layer enables several significant

   Encryption By Default
      With the use of pre-shared keys, in-transit encryption can be
      enabled immediately after installation without additional
      administrative actions such as identifying the host system to a
      trust authority, generating additional key material, or
      provisioning a secure network tunnel.

   Protection of Existing Protocols
      The imposition of encryption at the transport layer protects any
      Upper Layer protocol that employs RPC without alteration of that
      protocol.  RPC transport layer encryption can protect recent
      versions of NFS such as NFS version 4.2 [RFC7862] and indeed
      legacy NFS versions such as NFS version 3 [RFC1813] and NFS side-
      band protocols such as the MNT protocol [RFC1813].

   Decoupled User and Host Identities
      RPCSEC GSS provides a framework for cryptographically protecting
      user and host identities, but assumes that both are managed by the
      same security authority.

   Encryption Offload
      The use of a well-established transport encryption mechanism that
      is also employed by other very common network protocols makes it
      possible to use hardware encryption implementations so that the
      host CPU is not burdened with the work of encrypting and
      decrypting large RPC arguments and results.

   This document adopts the terminology introduced in Section 3 of
   [RFC6973], and assumes a working knowledge of the Remote Procedure
   Call (RPC) version 2 protocol [RFC5531] and the Transport Layer
   Security (TLS) version 1.3 protocol [RFC8446].

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119] [RFC8174]
   when, and only when, they appear in all capitals, as shown here.

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3.  RPC on TLS in Operation

3.1.  Discovering Server-side TLS Support

   The mechanism described in this document interoperates fully with
   implementations that do not support it.  Encryption (TLS) is
   automatically disabled in these cases.  To achieve this, we introduce
   a new authentication flavor called AUTH_TLS.


   enum auth_flavor {
           AUTH_NONE       = 0,
           AUTH_SYS        = 1,
           AUTH_SHORT      = 2,
           AUTH_DH         = 3,
           AUTH_KERB       = 4,
           AUTH_RSA        = 5,
           RPCSEC_GSS      = 6,
           AUTH_TLS        = 7,

           /* and more to be defined */


   This new flavor is used to signal that the client wants to initiate
   TLS security negotiation if the server supports it.  The length of
   the opaque data constituting the credential MUST be zero.  The
   verifier accompanying the credential MUST be an AUTH_NONE verifier of
   length zero.  The flavor value of the verifier received in the reply
   message from the server MUST be AUTH_NONE.  The bytes of the
   verifier's string encode the fixed ASCII characters "STARTTLS".

   When an RPC client is ready to initiate TLS negotiation, it sends a
   NULL RPC request with an auth_flavor of AUTH_TLS.  The server can
   respond in one of three ways:

   o  If the server does not recognise the AUTH_TLS authentication
      flavor, it responds with a reject_stat of AUTH_ERROR.  The client
      then knows that this server does not support TLS.

   o  If the server accepts the NULL RPC procedure, but fails to return
      an AUTH_NONE verifier containing the string "STARTTLS", the client
      knows that this server does not support TLS.

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   o  If the server accepts the NULL RPC procedure, and returns an
      AUTH_NONE verifier containing the string "STARTTLS", the client
      MAY proceed with TLS security negotiation.

   If a client attempts to use AUTH_TLS for anything other than the NULL
   RPC procedure, the server responds with a reject_stat of AUTH_ERROR.

   Once TLS security negotiation is complete, the client and server will
   have established a secure channel for communicating and can proceed
   to use standard security flavours within that channel, presumably
   after negotiating down the irrelevant RPCSEC_GSS privacy and
   integrity services and applying channel binding.

   If TLS negotiation fails for any reason (for example the server
   rejects the certificate presented by the client), the RPC client
   reports this failure to the calling application the same way it would
   report an AUTH_ERROR rejection from the server.

3.2.  Streams and Datagrams

   RPC commonly operates on stream transports and datagram transports.
   When operating on a stream transport, using TLS [RFC8446] is
   appropriate.  On a datagram transport, RPC should use DTLS [RFC6347].

   RPC-over-RDMA [RFC8166] may make use of transport layer security
   below the RDMA transport layer.

3.3.  Authentication

   Both RPC and TLS have their own in-built forms of host and user
   authentication.  Each have their strengths and weaknesses.  We
   believe the combination of host authentication via TLS and user
   authentication via RPC provides optimal security, efficiency, and
   flexibility, although many combinations are possible.

   TLS Encryption-only with AUTH_SYS:  A pre-shared key enables TLS
      encryption.  The RPC client uses AUTH_SYS to identify users with
      the guarantee that the UID and GID values cannot be observed or
      altered in transit.

   TLS Encryption-only with RPCSEC GSS Kerberos:  A pre-shared key
      enables TLS encryption in encryption-only mode.  The RPC client
      uses Kerberos to identify the client host and its users, and does
      not need to additionally require costly GSS integrity or privacy

   TLS per-client certificate with AUTH_SYS:  During TLS negotiation,
      the client identifies itself to the server with a unique

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      certificate.  The server can use this identity to perform
      additional authorization of the client's requests.

   TLS per-user certificate with AUTH_NONE:  Each user establishes her
      own TLS context with the server, identified by a unique
      certficate.  There is no need for any additional information at
      the RPC layer, so the RPC client can use the simplest
      authentication flavor for RPC transactions.

4.  Security Considerations

   One purpose of the mechanism described in this document is to protect
   RPC-based applications against threats to the privacy of RPC
   transactions and RPC user identities.  A taxonomy of these threats
   appears in Section 5 of [RFC6973].  In addition, Section 6 of
   [RFC7525] contains a detailed discussion of technologies used in
   conjunction with TLS.  Implementers should familiarize themselves
   with these materials.

   The NFS version 4 protocol permits more than one user to use an NFS
   client at the same time [RFC7862].  Typically that NFS client will
   conserve connection resources by routing RPC transactions from all of
   its users over a few or a single connection.  In circumstances where
   the users on that NFS client belong to multiple distinct security
   domains, it may be necessary to establish separate TLS-protected
   connections that do not share the same encryption parameters.

5.  IANA Considerations

   This document does not require actions by IANA.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5531]  Thurlow, R., "RPC: Remote Procedure Call Protocol
              Specification Version 2", RFC 5531, DOI 10.17487/RFC5531,
              May 2009, <>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <>.

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   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <>.

   [RFC7861]  Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
              Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
              November 2016, <>.

   [RFC8166]  Lever, C., Ed., Simpson, W., and T. Talpey, "Remote Direct
              Memory Access Transport for Remote Procedure Call Version
              1", RFC 8166, DOI 10.17487/RFC8166, June 2017,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,

6.2.  Informative References

   [LJNL]     Fisher, C., "Encrypting NFSv4 with Stunnel TLS", August
              2018, <

   [RFC1813]  Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
              Version 3 Protocol Specification", RFC 1813,
              DOI 10.17487/RFC1813, June 1995,

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <>.

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   [RFC7862]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
              November 2016, <>.


   Special mention goes to Charles Fisher, author of "Encrypting NFSv4
   with Stunnel TLS" [LJNL].  His article inspired the mechanism
   described in this document.

   The authors wish to thank Bill Baker, David Black, Benjamin Kaduk
   Greg Marsden, David Noveck, and Justin Mazzola Paluska for their
   input and support of this work.

   Special thanks go to Transport Area Director Spencer Dawkins, NFSV4
   Working Group Chairs Spencer Shepler and Brian Pawlowski, and NFSV4
   Working Group Secretary Thomas Haynes for their guidance and

Authors' Addresses

   Trond Myklebust
   Hammerspace Inc
   4300 El Camino Real Ste 105
   Los Altos, CA  94022
   United States of America


   Charles Lever (editor)
   Oracle Corporation
   1015 Granger Avenue
   Ann Arbor, MI  48104
   United States of America


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