Network File System Version 4                               T. Myklebust
Internet-Draft                                               Hammerspace
Updates: 5531 (if approved)                                C. Lever, Ed.
Intended status: Standards Track                                  Oracle
Expires: May 23, 2019                                  November 19, 2018

              Remote Procedure Call Encryption By Default


   This document describes a mechanism that enables encryption of in-
   transit Remote Procedure Call (RPC) transactions with little
   administrative overhead and full interoperation with RPC
   implementations that do not support this mechanism.  This document
   updates RFC 5531.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  RPC-Over-TLS in Operation . . . . . . . . . . . . . . . . . .   4
     4.1.  Discovering Server-side TLS Support . . . . . . . . . . .   4
     4.2.  Streams and Datagrams . . . . . . . . . . . . . . . . . .   5
     4.3.  Authentication  . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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
   three decades (see [RFC5531] and its antecedants).  Eisler et al.
   first introduced an in-transit encryption mechanism for RPC with
   RPCSEC GSS years ago [RFC2203].  However, experience has shown that
   RPCSEC GSS is challenging to deploy, especially in environments

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

   Encrypting at the RPC transport layer enables several significant

   Encryption By Default
      Via the use of self-signed certificates, 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

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      host CPU is not burdened with the work of encrypting and
      decrypting large RPC arguments and results.

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.

3.  Terminology

   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].

   Note also that the NFS community uses the term "privacy" where other
   Internet communities might use "confidentiality".  In this document
   the two terms are synonymous.

4.  RPC-Over-TLS in Operation

4.1.  Discovering Server-side TLS Support

   The mechanism described in this document interoperates fully with
   implementations that do not support it.  The use of TLS is
   automatically disabled in these cases.  To achieve this, we introduce
   a new authentication flavor called AUTH_TLS.  This new flavor is used
   to signal that the client wants to initiate TLS negotiation if the
   server supports it.


   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 */


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   The length of the opaque data constituting the credential sent in the
   call message 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 a TLS handshake, it sends a
   NULL RPC request with an auth_flavor of AUTH_TLS.  The NULL request
   is made to the same port as if TLS were not in use.

   The RPC server can respond in one of three ways:

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

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

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

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

   Once the TLS handshake is complete, the RPC client and server will
   have established a secure channel for communicating and can proceed
   to use standard security flavors within that channel, presumably
   after negotiating down the irrelevant RPCSEC_GSS privacy and
   integrity services and applying channel binding [RFC7861].

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

4.2.  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 can use DTLS [RFC6347].

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

4.3.  Authentication

   Both RPC and TLS have their own forms of host and user
   authentication.  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 self-signed certificate 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.  End-to-end encryption is provided via per-
      client certificate material that can be generated automatically.

   TLS per-client certificate with AUTH_SYS:  During TLS negotiation,
      the client identifies itself to the server with a unique
      certificate.  As with encryption-only with AUTH_SYS, UID and GID
      values are well protected.  In addition, the server can use the
      client's identity to perform additional authorization of this
      client's requests.

   TLS encryption-only with RPCSEC GSS Kerberos:  A self-signed
      certificate enables TLS encryption in encryption-only mode.  The
      RPC client uses Kerberos to identify the client host and its
      users, and therefore does not need to enable costly GSS integrity
      or privacy services.

   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.  This configuration is
      not typical for NFS deployments, but it does enable strong
      certificate-based user authentication, which is currently not
      afforded by GSS.

   [ This is currently the most skeletal section in the document.  There
   are two key areas for improvement:

   o  The interoperability of this new security flavor likely depends on
      us culling the "many combinations" down to just a few.  At least
      we need to identify which ones are least workable, and provide
      some operational details for the important commonly deployed

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   o  There might be opportunity to re-examine the efficacy of host
      authentication.  If host authentication does not provide
      significant increases in security, perhaps we can get away with
      specifying only encryption-only configurations.

   -Ed. ]

5.  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.

6.  IANA Considerations

   This document does not require actions by IANA.

7.  References

7.1.  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,

7.2.  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,

   [RFC2203]  Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
              Specification", RFC 2203, DOI 10.17487/RFC2203, September
              1997, <>.

   [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,

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   [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, <>.

   [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 are grateful to Bill Baker, David Black, Benjamin Kaduk
   Greg Marsden, David Noveck, Justin Mazzola Paluska, and Tom Talpey
   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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