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Versions: (draft-cel-nfsv4-rpc-tls) 00 01 02 03 04 05 06 07 08 09 10 11

Network File System Version 4                               T. Myklebust
Internet-Draft                                               Hammerspace
Updates: 5531 (if approved)                                C. Lever, Ed.
Intended status: Standards Track                                  Oracle
Expires: September 26, 2019                               March 25, 2019

              Remote Procedure Call Encryption By Default


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

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 26, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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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
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
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   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  RPC-Over-TLS in Operation . . . . . . . . . . . . . . . . . .   4
     4.1.  Discovering Server-side TLS Support . . . . . . . . . . .   5
     4.2.  RPC Authentication  . . . . . . . . . . . . . . . . . . .   6
       4.2.1.  Server-only Host Authentication . . . . . . . . . . .   6
       4.2.2.  Mutual Host Authentication  . . . . . . . . . . . . .   7
       4.2.3.  Advanced Forms of RPC Authentication  . . . . . . . .   7
   5.  TLS Requirements  . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Connection Types  . . . . . . . . . . . . . . . . . . . .   8
       5.1.1.  Operation on TCP  . . . . . . . . . . . . . . . . . .   8
       5.1.2.  Operation on UDP  . . . . . . . . . . . . . . . . . .   8
       5.1.3.  Operation on an RDMA Transport  . . . . . . . . . . .   8
     5.2.  TLS Peer Authentication . . . . . . . . . . . . . . . . .   8
       5.2.1.  X.509 Certificates Using PKIX trust . . . . . . . . .   8
       5.2.2.  X.509 Certificates Using Fingerprints . . . . . . . .  10
       5.2.3.  Pre-Shared Keys . . . . . . . . . . . . . . . . . . .  10
       5.2.4.  Token Binding . . . . . . . . . . . . . . . . . . . .  10
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Linux NFS server and client . . . . . . . . . . . . . . .  11
     6.2.  DESY NFS server . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
     7.1.  Implications for AUTH_SYS . . . . . . . . . . . . . . . .  12
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

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

   o  Per-client deployment and administrative costs are not scalable.
      Keying material must be provided for each RPC client, including
      transient clients.

   o  Parts of the RPC header remain in clear-text, and can constitute a
      significant security exposure.

   o  On-host cryptographic manipulation of data payloads can exact a
      significant CPU cost on both clients and the server.

   o  Host identity management and user identity management must be
      carried out in the same security realm.  In certain environments,
      different authorities might be responsible for provisioning client
      systems versus provisioning new users.

   However strong a privacy service is, it can not provide any security
   if the difficulties of deploying and using it result in it not being
   used at all.

   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
      In-transit encryption can be enabled without additional
      administrative actions such as identifying the host system to a

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      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
      TLS can be used to authenticate hosts using certificates while
      other security mechanisms can handle user authentictation.

   Encryption Offload
      The use of a well-established transport encryption mechanism that
      is also employed by other very common network protocols makes it
      likely that a hardware encryption implementation will be available
      to offload encryption and decryption.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [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 use "confidentiality".  In this document the two
   terms are synonymous.

4.  RPC-Over-TLS in Operation

   In this section we cleave to the convention that a "client" is the
   peer host that actively initiates a connection, and a "server" is the
   peer host that passively accepts a connection request.

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4.1.  Discovering Server-side TLS Support

   The mechanism described in this document interoperates fully with RPC
   implementations that do not support TLS.  The use of TLS is
   automatically disabled in these cases.

   To achieve this, we introduce a new RPC 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.  Except for the
   modifications described in this section, the RPC protocol is largely
   unaware of security encapsulation.


   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 */


   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 begin sending traffic to a server, it
   starts with 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.

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   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 SHOULD 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
   AUTH_ERROR.  In addition, a client MUST NOT attempt a TLS handshake
   after the initial exchange.

   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.  RPC Authentication

   Both RPC and TLS have their own variants of authentication, and there
   is some overlap in capability.  The goal of interoperability with
   implementations that do not support TLS requires that we limit the
   combinations that are allowed and precisely specify the role that
   each layer plays.  We also want to handle TLS such that an RPC
   implementation can make the use of TLS invisible to existing RPC
   consumer applications.

   Toward these ends, there are two deployment modes.

4.2.1.  Server-only Host Authentication

   In a basic deployment, a server possesses a unique global identity
   (e.g., a certificate that is self-signed or signed by a well-known
   trust anchor) while its clients are anonymous (i.e., present no
   identifier).  In this situation, the client SHOULD authenticate the
   server host using the presented TLS identity, but the server cannot
   authenticate connecting clients.  Here, a TLS session is established
   and the RPC requests in transit carry user and group identities
   according to the conventions of the RPC protocol.

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4.2.2.  Mutual Host Authentication

   In this type of deployment, both the server and its clients possess
   unique identities (e.g., certificates).  As part of the TLS
   handshake, both peer hosts SHOULD authenticate using the presented
   TLS identities.  Should authentication of either peer fail, or should
   authorization based on those identities block access to the server,
   the connection MAY be rejected.  However, once a TLS session is
   established, the server MUST NOT utilize TLS identity for the purpose
   of authorizing RPC requests.

   In some cases, a client might choose to present a certificate that
   represents a user rather than one that is bound to the client host.
   As above, the server MUST NOT utilize this identity for the purpose
   of authorizing RPC requests.  The TLS identities of the peer hosts
   are fully independent of RPC user identities.

4.2.3.  Advanced Forms of RPC Authentication

   RPCSEC GSS can provide integrity or privacy (also known as
   confidentiality) services.  When operating over a TLS session, these
   services become redundant.  Each RPC implementation is responsible
   for using channel binding for detecting when GSS integrity or privacy
   is unnecessary and can therefore be disabled.  See Section 2.5 of
   [RFC7861] for details.

   Note that a GSS service principal is still required on the server,
   and mutual GSS authentication of server and client still occurs after
   the TLS session is established.

5.  TLS Requirements

   When a TLS session is negotiated for the purpose of transporting RPC,
   the following restrictions apply:

   o  Implementations MUST NOT negotiate TLS versions prior to v1.3
      [RFC8446].  Support for mandatory-to-implement ciphersuites for
      the negotiated TLS version is REQUIRED.

   o  Implementations MUST support certificate-based mutual
      authentication.  Support for TLS-PSK mutual authentication
      [RFC4279] is OPTIONAL.  See Section 4.2 for further details.

   o  Negotiation of a ciphersuite providing for confidentiality as well
      as integrity protection is REQUIRED.  Support for and negotiation
      of compression is OPTIONAL.

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5.1.  Connection Types

5.1.1.  Operation on TCP

   RPC over TCP is protected by using TLS [RFC8446].  As soon as a
   client completes the TCP handshake, it uses the mechanism described
   in Section 4.1 to discover TLS support and then negotiate a TLS

5.1.2.  Operation on UDP

   RPC over UDP is protected using DTLS [RFC6347].  As soon as a client
   initializes a socket for use with an unfamiliar server, it uses the
   mechanism described in Section 4.1 to discover DTLS support and then
   negotiate a DTLS session.  Connected operation is RECOMMENDED.

   Using a DTLS transport does not introduce reliable or in-order
   semantics to RPC on UDP.  Also, DTLS does not support fragmentation
   of RPC messages.  One RPC message fits in a single DTLS datagram.
   DTLS encapsulation has overhead which reduces the effective Path MTU
   (PMTU) and thus the maximum RPC payload size.

5.1.3.  Operation on an RDMA Transport

   RPC-over-RDMA can make use of Transport Layer Security below the RDMA
   transport layer [RFC8166].  The exact mechanism is not within the
   scope of this document.

5.2.  TLS Peer Authentication

   Peer authentication can be performed by TLS using any of the
   following mechanisms:

5.2.1.  X.509 Certificates Using PKIX trust

   Implementations are REQUIRED to support this mechanism.  In this
   mode, an RPC client is uniquely identified by the tuple (serial
   number of presented client certificate;Issuer).

   o  Implementations MUST allow the configuration of a list of trusted
      Certification Authorities for incoming connections.

   o  Certificate validation MUST include the verification rules as per

   o  Implementations SHOULD indicate their trusted Certification
      Authorities (CAs).

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   o  Peer validation always includes a check on whether the locally
      configured expected DNS name or IP address of the server that is
      contacted matches its presented certificate.  DNS names and IP
      addresses can be contained in the Common Name (CN) or
      subjectAltName entries.  For verification, only one of these
      entries is to be considered.  The following precedence applies:
      for DNS name validation, subjectAltName:DNS has precedence over
      CN; for IP address validation, subjectAltName:iPAddr has
      precedence over CN.  Implementors of this specification are
      advised to read Section 6 of [RFC6125] for more details on DNS
      name validation.

   o  Implementations MAY allow the configuration of a set of additional
      properties of the certificate to check for a peer's authorization
      to communicate (e.g., a set of allowed values in
      subjectAltName:URI or a set of allowed X509v3 Certificate

   o  When the configured trust base changes (e.g., removal of a CA from
      the list of trusted CAs; issuance of a new CRL for a given CA),
      implementations MAY renegotiate the TLS session to reassess the
      connecting peer's continued authorization.

   Having identified a connecting entity does not mean the RPC server
   necessarily wants to communicate with that client.  For example, if
   the Issuer is not in a trusted set of Issuers, the RPC server may
   decline to perform RPC transactions with this client.
   Implementations that want to support a wide variety of trust models
   should expose as many details of the presented certificate to the
   administrator as possible so that the trust model can be implemented
   by the administrator.  As a suggestion, at least the following
   parameters of the X.509 client certificate should be exposed:

   o  Originating IP address

   o  Certificate Fingerprint

   o  Issuer

   o  Subject

   o  all X509v3 Extended Key Usage

   o  all X509v3 Subject Alternative Name

   o  all X509v3 Certificate Policies

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5.2.2.  X.509 Certificates Using Fingerprints

   This mechanism is OPTIONAL to implement.  In this mode, an RPC client
   is uniquely identified by the fingerprint of the presented client

   Implementations SHOULD allow the configuration of a list of trusted
   certificates, identified via fingerprint of the DER encoded
   certificate octets.  Implementations MUST support SHA-1 as the hash
   algorithm for the fingerprint.  To prevent attacks based on hash
   collisions, support for a more contemporary hash function, such as

5.2.3.  Pre-Shared Keys

   This mechanism is OPTIONAL to implement.  In this mode, an RPC client
   is uniquely identified by its TLS identifier.  At least the following
   parameters of the TLS connection should be exposed:

   o  Originating IP address

   o  TLS Identifier

5.2.4.  Token Binding

   This mechanism is OPTIONAL to implement.  In this mode, an RPC client
   is uniquely identified by a token.

   Versions of TLS subsequent to TLS 1.2 feature a token binding
   mechanism which is nominally more secure than using certificates.
   This is discussed in further detail in [RFC8471].

6.  Implementation Status

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to

   Please note that the listing of any individual implementation here
   does not imply endorsement by the IETF.  Furthermore, no effort has
   been spent to verify the information presented here that was supplied
   by IETF contributors.  This is not intended as, and must not be
   construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may

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6.1.  Linux NFS server and client

   Organization:  The Linux Foundation

   URL:       https://www.kernel.org

   Maturity:  Prototype software based on early versions of this

   Coverage:  The bulk of this specification is implemented.  The use of
              DTLS functionality is not implemented.

   Licensing: GPLv2

   Implementation experience:  No comments from implementors.

6.2.  DESY NFS server

   Organization:  DESY

   URL:       https://desy.de

   Maturity:  Prototype software based on early versions of this

   Coverage:  The bulk of this specification is implemented.  The use of
              DTLS functionality is not implemented.

   Licensing: Freely distributable with acknowledgment.

   Implementation experience:  No comments from implementors.

7.  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

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   domains, the client MUST establish independent TLS sessions for each
   distinct security domain.

7.1.  Implications for AUTH_SYS

   Ever since the IETF NFSV4 Working Group took over the maintenance of
   the NFSv4 family of protocols (currently specified in [RFC7530],
   [RFC5661], and [RFC7863], among others), it has encouraged the use of
   RPCSEC GSS over AUTH_SYS.  For various reasons, unfortunately
   AUTH_SYS continues to be the primary authentication mechanism
   deployed by NFS administrators.  As a result, NFS security remains in
   an unsatisfactory state.

   A deeper purpose of this document is to attempt to address some of
   the shortcomings of AUTH_SYS so that, where it has been impractical
   to deploy RPCSEC GSS, better NFSv4 security can nevertheless be

   When AUTH_SYS is used with TLS and no client certificate is
   available, the RPC server is still acting on RPC requests for which
   there is no trustworthy authentication.  In-transit traffic is
   protected, but the client itself can still misrepresent user identity
   without detection.  This is an improvement from AUTH_SYS without
   encryption, but it leaves a critical security exposure.

   Therefore, the RECOMMENDED deployment mode is that clients have
   certificate material configured and used so that servers can have a
   degree of trust that clients are acting responsibly.

8.  IANA Considerations

   In accordance with Section 6 of [RFC7301], the authors request that
   IANA allocate the following value in the "Application-Layer Protocol
   Negotiation (ALPN) Protocol IDs" registry.  The "sunrpc" string
   identifies SunRPC when used over TLS.


   Identification Sequence:
      0x73 0x75 0x6e 0x72 0x70 0x63 ("sunrpc")


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9.  References

9.1.  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,

   [RFC4279]  Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
              Ciphersuites for Transport Layer Security (TLS)",
              RFC 4279, DOI 10.17487/RFC4279, December 2005,

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,

   [RFC5531]  Thurlow, R., "RPC: Remote Procedure Call Protocol
              Specification Version 2", RFC 5531, DOI 10.17487/RFC5531,
              May 2009, <https://www.rfc-editor.org/info/rfc5531>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <https://www.rfc-editor.org/info/rfc7258>.

   [RFC7301]  Friedl, S., Popov, A., Langley, A., and E. Stephan,
              "Transport Layer Security (TLS) Application-Layer Protocol
              Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
              July 2014, <https://www.rfc-editor.org/info/rfc7301>.

   [RFC7861]  Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
              Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
              November 2016, <https://www.rfc-editor.org/info/rfc7861>.

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   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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

9.2.  Informative References

   [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, <https://www.rfc-editor.org/info/rfc2203>.

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

   [RFC5661]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,

   [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, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC7530]  Haynes, T., Ed. and D. Noveck, Ed., "Network File System
              (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
              March 2015, <https://www.rfc-editor.org/info/rfc7530>.

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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, <https://www.rfc-editor.org/info/rfc7862>.

   [RFC7863]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 External Data Representation Standard (XDR)
              Description", RFC 7863, DOI 10.17487/RFC7863, November
              2016, <https://www.rfc-editor.org/info/rfc7863>.

   [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,

   [RFC8471]  Popov, A., Ed., Nystroem, M., Balfanz, D., and J. Hodges,
              "The Token Binding Protocol Version 1.0", RFC 8471,
              DOI 10.17487/RFC8471, October 2018,

9.3.  URIs

   [1] https://www.linuxjournal.com/content/encrypting-nfsv4-stunnel-tls


   Special mention goes to Charles Fisher, author of "Encrypting NFSv4
   with Stunnel TLS" [1].  His article inspired the mechanism described
   in this document.

   The authors are grateful to Bill Baker, David Black, Alan DeKok, Lars
   Eggert, Benjamin Kaduk, Greg Marsden, Alex McDonald, Tigran
   Mkrtchyan, David Noveck, Justin Mazzola Paluska, and Tom Talpey for
   their input and support of this work.

   Special thanks go to Transport Area Director Magnus Westerlund, 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

   Email: trond.myklebust@hammerspace.com

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   Charles Lever (editor)
   Oracle Corporation
   United States of America

   Email: chuck.lever@oracle.com

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