draft-ietf-nfsv4-rpc-tls.xml

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
<?xml-stylesheet type="text/xsl" href="rfc2629.xslt"?>

<rfc
 category="std"
 docName="draft-ietf-nfsv4-rpc-tls-latest"
 ipr="trust200902"
 obsoletes=""
 scripts="Common,Latin"
 sortRefs="true"
 submissionType="IETF"
 symRefs="true"
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 updates="5531"
 version="3"
 xml:lang="en">

<front>

<title abbrev="RPC-With-TLS">
Towards Remote Procedure Call Encryption By Default
</title>

<seriesInfo name="Internet-Draft" value="draft-ietf-nfsv4-rpc-tls-latest"/>

<author initials="T." surname="Myklebust" fullname="Trond Myklebust">
<organization abbrev="Hammerspace" showOnFrontPage="true">
Hammerspace Inc
</organization>
<address>
<postal>
<street>4300 El Camino Real Ste 105</street>
<city>Los Altos</city>
<region>CA</region>
<code>94022</code>
<country>United States of America</country>
</postal>
<email>trond.myklebust@hammerspace.com</email>
</address>
</author>

<author initials="C." surname="Lever" fullname="Charles Lever" role="editor">
<organization abbrev="Oracle" showOnFrontPage="true">
Oracle Corporation
</organization>
<address>
<postal>
<street/>
<city/>
<region/>
<code/>
<country>United States of America</country>
</postal>
<email>chuck.lever@oracle.com</email>
</address>
</author>

<date/>

<area>Transport</area>
<workgroup>Network File System Version 4</workgroup>

<abstract>
<t>
This document describes a mechanism that,
through the use of opportunistic Transport Layer Security (TLS),
enables encryption of Remote Procedure Call (RPC) transactions
while they are in-transit.
The proposed mechanism interoperates with ONC RPC implementations
that do not support it.
This document updates RFC 5531.
</t>
</abstract>

<note removeInRFC="true">
<t>
Discussion of this draft takes place
on the NFSv4 working group mailing list (nfsv4@ietf.org),
which is archived at
<eref target="https://mailarchive.ietf.org/arch/browse/nfsv4/"/>.
Working Group information can be found at
<eref target="https://datatracker.ietf.org/wg/nfsv4/about/"/>.
</t>
<t>
The source for this draft is maintained in GitHub.
Suggested changes should be submitted as pull requests at
<eref target="https://github.com/chucklever/i-d-rpc-tls"/>.
Instructions are on that page as well.
</t>
</note>

</front>

<middle>

<section
 anchor="section_8F035331-8EB8-4FBC-973A-673FBA5FE952"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Introduction</name>
<t>
In 2014 the IETF published
a document entitled "Pervasive Monitoring Is an Attack"
<xref target="RFC7258" format="default" sectionFormat="of"/>,
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
should make a genuine effort to mitigate monitoring attacks.
Typically this mitigation includes encrypting data in transit.
</t>
<t>
The Remote Procedure Call version 2 protocol
has been a Proposed Standard for three decades
(see
<xref target="RFC5531" format="default" sectionFormat="of"/>
and its antecedents).
Over twenty years ago,
Eisler et al. first introduced RPCSEC GSS
as an in-transit encryption mechanism for RPC
<xref target="RFC2203" format="default" sectionFormat="of"/>.
However, experience has shown
that RPCSEC GSS with in-transit encryption
can be challenging to use in practice:
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
Parts of each RPC header remain in clear-text,
constituting a loss of metadata confidentiality.
</li>
<li>
Offloading the GSS privacy service is not practical
in large multi-user deployments
since each message is encrypted using a key based
on the issuing RPC user.
</li>
</ul>
<t>
However strong GSS-provided confidentiality is,
it cannot provide any security if the challenges
of using it result in choosing not to deploy it at all.
</t>
<t>
Moreover, the use of AUTH_SYS
remains common despite the adverse effects
that acceptance of UIDs and GIDs
from unauthenticated clients brings with it.
Continued use is in part because:
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
Per-client deployment and administrative costs
for the only well-defined alternative to AUTH_SYS
are expensive at scale.
For instance, administrators must provide keying material
for each RPC client, including transient clients.
</li>
<li>
GSS host identity management and user identity management
typically must be enforced in the same security realm.
However, cloud providers, for instance, might prefer
to remain authoritative for host identity
but
allow tenants to manage user identities within their private networks.
</li>
</ul>
<t>
In view of the challenges with the
currently available mechanisms
for
authenticating
and
protecting the confidentiality
of RPC transactions,
this document specifies a transport-layer security mechanism
that complements the existing ones.
The
Transport Layer Security
<xref target="RFC8446" format="default" sectionFormat="of"/>
(TLS)
and
Datagram Transport Layer Security
<xref target="I-D.ietf-tls-dtls13" format="default" sectionFormat="of"/>
(DTLS)
protocols are a well-established Internet building blocks
that protect many standard Internet protocols
such as the Hypertext Transport Protocol (HTTP)
<xref target="RFC2818" format="default" sectionFormat="of"/>.
</t>
<t>
Encrypting at the RPC transport layer accords several significant benefits:
</t>
<dl newline="false" spacing="normal">
<dt>Encryption By Default:</dt>
<dd>
Transport encryption can be enabled
without additional administrative tasks such as
identifying client systems to a trust authority
and
providing each with keying material.
</dd>
<dt>Encryption Offload:</dt>
<dd>
Hardware support for the GSS privacy service has not appeared in the marketplace.
However, the use of a well-established transport encryption mechanism
that is employed by other ubiquitous network protocols
makes it more likely that encryption offload for RPC
is practicable.
</dd>
<dt>Securing AUTH_SYS:</dt>
<dd>
Most critically, transport encryption can
significantly reduce several security issues
inherent in the current widespread use of AUTH_SYS
(i.e., acceptance of UIDs and GIDs
generated by an unauthenticated client).
</dd>
<dt>Decoupled User and Host Identities:</dt>
<dd>
TLS can be used to authenticate peer hosts
while other security mechanisms can handle user authentication.
</dd>
<dt>Compatibility:</dt>
<dd>
The imposition of encryption at the transport layer
protects any upper-layer protocol that employs RPC,
without alteration of the upper-layer protocol.
</dd>
</dl>
<t>
Further,
<xref target="section_2AE49383-E6B2-4830-8407-995FEBF727F2" format="default" sectionFormat="of"/>
of the current document defines policies in line with
<xref target="RFC7435" format="default" sectionFormat="of"/>
which enable RPC-with-TLS to be deployed opportunistically
in environments that contain RPC implementations that do not support TLS.
However, specifications for RPC-based upper-layer protocols
should choose to require even stricter policies that guarantee
encryption
and
host authentication
is used for all RPC transactions
to mitigate against pervasive monitoring attacks
<xref target="RFC7258" format="default" sectionFormat="of"/>.
Enforcing the use of RPC-with-TLS is of particular importance
for existing upper-layer protocols whose security infrastructure is weak.
</t>
<t>
The protocol specification in the current document assumes
that support for
ONC RPC
<xref target="RFC5531" format="default" sectionFormat="of"/>,
TLS
<xref target="RFC8446" format="default" sectionFormat="of"/>,
PKIX
<xref target="RFC5280" format="default" sectionFormat="of"/>,
DNSSEC/DANE
<xref target="RFC6698" format="default" sectionFormat="of"/>,
and optionally
RPCSEC_GSS
<xref target="RFC2203" format="default" sectionFormat="of"/>
is available within the platform
where RPC-with-TLS support is to be added.
</t>
</section>

<section
 anchor="section_024237C9-5504-49B4-A2D3-2D2A5EFBB967"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Requirements Language</name>
<t>
The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
"<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
"<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>",
"<bcp14>SHOULD NOT</bcp14>",
"<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>"
in this document are to be interpreted
as described in BCP&nbsp;14
<xref target="RFC2119" format="default" sectionFormat="of"/>
<xref target="RFC8174" format="default" sectionFormat="of"/>
when, and only when, they appear in all capitals, as shown here.
</t>
</section>

<section
 anchor="section_0EB1100E-DAA8-4B2C-98AE-94258CFDCB1B"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Terminology</name>
<t>
This document adopts the terminology introduced in
<xref target="RFC6973" section="3" format="default" sectionFormat="of"/>
and assumes a working knowledge of
the Remote Procedure Call (RPC) version 2 protocol
<xref target="RFC5531" format="default" sectionFormat="of"/>
and
the Transport Layer Security (TLS) version 1.3 protocol
<xref target="RFC8446" format="default" sectionFormat="of"/>.
</t>
<t>
Note also that the NFS community long ago adopted the
use of the term "privacy" from documents such as
<xref target="RFC2203" format="default" sectionFormat="of"/>.
In the current document, the authors use the term
"privacy" only when referring specifically
to the historic GSS privacy service defined in
<xref target="RFC2203" format="default" sectionFormat="of"/>.
Otherwise, the authors use the term "confidentiality",
following the practices of contemporary security communities.
</t>
<t>
We adhere to the convention that a "client"
is a network host that actively initiates an association,
and
a "server" is a network host that passively accepts an association request.
</t>
<t>
RPC documentation historically refers to
the authentication of a connecting host as "machine authentication"
or "host authentication".
TLS documentation refers to the same as "peer authentication".
In the current document there is little distinction between these terms.
</t>
<t>
The term "user authentication" in the current document refers specifically
to the RPC caller's credential, provided in the
"cred"
and
"verf"
fields in each RPC Call.
</t>
</section>

<section
 anchor="section_EC3FEED5-1DE0-454B-9AB3-CE47BA901583"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>RPC-With-TLS in Operation</name>

<section
 anchor="section_0A03673B-14BA-4228-8A8A-F76AA318CA73"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Discovering Server-side TLS Support</name>
<t>
The mechanism described in the current document
interoperates fully with RPC implementations
that do not support RPC-with-TLS.
When an RPC-with-TLS-enabled peer encounters a peer that
does not support RPC-with-TLS,
policy settings on the RPC-with-TLS-enabled peer determine
whether RPC operation continues without the use of TLS,
or RPC operation is not permitted.
</t>
<t>
To achieve this interoperability,
we introduce a new RPC authentication flavor called AUTH_TLS.
The AUTH_TLS authentication flavor signals 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 unaware of security encapsulation
at the transport layer.
The value of AUTH_TLS is defined in
<xref target="section_2CD51855-CE40-4B8D-A220-F211C477964F" format="default" sectionFormat="of"/>.
</t>
<t>
An RPC client begins its communication with an RPC server
by selecting a transport and destination port.
The choice of transport and port is
typically based on the RPC program that is to be used.
The RPC client might query the RPC server's RPCBIND service
to make this selection
(The RPCBIND service is described in
<xref target="RFC1833" format="default" sectionFormat="of"/>).
The mechanism described in the current document
does not support RPC transports other than TCP and UDP.
In all cases, an RPC server <bcp14>MUST</bcp14> listen on the same ports
for (D)TLS-protected RPC programs
as the ports used when (D)TLS is not available.
</t>
<t>
To protect RPC traffic to a TCP port,
the RPC client opens a TCP connection to that port
and sends a NULL RPC procedure
with an auth_flavor of AUTH_TLS on that connection.
To protect RPC traffic to a UDP port,
the RPC client sends a UDP datagram to that port
containing a NULL RPC procedure with an auth_flavor of AUTH_TLS.
The client constructs this RPC procedure as follows:
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
The length of the opaque data constituting the credential
sent in the RPC Call message <bcp14>MUST</bcp14> be zero.
</li>
<li>
The verifier accompanying the credential <bcp14>MUST</bcp14> be an AUTH_NONE
verifier of length zero.
</li>
<li>
The flavor value of the verifier in the RPC Reply message
received from the server <bcp14>MUST</bcp14> be AUTH_NONE.
</li>
<li>
The length of the verifier's body field is eight.
</li>
<li>
The bytes of the verifier's body field encode the ASCII characters
"STARTTLS" as a fixed-length opaque.
</li>
</ul>
<t>
The RPC server signals its corresponding support for RPC-with-TLS
by replying with
a reply_stat of MSG_ACCEPTED
and
an AUTH_NONE verifier containing the "STARTTLS" token.
The client <bcp14>SHOULD</bcp14> proceed with TLS session establishment,
even if the Reply's accept_stat is not SUCCESS.
If the AUTH_TLS probe was done via TCP,
the RPC client <bcp14>MUST</bcp14> send the "ClientHello" message
on the same connection.
If the AUTH_TLS probe was done via UDP,
the RPC client <bcp14>MUST</bcp14> send the "ClientHello" message
to the same UDP destination port.
</t>
<t>
Conversely,
if the Reply's reply_stat is not MSG_ACCEPTED,
if its verifier flavor is not AUTH_NONE,
or if its verifier does not contain the "STARTTLS" token,
the RPC client <bcp14>MUST NOT</bcp14> send a "ClientHello" message.
RPC operation may continue,
depending on local policy, but without
confidentiality,
integrity,
or
peer authentication protection
from (D)TLS.
</t>
<t>
If, after a successful RPC AUTH_TLS probe,
the subsequent (D)TLS handshake should fail for any reason,
the RPC client reports this failure
to the upper-layer application
the same way it reports an AUTH_ERROR rejection
from the RPC server.
</t>
<t>
If an RPC client uses the AUTH_TLS authentication flavor
on any procedure other than the NULL procedure,
or an RPC client sends an RPC AUTH_TLS probe within
an existing (D)TLS session,
the RPC server <bcp14>MUST</bcp14> reject that RPC Call
by returning a reply_stat of MSG_DENIED
with a reject_stat of AUTH_ERROR
and an auth_stat of AUTH_BADCRED.
</t>
<t>
Once the TLS session handshake is complete,
the RPC client and server have established
a secure channel for exchanging RPC transactions.
A successful AUTH_TLS probe on one particular port/transport tuple
does not imply that RPC-with-TLS is available on that same server
using a different port/transport tuple,
nor does it imply that
RPC-with-TLS will be available in the future
using the successfully probed port.
</t>
</section>

<section
 anchor="section_6EDEF553-C95A-47D7-ABBA-0B537FE3A959"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Authentication</name>
<t>
There is some overlap between the authentication
capabilities of RPC and TLS.
The goal of interoperability with implementations
that do not support TLS requires
limiting the combinations that are allowed
and
precisely specifying the role that each layer plays.
</t>
<t>
Each RPC server that supports RPC-with-TLS <bcp14>MUST</bcp14> possess a unique global identity
(e.g., a certificate that is signed by a well-known trust anchor).
Such an RPC server <bcp14>MUST</bcp14> request a TLS peer identity from each client
upon first contact.
There are two different modes of client deployment:
</t>
<dl newline="true" spacing="normal">
<dt>Server-only Host Authentication</dt>
<dd>
In this type of deployment,
the client can authenticate the server host
using the presented server peer TLS identity,
but the server cannot authenticate the client.
In this situation,
RPC-with-TLS clients are anonymous.
They present no globally unique identifier to the server peer.
</dd>
<dt>Mutual Host Authentication</dt>
<dd>
In this type of deployment,
the client possesses an identity that is backed by a trusted entity
(e.g. a pre-shared key or a certificate validated with a certification path).
As part of the TLS handshake, both peers authenticate using the presented TLS identities.
If authentication of either peer fails,
or
if authorization based on those identities blocks access to the server,
the peers <bcp14>MUST</bcp14> reject the association.
Further explanation appears in
<xref target="section_936921ED-67BB-46BF-B316-6740E07F6652" format="default" sectionFormat="of"/>.
</dd>
</dl>
<t>
In either of these modes, RPC user authentication is not affected
by the use of transport layer security.
When a client presents a TLS peer identity to an RPC server,
the protocol extension described in the current document
provides no way for the server to know
whether that identity represents one RPC user on that client,
or
is shared amongst many RPC users.
Therefore, a server implementation cannot utilize
the remote TLS peer identity to authenticate RPC users.
</t>

<section
 anchor="section_12D92596-F310-48C8-A4E0-B6CA038524E5"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Using TLS with RPCSEC GSS</name>
<t>
To use GSS, an RPC server has to possess a GSS service principal.
On a TLS session, GSS mutual (peer) authentication occurs as usual,
but only after a TLS session has been established for communication.
Authentication of RPCSEC GSS users is unchanged by the use of TLS.
</t>
<t>
RPCSEC GSS can also perform
per-request integrity or confidentiality protection.
When operating over a TLS session,
these GSS services become largely redundant.
An RPC implementation capable of concurrently using TLS and RPCSEC GSS
<bcp14>MUST</bcp14>
use GSS-API channel binding, as defined in
<xref target="RFC5056" format="default" sectionFormat="of"/>,
to determine when an underlying transport
provides a sufficient degree of confidentiality.
RPC-with-TLS implementations
<bcp14>MUST</bcp14>
provide the "tls-exporter" channel binding type, as defined in
<xref target="I-D.ietf-kitten-tls-channel-bindings-for-tls13" format="default" sectionFormat="of"/>.
</t>
</section>

</section>

</section>

<section
 anchor="section_D93526DA-7B9D-419B-BE84-4AD8DA48577E"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>TLS Requirements</name>
<t>
When peers negotiate a TLS session that is to transport RPC,
the following restrictions apply:
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
Implementations <bcp14>MUST NOT</bcp14> negotiate TLS versions prior to v1.3
(for TLS
<xref target="RFC8446" format="default" sectionFormat="of"/>
or DTLS
<xref target="I-D.ietf-tls-dtls13" format="default" sectionFormat="of"/>
respectively).
Support for mandatory-to-implement ciphersuites
for the negotiated TLS version is <bcp14>REQUIRED</bcp14>.
</li>
<li>
Implementations
<bcp14>MUST</bcp14>
conform to the recommendations for TLS usage specified in BCP 195
<xref target="RFC7525" format="default" sectionFormat="of"/>.
Although RFC 7525 permits the use of TLS v1.2,
the requirement to use TLS v1.3 or later for RPC-with-TLS takes precedence.
Further, because TLS v1.3 ciphers
are qualitatively different than cipher suites in previous versions of TLS
and RFC 7525 predates TLS v1.3,
the cipher suite recommendations in RFC 7525 do not apply to RPC-with-(D)TLS.
A strict TLS mode for RPC-with-TLS that protects against STRIPTLS attacks
is discussed in detail in
<xref target="section_8894BDD2-0E0B-47A3-A2CB-70E4D93B55B0" format="default" sectionFormat="of"/>.
</li>
<li>
Implementations <bcp14>MUST</bcp14> support
certificate-based mutual authentication.
Support for PSK mutual authentication
is <bcp14>OPTIONAL</bcp14>;
see
<xref target="section_6DA9ED5F-BAD9-4126-95B7-E2331655A01E" format="default" sectionFormat="of"/>
for further details.
</li>
<li>
Negotiation of a ciphersuite providing confidentiality as
well as integrity protection is <bcp14>REQUIRED</bcp14>.
</li>
</ul>
<t>
Client implementations <bcp14>MUST</bcp14> include the
"application_layer_protocol_negotiation(16)" extension
<xref target="RFC7301" format="default" sectionFormat="of"/>
in their "ClientHello" message
and <bcp14>MUST</bcp14> include the protocol identifier
defined in
<xref target="section_58905D7A-06B1-4469-964A-DAC607DAC500" format="default" sectionFormat="of"/>
in that message's ProtocolNameList value.
</t>
<t>
Similarly, in response to the "ClientHello" message,
server implementations <bcp14>MUST</bcp14> include the
"application_layer_protocol_negotiation(16)" extension
<xref target="RFC7301" format="default" sectionFormat="of"/>
in their "ServerHello" message
and <bcp14>MUST</bcp14> include only the protocol identifier
defined in
<xref target="section_58905D7A-06B1-4469-964A-DAC607DAC500" format="default" sectionFormat="of"/>
in that message's ProtocolNameList value.
</t>
<t>
If the server responds incorrectly
(for instance, if the "ServerHello" message does not conform to the above requirements),
the client <bcp14>MUST NOT</bcp14> establish a TLS session for use with RPC
on this connection.
See
<xref target="RFC7301" format="default" sectionFormat="of"/>
for further details about how to form these messages properly.
</t>

<section
 anchor="section_CC204592-F561-49BD-B1C9-DE0FF7F0E7AB"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Base Transport Considerations</name>
<t>
There is traditionally a strong association between an RPC program
and a destination port number.
The use of TLS or DTLS does not change that association.
Thus it is frequently --
though not always --
the case that a single TLS session
carries traffic for only one RPC program.
</t>

<section
 anchor="section_74B43C7E-5ADC-4FBD-B4EA-FF8F470994A8"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Protected Operation on TCP</name>
<t>
The use of the Transport Layer Security (TLS) protocol
<xref target="RFC8446" format="default" sectionFormat="of"/>
protects RPC on TCP connections.
Typically,
once an RPC client completes the TCP handshake,
it uses the mechanism described in
<xref target="section_0A03673B-14BA-4228-8A8A-F76AA318CA73" format="default" sectionFormat="of"/>
to discover RPC-with-TLS support for that RPC program on that connection.
Until an AUTH_TLS probe is done on a connection,
the RPC server treats all traffic as RPC messages.
If spurious traffic appears on a TCP connection
between the initial clear-text AUTH_TLS probe
and
the TLS session handshake,
receivers <bcp14>MUST</bcp14> discard that data without response
and then <bcp14>SHOULD</bcp14> drop the connection.
</t>
<t>
The protocol convention specified in the current document
assumes there can be no more than one concurrent TLS session
per TCP connection.
This is true of current generations of TLS,
but might be different in a future version of TLS.
</t>
<t>
Once a TLS session is established on a TCP connection,
no further clear-text communication can occur on that connection
until the session is terminated.
The use of TLS does not alter RPC record framing used on TCP transports.
</t>
<t>
Furthermore,
if an RPC server responds with PROG_UNAVAIL
to an RPC Call within an established TLS session,
that does not imply that RPC server will subsequently
reject the same RPC program on a different TCP connection.
</t>
<t>
Reverse-direction operation occurs only on connected transports such as TCP
(see
<xref target="RFC8167" section="2" format="default" sectionFormat="of"/>).
To protect reverse-direction RPC operations,
the RPC server does not establish a separate TLS session on the TCP connection,
but instead uses the existing TLS session on that connection to protect
these operations.
</t>
<t>
When operation is complete,
an RPC peer terminates a TLS session by sending a TLS Closure Alert.
It may then close the TCP connection.
</t>
</section>

<section
 anchor="section_B8BF600E-96DC-4C82-AADF-D593826E9B75"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Protected Operation on UDP</name>
<t>
RFC Editor:
In the following section,
please replace TBD with the connection_id extension number
that is to be assigned in
<xref target="I-D.ietf-tls-dtls-connection-id" format="default" sectionFormat="of"/>.
And, please remove this Editor's Note
before this document is published.
</t>
<t>
The use of the Datagram Transport Layer Security (DTLS) protocol
<xref target="I-D.ietf-tls-dtls13" format="default" sectionFormat="of"/>
protects RPC carried in UDP datagrams.
As soon as a client initializes a UDP socket
for use with an RPC service,
it uses the mechanism described in
<xref target="section_0A03673B-14BA-4228-8A8A-F76AA318CA73" format="default" sectionFormat="of"/>
to discover RPC-with-DTLS support for that RPC program on that port.
If spurious traffic appears on a 5-tuple between
the initial clear-text AUTH_TLS probe
and
the DTLS association handshake,
receivers
<bcp14>MUST</bcp14>
discard that traffic without response.
</t>
<t>
Using DTLS does not introduce
reliable
or
in-order
semantics to RPC on UDP.
The use of DTLS record replay protection is <bcp14>REQUIRED</bcp14>
when transporting RPC traffic.
</t>
<t>
Each RPC message <bcp14>MUST</bcp14> fit in a single DTLS record.
DTLS encapsulation has overhead,
which reduces the Packetization Layer Path MTU (PLPMTU)
and thus the maximum RPC payload size.
A possible PLPMTU discovery mechanism is offered in
<xref target="RFC8899" format="default" sectionFormat="of"/>.
</t>
<t>
The current document does not specify a mechanism
that enables a server to distinguish between
DTLS traffic
and
unprotected RPC traffic
directed to the same port.
To make this distinction,
each peer matches ingress datagrams
that appear to be DTLS traffic to existing DTLS session state.
A peer treats any datagram that fails the matching process as an RPC message.
</t>
<t>
Multi-homed RPC clients and servers may send protected RPC messages
via network interfaces that were not involved in the handshake that
established the DTLS session.
Therefore, when protecting RPC traffic,
each DTLS handshake <bcp14>MUST</bcp14> include the "connection_id(TBD)" extension
described in
<xref target="I-D.ietf-tls-dtls13" section="9" format="default" sectionFormat="of"/>,
and RPC-with-DTLS peer endpoints
<bcp14>MUST</bcp14>
provide a ConnectionID
with a non-zero length.
Endpoints implementing RPC programs
that expect a significant number of concurrent clients
<bcp14>SHOULD</bcp14>
employ ConnectionIDs of at least 4 bytes in length.
</t>
<t>
Sending a TLS Closure Alert terminates a DTLS session.
Because neither DTLS nor UDP provide in-order delivery,
after session closure there can be ambiguity
as to whether a datagram should be interpreted as DTLS protected or not.
Therefore receivers
<bcp14>MUST</bcp14>
discard datagrams
exchanged using the same 5-tuple that just
terminated the DTLS session for a
sufficient length of time to ensure that retransmissions have ceased and
packets already in the network have been delivered.
In the absence of more specific data,
a period of 60 seconds is expected to suffice.
</t>
</section>

<section
 anchor="section_BFCC24B1-E6D4-4ABC-A5F3-B71E8E96878F"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Protected Operation on Other Transports</name>
<t>
Transports that provide intrinsic TLS-level security
(e.g., QUIC)
need to be addressed separately from the current document.
In such cases, the use of TLS is not opportunistic
as it can be for TCP or UDP.
</t>
<t>
RPC-over-RDMA can make use of transport layer security
below the RDMA transport layer
<xref target="RFC8166" format="default" sectionFormat="of"/>.
The exact mechanism is not within the scope of the current document.
Because there might not be other provisions
to exchange client and server certificates,
authentication material exchange
needs to be provided by facilities
within a future version
of the RPC-over-RDMA transport protocol.
</t>
</section>

</section>

<section
 anchor="section_936921ED-67BB-46BF-B316-6740E07F6652"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>TLS Peer Authentication</name>
<t>
TLS can perform peer authentication
using any of the following mechanisms.
</t>

<section
 anchor="section_7A68F518-2C02-4705-8218-4F13E51372F4"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>X.509 Certificates Using PKIX Trust</name>
<t>
X.509 certificates are specified in
<xref target="X.509" format="default" sectionFormat="of"/>.
<xref target="RFC5280" format="default" sectionFormat="of"/>
provides a profile of Internet PKI X.509 public key infrastructure.
RPC-with-TLS implementations are
<bcp14>REQUIRED</bcp14>
to support the PKIX mechanism described in
<xref target="RFC5280" format="default" sectionFormat="of"/>.
</t>
<t>
The rules and guidelines defined in
<xref target="RFC6125" format="default" sectionFormat="of"/>
apply to RPC-with-TLS certificates
with the following considerations:
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
The DNS-ID identifier type is a subjectAltName extension
that contains a dNSName, as defined in
<xref target="RFC5280" section="4.2.1.6" format="default" sectionFormat="of"/>.
Support for the DNS-ID identifier type is
<bcp14>REQUIRED</bcp14>
in RPC-with-TLS client and server implementations.
Certification authorities that issue such certificates
<bcp14>MUST</bcp14>
support the DNS-ID identifier type.
</li>
<li>
To specify the identity of an RPC peer as
a domain name,
the certificate
<bcp14>MUST</bcp14>
contain a subjectAltName extension that contains a dNSName.
DNS domain names in RPC-with-TLS certificates
<bcp14>MUST NOT</bcp14>
contain the wildcard character '*'
within the identifier.
</li>
<li>
To specify the identity of an RPC peer as
a network identifier (netid)
or
a universal network address (uaddr),
the certificate
<bcp14>MUST</bcp14>
contain a subjectAltName extension that contains an iPAddress.
</li>
</ul>
<t>
When validating a server certificate,
an RPC-with-TLS client implementation
takes the following into account:
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
Certificate validation
<bcp14>MUST</bcp14>
include the verification rules as per
<xref target="RFC5280" section="6" format="default" sectionFormat="of"/>
and
<xref target="RFC6125" section="6" format="default" sectionFormat="of"/>.
</li>
<li>
Server certificate validation
<bcp14>MUST</bcp14>
include a check on whether
the locally configured expected
DNS-ID
or
iPAddress subjectAltName
of the server that is contacted
matches its presented certificate.
</li>
<li>
For RPC services accessed by their
network identifiers (netids)
and
universal network addresses (uaddr),
the iPAddress subjectAltName
<bcp14>MUST</bcp14>
be present in the certificate
and
<bcp14>MUST</bcp14>
exactly match the address represented by the universal network address.
</li>
</ul>
<t>
An RPC client's
domain name
and
IP address
are often assigned dynamically,
thus RPC servers cannot rely on those to verify client certificates.
Therefore, when an RPC-with-TLS client presents a certificate
to an RPC-with-TLS server,
the server takes the following into account:
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
The server
<bcp14>MUST</bcp14>
use a procedure conformant to
<xref target="RFC5280" section="6" format="default" sectionFormat="of"/>)
to validate the client certificate's certification path.
</li>
<li>
The tuple (serial number of the presented certificate; Issuer)
uniquely identifies the RPC client.
The meaning and syntax of these fields is defined in
<xref target="RFC5280" section="4" format="default" sectionFormat="of"/>).
</li>
</ul>


<t>
RPC-with-TLS implementations
<bcp14>MAY</bcp14>
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,
a set of allowed X.509v3 Certificate Policies,
or
a set of extended key usages).
</t>
<t>
When the configured set of trust anchors changes
(e.g., removal of a CA from the list of trusted CAs;
issuance of a new CRL for a given CA),
implementations
<bcp14>SHOULD</bcp14>
reevaluate the certificate originally presented
in the context of the new configuration
and
terminate the TLS session if the certificate is no longer trustworthy.
</t>

<section
 anchor="section_685D3F88-94FF-4C91-8CCB-860DBA602B2F"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Extended Key Usage Values</name>
<t>
<xref target="RFC5280" section="4.2.1.12" format="default" sectionFormat="of"/>
specifies the extended key usage X.509 certificate extension.
This extension, which may appear in end-entity certificates,
indicates one or more purposes for which the certified public key may be used
in addition to or in place of the basic purposes indicated in the key usage extension.
</t>
<t>
The current document defines two new KeyPurposeId values:
one that identifies the RPC-with-TLS peer as an RPC client,
and
one that identifies the RPC-with-TLS peer as an RPC server.
</t>
<t>
The inclusion of the RPC server value (id-kp-rpcTLSServer)
indicates that the certificate has been issued
for allowing the holder to process RPC transactions.
</t>
<t>
The inclusion of the RPC client value (id-kp-rpcTLSClient)
indicates that the certificate has been issued
for allowing the holder to request RPC transactions.
</t>

</section>

</section>

<section
 anchor="section_6DA9ED5F-BAD9-4126-95B7-E2331655A01E"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Pre-Shared Keys</name>
<t>
This mechanism is <bcp14>OPTIONAL</bcp14> to implement.
In this mode, the RPC peer can be uniquely identified
by keying material that has been shared out-of-band
(see
<xref target="RFC8446" section="2.2" format="default" sectionFormat="of"/>).
The
PSK Identifier
<bcp14>SHOULD</bcp14>
be exposed at the RPC layer.
</t>
</section>

</section>

</section>

<section
 anchor="section_88BBA4D6-ED42-4FE6-A208-9D277B68729A"
 numbered="true"
 removeInRFC="true"
 toc="default">
<name>Implementation Status</name>
<t>
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
<xref target="RFC7942" format="default" sectionFormat="of"/>.
The description of implementations in this section is
intended to assist the IETF in its decision processes in
progressing drafts to RFCs.
</t>
<t>
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 exist.
</t>

<section
 anchor="section_94AA7844-E393-4353-A35D-DA01D13C909B"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>DESY NFS server</name>
<dl newline="false" spacing="normal" indent="11">
<dt>Organization:</dt>
<dd>
DESY
</dd>
<dt>URL:</dt>
<dd>
<eref target="https://desy.de"/>
</dd>
<dt>Maturity:</dt>
<dd>
Implementation will be based on mature versions of the current document.
</dd>
<dt>Coverage:</dt>
<dd>
The bulk of this specification is implemented including DTLS.
</dd>
<dt>Licensing:</dt>
<dd>
LGPL
</dd>
<dt>Implementation experience:</dt>
<dd>
The implementer has read and commented on the current document.
</dd>
</dl>
</section>

<section
 anchor="section_B387F281-958F-470D-B4D4-1D85907B89F1"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Hammerspace NFS server</name>
<dl newline="false" spacing="normal" indent="11">
<dt>Organization:</dt>
<dd>
Hammerspace
</dd>
<dt>URL:</dt>
<dd>
<eref target="https://hammerspace.com"/>
</dd>
<dt>Maturity:</dt>
<dd>
Prototype software based on early versions of the current document.
</dd>
<dt>Coverage:</dt>
<dd>
The bulk of this specification is implemented.
The use of DTLS functionality is not implemented.
</dd>
<dt>Licensing:</dt>
<dd>
Proprietary
</dd>
<dt>Implementation experience:</dt>
<dd>
No comments from implementors.
</dd>
</dl>
</section>

<section
 anchor="section_BF03B3A2-4483-4404-9E7A-F60FCD850F31"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Linux NFS server and client</name>
<dl newline="false" spacing="normal" indent="11">
<dt>Organization:</dt>
<dd>
The Linux Foundation
</dd>
<dt>URL:</dt>
<dd>
<eref target="https://www.kernel.org"/>
</dd>
<dt>Maturity:</dt>
<dd>
Not complete.
</dd>
<dt>Coverage:</dt>
<dd>
The bulk of this specification has yet to be implemented.
The use of DTLS functionality is not planned.
</dd>
<dt>Licensing:</dt>
<dd>
GPLv2
</dd>
<dt>Implementation experience:</dt>
<dd>
A Linux in-kernel prototype is underway,
but implementation delays have resulted from the challenges of
handling a TLS handshake in a kernel environment.
Those issues stem from the architecture of TLS and the kernel,
not from the design of RPC-with-TLS.
</dd>
</dl>
</section>

<section
 anchor="section_86689813-E907-4046-ADF1-58E2BF668546"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>FreeBSD NFS server and client</name>
<dl newline="false" spacing="normal" indent="11">
<dt>Organization:</dt>
<dd>
The FreeBSD Project
</dd>
<dt>URL:</dt>
<dd>
<eref target="https://www.freebsd.org"/>
</dd>
<dt>Maturity:</dt>
<dd>
Prototype software based on early versions of the current document.
</dd>
<dt>Coverage:</dt>
<dd>
The bulk of this specification is implemented.
The use of DTLS functionality is not planned.
</dd>
<dt>Licensing:</dt>
<dd>
BSD
</dd>
<dt>Implementation experience:</dt>
<dd>
Implementers have read and commented on the current document.
</dd>
</dl>
</section>

</section>

<section
 anchor="section_2AE49383-E6B2-4830-8407-995FEBF727F2"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Security Considerations</name>
<t>
One purpose of the mechanism described in the current document
is to protect RPC-based applications against threats
to the confidentiality of RPC transactions
and
RPC user identities.
A taxonomy of these threats appears in
<xref target="RFC6973" section="5" format="default" sectionFormat="of"/>.
Also,
<xref target="RFC7525" section="6" format="default" sectionFormat="of"/>
contains a detailed discussion
of technologies used in conjunction with TLS.
<xref target="RFC5280" section="8" format="default" sectionFormat="of"/>
covers important considerations about handling certificate material securely.
Implementers should familiarize themselves with these materials.
</t>
<t>
Once a TLS session is established,
the RPC payload carried on TLS version 1.3 is forward-secure.
However, implementers need to be aware that replay attacks
can occur during session establishment.
Remedies for such attacks are discussed in detail in
<xref target="RFC8446" section="8" format="default" sectionFormat="of"/>.
Further, the current document does not
provide a profile that defines the use of 0-RTT data
(see
Appendix&nbsp;E.5 of
<xref target="RFC8446" format="default" sectionFormat="of"/>).
Therefore, RPC-with-TLS implementations MUST NOT
use 0-RTT data.
</t>

<section
 anchor="section_51737BB5-2B65-441E-AD1D-7EBF5123C079"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>The Limitations of Opportunistic Security</name>
<t>
Readers can find the definition of Opportunistic Security in
<xref target="RFC7435" format="default" sectionFormat="of"/>.
A discussion of its underlying principals
appears in Section&nbsp;3 of that document.
</t>
<t>
The purpose of using an explicitly opportunistic approach
is to enable interoperation
with implementations that do not support RPC-with-TLS.
A range of options is allowed by this approach,
from "no peer authentication or encryption"
to
"server-only authentication with encryption"
to
"mutual authentication with encryption".
The actual security level may indeed
be selected based on policy and without user intervention.
</t>
<t>
In environments where interoperability is a priority,
the security benefits of TLS are partially or entirely waived.
Implementations of the mechanism described in the current document
must take care to accurately represent to all RPC consumers
the level of security that is actually in effect,
and are <bcp14>REQUIRED</bcp14> to provide an audit log
of RPC-with-TLS security mode selection.
</t>
<t>
In all other cases,
the adoption, implementation, and deployment of
RPC-based upper-layer protocols that enforce the use of
TLS authentication and encryption
(when similar RPCSEC GSS services are not in use)
is strongly encouraged.
</t>

<section
 anchor="section_8894BDD2-0E0B-47A3-A2CB-70E4D93B55B0"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>STRIPTLS Attacks</name>
<t>
A classic form of attack on network protocols that initiate an association
in plain-text to discover support for TLS is a man-in-the-middle
that alters the plain-text handshake to make it appear as though
TLS support is not available on one or both peers.
Client implementers can choose from the following to mitigate
STRIPTLS attacks:
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
A TLSA record
<xref target="RFC6698" format="default" sectionFormat="of"/>
can alert clients that TLS is expected to work,
and provide a binding of hostname to X.509 identity.
If TLS cannot be negotiated or authentication fails,
the client disconnects and reports the problem.
When an opportunistic security policy is in place,
a client
<bcp14>SHOULD</bcp14>
check for the existence of a TLSA record for the target
server before initiating an RPC-with-TLS association.
</li>
<li>
Client security policy can require
that a TLS session is established on every connection.
If an attacker spoofs the handshake,
the client disconnects and reports the problem.
This policy prevents an attacker from causing the client to silently fall back to plaintext.
If TLSA records are not available, this approach is strongly encouraged.
</li>
</ul>
</section>

<section
 anchor="section_9C03417D-1D3D-4D43-BC43-6F7387736AF7"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Privacy Leakage Before Session Establishment</name>
<t>
As mentioned earlier,
communication between an RPC client and server
appears in the clear on the network
prior to the establishment of a TLS session.
This clear-text information usually includes
transport connection handshake exchanges,
the RPC NULL procedure probing support for TLS,
and the initial parts of TLS session establishment.
Appendix C of
<xref target="RFC8446" format="default" sectionFormat="of"/>
discusses precautions that can mitigate exposure during
the exchange of connection handshake information
and
TLS certificate material that might enable attackers
to track the RPC client.
Note that when PSK authentication is used,
the PSK identifier is exposed during the TLS handshake,
and can be used to track the RPC client.
</t>
<t>
Any RPC traffic that appears on the network before
a TLS session has been established is vulnerable to
monitoring or undetected modification.
A secure client implementation limits or prevents
any RPC exchanges that are not protected.
</t>
<t>
The exception to this edict is
the initial RPC NULL procedure that acts as a STARTTLS message,
which cannot be protected.
This RPC NULL procedure contains no arguments or results,
and the AUTH_TLS authentication flavor it uses
does not contain user information,
so there is negligible privacy impact from this exception.
</t>
</section>

</section>

<section
 anchor="section_B9F8A982-CB0E-40FC-9460-680E89DB0001"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>TLS Identity Management on Clients</name>
<t>
The goal of RPC-with-TLS
is to hide the content of RPC requests while they are in transit.
RPC-with-TLS by itself cannot protect
against exposure of a user's RPC requests to other users on the same client.
</t>
<t>
Moreover, client implementations are free to transmit RPC requests
for more than one RPC user using the same TLS session.
Depending on the details of the client RPC implementation,
this means that the client's TLS credentials
are potentially visible to every RPC user that shares a TLS session.
Privileged users may also be able to access this TLS identity.
</t>
<t>
As a result,
client implementations need to carefully segregate
TLS credentials so that local access to it
is restricted to only the local users that are authorized
to perform operations on the remote RPC server.
</t>
</section>

<section
 anchor="section_552B02A0-F19E-4B46-809C-672A6AE931A1"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Security Considerations for AUTH_SYS on TLS</name>
<t>
Using a TLS-protected transport
when the AUTH_SYS authentication flavor is in use
addresses several longstanding weaknesses in AUTH_SYS
(as detailed in
<xref target="section_C7FB9DB5-5F4F-45AD-8BF7-74FFCA08BEBB" format="default" sectionFormat="of"/>).
TLS augments AUTH_SYS by providing both
integrity protection and confidentiality
that AUTH_SYS lacks.
TLS protects
data payloads,
RPC headers,
and
user identities
against monitoring and alteration while in transit.
</t>
<t>
TLS guards against in-transit insertion and deletion of RPC messages,
thus ensuring the integrity of the message stream
between RPC client and server.
DTLS does not provide full message stream protection,
but it does enable receivers to reject non-participant messages.
In particular, transport layer encryption plus peer authentication
protects receiving XDR decoders from deserializing untrusted data,
a common coding vulnerability.
However, these decoders would still be exposed to untrusted input
in the case of the compromise of a trusted peer or Certificate Authority.
</t>
<t>
The use of TLS enables strong authentication
of the communicating RPC peers,
providing a degree of non-repudiation.
When AUTH_SYS is used with TLS,
but the RPC client is unauthenticated,
the RPC server still acts on RPC requests
for which there is no trustworthy authentication.
In-transit traffic is protected, but the RPC client itself
can still misrepresent user identity without server detection.
TLS without authentication is an improvement
from AUTH_SYS without encryption,
but it leaves a critical security exposure.
</t>
<t>
In light of the above, when AUTH_SYS is used,
the use of a TLS mutual authentication mechanism is
<bcp14>RECOMMENDED</bcp14>
to prove that the RPC client is known to the RPC server.
The server can then determine whether the UIDs and GIDs
in AUTH_SYS requests from that client can be accepted,
based on the authenticated identity of the client.
</t>
<t>
The use of TLS does not enable RPC clients to detect compromise
that leads to the impersonation of RPC users.
Also, there continues to be a requirement
that the mapping of 32-bit user and group ID values
to user identities
is the same on both the RPC client and server.
</t>
</section>

<section
 anchor="section_55D006D3-8CA6-4D7F-AF0D-BFB0FFEF7595"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Best Security Policy Practices</name>
<t>
RPC-with-TLS implementations and deployments
are strongly encouraged to adhere to the following policies
to achieve the strongest possible security with RPC-with-TLS.
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
When using AUTH_NULL or AUTH_SYS, both peers are
<bcp14>RECOMMENDED</bcp14>
to have DNSSEC TLSA records,
keys with which to perform mutual peer authentication
using one of the methods described in
<xref target="section_936921ED-67BB-46BF-B316-6740E07F6652" format="default" sectionFormat="of"/>,
and
a security policy that requires mutual peer authentication
and
rejection of a connection when host authentication fails.
</li>
<li>
RPCSEC GSS provides integrity and privacy services
which are largely redundant when TLS is in use.
These services
<bcp14>SHOULD</bcp14>
be disabled in that case.
</li>
</ul>
</section>

</section>

<section
 anchor="section_7B126473-2A13-453B-9BCA-66BC11B7B018"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>IANA Considerations</name>
<t>
RFC Editor: In the following subsections,
please replace RFC-TBD with the RFC number assigned to this document.
And, please remove this Editor's Note
before this document is published.
</t>

<section
 anchor="section_2CD51855-CE40-4B8D-A220-F211C477964F"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>RPC Authentication Flavor</name>
<t>
Following Appendix B of
<xref target="RFC5531" format="default" sectionFormat="of"/>,
the authors request a single new entry
in the RPC Authentication Flavor Numbers registry.
The purpose of the new authentication flavor
is to signal the use of TLS with RPC.
This new flavor is not a pseudo-flavor.
</t>
<t>
The fields in the new entry are assigned as follows:
</t>
<dl newline="false" spacing="normal">
<dt>Identifier String:</dt>
<dd>
AUTH_TLS
</dd>
<dt>Flavor Name:</dt>
<dd>
TLS
</dd>
<dt>Value:</dt>
<dd>
7 (to be confirmed by IANA)
</dd>
<dt>Description:</dt>
<dd>
Indicates support for RPC-with-TLS.
</dd>
<dt>Reference:</dt>
<dd>
RFC-TBD
</dd>
</dl>
</section>

<section
 anchor="section_58905D7A-06B1-4469-964A-DAC607DAC500"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>ALPN Identifier for SUNRPC</name>
<t>
Following
<xref target="RFC7301" section="6" format="default" sectionFormat="of"/>,
the authors request the allocation of the following value
in the "Application-Layer Protocol Negotiation (ALPN) Protocol IDs" registry.
The "sunrpc" string identifies SunRPC when used over TLS.
</t>
<dl newline="false" spacing="normal">
<dt>Protocol:</dt>
<dd>
SunRPC
</dd>
<dt>Identification Sequence:</dt>
<dd>
0x73 0x75 0x6e 0x72 0x70 0x63 ("sunrpc")
</dd>
<dt>Reference:</dt>
<dd>
RFC-TBD
</dd>
</dl>
</section>

<section
 anchor="section_62E5E930-706A-4216-9A32-D7AC5952A507"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Object Identifier for PKIX Extended Key Usage</name>
<t>
RFC Editor: In the following subsection,
please replace XXX and YYY with the IANA numbers assigned to these new entries.
And, please remove this Editor's Note
before this document is published.
</t>
<t>
Per the Specification Required policy as defined in
<xref target="RFC8126" section="4.6" format="default" sectionFormat="of"/>,
the authors request the reservation of the following new values:
</t>
<ul spacing="normal" bare="false" empty="false">
<li>
The RPC-with-TLS ASN.1 module in the
"SMI Security for PKIX Extended Key Purpose" registry (1.3.6.1.5.5.7.3)
(see
<xref target="section_685D3F88-94FF-4C91-8CCB-860DBA602B2F" format="default" sectionFormat="of"/>
and
<xref target="section_B08B45C1-1E10-4F7A-935B-1198BAF255C0" format="default" sectionFormat="of"/>.
</li>
<li>
The RPC-with-TLS client certificate extended key usage (1.3.6.1.5.5.7.3.XXX).
The description of this new entry should be "id-kp-rpcTLSClient".
</li>
<li>
The RPC-with-TLS server certificate extended key usage (1.3.6.1.5.5.7.3.YYY).
The description of this new entry should be "id-kp-rpcTLSServer".
</li>
</ul>
<t>
IANA should use the current document (RFC-TBD) as the reference for the new entries.
</t>
</section>

</section>

</middle>

<back>

<references>
<name>References</name>

<references>
<name>Normative References</name>

<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.draft-ietf-tls-dtls13-38.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.draft-ietf-tls-dtls-connection-id-07.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.draft-ietf-kitten-tls-channel-bindings-for-tls13-00.xml"/>

<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5056.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5280.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5531.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6125.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7301.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7525.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7942.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8446.xml"/>

<reference anchor="X.509">
<front>
<title>
ITU-T X.509 - Information technology -
The Directory: Public-key and attribute certificate frameworks.
</title>
<seriesInfo name="ISO/IEC" value="9594-8"/>
<seriesInfo name="CCITT Recommendation" value="X.509"/>
<author>
<organization showOnFrontPage="true">
International Telephone and Telegraph Consultative Committee
</organization>
</author>
<date month="October" year="2019"/>
<abstract>
<t>
Recommendation ITU-T X.509 | ISO/IEC 9594-8 defines frameworks for public-key infrastructure (PKI) and privilege management infrastructure (PMI).
It introduces the basic concept of asymmetric cryptographic techniques.
It specifies the following data types: public-key certificate, attribute certificate, certificate revocation list (CRL) and attribute certificate revocation list (ACRL).
It also defines several certificates and CRL extensions, and it defines directory schema information allowing PKI and PMI related data to be stored in a directory.
In addition, it defines entity types, such as certification authority (CA), attribute authority (AA), relying party, privilege verifier, trust broker and trust anchor.
It specifies the principles for certificate validation, validation path, certificate policy, etc.
It also includes a specification for authorization validation lists that allow for fast validation and restrictions on communications.
</t>
</abstract>
</front>
</reference>

</references>

<references>
<name>Informative References</name>

<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.1833.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2203.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2818.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6698.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6973.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7258.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7435.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8166.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8167.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
 href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8899.xml"/>

</references>

</references>

<section
 anchor="section_C7FB9DB5-5F4F-45AD-8BF7-74FFCA08BEBB"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>Known Weaknesses of the AUTH_SYS Authentication Flavor</name>
<t>
The ONC RPC protocol, as specified in
<xref target="RFC5531" format="default" sectionFormat="of"/>,
provides several modes of security,
traditionally referred to as "authentication flavors".
Some of these flavors provide much more than an authentication service.
We refer to these as
authentication flavors,
security flavors,
or simply,
flavors.
One of the earliest and most basic flavors is AUTH_SYS,
also known as AUTH_UNIX.
Appendix A of
<xref target="RFC5531" format="default" sectionFormat="of"/>
specifies AUTH_SYS.
</t>
<t>
AUTH_SYS assumes that the RPC client and server
both use POSIX-style user and group identifiers
(each user and group can be distinctly represented
as a 32-bit unsigned integer).
It also assumes that the client and server
both use the same mapping of user and group to an integer.
One user ID, one primary group ID, and up to 16 supplemental group IDs
are associated with each RPC request.
The combination of these identifies the entity on the client
that is making the request.
</t>
<t>
A string identifies peers (hosts) in each RPC request.
<xref target="RFC5531" format="default" sectionFormat="of"/>
does not specify any requirements for this string
other than that is no longer than 255 octets.
It does not have to be the same from request to request.
Also, it does not have to match the DNS hostname of the sending host.
For these reasons,
even though most implementations fill in their hostname in this field,
receivers typically ignore its content.
</t>
<t>
Appendix A of
<xref target="RFC5531" format="default" sectionFormat="of"/>
contains a brief explanation of security considerations:
</t>
<blockquote>
It should be noted that use of this flavor of authentication does not
guarantee any security for the users or providers of a service, in
itself.  The authentication provided by this scheme can be considered
legitimate only when applications using this scheme and the network
can be secured externally, and privileged transport addresses are
used for the communicating end-points (an example of this is the use
of privileged TCP/UDP ports in UNIX systems -- note that not all
systems enforce privileged transport address mechanisms).
</blockquote>
<t>
It should be clear, therefore, that AUTH_SYS by itself
(i.e., without strong client authentication)
offers little to no communication security:
</t>
<ol spacing="normal" type="1">
<li>
It does not protect the confidentiality or integrity of
RPC requests,
users,
or
payloads,
relying instead on "external" security.
</li>
<li>
It does not provide authentication of RPC peer machines,
other than inclusion of an unprotected domain name.
</li>
<li>
The use of 32-bit unsigned integers as user and group identifiers
is problematic because these data types are
not cryptographically signed or otherwise verified by any authority.
In addition, the mapping of these integers to users and groups
has to be consistent amongst a server and its cohort of clients.
</li>
<li>
Because the user and group ID fields are not integrity-protected,
AUTH_SYS does not provide non-repudiation.
</li>
</ol>
</section>

<section
 anchor="section_B08B45C1-1E10-4F7A-935B-1198BAF255C0"
 numbered="true"
 removeInRFC="false"
 toc="default">
<name>ASN.1 Module</name>
<t>
RFC Editor: In the following section,
please replace XXX and YYY with the IANA numbers assigned to these new entries.
And, please remove this Editor's Note
before this document is published.
</t>
<sourcecode name="" type="asn.1" markers="true">
<![CDATA[
RPCwithTLS-2021
  { iso(1) identified-organization(3) dod(6) internet(1)
    security(5) mechanisms(5) pkix(7) id-mod(0)
    id-mod-rpcWithTLS-2021(TBD) }

DEFINITIONS IMPLICIT TAGS ::=
BEGIN

-- OID Arc

id-kp OBJECT IDENTIFIER ::=
  { iso(1) identified-organization(3) dod(6) internet(1)
    security(5) mechanisms(5) pkix(7) kp(3) }

-- Extended Key Usage Values

id-kp-rpcTLSClient OBJECT IDENTIFIER ::= { id-kp XXX }
id-kp-rpcTLSServer OBJECT IDENTIFIER ::= { id-kp YYY }

END
]]>
</sourcecode>
</section>

<section
 anchor="section_4959412F-37AD-42B8-9169-D477148F81A8"
 numbered="false"
 removeInRFC="false"
 toc="default">
<name>Acknowledgments</name>
<t>
Special mention goes to
<contact fullname="Charles Fisher"/>,
author of
<eref target="https://www.linuxjournal.com/content/encrypting-nfsv4-stunnel-tls">
"Encrypting NFSv4 with Stunnel TLS"
</eref>.
His article inspired the mechanism described in the current document.
</t>
<t>
Many thanks to
<contact fullname="Tigran Mkrtchyan"/>
and
<contact fullname="Rick Macklem"/>
for their work on prototype implementations and feedback on the current document.
</t>
<t>
Thanks to
<contact fullname="Derrell Piper"/>
for numerous suggestions that improved both
this simple mechanism
and
the current document's security-related discussion.
</t>
<t>
Many thanks to
Transport Area Director
<contact fullname="Magnus Westerlund"/>
for his sharp questions and careful reading
of the final revisions of the current document.
The text of
<xref target="section_B8BF600E-96DC-4C82-AADF-D593826E9B75" format="default" sectionFormat="of"/>
is mostly his contribution.
Also, thanks to
<contact fullname="Benjamin Kaduk"/>
for his expert guidance on the use of PKIX and TLS.
In addition,
the authors thank the other members of the IESG for
their astute review comments.
These contributors made this a significantly better document.
</t>
<t>
The authors are additionally grateful to
<contact fullname="Bill Baker"/>,
<contact fullname="David Black"/>,
<contact fullname="Alan DeKok"/>,
<contact fullname="Lars Eggert"/>,
<contact fullname="Olga Kornievskaia"/>,
<contact fullname="Greg Marsden"/>,
<contact fullname="Alex McDonald"/>,
<contact fullname="Justin Mazzola Paluska"/>,
<contact fullname="Tom Talpey"/>,
<contact fullname="Martin Thomson"/>,
and
<contact fullname="Nico Williams"/>,
for their input and support of this work.
</t>
<t>
Finally, special thanks to
NFSV4 Working Group Chair and document shepherd
<contact fullname="David Noveck"/>,
NFSV4 Working Group Chairs
<contact fullname="Spencer Shepler"/>
and
<contact fullname="Brian Pawlowski"/>,
and
NFSV4 Working Group Secretary
<contact fullname="Thomas Haynes"/>
for their guidance and oversight.
</t>
</section>

</back>

</rfc>