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Versions: 00

Network Working Group                                        D. Schinazi
Internet-Draft                                                Google LLC
Intended status: Experimental                          February 28, 2019
Expires: September 1, 2019


                          The MASQUE Protocol
                        draft-schinazi-masque-00

Abstract

   This document describes MASQUE (Multiplexed Application Substrate
   over QUIC Encryption).  MASQUE is a mechanism that allows co-locating
   and obfuscating networking applications behind an HTTPS web server.
   The currently prevalent use-case is to allow running a VPN server
   that is indistinguishable from an HTTPS server to any unauthenticated
   observer.  We do not expect major providers and CDNs to deploy this
   behind their main TLS certificate, as they are not willing to take
   the risk of getting blocked, as shown when domain fronting was
   blocked.  An expected use would be for individuals to enable this
   behind their personal websites via easy to configure open-source
   software.

   This document is a straw-man proposal.  It does not contain enough
   details to implement the protocol, and is currently intended to spark
   discussions on the approach it is taking.  As we have not yet found a
   home for this work, discussion is encouraged to happen on the GitHub
   repository which contains the draft:
   https://github.com/DavidSchinazi/masque-drafts [1].

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 1, 2019.





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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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Definitions . . . . . . . . . . . . . . .   3
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Invisibility of VPN Usage . . . . . . . . . . . . . . . .   3
     2.2.  Invisibility of the Server  . . . . . . . . . . . . . . .   3
     2.3.  Fallback to HTTP/2 over TLS over TCP  . . . . . . . . . .   4
   3.  Overview of the Mechanism . . . . . . . . . . . . . . . . . .   4
   4.  Mechanisms the Server Can Advertise to Authenticated Clients    5
     4.1.  HTTP Proxy  . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  DNS over HTTPS  . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  UDP Proxying  . . . . . . . . . . . . . . . . . . . . . .   5
     4.4.  IP Proxying . . . . . . . . . . . . . . . . . . . . . . .   6
     4.5.  Path MTU Discovery  . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
     7.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Design Justifications . . . . . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   This document describes MASQUE (Multiplexed Application Substrate
   over QUIC Encryption).  MASQUE is a mechanism that allows co-locating
   and obfuscating networking applications behind an HTTPS web server.
   The currently prevalent use-case is to allow running a VPN server
   that is indistinguishable from an HTTPS server to any unauthenticated
   observer.  We do not expect major providers and CDNs to deploy this



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   behind their main TLS certificate, as they are not willing to take
   the risk of getting blocked, as shown when domain fronting was
   blocked.  An expected use would be for individuals to enable this
   behind their personal websites via easy to configure open-source
   software.

   This document is a straw-man proposal.  It does not contain enough
   details to implement the protocol, and is currently intended to spark
   discussions on the approach it is taking.  As we have not yet found a
   home for this work, discussion is encouraged to happen on the GitHub
   repository which contains the draft:
   https://github.com/DavidSchinazi/masque-drafts [2].

   MASQUE leverages the efficient head-of-line blocking prevention
   features of the QUIC transport protocol [I-D.ietf-quic-transport]
   when MASQUE is used in an HTTP/3 [I-D.ietf-quic-http] server.  MASQUE
   can also run in an HTTP/2 server [RFC7540] but at a performance cost.

1.1.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "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.

2.  Requirements

   This section describes the goals and requirements chosen for the
   MASQUE protocol.

2.1.  Invisibility of VPN Usage

   An authenticated client using the VPN appears to observers as a
   regular HTTPS client.  Observers only see that HTTP/3 or HTTP/2 is
   being used over an encrypted channel.  No part of the exchanges
   between client and server may stick out.  Note that traffic analysis
   is currently considered out of scope.

2.2.  Invisibility of the Server

   To anyone without private keys, the server is indistinguishable from
   a regular web server.  It is impossible to send an unauthenticated
   probe that the server would reply to differently than if it were a
   normal web server.






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2.3.  Fallback to HTTP/2 over TLS over TCP

   When QUIC is blocked, MASQUE can run over TCP and still satisfy
   previous requirements.  Note that in this scenario performance may be
   negatively impacted.

3.  Overview of the Mechanism

   The server runs an HTTPS server on port 443, and has a valid TLS
   certificate for its domain.  The client has a public/private key
   pair, and the server maintains a list of authorized MASQUE clients,
   and their public key.  (Alternatively, clients can also be
   authenticated using a shared secret.)  The client starts by
   establishing a regular HTTPS connection to the server (HTTP/3 over
   QUIC or HTTP/2 over TLS 1.3 [RFC8446] over TCP), and validates the
   server's TLS certificate as it normally would for HTTPS.  If
   validation fails, the connection is aborted.  The client then uses a
   TLS keying material exporter [RFC5705] with label "EXPORTER-masque"
   and no context to generate a 32-byte key.  This key is then used as a
   nonce to prevent replay attacks.  The client then sends an HTTP
   CONNECT request for "/.well-known/masque/initial" with the :protocol
   pseudo-header field set to "masque", and a "Masque-Authentication:"
   header.  The MASQUE authentication header differs from the HTTP
   "Authorization" header in that it applies to the underlying
   connection instead of being per-request.  It can use either a shared
   secret or asymmetric authentication.  The asymmetric variant uses
   authentication method "PublicKey", and it transmits a signature of
   the nonce with the client's public key encoded in base64 format,
   followed by other information such as the client username and
   signature algorithm OID.  The symmetric variant uses authentication
   method "HMAC" and transmits an HMAC of the nonce with the shared
   secret instead of a signature.  For example this header could look
   like:

  Masque-Authentication: PublicKey u="am9obi5kb2U=";a=1.3.101.112;
  s="SW5zZXJ0IHNpZ25hdHVyZSBvZiBub25jZSBoZXJlIHdo
  aWNoIHRha2VzIDUxMiBiaXRzIGZvciBFZDI1NTE5IQ=="

  Masque-Authentication: HMAC u="am9obi5kb2U=";a=2.16.840.1.101.3.4.2.3;
  s="SW5zZXJ0IHNpZ25hdHVyZSBvZiBub25jZSBoZXJlIHdo
  aWNoIHRha2VzIDUxMiBiaXRzIGZvciBFZDI1NTE5IQ=="

              Figure 1: MASQUE Authentication Format Example

   When the server receives this CONNECT request, it verifies the
   signature and if that fails responds with code "405 Method Not
   Allowed", making sure its response is the same as what it would
   return for any unexpected CONNECT request.  If the signature



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   verifies, the server responds with code "101 Switching Protocols",
   and from then on this HTTP stream is now dedicated to the MASQUE
   protocol.  That protocol provides a reliable bidirectional message
   exchange mechanism, which is used by the client and server to
   negotiate what protocol options are supported and enabled by policy,
   and client VPN configuration such as IP addresses.  When using QUIC,
   this protocol also allows endpoints to negotiate the use of QUIC
   extensions, such as support for the DATAGRAM extension
   [I-D.pauly-quic-datagram].

4.  Mechanisms the Server Can Advertise to Authenticated Clients

   Once a server has authenticated the client's MASQUE CONNECT request,
   it advertises services that the client may use.  These services allow
   for example varying degrees of proxying services to help a client
   obfuscate the ultimate destination of their traffic.

4.1.  HTTP Proxy

   The client can make proxied HTTP requests through the server to other
   servers.  In practice this will mean using the CONNECT method to
   establish a stream over which to run TLS to a different remote
   destination.

4.2.  DNS over HTTPS

   The client can send DNS queries using DNS over HTTPS (DoH) [RFC8484]
   to the MASQUE server.

4.3.  UDP Proxying

   In order to support WebRTC or QUIC to further servers, clients need a
   way to relay UDP onwards to a remote server.  In practice for most
   widely deployed protocols other than DNS, this involves many
   datagrams over the same ports.  Therefore this mechanism implements
   that efficiently: clients can use the MASQUE protocol stream to
   request an UDP association to an IP address and UDP port pair.  In
   QUIC, the server would reply with a DATAGRAM_ID that the client can
   then use to have UDP datagrams sent to this remote server.  Datagrams
   are then simply transferred between the DATAGRAMs with this ID and
   the outer server.  There will also be a message on the MASQUE
   protocol stream to request shutdown of a UDP association to save
   resources when it is no longer needed.  When running over TCP, the
   client opens a new stream with a CONNECT request to the "masque-udp-
   proxy" protocol and then sends datagrams encapsulated inside the
   stream with a two-byte length prefix in network byte order.  The
   target IP and port are sent as part of the URL query.  Resetting that
   stream instructs the server to release any associates resources.



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4.4.  IP Proxying

   For the rare cases where the previous mechanisms are not sufficient,
   proxying can be performed at the IP layer.  This would use a
   different DATAGRAM_ID and IP datagrams would be encoded inside it
   without framing.  Over TCP, a dedicated stream with two byte length
   prefix would be used.  The server can inspect the IP datagram to look
   for the destination address in the IP header.

4.5.  Path MTU Discovery

   In the main deployment of this mechanism, QUIC will be used between
   client and server, and that will most likely be the smallest MTU link
   in the path due to QUIC header and authentication tag overhead.  The
   client is responsible for not sending overly large UDP packets and
   notifying the server of the low MTU.  Therefore PMTUD is currently
   seen as out of scope of this document.

5.  Security Considerations

   Here be dragons.  TODO: slay the dragons.

6.  IANA Considerations

   We will need to register:

   o  the TLS keying material exporter label "EXPORTER-masque" (spec
      required)

   https://www.iana.org/assignments/tls-parameters/tls-
   parameters.xhtml#exporter-labels [3]

   o  the new HTTP header "Masque-Authentication"

   https://www.iana.org/assignments/message-headers/message-
   headers.xhtml [4]

   o  the "/.well-known/masque/" URI (expert review)

   https://www.iana.org/assignments/well-known-uris/well-known-
   uris.xhtml [5]

   o  The "masque" and "masque-udp-proxy" extended HTTP CONNECT
      protocols

   We will also need to define the MASQUE control protocol and that will
   be likely to define new registries of its own.




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7.  References

7.1.  Normative References

   [I-D.ietf-quic-http]
              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", draft-ietf-quic-http-18 (work in progress),
              January 2019.

   [I-D.ietf-quic-transport]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-18 (work
              in progress), January 2019.

   [I-D.pauly-quic-datagram]
              Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
              Datagram Extension to QUIC", draft-pauly-quic-datagram-02
              (work in progress), February 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5705]  Rescorla, E., "Keying Material Exporters for Transport
              Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705,
              March 2010, <https://www.rfc-editor.org/info/rfc5705>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/info/rfc7540>.

   [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,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.







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7.2.  Informative References

   [I-D.ietf-httpbis-http2-secondary-certs]
              Bishop, M., Sullivan, N., and M. Thomson, "Secondary
              Certificate Authentication in HTTP/2", draft-ietf-httpbis-
              http2-secondary-certs-03 (work in progress), October 2018.

   [I-D.pardue-httpbis-http-network-tunnelling]
              Pardue, L., "HTTP-initiated Network Tunnelling (HiNT)",
              draft-pardue-httpbis-http-network-tunnelling-01 (work in
              progress), October 2018.

   [I-D.schwartz-httpbis-helium]
              Schwartz, B., "Hybrid Encapsulation Layer for IP and UDP
              Messages (HELIUM)", draft-schwartz-httpbis-helium-00 (work
              in progress), June 2018.

   [I-D.sullivan-tls-post-handshake-auth]
              Sullivan, N., Thomson, M., and M. Bishop, "Post-Handshake
              Authentication in TLS", draft-sullivan-tls-post-handshake-
              auth-00 (work in progress), August 2016.

   [RFC7427]  Kivinen, T. and J. Snyder, "Signature Authentication in
              the Internet Key Exchange Version 2 (IKEv2)", RFC 7427,
              DOI 10.17487/RFC7427, January 2015,
              <https://www.rfc-editor.org/info/rfc7427>.

   [RFC8441]  McManus, P., "Bootstrapping WebSockets with HTTP/2",
              RFC 8441, DOI 10.17487/RFC8441, September 2018,
              <https://www.rfc-editor.org/info/rfc8441>.

   [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,
              <https://www.rfc-editor.org/info/rfc8471>.

7.3.  URIs

   [1] https://github.com/DavidSchinazi/masque-drafts

   [2] https://github.com/DavidSchinazi/masque-drafts

   [3] https://www.iana.org/assignments/tls-parameters/tls-
       parameters.xhtml#exporter-labels

   [4] https://www.iana.org/assignments/message-headers/message-
       headers.xhtml




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   [5] https://www.iana.org/assignments/well-known-uris/well-known-
       uris.xhtml

Acknowledgments

   This proposal was inspired directly or indirectly by prior work from
   many people.  In particular, this work is related to
   [I-D.schwartz-httpbis-helium] and
   [I-D.pardue-httpbis-http-network-tunnelling].  The mechanism used to
   run the MASQUE protocol over HTTP/2 streams was inspired by
   [RFC8441].  Using the OID for the signature algorithm was inspired by
   Signature Authentication in IKEv2 [RFC7427].

   The author would like to thank Christophe A., an inspiration and true
   leader of VPNs.

Design Justifications

   Using an exported key as a nonce allows us to prevent replay attacks
   (since it depends on randomness from both endpoints of the TLS
   connection) without requiring the server to send an explicit nonce
   before it has authenticated the client.  Adding an explicit nonce
   mechanism would expose the server as it would need to send these
   nonces to clients that have not been authenticated yet.

   The rationale for a separate MASQUE protocol stream is to allow
   server-initiated messages.  If we were to use HTTP semantics, we
   would only be able to support the client-initiated request-response
   model.  We could have used WebSocket for this purpose but that would
   have added wire overhead and dependencies without providing useful
   features.

   There are many other ways to authenticate HTTP, however the
   authentication used here needs to work in a single client-initiated
   message to meet the requirement of not exposing the server.

   The current proposal would also work with TLS 1.2, but in that case
   TLS false start and renegotiation must be disabled, and the extended
   master secret and renegotiation indication TLS extensions must be
   enabled.

   If the server or client want to hide that HTTP/2 is used, the client
   can set its ALPN to an older version of HTTP and then use the Upgrade
   header to upgrade to HTTP/2 inside the TLS encryption.

   The client authentication used here is similar to how Token Binding
   [RFC8471] operates, but it has very different goals.  MASQUE does not
   use token binding directly because using token binding requires



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   sending the token_binding TLS extension in the TLS ClientHello, and
   that would stick out compared to a regular TLS connection.

   TLS post-handshake authentication
   [I-D.sullivan-tls-post-handshake-auth] is not used by this proposal
   because that requires sending the "post_handshake_auth" extension in
   the TLS ClientHello, and that would stick out from a regular HTTPS
   connection.

   Client authentication could have benefited from Secondary Certificate
   Authentication in HTTP/2 [I-D.ietf-httpbis-http2-secondary-certs],
   however that has two downsides: it requires the server advertising
   that it supports it in its SETTINGS, and it cannot be sent unprompted
   by the client, so the server would have to request authentication.
   Both of these would make the server stick out from regular HTTP/2
   servers.

   MASQUE proposes a new client authentication method (as opposed to
   reusing something like HTTP basic authentication) because HTTP
   authentication methods are conceptually per-request (they need to be
   repeated on each request) whereas the new method is bound to the
   underlying connection (be it QUIC or TLS).  In particular, this
   allows sending QUIC DATAGRAM frames without authenticating every
   frame individually.  Additionally, HMAC and asymmetric keying are
   preferred to sending a password for client authentication since they
   have a tighter security bound.  Going into the design rationale,
   HMACs (and signatures) need some data to sign, and to avoid replay
   attacks that should be a fresh nonce provided by the remote peer.
   Having the server provide an explicit nonce would leak the existence
   of the server so we use TLS keying material exporters as they provide
   us with a nonce that contains entropy from the server without
   requiring explicit communication.

Author's Address

   David Schinazi
   Google LLC
   1600 Amphitheatre Parkway
   Mountain View, California 94043
   United States of America

   Email: dschinazi.ietf@gmail.com









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