taps                                                             M. Duke
Internet-Draft                                         F5 Networks, Inc.
Intended status: Informational                              9 April 2021
Expires: 11 October 2021

                        TAPS Transport Discovery


   The Transport Services architecture decouples applications from the
   protocol implementations that transport their data.  While it is
   often straightforward to connect applications with transports that
   are present in the host operating system, providing a means of
   discovering user-installed implementations dramatically enlarges the
   use cases.  This document discusses considerations for the design of
   a discovery mechanism and an example of such a design.

   Discussion of this work is encouraged to happen on the TAPS IETF
   mailing list taps@ietf.org or on the GitHub repository which contains
   the draft: https://github.com/martinduke/draft-duke-taps-transport-

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
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   This Internet-Draft will expire on 11 October 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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 carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must 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
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Entities  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Protocol Implementation . . . . . . . . . . . . . . . . . . .   4
   5.  Protocol Installer  . . . . . . . . . . . . . . . . . . . . .   4
   6.  TAPS  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Informative References  . . . . . . . . . . . . . . . . . . .   6
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The Transport Services architecture [I-D.ietf-taps-arch] enables
   applications to be protocol-agnostic by presenting an interface where
   applications can specify their required properties, and the service
   will select whichever protocol implementation available in the system
   best meets those requirements.  This increases application
   portability and eases the introduction of new transport innovations
   by not requiring changes to applications.

   It is sometimes straightforward for a Transport Services interface to
   identify the transports available in the host operating system.
   However, including transports installed by the user greatly expands
   use cases for the architecture.  This document presents
   considerations for the secure design of a system for discovery of new
   protocol implementations.

   Protocol Discovery would ideally have several desirable properties.

   *  The transport services API should not have to recompile when
      installing new implementations.  This would not only disrupt
      ongoing connections, but also involve ordinary users in the
      complex business of downloading and building source code.

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   *  It should support user-space implementations.  Most protocol
      innovation begins with user space implementations, and many
      transports (e.g.  TLS, HTTP, QUIC) are usually implemented outside
      the kernel long after reaching maturity.

   *  Protocol Discovery should not subject ordinary users to security
      vulnerabilities.  A new protocol installation is an opportunity to
      hijack a user's networking stack, and Protocol Discovery requires
      strong protections against arbitrary code performing operations
      other than advertised on application data.

   *  Conversely, sophisticated users need a means of discovering
      implementations that are too new to have fully developed internet
      trust mechanisms.  This is the only means of initially deploying
      new protocols for existing apps, and is the most plausible model
      to deploy transport services API shims for existing protocol
      libraries (e.g., the common TLS implementations) before their
      proponents deploy native support.

   *  Applications should not have to bring their own implementations.
      The Transport Services API has the concept of "framers" (see Sec.
      7.1 of [I-D.ietf-taps-interface]) that provide some ability for
      applications to provide additional protocol encapsulation around
      their messages.  However, one important advantage of Transport
      Services is that applications do not have to rely on a third-party
      implementation that might not offer long term support, or add to
      their footprint where a functionally equivalent protocol
      implementation is already present on the system.

   This document attempts to resolve the tension between some of these

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   "TAPS" is an abbreviation for the transport services API.

   For brevity, this document will use "app" as a shorthand for

   As in other TAPS documents, the concept of a "transport protocol" is
   expanded beyond the traditional "transport layer" to include other
   protocols that encapsulate application data, such as TLS, HTTP, and

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3.  Entities

   The Transport Services API (TAPS) is responsible for matching
   protocol capabilities with application requirements, and mediating
   further app communication with the selected protocol implementation.
   In this document, it actively discovers what implementations are
   available in the system.

   The protocol implementation instantiates the transport.  In this
   document, it offers a dynamically linked library that conforms to
   standard interfaces so that TAPS can interchangeability interact with
   it.  In practice, this may be a shim layer if the underlying
   implementation does not support TAPS.

   The protocol installer, aside from installing the implementation
   library and/or a TAPS shim layer, also is responsible for notifying
   TAPS that the implementation is present, and what its capabilities

   Finally, the application leverages TAPS to initiate, manage, and
   terminate communications with other endpoints.  This document does
   not require any changes to application behavior beyond those in the
   core TAPS design.

   More detailed requirements for each of these entities is below.

4.  Protocol Implementation

   The protocol implementation must offer a dynamically linked library
   that offers certain APIs.

   These APIs are TBD.

5.  Protocol Installer

   The installer might use the operating system's package manager or
   "app store", or be a simple script.  Besides installing the
   implementation, the installer also writes data to a registry that
   TAPS will access to discover the implementation.

   This data will include:

   *  the name of the supported protocol(s);

   *  optionally, the versions of those protocols;

   *  the path to the implementations TAPS-compliant library;

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   *  the properties that the protocol implementation supports, as
      described in Section 4.2 of [I-D.ietf-taps-interface]; and

   *  information to authenticate the entry (see Section 7).

   Of course, a de-installer should remove the appropriate registry

6.  TAPS

   TAPS creates a registry for protocol implementations, which might be
   a database or a directory.  To prevent inadvertent security
   vulnerabilities, the host system SHOULD, at minimum, require
   administrative privileges to write to the registry.

   No later than upon receipt of request for a Preconnection, TAPS MUST
   access the registry to determine the available protocols and their
   properties.  It is perfectly valid for there to be multiple
   implementations of a protocol.

   TAPS SHOULD validate entries in the registry using the provided
   authentication data.

7.  Security Considerations

   User-space installation of protocols provides enormous opportunities
   for attackers to hijack a network stack.  While this has always been
   possible with arbitrary protocol implementations, with TAPS
   applications completely unaware of the installation can be victims of
   such an attack.

   An implementation might advertise properties it does not actually
   provide to attract more traffic.  For example, a "TLS" implementation
   might not encrypt anything at all.

   Moreover, in principle an implementation could deliver application
   data anywhere it wanted with little visibility to the application,
   much less the user.

   The origin of the protocol installer is important to the trust model.
   Obviously, transports in the kernel do not introduce vulnerabilities
   specific to TAPS.  A trusted package manager (e.g. the Apple App
   Store or yum) may imply a minimal level of veracity of the available
   packages.  Protocol implementations directly downloaded from the
   internet without mediation throught these mechanisms require the
   greatest care.

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   Ongoing work on this document will largely focus on building
   mechanisms to mitigate this weakness.  Some promising approaches

   *  administrative privileges to alter the TAPS registry;

   *  a special certificate authority that provides an authentication of
      the implementation's explicit and implicit claims, as well as the
      integrity of the installed binary;

   *  each installer generates a private key and provides the
      corresponding public key, so that only possessors of the private
      key can modify or delete the registry entry;

   *  confirmation by a human, prominently warned of potential
      consequences, if the installation is not mediated through a
      trusted authority.

8.  IANA Considerations

   This document has no IANA requirements.

9.  Informative References

              Pauly, T., Trammell, B., Brunstrom, A., Fairhurst, G.,
              Perkins, C., Tiesel, P., and C. Wood, "An Architecture for
              Transport Services", Work in Progress, Internet-Draft,
              draft-ietf-taps-arch-09, 2 November 2020,

              Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G.,
              Kuehlewind, M., Perkins, C., Tiesel, P., Wood, C., and T.
              Pauly, "An Abstract Application Layer Interface to
              Transport Services", Work in Progress, Internet-Draft,
              draft-ietf-taps-interface-10, 2 November 2020,

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

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Appendix A.  Acknowledgments

   Tim Worsley contributed important ideas to this document.

Author's Address

   Martin Duke
   F5 Networks, Inc.

   Email: martin.h.duke@gmail.com

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