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Network Working Group                                        T. Enghardt
Internet-Draft                                                 TU Berlin
Intended status: Informational                                  T. Pauly
Expires: May 21, 2020                                         Apple Inc.
                                                              C. Perkins
                                                   University of Glasgow
                                                                 K. Rose
                                               Akamai Technologies, Inc.
                                                            C. Wood, Ed.
                                                              Apple Inc.
                                                       November 18, 2019


  A Survey of the Interaction Between Security Protocols and Transport
                                Services
                 draft-ietf-taps-transport-security-10

Abstract

   This document provides a survey of commonly used or notable network
   security protocols, with a focus on how they interact and integrate
   with applications and transport protocols.  Its goal is to supplement
   efforts to define and catalog transport services by describing the
   interfaces required to add security protocols.  This survey is not
   limited to protocols developed within the scope or context of the
   IETF, and those included represent a superset of features a Transport
   Services system may need to support.

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 May 21, 2020.







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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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Non-Goals . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Transport Security Protocol Descriptions  . . . . . . . . . .   6
     3.1.  Application Payload Security Protocols  . . . . . . . . .   6
       3.1.1.  TLS . . . . . . . . . . . . . . . . . . . . . . . . .   6
       3.1.2.  DTLS  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Application-Specific Security Protocols . . . . . . . . .   6
       3.2.1.  Secure RTP  . . . . . . . . . . . . . . . . . . . . .   6
       3.2.2.  ZRTP for Media Path Key Agreement . . . . . . . . . .   7
     3.3.  Transport-Layer Security Protocols  . . . . . . . . . . .   7
       3.3.1.  QUIC with TLS . . . . . . . . . . . . . . . . . . . .   7
       3.3.2.  Google QUIC . . . . . . . . . . . . . . . . . . . . .   7
       3.3.3.  tcpcrypt  . . . . . . . . . . . . . . . . . . . . . .   7
       3.3.4.  MinimalT  . . . . . . . . . . . . . . . . . . . . . .   7
       3.3.5.  CurveCP . . . . . . . . . . . . . . . . . . . . . . .   8
     3.4.  Packet Security Protocols . . . . . . . . . . . . . . . .   8
       3.4.1.  IKEv2 with ESP  . . . . . . . . . . . . . . . . . . .   8
       3.4.2.  WireGuard . . . . . . . . . . . . . . . . . . . . . .   8
       3.4.3.  OpenVPN . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Transport Dependencies  . . . . . . . . . . . . . . . . . . .   9
     4.1.  Reliable Byte-Stream Transports . . . . . . . . . . . . .   9
     4.2.  Unreliable Datagram Transports  . . . . . . . . . . . . .   9
       4.2.1.  Datagram Protocols with Defined Byte-Stream Mappings   10
     4.3.  Transport-Specific Dependencies . . . . . . . . . . . . .  10
   5.  Application Interface . . . . . . . . . . . . . . . . . . . .  10
     5.1.  Pre-Connection Interfaces . . . . . . . . . . . . . . . .  11
     5.2.  Connection Interfaces . . . . . . . . . . . . . . . . . .  13
     5.3.  Post-Connection Interfaces  . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15



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   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  15
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   10. Informative References  . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   Services and features provided by transport protocols have been
   cataloged in [RFC8095].  This document supplements that work by
   surveying commonly used and notable network security protocols, and
   identifying the services and features a Transport Services system (a
   system that provides a transport API) needs to provide in order to
   add transport security.  It examines Transport Layer Security (TLS),
   Datagram Transport Layer Security (DTLS), QUIC + TLS, tcpcrypt,
   Internet Key Exchange with Encapsulating Security Protocol (IKEv2 +
   ESP), SRTP (with DTLS), WireGuard, CurveCP, and MinimalT.  For each
   protocol, this document provides a brief description, the
   dependencies it has on the underlying transports, and the interfaces
   provided to applications.

   Selected protocols represent a superset of functionality and features
   a Transport Services system may need to support, both internally and
   externally (via an API) for applications [I-D.ietf-taps-arch].
   Ubiquitous IETF protocols such as (D)TLS, as well as non-standard
   protocols such as Google QUIC, are both included despite overlapping
   features.  As such, this survey is not limited to protocols developed
   within the scope or context of the IETF.  Outside of this candidate
   set, protocols that do not offer new features are omitted.  For
   example, newer protocols such as WireGuard make unique design choices
   that have implications and limitations on application usage.  In
   contrast, protocols such as ALTS [ALTS] are omitted since they do not
   provide interfaces deemed unique.

   Authentication-only protocols such as TCP-AO [RFC5925] and IPsec AH
   [RFC4302] are excluded from this survey.  TCP-AO adds authenticity
   protections to long-lived TCP connections, e.g., replay protection
   with per-packet Message Authentication Codes.  (This protocol
   obsoletes TCP MD5 "signature" options specified in [RFC2385].)  One
   prime use case of TCP-AO is for protecting BGP connections.
   Similarly, AH adds per-datagram authenticity and adds similar replay
   protection.  Despite these improvements, neither protocol sees
   general use and both lack critical properties important for emergent
   transport security protocols: confidentiality, privacy protections,
   and agility.  Such protocols are thus omitted from this survey.






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1.1.  Goals

   This survey is intended to help identify the most common interface
   surfaces between security protocols and transport protocols, and
   between security protocols and applications.

   One of the goals of Transport Services is to define a common
   interface for using transport protocols that allows software using
   transport protocols to easily adopt new protocols that provide
   similar feature-sets.  The survey of the dependencies security
   protocols have upon transport protocols can guide implementations in
   determining which transport protocols are appropriate to be able to
   use beneath a given security protocol.  For example, a security
   protocol that expects to run over a reliable stream of bytes, like
   TLS, restrict the set of transport protocols that can be used to
   those that offer a reliable stream of bytes.

   Defining the common interfaces that security protocols provide to
   applications also allows interfaces to be designed in a way that
   common functionality can use the same APIs.  For example, many
   security protocols that provide authentication let the application be
   involved in peer identity validation.  Any interface to use a secure
   transport protocol stack thus needs to allow applications to perform
   this action during connection establishment.

1.2.  Non-Goals

   While this survey provides similar analysis to that which was
   performed for transport protocols in [RFC8095], it is important to
   distinguish that the use of security protocols requires more
   consideration.

   It is not a goal to allow software implementations to automatically
   switch between different security protocols, even where their
   interfaces to transport and applications are equivalent.  Even
   between versions, security protocols have subtly different guarantees
   and vulnerabilities.  Thus, any implementation needs to only use the
   set of protocols and algorithms that are requested by applications or
   by a system policy.

2.  Terminology

   The following terms are used throughout this document to describe the
   roles and interactions of transport security protocols:

   o  Transport Feature: a specific end-to-end feature that the
      transport layer provides to an application.  Examples include




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      confidentiality, reliable delivery, ordered delivery, message-
      versus-stream orientation, etc.

   o  Transport Service: a set of Transport Features, without an
      association to any given framing protocol, which provides
      functionality to an application.

   o  Transport Protocol: an implementation that provides one or more
      different transport services using a specific framing and header
      format on the wire.  A Transport Protocol services an application.

   o  Application: an entity that uses a transport protocol for end-to-
      end delivery of data across the network.  This may also be an
      upper layer protocol or tunnel encapsulation.

   o  Security Protocol: a defined network protocol that implements one
      or more security features, such as authentication, encryption, key
      generation, session resumption, and privacy.  Security protocols
      may be used alongside transport protocols, and in combination with
      other security protocols when appropriate.

   o  Handshake Protocol: a protocol that enables peers to validate each
      other and to securely establish shared cryptographic context.

   o  Record: Framed protocol messages.

   o  Record Protocol: a security protocol that allows data to be
      divided into manageable blocks and protected using shared
      cryptographic context.

   o  Session: an ephemeral security association between applications.

   o  Connection: the shared state of two or more endpoints that
      persists across messages that are transmitted between these
      endpoints.  A connection is a transient participant of a session,
      and a session generally lasts between connection instances.

   o  Peer: an endpoint application party to a session.

   o  Client: the peer responsible for initiating a session.

   o  Server: the peer responsible for responding to a session
      initiation.








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3.  Transport Security Protocol Descriptions

   This section contains brief descriptions of the various security
   protocols currently used to protect data being sent over a network.
   The interfaces between these protocols and transports are described
   in Section 4; the interfaces between these protocols and applications
   are described in Section 5.

3.1.  Application Payload Security Protocols

   The following protocols provide security that protects application
   payloads sent over a transport.  They do not specifically protect any
   headers used for transport-layer functionality.

3.1.1.  TLS

   TLS (Transport Layer Security) [RFC8446] is a common protocol used to
   establish a secure session between two endpoints.  Communication over
   this session "prevents eavesdropping, tampering, and message
   forgery."  TLS consists of a tightly coupled handshake and record
   protocol.  The handshake protocol is used to authenticate peers,
   negotiate protocol options, such as cryptographic algorithms, and
   derive session-specific keying material.  The record protocol is used
   to marshal (possibly encrypted) data from one peer to the other.
   This data may contain handshake messages or raw application data.

3.1.2.  DTLS

   DTLS (Datagram Transport Layer Security) [RFC6347] is based on TLS,
   but differs in that it is designed to run over unreliable datagram
   protocols like UDP instead of TCP.  DTLS modifies the protocol to
   make sure it can still provide the same security guarantees as TLS
   even without reliability from the transport.  DTLS was designed to be
   as similar to TLS as possible, so this document assumes that all
   properties from TLS are carried over except where specified.

3.2.  Application-Specific Security Protocols

   The following protocols provide application-specific security by
   protecting application payloads used for specific use-cases.  Unlike
   the protocols above, these are not intended for generic application
   use.

3.2.1.  Secure RTP

   Secure RTP (SRTP) is a profile for RTP that provides confidentiality,
   message authentication, and replay protection for RTP data packets
   and RTP control protocol (RTCP) packets [RFC3711].



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3.2.2.  ZRTP for Media Path Key Agreement

   ZRTP [RFC6189] is an alternative key agreement protocol for SRTP.  It
   uses standard SRTP to protect RTP data packets and RTCP packets, but
   provides alternative key agreement and identity management protocols.
   Key agreement is performed using a Diffie-Hellman key exchange that
   runs on the media path.  This generates a shared secret that is then
   used to generate the master key and salt for SRTP.

3.3.  Transport-Layer Security Protocols

   The following security protocols provide protection for both
   application payloads and headers that are used for transport
   services.

3.3.1.  QUIC with TLS

   QUIC is a new standards-track transport protocol that runs over UDP,
   loosely based on Google's original proprietary gQUIC protocol
   [I-D.ietf-quic-transport] (See Section 3.3.2 for more details).  The
   QUIC transport layer itself provides support for data confidentiality
   and integrity.  This requires keys to be derived with a separate
   handshake protocol.  A mapping for QUIC of TLS 1.3
   [I-D.ietf-quic-tls] has been specified to provide this handshake.

3.3.2.  Google QUIC

   Google QUIC (gQUIC) is a UDP-based multiplexed streaming protocol
   designed and deployed by Google following experience from deploying
   SPDY, the proprietary predecessor to HTTP/2.  gQUIC was originally
   known as "QUIC": this document uses gQUIC to unambiguously
   distinguish it from the standards-track IETF QUIC.  The proprietary
   technical forebear of IETF QUIC, gQUIC was originally designed with
   tightly-integrated security and application data transport protocols.

3.3.3.  tcpcrypt

   Tcpcrypt [RFC8548] is a lightweight extension to the TCP protocol for
   opportunistic encryption.  Applications may use tcpcrypt's unique
   session ID for further application-level authentication.  Absent this
   authentication, tcpcrypt is vulnerable to active attacks.

3.3.4.  MinimalT

   MinimalT is a UDP-based transport security protocol designed to offer
   confidentiality, mutual authentication, DoS prevention, and
   connection mobility [MinimalT].  One major goal of the protocol is to
   leverage existing protocols to obtain server-side configuration



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   information used to more quickly bootstrap a connection.  MinimalT
   uses a variant of TCP's congestion control algorithm.

3.3.5.  CurveCP

   CurveCP [CurveCP] is a UDP-based transport security protocol from
   Daniel J.  Bernstein.  Unlike other security protocols, it is based
   entirely upon highly efficient public key algorithms.  This removes
   many pitfalls associated with nonce reuse and key synchronization.
   CurveCP provides its own reliability for application data as part of
   its protocol.

3.4.  Packet Security Protocols

   The following protocols provide protection for IP packets.  These are
   generally used as tunnels, such as for Virtual Private Networks
   (VPNs).  Often, applications will not interact directly with these
   protocols.  However, applications that implement tunnels will
   interact directly with these protocols.

3.4.1.  IKEv2 with ESP

   IKEv2 [RFC7296] and ESP [RFC4303] together form the modern IPsec
   protocol suite that encrypts and authenticates IP packets, either for
   creating tunnels (tunnel-mode) or for direct transport connections
   (transport-mode).  This suite of protocols separates out the key
   generation protocol (IKEv2) from the transport encryption protocol
   (ESP).  Each protocol can be used independently, but this document
   considers them together, since that is the most common pattern.

3.4.2.  WireGuard

   WireGuard is an IP-layer protocol designed as an alternative to IPsec
   [WireGuard] for certain use cases.  It uses UDP to encapsulate IP
   datagrams between peers.  Unlike most transport security protocols,
   which rely on PKI for peer authentication, WireGuard authenticates
   peers using pre-shared public keys delivered out-of-band, each of
   which is bound to one or more IP addresses.  Moreover, as a protocol
   suited for VPNs, WireGuard offers no extensibility, negotiation, or
   cryptographic agility.

3.4.3.  OpenVPN

   OpenVPN [OpenVPN] is a commonly used protocol designed as an
   alternative to IPsec.  A major goal of this protocol is to provide a
   VPN that is simple to configure and works over a variety of
   transports.  OpenVPN encapsulates either IP packets or Ethernet
   frames within a secure tunnel and can run over UDP or TCP.



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4.  Transport Dependencies

   Across the different security protocols listed above, the primary
   dependency on transport protocols is the presentation of data: either
   an unbounded stream of bytes, or framed messages.  Within protocols
   that rely on the transport for message framing, most are built to run
   over transports that inherently provide framing, like UDP, but some
   also define how their messages can be framed over byte-stream
   transports.

4.1.  Reliable Byte-Stream Transports

   The following protocols all depend upon running on a transport
   protocol that provides a reliable, in-order stream of bytes.  This is
   typically TCP.

   Application Payload Security Protocols:

   o  TLS

   Transport-Layer Security Protocols:

   o  tcpcrypt

   Packet Security Protocols:

   o  OpenVPN

4.2.  Unreliable Datagram Transports

   The following protocols all depend on the transport protocol to
   provide message framing to encapsulate their data.  These protocols
   are built to run using UDP, and thus do not have any requirement for
   reliability.  Running these protocols over a protocol that does
   provide reliability will not break functionality, but may lead to
   multiple layers of reliability if the security protocol is
   encapsulating other transport protocol traffic.

   Application Payload Security Protocols:

   o  DTLS

   o  SRTP

   o  ZRTP

   Transport-Layer Security Protocols:




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   o  QUIC

   o  MinimalT

   o  CurveCP

   Packet Security Protocols:

   o  IKEv2 and ESP

   o  WireGuard

4.2.1.  Datagram Protocols with Defined Byte-Stream Mappings

   Of the protocols listed above that depend on the transport for
   message framing, some do have well-defined mappings for sending their
   messages over byte-stream transports like TCP.

   Application Payload Security Protocols:

   o  SRTP [RFC7201]

   Packet Security Protocols:

   o  IKEv2 and ESP [RFC8229]

4.3.  Transport-Specific Dependencies

   One protocol surveyed, tcpcrypt, has an direct dependency on a
   feature in the transport that is needed for its functionality.
   Specific, tcpcrypt is designed to run on top of TCP, and uses the TCP
   Encryption Negotiation Option (ENO) [RFC8547] to negotiate its
   protocol support.

   QUIC, CurveCP, and MinimalT provide both transport functionality and
   security functionality.  They have a dependencies on running over a
   framed protocol like UDP, but they add their own layers of
   reliability and other transport services.  Thus, an application that
   uses one of these protocols cannot decouple the security from
   transport functionality.

5.  Application Interface

   This section describes the interface surface exposed by the security
   protocols described above.  Note that not all protocols support each
   interface.  We partition these interfaces into pre-connection
   (configuration), connection, and post-connection interfaces,




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   following conventions in [I-D.ietf-taps-interface] and
   [I-D.ietf-taps-arch].

5.1.  Pre-Connection Interfaces

   Configuration interfaces are used to configure the security protocols
   before a handshake begins or the keys are negotiated.

   o  Identities and Private Keys: The application can provide its
      identities (certificates) and private keys, or mechanisms to
      access these, to the security protocol to use during handshakes.

      *  TLS

      *  DTLS

      *  SRTP

      *  QUIC

      *  MinimalT

      *  CurveCP

      *  IKEv2

      *  WireGuard

   o  Supported Algorithms (Key Exchange, Signatures, and Ciphersuites):
      The application can choose the algorithms that are supported for
      key exchange, signatures, and ciphersuites.

      *  TLS

      *  DTLS

      *  SRTP

      *  QUIC

      *  tcpcrypt

      *  MinimalT

      *  IKEv2






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   o  Extensions (Application-Layer Protocol Negotiation): The
      application enables or configures extensions that are to be
      negotiated by the security protocol, such as ALPN [RFC7301].

      *  TLS

      *  DTLS

      *  QUIC

   o  Session Cache Management: The application provides the ability to
      save and retrieve session state (such as tickets, keying material,
      and server parameters) that may be used to resume the security
      session.

      *  TLS

      *  DTLS

      *  QUIC

      *  MinimalT

   o  Authentication Delegation: The application provides access to a
      separate module that will provide authentication, using EAP for
      example.

      *  SRTP

      *  IKEv2

   o  Pre-Shared Key Import: Either the handshake protocol or the
      application directly can supply pre-shared keys for the record
      protocol use for encryption/decryption and authentication.  If the
      application can supply keys directly, this is considered explicit
      import; if the handshake protocol traditionally provides the keys
      directly, it is considered direct import; if the keys can only be
      shared by the handshake, they are considered non-importable.

      *  Explicit import: QUIC, ESP

      *  Direct import: TLS, DTLS, tcpcrypt, MinimalT, WireGuard

      *  Non-importable: CurveCP







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5.2.  Connection Interfaces

   o  Identity Validation: During a handshake, the security protocol
      will conduct identity validation of the peer.  This can call into
      the application to offload validation.

      *  TLS

      *  DTLS

      *  SRTP

      *  QUIC

      *  MinimalT

      *  CurveCP

      *  IKEv2

      *  WireGuard

      *  OpenVPN

   o  Source Address Validation: The handshake protocol may delegate
      validation of the remote peer that has sent data to the transport
      protocol or application.  This involves sending a cookie exchange
      to avoid DoS attacks.  Protocols: QUIC + TLS, DTLS, WireGuard

      *  DTLS

      *  QUIC

      *  WireGuard

5.3.  Post-Connection Interfaces

   o  Connection Termination: The security protocol may be instructed to
      tear down its connection and session information.  This is needed
      by some protocols to prevent application data truncation attacks.

      *  TLS

      *  DTLS

      *  QUIC

      *  tcpcrypt



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      *  MinimalT

      *  IKEv2

   o  Key Update: The handshake protocol may be instructed to update its
      keying material, either by the application directly or by the
      record protocol sending a key expiration event.

      *  TLS

      *  DTLS

      *  QUIC

      *  tcpcrypt

      *  MinimalT

      *  IKEv2

   o  Pre-Shared Key Export: The handshake protocol will generate one or
      more keys to be used for record encryption/decryption and
      authentication.  These may be explicitly exportable to the
      application, traditionally limited to direct export to the record
      protocol, or inherently non-exportable because the keys must be
      used directly in conjunction with the record protocol.

      *  Explicit export: TLS (for QUIC), DTLS (for SRTP), tcpcrypt,
         IKEv2

      *  Direct export: TLS, DTLS, MinimalT

      *  Non-exportable: CurveCP

   o  Key Expiration: The record protocol can signal that its keys are
      expiring due to reaching a time-based deadline, or a use-based
      deadline (number of bytes that have been encrypted with the key).
      This interaction is often limited to signaling between the record
      layer and the handshake layer.

      *  ESP

   o  Mobility Events: The record protocol can be signaled that it is
      being migrated to another transport or interface due to connection
      mobility, which may reset address and state validation and induce
      state changes such as use of a new Connection Identifier (CID).

      *  QUIC



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      *  MinimalT

      *  CurveCP

      *  ESP

      *  WireGuard

6.  IANA Considerations

   This document has no request to IANA.

7.  Security Considerations

   This document summarizes existing transport security protocols and
   their interfaces.  It does not propose changes to or recommend usage
   of reference protocols.  Moreover, no claims of security and privacy
   properties beyond those guaranteed by the protocols discussed are
   made.  For example, metadata leakage via timing side channels and
   traffic analysis may compromise any protocol discussed in this
   survey.  Applications using Security Interfaces should take such
   limitations into consideration when using a particular protocol
   implementation.

8.  Privacy Considerations

   Analysis of how features improve or degrade privacy is intentionally
   omitted from this survey.  All security protocols surveyed generally
   improve privacy by reducing information leakage via encryption.
   However, varying amounts of metadata remain in the clear across each
   protocol.  For example, client and server certificates are sent in
   cleartext in TLS 1.2 [RFC5246], whereas they are encrypted in TLS 1.3
   [RFC8446].  A survey of privacy features, or lack thereof, for
   various security protocols could be addressed in a separate document.

9.  Acknowledgments

   The authors would like to thank Bob Bradley, Frederic Jacobs, Mirja
   Kuehlewind, Yannick Sierra, Brian Trammell, and Magnus Westerlund for
   their input and feedback on this draft.

10.  Informative References

   [ALTS]     Ghali, C., Stubblefield, A., Knapp, E., Li, J., Schmidt,
              B., and J. Boeuf, "Application Layer Transport Security",
              <https://cloud.google.com/security/encryption-in-transit/
              application-layer-transport-security/>.




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   [CurveCP]  Bernstein, D., "CurveCP -- Usable security for the
              Internet", <http://curvecp.org>.

   [I-D.ietf-quic-tls]
              Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
              draft-ietf-quic-tls-23 (work in progress), September 2019.

   [I-D.ietf-quic-transport]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-23 (work
              in progress), September 2019.

   [I-D.ietf-taps-arch]
              Pauly, T., Trammell, B., Brunstrom, A., Fairhurst, G.,
              Perkins, C., Tiesel, P., and C. Wood, "An Architecture for
              Transport Services", draft-ietf-taps-arch-04 (work in
              progress), July 2019.

   [I-D.ietf-taps-interface]
              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", draft-ietf-taps-interface-04 (work in
              progress), July 2019.

   [MinimalT]
              Petullo, W., Zhang, X., Solworth, J., Bernstein, D., and
              T. Lange, "MinimaLT -- Minimal-latency Networking Through
              Better Security",
              <http://dl.acm.org/citation.cfm?id=2516737>.

   [OpenVPN]  "OpenVPN cryptographic layer", <https://openvpn.net/
              community-resources/openvpn-cryptographic-layer/>.

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
              1998, <https://www.rfc-editor.org/info/rfc2385>.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, DOI 10.17487/RFC3711, March 2004,
              <https://www.rfc-editor.org/info/rfc3711>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,
              <https://www.rfc-editor.org/info/rfc4302>.





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   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC6189]  Zimmermann, P., Johnston, A., Ed., and J. Callas, "ZRTP:
              Media Path Key Agreement for Unicast Secure RTP",
              RFC 6189, DOI 10.17487/RFC6189, April 2011,
              <https://www.rfc-editor.org/info/rfc6189>.

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

   [RFC7201]  Westerlund, M. and C. Perkins, "Options for Securing RTP
              Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014,
              <https://www.rfc-editor.org/info/rfc7201>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <https://www.rfc-editor.org/info/rfc7296>.

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

   [RFC8095]  Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind,
              Ed., "Services Provided by IETF Transport Protocols and
              Congestion Control Mechanisms", RFC 8095,
              DOI 10.17487/RFC8095, March 2017,
              <https://www.rfc-editor.org/info/rfc8095>.

   [RFC8229]  Pauly, T., Touati, S., and R. Mantha, "TCP Encapsulation
              of IKE and IPsec Packets", RFC 8229, DOI 10.17487/RFC8229,
              August 2017, <https://www.rfc-editor.org/info/rfc8229>.






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   [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>.

   [RFC8547]  Bittau, A., Giffin, D., Handley, M., Mazieres, D., and E.
              Smith, "TCP-ENO: Encryption Negotiation Option", RFC 8547,
              DOI 10.17487/RFC8547, May 2019,
              <https://www.rfc-editor.org/info/rfc8547>.

   [RFC8548]  Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
              Q., and E. Smith, "Cryptographic Protection of TCP Streams
              (tcpcrypt)", RFC 8548, DOI 10.17487/RFC8548, May 2019,
              <https://www.rfc-editor.org/info/rfc8548>.

   [WireGuard]
              Donenfeld, J., "WireGuard -- Next Generation Kernel
              Network Tunnel",
              <https://www.wireguard.com/papers/wireguard.pdf>.

Authors' Addresses

   Theresa Enghardt
   TU Berlin
   Marchstr. 23
   10587 Berlin
   Germany

   Email: theresa@inet.tu-berlin.de


   Tommy Pauly
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014
   United States of America

   Email: tpauly@apple.com


   Colin Perkins
   University of Glasgow
   School of Computing Science
   Glasgow  G12 8QQ
   United Kingdom

   Email: csp@csperkins.org





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   Kyle Rose
   Akamai Technologies, Inc.
   150 Broadway
   Cambridge, MA 02144
   United States of America

   Email: krose@krose.org


   Christopher A. Wood (editor)
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014
   United States of America

   Email: cawood@apple.com



































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