Internet Engineering Task Force (IETF) T. Enghardt

Internet Engineering Task Force (IETF) T. Enghardt
Request for Comments: 8922 TU Berlin
Category: Informational T. Pauly
ISSN: 2070-1721 Apple Inc.
C. Perkins
University of Glasgow
K. Rose
Akamai Technologies, Inc.
C. Wood
Cloudflare
October 2020

A Survey of the Interaction between Security Protocols and Transport
Services

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 document is not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8922.

Copyright Notice

Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.

Table of Contents

1. Introduction
1.1. Goals
1.2. Non-goals
2. Terminology
3. Transport Security Protocol Descriptions
3.1. Application Payload Security Protocols
3.1.1. TLS
3.1.2. DTLS
3.2. Application-Specific Security Protocols
3.2.1. Secure RTP
3.3. Transport-Layer Security Protocols
3.3.1. IETF QUIC
3.3.2. Google QUIC
3.3.3. tcpcrypt
3.3.4. MinimaLT
3.3.5. CurveCP
3.4. Packet Security Protocols
3.4.1. IPsec
3.4.2. WireGuard
3.4.3. OpenVPN
4. Transport Dependencies
4.1. Reliable Byte-Stream Transports
4.2. Unreliable Datagram Transports
4.2.1. Datagram Protocols with Defined Byte-Stream Mappings
4.3. Transport-Specific Dependencies
5. Application Interface
5.1. Pre-connection Interfaces
5.2. Connection Interfaces
5.3. Post-connection Interfaces
5.4. Summary of Interfaces Exposed by Protocols
6. IANA Considerations
7. Security Considerations
8. Privacy Considerations
9. Informative References
Acknowledgments
Authors' Addresses

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 interfaces between these protocols and both transport
protocols and applications. It examines Transport Layer Security
(TLS), Datagram Transport Layer Security (DTLS), IETF QUIC, Google
QUIC (gQUIC), tcpcrypt, Internet Protocol Security (IPsec), Secure
Real-time Transport Protocol (SRTP) with DTLS, WireGuard, CurveCP,
and MinimaLT. For each protocol, this document provides a brief
description. Then, it describes the interfaces between these
protocols and transports in Section 4 and the interfaces between
these protocols and applications in Section 5.

A Transport Services system exposes an interface for applications to
access various (secure) transport protocol features. The security
protocols included in this survey represent a superset of
functionality and features a Transport Services system may need to
support both internally and externally (via an API) for applications
[TAPS-ARCH]. Ubiquitous IETF protocols such as (D)TLS, as well as
non-standard protocols such as gQUIC, are 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 for and limitations on
application usage. In contrast, protocols such as secure shell (SSH)
[RFC4253], GRE [RFC2890], the Layer 2 Tunneling Protocol (L2TP)
[RFC5641], and Application Layer Transport Security (ALTS) [ALTS] are
omitted since they do not provide interfaces deemed unique.

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

This document only surveys point-to-point protocols; multicast
protocols are out of scope.

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 the Transport Services effort 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, restricts 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.

Different security protocols also can use incompatible notions of
peer identity and authentication, and cryptographic options. It is
not a goal to identify a common set of representations for these
concepts.

The protocols surveyed in this document represent a superset of
functionality and features a Transport Services system may need to
support. It does not list all transport protocols that a Transport
Services system may need to implement, nor does it mandate that a
Transport Service system implement any particular protocol.

A Transport Services system may implement any secure transport
protocol that provides the described features. In doing so, it may
need to expose an interface to the application to configure these
features.

2. Terminology

The following terms are used throughout this document to describe the
roles and interactions of transport security protocols (some of which
are also defined in [RFC8095]):

Transport Feature: a specific end-to-end feature that the transport
layer provides to an application. Examples include
confidentiality, reliable delivery, ordered delivery, and message-
versus-stream orientation.

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

Transport Services system: a software component that exposes an
interface to different Transport Services to an application.

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,
whether directly or in conjunction with a security protocol.

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.

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.

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

Record: framed protocol messages.

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

Session: an ephemeral security association between applications.

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.

Peer: an endpoint application party to a session.

Client: the peer responsible for initiating a session.

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

3. Transport Security Protocol Descriptions

This section contains brief transport and security descriptions of
various security protocols currently used to protect data being sent
over a network. These protocols are grouped based on where in the
protocol stack they are implemented, which influences which parts of
a packet they protect: Generic application payload, application
payload for specific application-layer protocols, both application
payload and transport headers, or entire IP packets.

Note that not all security protocols can be easily categorized, e.g.,
as some protocols can be used in different ways or in combination
with other protocols. One major reason for this is that channel
security protocols often consist of two components:

* A handshake protocol, which is responsible for negotiating
parameters, authenticating the endpoints, and establishing shared
keys.

* A record protocol, which is used to encrypt traffic using keys and
parameters provided by the handshake protocol.

For some protocols, such as tcpcrypt, these two components are
tightly integrated. In contrast, for IPsec, these components are
implemented in separate protocols: AH and the Encapsulating Security
Payload (ESP) are record protocols, which can use keys supplied by
the handshake protocol Internet Key Exchange Protocol Version 2
(IKEv2), by other handshake protocols, or by manual configuration.
Moreover, some protocols can be used in different ways: While the
base TLS protocol as defined in [RFC8446] has an integrated handshake
and record protocol, TLS or DTLS can also be used to negotiate keys
for other protocols, as in DTLS-SRTP, or the handshake protocol can
be used with a separate record layer, as in QUIC [QUIC-TRANSPORT].

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 and, once the handshake has sufficiently progressed,
encrypt 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] [DTLS-1.3] 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 equivalent security
guarantees to TLS with the exception of order protection/non-
replayability. 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]. SRTP provides a
record layer only, and requires a separate handshake protocol to
provide key agreement and identity management.

The commonly used handshake protocol for SRTP is DTLS, in the form of
DTLS-SRTP [RFC5764]. This is an extension to DTLS that negotiates
the use of SRTP as the record layer and describes how to export keys
for use with SRTP.

ZRTP [RFC6189] is an alternative key agreement and identity
management protocol for SRTP. ZRTP 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. IETF QUIC

QUIC is a new standards-track transport protocol that runs over UDP,
loosely based on Google's original proprietary gQUIC protocol
[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 [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 [MinimaLT] is a UDP-based transport security protocol
designed to offer confidentiality, mutual authentication, DoS
prevention, and connection mobility. One major goal of the protocol
is to leverage existing protocols to obtain server-side configuration
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 that, unlike many
other security protocols, is based entirely upon public key
algorithms. 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. IPsec

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 [WireGuard] is an IP-layer protocol designed as an
alternative to IPsec for certain use cases. It uses UDP to
encapsulate IP datagrams between peers. Unlike most transport
security protocols, which rely on Public Key Infrastructure (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 either UDP or TCP.
For key establishment, OpenVPN can either use TLS as a handshake
protocol or use pre-shared keys.

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:

* TLS

Transport-Layer Security Protocols:

* tcpcrypt

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:

* DTLS

* ZRTP

* SRTP

Transport-Layer Security Protocols:

* QUIC

* MinimaLT

* CurveCP

Packet Security Protocols:

* IPsec

* WireGuard

* OpenVPN

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:

* DTLS when used as a handshake protocol for SRTP [RFC7850]

* ZRTP [RFC6189]

* SRTP [RFC4571][RFC3711]

Packet Security Protocols:

* IPsec [RFC8229]

4.3. Transport-Specific Dependencies

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

QUIC, CurveCP, and MinimaLT provide both transport functionality and
security functionality. They depend 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 exposed by the security
protocols described above. We partition these interfaces into pre-
connection (configuration), connection, and post-connection
interfaces, following conventions in [TAPS-INTERFACE] and
[TAPS-ARCH].

Note that not all protocols support each interface. The table in
Section 5.4 summarizes which protocol exposes which of the
interfaces. In the following sections, we provide abbreviations of
the interface names to use in the summary table.

5.1. Pre-connection Interfaces

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

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

* TLS

* DTLS

* ZRTP

* QUIC

* MinimaLT

* CurveCP

* IPsec

* WireGuard

* OpenVPN

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

* TLS

* DTLS

* ZRTP

* QUIC

* tcpcrypt

* MinimaLT

* IPsec

* OpenVPN

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

* TLS

* DTLS

* QUIC

Session Cache Management (CM): 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

* ZRTP

* QUIC

* tcpcrypt

* MinimaLT

Authentication Delegation (AD): The application provides access to a
separate module that will provide authentication, using the
Extensible Authentication Protocol (EAP) [RFC3748] for example.

* IPsec

* tcpcrypt

Pre-Shared Key Import (PSKI): Either the handshake protocol or the
application directly can supply pre-shared keys for use in
encrypting (and authenticating) communication with a peer.

* TLS

* DTLS

* ZRTP

* QUIC

* tcpcrypt

* MinimaLT

* IPsec

* WireGuard

* OpenVPN

5.2. Connection Interfaces

Identity Validation (IV): During a handshake, the security protocol
will conduct identity validation of the peer. This can offload
validation or occur transparently to the application.

* TLS

* DTLS

* ZRTP

* QUIC

* MinimaLT

* CurveCP

* IPsec

* WireGuard

* OpenVPN

Source Address Validation (SAV): The handshake protocol may interact
with the transport protocol or application to validate the address
of the remote peer that has sent data. This involves sending a
cookie exchange to avoid DoS attacks. (This list omits protocols
that depend on TCP and therefore implicitly perform SAV.)

* DTLS

* QUIC

* IPsec

* WireGuard

5.3. Post-connection Interfaces

Connection Termination (CT): The security protocol may be instructed
to tear down its connection and session information. This is
needed by some protocols, e.g., to prevent application data
truncation attacks in which an attacker terminates an underlying
insecure connection-oriented protocol to terminate the session.

* TLS

* DTLS

* ZRTP

* QUIC

* tcpcrypt

* MinimaLT

* IPsec

* OpenVPN

Key Update (KU): 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

* IPsec

Shared Secret Key Export (SSKE): The handshake protocol may provide
an interface for producing shared secrets for application-specific
uses.

* TLS

* DTLS

* tcpcrypt

* IPsec

* OpenVPN

* MinimaLT

Key Expiration (KE): 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.

* IPsec

Mobility Events (ME): 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).

* DTLS (version 1.3 only [DTLS-1.3])

* QUIC

* MinimaLT

* CurveCP

* IPsec [RFC4555]

* WireGuard

5.4. Summary of Interfaces Exposed by Protocols

The following table summarizes which protocol exposes which
interface.

+===========+===+====+=====+==+==+======+==+=====+==+==+======+==+==+
| Protocol |IPK|ALG | EXT |CM|AD| PSKI |IV| SAV |CT|KU| SSKE |KE|ME|
+===========+===+====+=====+==+==+======+==+=====+==+==+======+==+==+
| TLS | x | x | x |x | | x |x | |x |x | x | | |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+
| DTLS | x | x | x |x | | x |x | x |x |x | x | |x |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+
| ZRTP | x | x | |x | | x |x | |x | | | | |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+
| QUIC | x | x | x |x | | x |x | x |x |x | | |x |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+
| tcpcrypt | | x | |x |x | x | | |x |x | x | | |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+
| MinimaLT | x | x | |x | | x |x | |x |x | x | |x |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+
| CurveCP | x | | | | | |x | | | | | |x |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+
| IPsec | x | x | | |x | x |x | x |x |x | x |x |x |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+
| WireGuard | x | | | | | x |x | x | | | | |x |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+
| OpenVPN | x | x | | | | x |x | |x | | x | | |
+-----------+---+----+-----+--+--+------+--+-----+--+--+------+--+--+

Table 1

x = Interface is exposed
(blank) = Interface is not exposed

6. IANA Considerations

This document has no IANA actions.

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 using encryption to reduce information leakage.
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. 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/>.

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

[DTLS-1.3] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
dtls13-38, 29 May 2020,
<https://tools.ietf.org/html/draft-ietf-tls-dtls13-38>.

[MinimaLT] Petullo, W., Zhang, X., Solworth, J., Bernstein, D., and
T. Lange, "MinimaLT: minimal-latency networking through
better security", DOI 10.1145/2508859.2516737,
<https://dl.acm.org/citation.cfm?id=2516737>.

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

[QUIC-TLS] Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
Work in Progress, Internet-Draft, draft-ietf-quic-tls-31,
24 September 2020,
<https://tools.ietf.org/html/draft-ietf-quic-tls-31>.

[QUIC-TRANSPORT]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", Work in Progress, Internet-Draft,
draft-ietf-quic-transport-31, 24 September 2020,
<https://tools.ietf.org/html/draft-ietf-quic-transport-
31>.

[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>.

[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, DOI 10.17487/RFC2890, September 2000,
<https://www.rfc-editor.org/info/rfc2890>.

[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>.

[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
<https://www.rfc-editor.org/info/rfc3748>.

[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
January 2006, <https://www.rfc-editor.org/info/rfc4253>.

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

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

[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,
<https://www.rfc-editor.org/info/rfc4555>.

[RFC4571] Lazzaro, J., "Framing Real-time Transport Protocol (RTP)
and RTP Control Protocol (RTCP) Packets over Connection-
Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July
2006, <https://www.rfc-editor.org/info/rfc4571>.

[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>.

[RFC5641] McGill, N. and C. Pignataro, "Layer 2 Tunneling Protocol
Version 3 (L2TPv3) Extended Circuit Status Values",
RFC 5641, DOI 10.17487/RFC5641, August 2009,
<https://www.rfc-editor.org/info/rfc5641>.

[RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer
Security (DTLS) Extension to Establish Keys for the Secure
Real-time Transport Protocol (SRTP)", RFC 5764,
DOI 10.17487/RFC5764, May 2010,
<https://www.rfc-editor.org/info/rfc5764>.

[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>.

[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>.

[RFC7850] Nandakumar, S., "Registering Values of the SDP 'proto'
Field for Transporting RTP Media over TCP under Various
RTP Profiles", RFC 7850, DOI 10.17487/RFC7850, April 2016,
<https://www.rfc-editor.org/info/rfc7850>.

[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>.

[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>.

[TAPS-ARCH]
Pauly, T., Trammell, B., Brunstrom, A., Fairhurst, G.,
Perkins, C., Tiesel, P. S., and C. A. Wood, "An
Architecture for Transport Services", Work in Progress,
Internet-Draft, draft-ietf-taps-arch-08, 13 July 2020,
<https://tools.ietf.org/html/draft-ietf-taps-arch-08>.

[TAPS-INTERFACE]
Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G.,
Kuehlewind, M., Perkins, C., Tiesel, P. S., Wood, C. A.,
and T. Pauly, "An Abstract Application Layer Interface to
Transport Services", Work in Progress, Internet-Draft,
draft-ietf-taps-interface-09, 27 July 2020,
<https://tools.ietf.org/html/draft-ietf-taps-interface-
09>.

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

Acknowledgments

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

Authors' Addresses

Theresa Enghardt
TU Berlin
Marchstr. 23
10587 Berlin
Germany

Email: [email protected]

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

Email: [email protected]

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

Email: [email protected]

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

Email: [email protected]

Christopher A. Wood
Cloudflare
101 Townsend St
San Francisco,
United States of America

Email: [email protected]