<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-taps-transport-security-12" number="8922" obsoletes="" updates="" submissionType="IETF" category="info" consensus="true" xml:lang="en" tocInclude="true" sortRefs="true" symRefs="true" version="3">
<front>
<title abbrev="Transport Security Survey">A Survey of the Interaction
between Security Protocols and Transport Services</title>
<seriesInfo name="RFC" value="8922"/>
<author initials="T." surname="Enghardt" fullname="Theresa Enghardt">
<organization>TU Berlin</organization>
<address>
<postal>
<street>Marchstr. 23</street>
<city>Berlin</city>
<code>10587</code>
<country>Germany</country>
</postal>
<email>ietf@tenghardt.net</email>
</address>
</author>
<author initials="T." surname="Pauly" fullname="Tommy Pauly">
<organization>Apple Inc.</organization>
<address>
<postal>
<street>One Apple Park Way</street>
<city>Cupertino</city><region>California</region><code>95014</code>
<country>United States of America</country>
</postal>
<email>tpauly@apple.com</email>
</address>
</author>
<author initials="C." surname="Perkins" fullname="Colin Perkins">
<organization>University of Glasgow</organization>
<address>
<postal>
<street>School of Computing Science</street>
<city>Glasgow</city><code>G12 8QQ</code>
<country>United Kingdom</country>
</postal>
<email>csp@csperkins.org</email>
</address>
</author>
<author initials="K." surname="Rose" fullname="Kyle Rose">
<organization>Akamai Technologies, Inc.</organization>
<address>
<postal>
<street>150 Broadway</street>
<city>Cambridge</city><region>MA</region><code>02144</code>
<country>United States of America</country>
</postal>
<email>krose@krose.org</email>
</address>
</author>
<author initials="C." surname="Wood" fullname="Christopher A. Wood">
<organization>Cloudflare</organization>
<address>
<postal>
<street>101 Townsend St</street>
<city>San Francisco</city>
<country>United States of America</country>
</postal>
<email>caw@heapingbits.net</email>
</address>
</author>
<date year="2020" month="October"/>
<keyword>Transport Protocols</keyword>
<keyword>Transport Security</keyword>
<abstract>
<t>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.</t>
</abstract>
</front>
<middle>
<section anchor="introduction" numbered="true" toc="default">
<name>Introduction</name>
<t>Services and features provided by transport protocols have been
cataloged in <xref target="RFC8095" format="default"/>. 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 <xref target="transport-interface"
format="default"/> and the interfaces between these protocols and
applications in <xref target="application-interface"
format="default"/>.</t>
<t>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 <xref
target="I-D.ietf-taps-arch" format="default"/>. 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)
<xref target="RFC4253" format="default"/>, GRE <xref target="RFC2890"
format="default"/>, the Layer 2 Tunneling Protocol (L2TP) <xref
target="RFC5641" format="default"/>, and Application Layer Transport
Security (ALTS) <xref target="ALTS"
format="default"/> are omitted since they do not provide interfaces
deemed unique.</t>
<t>Authentication-only protocols such as the TCP Authentication Option
(TCP-AO) <xref target="RFC5925" format="default"/> and the IPsec
Authentication Header (AH) <xref target="RFC4302" format="default"/> 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 <xref target="RFC2385" format="default"/>.) 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.</t>
<t>This document only surveys point-to-point protocols; multicast protocols are out of scope.</t>
<section anchor="goals" numbered="true" toc="default">
<name>Goals</name>
<t>This survey is intended to help identify the most common interface
surfaces between security protocols and transport protocols, and
between security protocols and applications.</t>
<t>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.</t>
<t>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.</t>
</section>
<section anchor="non-goals" numbered="true" toc="default">
<name>Non-goals</name>
<t>While this survey provides similar analysis to that which was performed for transport protocols in <xref target="RFC8095" format="default"/>,
it is important to distinguish that the use of security protocols requires more consideration.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
</section>
<section anchor="terminology" numbered="true" toc="default">
<name>Terminology</name>
<t>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 <xref target="RFC8095" format="default"/>):</t>
<dl>
<dt>Transport Feature:</dt><dd>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.</dd>
<dt>Transport Service:</dt><dd>a set of Transport Features, without an
association to any given framing protocol, that provides
functionality to an application.</dd>
<dt>Transport Services system:</dt><dd>a software component that exposes an
interface to different Transport Services to an application.</dd>
<dt>Transport Protocol:</dt><dd>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.</dd>
<dt>Application:</dt><dd>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.</dd>
<dt>Security Protocol:</dt><dd>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.</dd>
<dt>Handshake Protocol:</dt><dd>a protocol that enables peers to validate each
other and to securely establish shared cryptographic context.</dd>
<dt>Record:</dt><dd>framed protocol messages.</dd>
<dt>Record Protocol:</dt><dd>a security protocol that allows data to be
divided into manageable blocks and protected using shared
cryptographic context.</dd>
<dt>Session:</dt><dd>an ephemeral security association between
applications.</dd>
<dt>Connection:</dt><dd>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.</dd>
<dt>Peer:</dt><dd>an endpoint application party to a session.</dd>
<dt>Client:</dt><dd>the peer responsible for initiating a session.</dd>
<dt>Server:</dt><dd>the peer responsible for responding to a session initiation.</dd>
</dl>
</section>
<section anchor="transport-security-protocol-descriptions" numbered="true" toc="default">
<name>Transport Security Protocol Descriptions</name>
<t>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.</t>
<t>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:</t>
<ul spacing="normal">
<li>A handshake protocol, which is responsible for negotiating parameters, authenticating the
endpoints, and establishing shared keys.</li>
<li>A record protocol, which is used to encrypt traffic using keys and parameters provided by the
handshake protocol.</li>
</ul>
<t>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 <xref target="RFC8446" format="default"/> 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 <xref
target="I-D.ietf-quic-transport" format="default"/>.</t>
<section anchor="application-payload-security-protocols" numbered="true" toc="default">
<name>Application Payload Security Protocols</name>
<t>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.</t>
<section anchor="tls" numbered="true" toc="default">
<name>TLS</name>
<t>TLS (Transport Layer Security) <xref target="RFC8446"
format="default"/> 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.</t>
</section>
<section anchor="dtls" numbered="true" toc="default">
<name>DTLS</name>
<t>DTLS (Datagram Transport Layer Security) <xref target="RFC6347"
format="default"/> <xref target="I-D.ietf-tls-dtls13"
format="default"/> 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.</t>
</section>
</section>
<section anchor="application-specific-security-protocols" numbered="true" toc="default">
<name>Application-Specific Security Protocols</name>
<t>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.</t>
<section anchor="secure-rtp" numbered="true" toc="default">
<name>Secure RTP</name>
<t>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 <xref target="RFC3711" format="default"/>.
SRTP provides a record layer only, and requires a separate handshake
protocol to provide key agreement and identity management.</t>
<t>The commonly used handshake protocol for SRTP is DTLS, in the form of
DTLS-SRTP <xref target="RFC5764" format="default"/>. 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.</t>
<t>ZRTP <xref target="RFC6189" format="default"/> 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.</t>
</section>
</section>
<section anchor="transport-layer-security-protocols" numbered="true" toc="default">
<name>Transport-Layer Security Protocols</name>
<t>The following security protocols provide protection for both application payloads and
headers that are used for Transport Services.</t>
<section anchor="quic" numbered="true" toc="default">
<name>IETF QUIC</name>
<t>QUIC is a new standards-track transport protocol that runs over UDP, loosely based on Google's
original proprietary gQUIC protocol <xref target="I-D.ietf-quic-transport" format="default"/> (See <xref target="gquic" format="default"/> 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 <xref target="I-D.ietf-quic-tls" format="default"/>
has been specified to provide this handshake.</t>
</section>
<section anchor="gquic" numbered="true" toc="default">
<name>Google QUIC</name>
<t>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.</t>
</section>
<section anchor="tcpcrypt" numbered="true" toc="default">
<name>tcpcrypt</name>
<t>Tcpcrypt <xref target="RFC8548" format="default"/> 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.</t>
</section>
<section anchor="minimalt" numbered="true" toc="default">
<name>MinimaLT</name>
<t>MinimaLT <xref target="MinimaLT" format="default"/> 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.</t>
</section>
<section anchor="curvecp" numbered="true" toc="default">
<name>CurveCP</name>
<t>CurveCP <xref target="CurveCP" format="default"/> 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.</t>
</section>
</section>
<section anchor="packet-security-protocols" numbered="true" toc="default">
<name>Packet Security Protocols</name>
<t>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.</t>
<section anchor="ipsec" numbered="true" toc="default">
<name>IPsec</name>
<t>IKEv2 <xref target="RFC7296" format="default"/> and ESP <xref
target="RFC4303" format="default"/> 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.</t>
</section>
<section anchor="wireguard" numbered="true" toc="default">
<name>WireGuard</name>
<t>WireGuard <xref target="WireGuard" format="default"/> 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.</t>
</section>
<section anchor="openvpn" numbered="true" toc="default">
<name>OpenVPN</name>
<t>OpenVPN <xref target="OpenVPN" format="default"/> 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.</t>
</section>
</section>
</section>
<section anchor="transport-interface" numbered="true" toc="default">
<name>Transport Dependencies</name>
<t>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.</t>
<section anchor="reliable-byte-stream-transports" numbered="true" toc="default">
<name>Reliable Byte-Stream Transports</name>
<t>The following protocols all depend upon running on a transport protocol that provides
a reliable, in-order stream of bytes. This is typically TCP.</t>
<t>Application Payload Security Protocols:</t>
<ul spacing="normal">
<li>TLS</li>
</ul>
<t>Transport-Layer Security Protocols:</t>
<ul spacing="normal">
<li>tcpcrypt</li>
</ul>
</section>
<section anchor="unreliable-datagram-transports" numbered="true" toc="default">
<name>Unreliable Datagram Transports</name>
<t>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.</t>
<t>Application Payload Security Protocols:</t>
<ul spacing="normal">
<li>DTLS</li>
<li>ZRTP</li>
<li>SRTP</li>
</ul>
<t>Transport-Layer Security Protocols:</t>
<ul spacing="normal">
<li>QUIC</li>
<li>MinimaLT</li>
<li>CurveCP</li>
</ul>
<t>Packet Security Protocols:</t>
<ul spacing="normal">
<li>IPsec</li>
<li>WireGuard</li>
<li>OpenVPN</li>
</ul>
<section anchor="datagram-protocols-with-defined-byte-stream-mappings" numbered="true" toc="default">
<name>Datagram Protocols with Defined Byte-Stream Mappings</name>
<t>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.</t>
<t>Application Payload Security Protocols:</t>
<ul spacing="normal">
<li>DTLS when used as a handshake protocol for SRTP <xref target="RFC7850" format="default"/></li>
<li>ZRTP <xref target="RFC6189" format="default"/></li>
<li>SRTP <xref target="RFC4571" format="default"/><xref target="RFC3711" format="default"/></li>
</ul>
<t>Packet Security Protocols:</t>
<ul spacing="normal">
<li>IPsec <xref target="RFC8229" format="default"/></li>
</ul>
</section>
</section>
<section anchor="transport-specific-dependencies" numbered="true" toc="default">
<name>Transport-Specific Dependencies</name>
<t>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) <xref
target="RFC8547" format="default"/> to negotiate its protocol
support.</t>
<t>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.</t>
</section>
</section>
<section anchor="application-interface" numbered="true" toc="default">
<name>Application Interface</name>
<t>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 <xref target="I-D.ietf-taps-interface" format="default"/> and <xref target="I-D.ietf-taps-arch" format="default"/>.</t>
<t>Note that not all protocols support each interface.
The table in <xref target="interface-protocols-table" format="default"/> 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.</t>
<section anchor="pre-connection-interfaces" numbered="true" toc="default">
<name>Pre-connection Interfaces</name>
<t>Configuration interfaces are used to configure the security protocols before a
handshake begins or keys are negotiated.</t>
<dl spacing="normal">
<dt>Identities and Private Keys (IPK):</dt>
<dd><t>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.
</t>
<ul spacing="normal">
<li>TLS</li>
<li>DTLS</li>
<li>ZRTP</li>
<li>QUIC</li>
<li>MinimaLT</li>
<li>CurveCP</li>
<li>IPsec</li>
<li>WireGuard</li>
<li>OpenVPN</li>
</ul>
</dd>
<dt>Supported Algorithms (Key Exchange, Signatures, and Ciphersuites) (ALG):</dt><dd><t>
The application can choose the algorithms that are supported for key exchange,
signatures, and ciphersuites.
</t>
<ul spacing="normal">
<li>TLS</li>
<li>DTLS</li>
<li>ZRTP</li>
<li>QUIC</li>
<li>tcpcrypt</li>
<li>MinimaLT</li>
<li>IPsec</li>
<li>OpenVPN</li>
</ul>
</dd>
<dt>Extensions (EXT):</dt><dd><t>
The application enables or configures extensions that are to be negotiated by
the security protocol, such as Application-Layer Protocol Negotiation (ALPN) <xref target="RFC7301" format="default"/>.
</t>
<ul spacing="normal">
<li>TLS</li>
<li>DTLS</li>
<li>QUIC</li>
</ul>
</dd>
<dt>Session Cache Management (CM):</dt><dd><t>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.
</t>
<ul spacing="normal">
<li>TLS</li>
<li>DTLS</li>
<li>ZRTP</li>
<li>QUIC</li>
<li>tcpcrypt</li>
<li>MinimaLT</li>
</ul>
</dd>
<dt>Authentication Delegation (AD):</dt><dd><t>
The application provides access to a separate module that will provide authentication,
using the Extensible Authentication Protocol (EAP) <xref target="RFC3748" format="default"/> for example.
</t>
<ul spacing="normal">
<li>IPsec</li>
<li>tcpcrypt</li>
</ul>
</dd>
<dt>Pre-Shared Key Import (PSKI):</dt><dd><t>
Either the handshake protocol or the application directly can supply pre-shared keys for use
in encrypting (and authenticating) communication with a peer.
</t>
<ul spacing="normal">
<li>TLS</li>
<li>DTLS</li>
<li>ZRTP</li>
<li>QUIC</li>
<li>tcpcrypt</li>
<li>MinimaLT</li>
<li>IPsec</li>
<li>WireGuard</li>
<li>OpenVPN</li>
</ul>
</dd>
</dl>
</section>
<section anchor="connection-interfaces" numbered="true" toc="default">
<name>Connection Interfaces</name>
<dl spacing="normal">
<dt>Identity Validation (IV):</dt><dd><t>
During a handshake, the security protocol will conduct identity validation of the peer.
This can offload validation or occur transparently to the application.
</t>
<ul spacing="normal">
<li>TLS</li>
<li>DTLS</li>
<li>ZRTP</li>
<li>QUIC</li>
<li>MinimaLT</li>
<li>CurveCP</li>
<li>IPsec</li>
<li>WireGuard</li>
<li>OpenVPN</li>
</ul>
</dd>
<dt>Source Address Validation (SAV):</dt><dd><t>
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.)
</t>
<ul spacing="normal">
<li>DTLS</li>
<li>QUIC</li>
<li>IPsec</li>
<li>WireGuard</li>
</ul>
</dd>
</dl>
</section>
<section anchor="post-connection-interfaces" numbered="true" toc="default">
<name>Post-connection Interfaces</name>
<dl spacing="normal">
<dt>Connection Termination (CT):</dt><dd><t>
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.
</t>
<ul spacing="normal">
<li>TLS</li>
<li>DTLS</li>
<li>ZRTP</li>
<li>QUIC</li>
<li>tcpcrypt</li>
<li>MinimaLT</li>
<li>IPsec</li>
<li>OpenVPN</li>
</ul>
</dd>
<dt>Key Update (KU):</dt><dd><t>
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.
</t>
<ul spacing="normal">
<li>TLS</li>
<li>DTLS</li>
<li>QUIC</li>
<li>tcpcrypt</li>
<li>MinimaLT</li>
<li>IPsec</li>
</ul>
</dd>
<dt>Shared Secret Key Export (SSKE):</dt><dd><t>
The handshake protocol may provide an interface for producing shared secrets for application-specific uses.
</t>
<ul spacing="normal">
<li>TLS</li>
<li>DTLS</li>
<li>tcpcrypt</li>
<li>IPsec</li>
<li>OpenVPN</li>
<li>MinimaLT</li>
</ul>
</dd>
<dt>Key Expiration (KE):</dt><dd><t>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.
</t>
<ul spacing="normal">
<li>IPsec</li>
</ul>
</dd>
<dt>Mobility Events (ME):</dt><dd><t> 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).
</t>
<ul spacing="normal">
<li>DTLS (version 1.3 only <xref target="I-D.ietf-tls-dtls13" format="default"/>)</li>
<li>QUIC</li>
<li>MinimaLT</li>
<li>CurveCP</li>
<li>IPsec <xref target="RFC4555" format="default"/></li>
<li>WireGuard</li>
</ul>
</dd>
</dl>
</section>
<section anchor="interface-protocols-table" numbered="true" toc="default">
<name>Summary of Interfaces Exposed by Protocols</name>
<t>The following table summarizes which protocol exposes which interface.</t>
<table align="center">
<thead>
<tr>
<th align="left">Protocol</th>
<th align="center">IPK</th>
<th align="center">ALG</th>
<th align="center">EXT</th>
<th align="center">CM</th>
<th align="center">AD</th>
<th align="center">PSKI</th>
<th align="center">IV</th>
<th align="center">SAV</th>
<th align="center">CT</th>
<th align="center">KU</th>
<th align="center">SSKE</th>
<th align="center">KE</th>
<th align="center">ME</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">TLS</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
</tr>
<tr>
<td align="left">DTLS</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
</tr>
<tr>
<td align="left">ZRTP</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
</tr>
<tr>
<td align="left">QUIC</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center">x</td>
</tr>
<tr>
<td align="left">tcpcrypt</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
</tr>
<tr>
<td align="left">MinimaLT</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
</tr>
<tr>
<td align="left">CurveCP</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center">x</td>
</tr>
<tr>
<td align="left">IPsec</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
</tr>
<tr>
<td align="left">WireGuard</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center">x</td>
</tr>
<tr>
<td align="left">OpenVPN</td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center">x</td>
<td align="center"> </td>
<td align="center"> </td>
</tr>
</tbody>
</table>
<t>x = Interface is exposed<br/>
(blank) = Interface is not exposed</t>
</section>
</section>
<section anchor="iana-considerations" numbered="true" toc="default">
<name>IANA Considerations</name>
<t>This document has no IANA actions.</t>
</section>
<section anchor="security-considerations" numbered="true" toc="default">
<name>Security Considerations</name>
<t>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.</t>
</section>
<section anchor="privacy-considerations" numbered="true" toc="default">
<name>Privacy Considerations</name>
<t>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 <xref target="RFC5246" format="default"/>, whereas they are encrypted in TLS 1.3 <xref target="RFC8446" format="default"/>. A survey of privacy
features, or lack thereof, for various security protocols could be addressed in a
separate document.</t>
</section>
</middle>
<back>
<displayreference target="I-D.ietf-taps-arch" to="TAPS-ARCH"/>
<displayreference target="I-D.ietf-quic-transport" to="QUIC-TRANSPORT"/>
<displayreference target="I-D.ietf-tls-dtls13" to="DTLS-1.3"/>
<displayreference target="I-D.ietf-quic-tls" to="QUIC-TLS"/>
<displayreference target="I-D.ietf-taps-interface" to="TAPS-INTERFACE"/>
<references>
<name>Informative References</name>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8095.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4253.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2890.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5641.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5925.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4302.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2385.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8548.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7296.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4303.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7850.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4571.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8229.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8547.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8446.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6347.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3711.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5764.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6189.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7301.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3748.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4555.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5246.xml"/>
ckrefs
<reference anchor="WireGuard" target="https://www.wireguard.com/papers/wireguard.pdf">
<front>
<title>WireGuard: Next Generation Kernel Network Tunnel</title>
<author initials="J" surname="Donenfeld">
<organization>WireGuard</organization>
</author>
</front>
</reference>
<reference anchor="ALTS" target="https://cloud.google.com/security/encryption-in-transit/application-layer-transport-security/">
<front>
<title>Application Layer Transport Security</title>
<author initials="C" surname="Ghali">
<organization/>
</author>
<author initials="A" surname="Stubblefield">
<organization/>
</author>
<author initials="E" surname="Knapp">
<organization/>
</author>
<author initials="J" surname="Li">
<organization/>
</author>
<author initials="B" surname="Schmidt">
<organization/>
</author>
<author initials="J" surname="Boeuf">
<organization/>
</author>
</front>
</reference>
<reference anchor="CurveCP" target="https://curvecp.org/">
<front>
<title>CurveCP: Usable security for the Internet</title>
<author initials="D" surname="Bernstein">
<organization>CurveCP</organization>
</author>
</front>
</reference>
<reference anchor="MinimaLT" target="https://dl.acm.org/citation.cfm?id=2516737">
<front>
<title>MinimaLT: minimal-latency networking through better security</title>
<author initials="W" surname="Petullo">
<organization>United States Military Academy, West Point, NY, USA</organization>
</author>
<author initials="X" surname="Zhang">
<organization>University of Illinois at Chicago, Chicago, IL, USA</organization>
</author>
<author initials="J" surname="Solworth">
<organization>University of Illinois at Chicago, Chicago, IL, USA</organization>
</author>
<author initials="D" surname="Bernstein">
<organization>University of Illinois at Chicago, Chicago, IL, USA</organization>
</author>
<author initials="T" surname="Lange">
<organization>TU Eindhoven, Eindhoven, Netherlands</organization>
</author>
</front>
<seriesInfo name="DOI" value="10.1145/2508859.2516737"/>
</reference>
<reference anchor="OpenVPN" target="https://openvpn.net/community-resources/openvpn-cryptographic-layer/">
<front>
<title>OpenVPN cryptographic layer</title>
<author>
<organization>OpenVPN</organization>
</author>
</front>
</reference>
<xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-taps-arch.xml"/>
<xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-quic-transport.xml"/>
<xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-tls-dtls13.xml"/>
<xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-quic-tls.xml"/>
<xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-taps-interface.xml"/>
</references>
<section anchor="acknowledgments" numbered="false" toc="default">
<name>Acknowledgments</name>
<t>The authors would like to thank <contact fullname="Bob Bradley"/>,
<contact fullname="Frederic Jacobs"/>, <contact fullname="Mirja
Kühlewind"/>, <contact fullname="Yannick Sierra"/>, <contact
fullname="Brian Trammell"/>, and <contact fullname="Magnus Westerlund"/>
for their input and feedback on this document.</t>
</section>
</back>
</rfc>