TU Berlin

Marchstr. 23 10587 Berlin Germany ietf@tenghardt.net

Apple Inc.

One Apple Park Way Cupertino, California 95014 United States of America tpauly@apple.com

University of Glasgow

School of Computing Science Glasgow G12 8QQ United Kingdom csp@csperkins.org

Akamai Technologies, Inc.

150 Broadway Cambridge, MA 02144 United States of America krose@krose.org

Cloudflare

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Internet-Draft 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.

Introduction Services and features provided by transport protocols have been cataloged in . 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 and the interfaces between these protocols and applications in . 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 . 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 SSH , GRE , L2TP , and ALTS are omitted since they do not provide interfaces deemed unique. Authentication-only protocols such as TCP-AO and IPsec Authentication Header (AH) 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 .) 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.

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.

Non-Goals While this survey provides similar analysis to that which was performed for transport protocols in , 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.

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 ):

• 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, which 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.

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 ESP are record protocols, which can use keys supplied by the handshake protocol 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 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 .

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.

TLS TLS (Transport Layer Security) 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.

DTLS DTLS (Datagram Transport Layer Security) 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.

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.

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 . 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 . 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 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.

Transport-Layer Security Protocols The following security protocols provide protection for both application payloads and headers that are used for transport services.

IETF QUIC QUIC is a new standards-track transport protocol that runs over UDP, loosely based on Google's original proprietary gQUIC protocol (See 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 has been specified to provide this handshake.

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.

tcpcrypt Tcpcrypt 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.

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.

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.

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.

IPsec IKEv2 and ESP 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.

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.

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.

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.

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

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

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
• ZRTP
• SRTP

Packet Security Protocols:

• IPsec

Transport-Specific Dependencies One protocol surveyed, tcpcrypt, has an 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 (ENO) 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.

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 and . Note that not all protocols support each interface. The table in 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.

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) .
  • 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 Extensible Authentication Protocol (EAP) 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

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 which depend on TCP and therefore implicitly perform SAV.)
  • DTLS
  • QUIC
  • IPsec
  • WireGuard

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 Export (PSKE): 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 )
  • QUIC
  • MinimaLT
  • CurveCP
  • IPsec
  • WireGuard

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	PSKE	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

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

IANA Considerations This document has no request to IANA.

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.

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 , whereas they are encrypted in TLS 1.3 . A survey of privacy features, or lack thereof, for various security protocols could be addressed in a separate document.

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.

Informative References United States Military Academy, West Point, NY, USA University of Illinois at Chicago, Chicago, IL, USA University of Illinois at Chicago, Chicago, IL, USA University of Illinois at Chicago, Chicago, IL, USA TU Eindhoven, Eindhoven, Netherlands This document describes, surveys, and classifies the protocol mechanisms provided by existing IETF protocols, as background for determining a common set of transport services. It examines the Transmission Control Protocol (TCP), Multipath TCP, the Stream Control Transmission Protocol (SCTP), the User Datagram Protocol (UDP), UDP-Lite, the Datagram Congestion Control Protocol (DCCP), the Internet Control Message Protocol (ICMP), the Real-Time Transport Protocol (RTP), File Delivery over Unidirectional Transport / Asynchronous Layered Coding (FLUTE/ALC) for Reliable Multicast, NACK- Oriented Reliable Multicast (NORM), Transport Layer Security (TLS), Datagram TLS (DTLS), and the Hypertext Transport Protocol (HTTP), when HTTP is used as a pseudotransport. This survey provides background for the definition of transport services within the TAPS working group. This document describes an architecture for exposing transport protocol features to applications for network communication, the Transport Services architecture. The Transport Services Application Programming Interface (API) is based on an asynchronous, event-driven interaction pattern. It uses messages for representing data transfer to applications, and it assumes an implementation that can use multiple IP addresses, multiple protocols, and multiple paths, and provide multiple application streams. This document further defines common terminology and concepts to be used in definitions of Transport Services APIs and implementations. The Secure Shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network. This document describes the SSH transport layer protocol, which typically runs on top of TCP/IP. The protocol can be used as a basis for a number of secure network services. It provides strong encryption, server authentication, and integrity protection. It may also provide compression. Key exchange method, public key algorithm, symmetric encryption algorithm, message authentication algorithm, and hash algorithm are all negotiated. This document also describes the Diffie-Hellman key exchange method and the minimal set of algorithms that are needed to implement the SSH transport layer protocol. [STANDARDS-TRACK] This document describes extensions by which two fields, Key and Sequence Number, can be optionally carried in the GRE Header. [STANDARDS-TRACK] This document defines additional Layer 2 Tunneling Protocol Version 3 (L2TPv3) bit values to be used within the "Circuit Status" Attribute Value Pair (AVP) to communicate finer-grained error states for Attachment Circuits (ACs) and pseudowires (PWs). It also generalizes the Active bit and deprecates the use of the New bit in the Circuit Status AVP, updating RFC 3931, RFC 4349, RFC 4454, RFC 4591, and RFC 4719. [STANDARDS-TRACK] This document specifies the TCP Authentication Option (TCP-AO), which obsoletes the TCP MD5 Signature option of RFC 2385 (TCP MD5). TCP-AO specifies the use of stronger Message Authentication Codes (MACs), protects against replays even for long-lived TCP connections, and provides more details on the association of security with TCP connections than TCP MD5. TCP-AO is compatible with either a static Master Key Tuple (MKT) configuration or an external, out-of-band MKT management mechanism; in either case, TCP-AO also protects connections when using the same MKT across repeated instances of a connection, using traffic keys derived from the MKT, and coordinates MKT changes between endpoints. The result is intended to support current infrastructure uses of TCP MD5, such as to protect long-lived connections (as used, e.g., in BGP and LDP), and to support a larger set of MACs with minimal other system and operational changes. TCP-AO uses a different option identifier than TCP MD5, even though TCP-AO and TCP MD5 are never permitted to be used simultaneously. TCP-AO supports IPv6, and is fully compatible with the proposed requirements for the replacement of TCP MD5. [STANDARDS-TRACK] This document describes an updated version of the IP Authentication Header (AH), which is designed to provide authentication services in IPv4 and IPv6. This document obsoletes RFC 2402 (November 1998). [STANDARDS-TRACK] This memo describes a TCP extension to enhance security for BGP. [STANDARDS-TRACK] This document defines the core of the QUIC transport protocol. Accompanying documents describe QUIC's loss detection and congestion control and the use of TLS for key negotiation. Note to Readers Discussion of this draft takes place on the QUIC working group mailing list (quic@ietf.org), which is archived at <https://mailarchive.ietf.org/arch/search/?email_list=quic>. Working Group information can be found at <https://github.com/ quicwg>; source code and issues list for this draft can be found at <https://github.com/quicwg/base-drafts/labels/-transport>. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. This document specifies version 1.2 of the Datagram Transport Layer Security (DTLS) protocol. The DTLS protocol provides communications privacy for datagram protocols. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. The DTLS protocol is based on the Transport Layer Security (TLS) protocol and provides equivalent security guarantees. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document updates DTLS 1.0 to work with TLS version 1.2. [STANDARDS-TRACK] This document specifies Version 1.3 of the Datagram Transport Layer Security (DTLS) protocol. DTLS 1.3 allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. The DTLS 1.3 protocol is intentionally based on the Transport Layer Security (TLS) 1.3 protocol and provides equivalent security guarantees with the exception of order protection/non-replayability. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document describes the Secure Real-time Transport Protocol (SRTP), a profile of the Real-time Transport Protocol (RTP), which can provide confidentiality, message authentication, and replay protection to the RTP traffic and to the control traffic for RTP, the Real-time Transport Control Protocol (RTCP). [STANDARDS-TRACK] This document describes a Datagram Transport Layer Security (DTLS) extension to establish keys for Secure RTP (SRTP) and Secure RTP Control Protocol (SRTCP) flows. DTLS keying happens on the media path, independent of any out-of-band signalling channel present. [STANDARDS-TRACK] This document defines ZRTP, a protocol for media path Diffie-Hellman exchange to agree on a session key and parameters for establishing unicast Secure Real-time Transport Protocol (SRTP) sessions for Voice over IP (VoIP) applications. The ZRTP protocol is media path keying because it is multiplexed on the same port as RTP and does not require support in the signaling protocol. ZRTP does not assume a Public Key Infrastructure (PKI) or require the complexity of certificates in end devices. For the media session, ZRTP provides confidentiality, protection against man-in-the-middle (MiTM) attacks, and, in cases where the signaling protocol provides end-to-end integrity protection, authentication. ZRTP can utilize a Session Description Protocol (SDP) attribute to provide discovery and authentication through the signaling channel. To provide best effort SRTP, ZRTP utilizes normal RTP/AVP (Audio-Visual Profile) profiles. ZRTP secures media sessions that include a voice media stream and can also secure media sessions that do not include voice by using an optional digital signature. This document is not an Internet Standards Track specification; it is published for informational purposes. This document describes how Transport Layer Security (TLS) is used to secure QUIC. This document specifies "tcpcrypt", a TCP encryption protocol designed for use in conjunction with the TCP Encryption Negotiation Option (TCP-ENO). Tcpcrypt coexists with middleboxes by tolerating resegmentation, NATs, and other manipulations of the TCP header. The protocol is self-contained and specifically tailored to TCP implementations, which often reside in kernels or other environments in which large external software dependencies can be undesirable. Because the size of TCP options is limited, the protocol requires one additional one-way message latency to perform key exchange before application data can be transmitted. However, the extra latency can be avoided between two hosts that have recently established a previous tcpcrypt connection. This document describes version 2 of the Internet Key Exchange (IKE) protocol. IKE is a component of IPsec used for performing mutual authentication and establishing and maintaining Security Associations (SAs). This document obsoletes RFC 5996, and includes all of the errata for it. It advances IKEv2 to be an Internet Standard. This document describes an updated version of the Encapsulating Security Payload (ESP) protocol, which is designed to provide a mix of security services in IPv4 and IPv6. ESP is used to provide confidentiality, data origin authentication, connectionless integrity, an anti-replay service (a form of partial sequence integrity), and limited traffic flow confidentiality. This document obsoletes RFC 2406 (November 1998). [STANDARDS-TRACK] The Real-time Transport Protocol (RTP) specification establishes a registry of profile names for use by higher-level control protocols, such as the Session Description Protocol (SDP), to refer to the transport methods. This specification describes the following new SDP transport protocol identifiers for transporting RTP Media over TCP: 'TCP/RTP/AVPF', 'TCP/RTP/SAVP', 'TCP/RTP/SAVPF', 'TCP/DTLS/RTP/SAVP', 'TCP/DTLS/RTP/SAVPF', 'TCP/TLS/RTP/AVP', and 'TCP/TLS/RTP/AVPF'. This memo defines a method for framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) packets onto connection-oriented transport (such as TCP). The memo also defines how session descriptions may specify RTP streams that use the framing method. [STANDARDS-TRACK] This document describes a method to transport Internet Key Exchange Protocol (IKE) and IPsec packets over a TCP connection for traversing network middleboxes that may block IKE negotiation over UDP. This method, referred to as "TCP encapsulation", involves sending both IKE packets for Security Association establishment and Encapsulating Security Payload (ESP) packets over a TCP connection. This method is intended to be used as a fallback option when IKE cannot be negotiated over UDP. Despite growing adoption of TLS, a significant fraction of TCP traffic on the Internet remains unencrypted. The persistence of unencrypted traffic can be attributed to at least two factors. First, some legacy protocols lack a signaling mechanism (such as a STARTTLS command) by which to convey support for encryption, thus making incremental deployment impossible. Second, legacy applications themselves cannot always be upgraded and therefore require a way to implement encryption transparently entirely within the transport layer. The TCP Encryption Negotiation Option (TCP-ENO) addresses both of these problems through a new TCP option kind providing out-of-band, fully backward-compatible negotiation of encryption. This document describes an abstract programming interface to the transport layer, following the Transport Services Architecture. It supports the asynchronous, atomic transmission of messages over transport protocols and network paths dynamically selected at runtime. It is intended to replace the traditional BSD sockets API as the lowest common denominator interface to the transport layer, in an environment where endpoints have multiple interfaces and potential transport protocols to select from. This document describes a Transport Layer Security (TLS) extension for application-layer protocol negotiation within the TLS handshake. For instances in which multiple application protocols are supported on the same TCP or UDP port, this extension allows the application layer to negotiate which protocol will be used within the TLS connection. This document defines the Extensible Authentication Protocol (EAP), an authentication framework which supports multiple authentication methods. EAP typically runs directly over data link layers such as Point-to-Point Protocol (PPP) or IEEE 802, without requiring IP. EAP provides its own support for duplicate elimination and retransmission, but is reliant on lower layer ordering guarantees. Fragmentation is not supported within EAP itself; however, individual EAP methods may support this. This document obsoletes RFC 2284. A summary of the changes between this document and RFC 2284 is available in Appendix A. [STANDARDS-TRACK] This document describes the MOBIKE protocol, a mobility and multihoming extension to Internet Key Exchange (IKEv2). MOBIKE allows the IP addresses associated with IKEv2 and tunnel mode IPsec Security Associations to change. A mobile Virtual Private Network (VPN) client could use MOBIKE to keep the connection with the VPN gateway active while moving from one address to another. Similarly, a multihomed host could use MOBIKE to move the traffic to a different interface if, for instance, the one currently being used stops working. [STANDARDS-TRACK] This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK]