Network Working Group                                           T. Pauly
Internet-Draft                                                Apple Inc.
Intended status: Informational                                C. Perkins
Expires: January 1, 2019                           University of Glasgow
                                                                 K. Rose
                                               Akamai Technologies, Inc.
                                                                 C. Wood
                                                              Apple Inc.
                                                           June 30, 2018

                A Survey of Transport Security Protocols


   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 [RFC8095] by
   describing the interfaces required to add security protocols.  It
   examines Transport Layer Security (TLS), Datagram Transport Layer
   Security (DTLS), Quick UDP Internet Connections with TLS (QUIC +
   TLS), MinimalT, CurveCP, tcpcrypt, Internet Key Exchange with
   Encapsulating Security Protocol (IKEv2 + ESP), SRTP (with DTLS), and
   WireGuard.  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 TAPS system may need to support.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 1, 2019.

Pauly, et al.            Expires January 1, 2019                [Page 1]

Internet-Draft          transport security survey              June 2018

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Security Features . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Transport Security Protocol Descriptions  . . . . . . . . . .   7
     4.1.  TLS . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
       4.1.1.  Protocol Description  . . . . . . . . . . . . . . . .   7
       4.1.2.  Protocol Features . . . . . . . . . . . . . . . . . .   8
       4.1.3.  Protocol Dependencies . . . . . . . . . . . . . . . .   9
     4.2.  DTLS  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
       4.2.1.  Protocol Description  . . . . . . . . . . . . . . . .   9
       4.2.2.  Protocol Features . . . . . . . . . . . . . . . . . .  10
       4.2.3.  Protocol Dependencies . . . . . . . . . . . . . . . .  10
     4.3.  (IETF) QUIC with TLS  . . . . . . . . . . . . . . . . . .  10
       4.3.1.  Protocol Description  . . . . . . . . . . . . . . . .  10
       4.3.2.  Protocol Features . . . . . . . . . . . . . . . . . .  11
       4.3.3.  Protocol Dependencies . . . . . . . . . . . . . . . .  11
       4.3.4.  Variant: Google QUIC  . . . . . . . . . . . . . . . .  11
     4.4.  IKEv2 with ESP  . . . . . . . . . . . . . . . . . . . . .  12
       4.4.1.  Protocol descriptions . . . . . . . . . . . . . . . .  12
       4.4.2.  Protocol features . . . . . . . . . . . . . . . . . .  13
       4.4.3.  Protocol dependencies . . . . . . . . . . . . . . . .  14
     4.5.  Secure RTP (with DTLS)  . . . . . . . . . . . . . . . . .  14
       4.5.1.  Protocol description  . . . . . . . . . . . . . . . .  14
       4.5.2.  Protocol features . . . . . . . . . . . . . . . . . .  15
       4.5.3.  Protocol dependencies . . . . . . . . . . . . . . . .  16
       4.5.4.  Variant: ZRTP for Media Path Key Agreement  . . . . .  16
     4.6.  tcpcrypt  . . . . . . . . . . . . . . . . . . . . . . . .  16
       4.6.1.  Protocol Description  . . . . . . . . . . . . . . . .  16
       4.6.2.  Protocol Features . . . . . . . . . . . . . . . . . .  17
       4.6.3.  Protocol Dependencies . . . . . . . . . . . . . . . .  18
     4.7.  WireGuard . . . . . . . . . . . . . . . . . . . . . . . .  18

Pauly, et al.            Expires January 1, 2019                [Page 2]

Internet-Draft          transport security survey              June 2018

       4.7.1.  Protocol description  . . . . . . . . . . . . . . . .  18
       4.7.2.  Protocol features . . . . . . . . . . . . . . . . . .  19
       4.7.3.  Protocol dependencies . . . . . . . . . . . . . . . .  19
     4.8.  MinimalT  . . . . . . . . . . . . . . . . . . . . . . . .  19
       4.8.1.  Protocol Description  . . . . . . . . . . . . . . . .  19
       4.8.2.  Protocol Features . . . . . . . . . . . . . . . . . .  20
       4.8.3.  Protocol Dependencies . . . . . . . . . . . . . . . .  20
     4.9.  CurveCP . . . . . . . . . . . . . . . . . . . . . . . . .  20
       4.9.1.  Protocol Description  . . . . . . . . . . . . . . . .  20
       4.9.2.  Protocol Features . . . . . . . . . . . . . . . . . .  22
       4.9.3.  Protocol Dependencies . . . . . . . . . . . . . . . .  22
   5.  Security Features and Transport Dependencies  . . . . . . . .  22
     5.1.  Mandatory Features  . . . . . . . . . . . . . . . . . . .  22
     5.2.  Optional Features . . . . . . . . . . . . . . . . . . . .  23
     5.3.  Optional Feature Availability . . . . . . . . . . . . . .  25
   6.  Transport Security Protocol Interfaces  . . . . . . . . . . .  25
     6.1.  Pre-Connection Interfaces . . . . . . . . . . . . . . . .  26
     6.2.  Connection Interfaces . . . . . . . . . . . . . . . . . .  27
     6.3.  Post-Connection Interfaces  . . . . . . . . . . . . . . .  27
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  28
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   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 [RFC8095] by
   describing the interfaces required to add security protocols.  It
   examines Transport Layer Security (TLS), Datagram Transport Layer
   Security (DTLS), Quick UDP Internet Connections with TLS (QUIC +
   TLS), MinimalT, CurveCP, tcpcrypt, Internet Key Exchange with
   Encapsulating Security Protocol (IKEv2 + ESP), SRTP (with DTLS), and
   WireGuard.  For each protocol, this document provides a brief
   description, the security features it provides, and the dependencies
   it has on the underlying transport.  This is followed by defining the
   set of transport security features shared by these protocols.
   Finally, we distill the application and transport interfaces provided
   by the transport security protocols.

   Selected protocols represent a superset of functionality and features
   a TAPS system may need to support, both internally and externally -
   via an API - for applications [I-D.ietf-taps-arch].  Ubiquitous IETF
   protocols such as (D)TLS, as well as non-standard protocols such as
   Google QUIC, are both included despite overlapping features.  As

Pauly, et al.            Expires January 1, 2019                [Page 3]

Internet-Draft          transport security survey              June 2018

   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 important implications on applications, such as how to best
   configure peer public keys and to delegate algorithm selection to the
   system.  In contrast, protocols such as ALTS [ALTS] are omitted since
   they do not represent features deemed unique.

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

2.  Terminology

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

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

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

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

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

   o  Security Feature: a feature that a network security layer provides
      to applications.  Examples include authentication, encryption, key
      generation, session resumption, and privacy.  Features may be
      Mandatory or Optional for an application's implementation.

Pauly, et al.            Expires January 1, 2019                [Page 4]

Internet-Draft          transport security survey              June 2018

   o  Security Protocol: a defined network protocol that implements one
      or more security features.  Security protocols may be used
      alongside transport protocols, and in combination with other
      security protocols when appropriate.

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

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

   o  Session: an ephemeral security association between applications.

   o  Cryptographic context: a set of cryptographic parameters,
      including but not necessarily limited to keys for encryption,
      authentication, and session resumption, enabling authorized
      parties to a session to communicate securely.

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

   o  Connection Mobility: a property of a connection that allows it to
      be multihomed or resilient across network interface or address

   o  Peer: an endpoint application party to a session.

   o  Client: the peer responsible for initiating a session.

   o  Server: the peer responsible for responding to a session

3.  Security Features

   In this section, we enumerate Security Features exposed by protocols
   discussed in the remainder of this document.  Protocol security
   properties that are unrelated to the API surface exposed by such
   protocols, such as client or server identity hiding, are not listed
   here as features.

   o  Forward-secure key establishment: Cryptographic key establishment
      with forward secure properties.

Pauly, et al.            Expires January 1, 2019                [Page 5]

Internet-Draft          transport security survey              June 2018

   o  Cryptographic algorithm negotiation: Negotiate support of protocol
      algorithms, including: encryption, hash, MAC (PRF), and digital
      signature algorithms.

   o  Stateful and stateless cross-connection session resumption:
      Connection establishment without needing to complete an entirely
      new handshake.

   o  Peer authentication (certificate, raw public key, pre-shared key,
      or EAP-based): Peer authentication using select or protocol-
      specific mechanisms.

   o  Mutual authentication: Connection establishment wherein both
      endpoints are authenticated.

   o  Record (channel or datagram) confidentiality and integrity:
      Encryption and authentication of application plaintext bytes sent
      between peers over a channel or in individual datagrams.

   o  Partial record confidentiality: Encryption of some portion of

   o  Optional record integrity: Optional authentication of certain

   o  Record replay prevention: Protocol detection and defense against
      record replays, e.g., due to in-network retransmissions.

   o  Application-layer feature negotiation: Securely negotiate
      application-specific functionality.

   o  Early data support (starting with TLS 1.3): Transmission of
      application data prior to connection (handshake) establishment.

   o  Connection mobility: Connection continuation in the presence of
      5-tuple changes beneath the secure transport protocol, e.g., due
      to NAT rebindings.

   o  Application-layer authentication delegation: Out-of-band peer
      authentication performed by applications outside of the connection

   o  Out-of-order record receipt: Processing of records received out-

   o  DoS mitigation (cookie or puzzle based): Peer DoS mitigation via
      explicit proof of origin (cookie) or work mechanisms (puzzles).

Pauly, et al.            Expires January 1, 2019                [Page 6]

Internet-Draft          transport security survey              June 2018

   o  Connection re-keying: In-band cryptographic handshake re-keying.

   o  Optional length-hiding and anti-amplification padding: Protocol-
      drive record padding aimed at hiding plaintext message length and
      mitigating amplification attack vectors.

4.  Transport Security Protocol Descriptions

   This section contains descriptions of security protocols currently
   used to protect data being sent over a network.

   For each protocol, we describe its provided features and dependencies
   on other protocols.

4.1.  TLS

   TLS (Transport Layer Security) [RFC5246] is a common protocol used to
   establish a secure session between two endpoints.  Communication over
   this session "prevents eavesdropping, tampering, and message
   forgery."  TLS consists of a tightly coupled handshake and record
   protocol.  The handshake protocol is used to authenticate peers,
   negotiate protocol options, such as cryptographic algorithms, and
   derive session-specific keying material.  The record protocol is used
   to marshal (possibly encrypted) data from one peer to the other.
   This data may contain handshake messages or raw application data.

4.1.1.  Protocol Description

   TLS is the composition of a handshake and record protocol
   [I-D.ietf-tls-tls13].  The record protocol is designed to marshal an
   arbitrary, in-order stream of bytes from one endpoint to the other.
   It handles segmenting, compressing (when enabled), and encrypting
   data into discrete records.  When configured to use an authenticated
   encryption with associated data (AEAD) algorithm, it also handles
   nonce generation and encoding for each record.  The record protocol
   is hidden from the client behind a bytestream-oriented API.

   The handshake protocol serves several purposes, including: peer
   authentication, protocol option (key exchange algorithm and
   ciphersuite) negotiation, and key derivation.  Peer authentication
   may be mutual; however, commonly, only the server is authenticated.
   X.509 certificates are commonly used in this authentication step,
   though other mechanisms, such as raw public keys [RFC7250], exist.
   The client is not authenticated unless explicitly requested by the
   server with a CertificateRequest handshake message.  Assuming strong
   cryptography, an infrastructure for trust establishment, correctly-
   functioning endpoints, and communication patterns free from side

Pauly, et al.            Expires January 1, 2019                [Page 7]

Internet-Draft          transport security survey              June 2018

   channels, server authentication is sufficient to establish a channel
   resistant to eavesdroppers.

   The handshake protocol is also extensible.  It allows for a variety
   of extensions to be included by either the client or server.  These
   extensions are used to specify client preferences, e.g., the
   application-layer protocol to be driven with the TLS connection
   [RFC7301], or signals to the server to aid operation, e.g., Server
   Name Indication (SNI) [RFC6066].  Various extensions also exist to
   tune the parameters of the record protocol, e.g., the maximum
   fragment length [RFC6066].

   Alerts are used to convey errors and other atypical events to the
   endpoints.  There are two classes of alerts: closure and error
   alerts.  A closure alert is used to signal to the other peer that the
   sender wishes to terminate the connection.  The sender typically
   follows a close alert with a TCP FIN segment to close the connection.
   Error alerts are used to indicate problems with the handshake or
   individual records.  Most errors are fatal and are followed by
   connection termination.  However, warning alerts may be handled at
   the discretion of the implementation.

   Once a session is disconnected all session keying material must be
   destroyed, with the exception of secrets previously established
   expressly for purposes of session resumption.  TLS supports stateful
   and stateless resumption.  (Here, "state" refers to bookkeeping on a
   per-session basis by the server.  It is assumed that the client must
   always store some state information in order to resume a session.)

4.1.2.  Protocol Features

   o  Forward-secure key establishment.

   o  Cryptographic algorithm negotiation.

   o  Stateful and stateless cross-connection session resumption.

   o  Peer authentication (Certificate, raw public key, and pre-shared

   o  Mandatory server authentication, optional client authentication.

   o  Record (channel) confidentiality and integrity.

   o  Record replay prevention.

   o  Application-layer feature negotiation.

Pauly, et al.            Expires January 1, 2019                [Page 8]

Internet-Draft          transport security survey              June 2018

   o  Early data support (starting with TLS 1.3).

   o  Optional length-hiding padding (starting with TLS 1.3).

4.1.3.  Protocol Dependencies

   o  TCP for in-order, reliable transport.

   o  (Optionally) A PKI trust store for certificate validation.

4.2.  DTLS

   DTLS (Datagram Transport Layer Security) [RFC6347] is based on TLS,
   but differs in that it is designed to run over UDP instead of TCP.
   Since UDP does not guarantee datagram ordering or reliability, DTLS
   modifies the protocol to make sure it can still provide the same
   security guarantees as TLS.  DTLS was designed to be as close to TLS
   as possible, so this document will assume that all properties from
   TLS are carried over except where specified.

4.2.1.  Protocol Description

   DTLS is modified from TLS to operate with the possibility of packet
   loss, reordering, and duplication that may occur when operating over
   UDP.  To enable out-of-order delivery of application data, the DTLS
   record protocol itself has no inter-record dependencies.  However, as
   the handshake requires reliability, each handshake message is
   assigned an explicit sequence number to enable retransmissions of
   lost packets and in-order processing by the receiver.  Handshake
   message loss is remedied by sender retransmission after a
   configurable period in which the expected response has not yet been

   As the DTLS handshake protocol runs atop the record protocol, to
   account for long handshake messages that cannot fit within a single
   record, DTLS supports fragmentation and subsequent reconstruction of
   handshake messages across records.  The receiver must reassemble
   records before processing.

   DTLS relies on unique UDP 4-tuples to identify connections.  Since
   all application-layer data is encrypted, demultiplexing over the same
   4-tuple requires the use of a connection identifier extension
   [I-D.ietf-tls-dtls-connection-id] to permit identification of the
   correct connection-specific cryptographic context without the use of
   trial decryption.  (Note that this extension is only supported in
   DTLS 1.2 and 1.3 {{I-D.ietf-tls-dtls13}.)

Pauly, et al.            Expires January 1, 2019                [Page 9]

Internet-Draft          transport security survey              June 2018

   Since datagrams can be replayed, DTLS provides optional anti-replay
   detection based on a window of acceptable sequence numbers [RFC6347].

4.2.2.  Protocol Features

   o  Record replay protection.

   o  Record (datagram) confidentiality and integrity.

   o  Out-of-order record receipt.

   o  DoS mitigation (cookie-based).

   See also the features from TLS.

4.2.3.  Protocol Dependencies

   o  Since DTLS runs over an unreliable, unordered datagram transport,
      it does not require any reliability features.

   o  The DTLS record protocol explicitly encodes record lengths, so
      although it runs over a datagram transport, it does not rely on
      the transport protocol's framing beyond requiring transport-level
      reconstruction of datagrams fragmented over packets.  (Note: DTLS
      1.3 short header records omit the explicit length field.)

   o  UDP 4-tuple uniqueness, or the connection identifier extension,
      for demultiplexing.

   o  Path MTU discovery.

4.3.  (IETF) QUIC with TLS

   QUIC (Quick UDP Internet Connections) is a new standards-track
   transport protocol that runs over UDP, loosely based on Google's
   original proprietary gQUIC protocol [I-D.ietf-quic-transport].  (See
   Section 4.3.4 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 over TLS 1.3 [I-D.ietf-quic-tls] has been specified
   to provide this handshake.

4.3.1.  Protocol Description

   As QUIC relies on TLS to secure its transport functions, it creates
   specific integration points between its security and transport

Pauly, et al.            Expires January 1, 2019               [Page 10]

Internet-Draft          transport security survey              June 2018

   o  Starting the handshake to generate keys and provide authentication
      (and providing the transport for the handshake).

   o  Client address validation.

   o  Key ready events from TLS to notify the QUIC transport.

   o  Exporting secrets from TLS to the QUIC transport.

   The QUIC transport layer support multiple streams over a single
   connection.  The first stream is reserved specifically for a TLS
   connection.  The TLS handshake, along with further records, are sent
   over this stream.  This TLS connection follows the TLS standards and
   inherits the security properties of TLS.  The handshake generates
   keys, which are then exported to the rest of the QUIC connection, and
   are used to protect the rest of the streams.

   Initial QUIC messages (packets) are encrypted using "fixed" keys
   derived from the QUIC version and public packet information
   (Connection ID).  Packets are later encrypted using keys derived from
   the TLS traffic secret upon handshake completion.  The TLS 1.3
   handshake for QUIC is used in either a single-RTT mode or a fast-open
   zero-RTT mode.  When zero-RTT handshakes are possible, the encryption
   first transitions to use the zero-RTT keys before using single-RTT
   handshake keys after the next TLS flight.

4.3.2.  Protocol Features

   o  DoS mitigation (cookie-based).

   See also the properties of TLS.

4.3.3.  Protocol Dependencies

   o  QUIC transport relies on UDP.

   o  QUIC transport relies on TLS 1.3 for peer authentication and
      initial key derivation.

   o  TLS within QUIC relies on QUIC for reliable handshake record
      transmission and receipt.

4.3.4.  Variant: 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

Pauly, et al.            Expires January 1, 2019               [Page 11]

Internet-Draft          transport security survey              June 2018

   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.

4.4.  IKEv2 with ESP

   IKEv2 [RFC7296] and ESP [RFC4303] together form the modern IPsec
   protocol suite that encrypts and authenticates IP packets, either as
   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

4.4.1.  Protocol descriptions  IKEv2

   IKEv2 is a control protocol that runs on UDP port 500.  Its primary
   goal is to generate keys for Security Associations (SAs).  An SA
   contains shared (cryptographic) information used for establishing
   other SAs or keying ESP; See Section  IKEv2 first uses a
   Diffie-Hellman key exchange to generate keys for the "IKE SA", which
   is a set of keys used to encrypt further IKEv2 messages.  It then
   goes through a phase of authentication in which both peers present
   blobs signed by a shared secret or private key, after which another
   set of keys is derived, referred to as the "Child SA".  These Child
   SA keys are used by ESP.

   IKEv2 negotiates which protocols are acceptable to each peer for both
   the IKE and Child SAs using "Proposals".  Each proposal may contain
   an encryption algorithm, an authentication algorithm, a Diffie-
   Hellman group, and (for IKE SAs only) a pseudorandom function
   algorithm.  Each peer may support multiple proposals, and the most
   preferred mutually supported proposal is chosen during the handshake.

   The authentication phase of IKEv2 may use Shared Secrets,
   Certificates, Digital Signatures, or an EAP (Extensible
   Authentication Protocol) method.  At a minimum, IKEv2 takes two round
   trips to set up both an IKE SA and a Child SA.  If EAP is used, this
   exchange may be expanded.

   Any SA used by IKEv2 can be rekeyed upon expiration, which is usually
   based either on time or number of bytes encrypted.

   There is an extension to IKEv2 that allows session resumption

Pauly, et al.            Expires January 1, 2019               [Page 12]

Internet-Draft          transport security survey              June 2018

   MOBIKE is a Mobility and Multihoming extension to IKEv2 that allows a
   set of Security Associations to migrate over different addresses and
   interfaces [RFC4555].

   When UDP is not available or well-supported on a network, IKEv2 may
   be encapsulated in TCP [RFC8229].  ESP

   ESP is a protocol that encrypts and authenticates IPv4 and IPv6
   packets.  The keys used for both encryption and authentication can be
   derived from an IKEv2 exchange.  ESP Security Associations come as
   pairs, one for each direction between two peers.  Each SA is
   identified by a Security Parameter Index (SPI), which is marked on
   each encrypted ESP packet.

   ESP packets include the SPI, a sequence number, an optional
   Initialization Vector (IV), payload data, padding, a length and next
   header field, and an Integrity Check Value.

   From [RFC4303], "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

   Since ESP operates on IP packets, it is not directly tied to the
   transport protocols it encrypts.  This means it requires little or no
   change from transports in order to provide security.

   ESP packets may be sent directly over IP, but where network
   conditions warrant (e.g., when a NAT is present or when a firewall
   blocks such packets) they may be encapsulated in UDP [RFC3948] or TCP

4.4.2.  Protocol features  IKEv2

   o  Forward-secure key establishment.

   o  Cryptographic algorithm negotiation.

   o  Peer authentication (Certificate, raw public key, pre-shared key,
      and EAP).

   o  Mutual authentication.

   o  Record (datagram) confidentiality and integrity.

Pauly, et al.            Expires January 1, 2019               [Page 13]

Internet-Draft          transport security survey              June 2018

   o  Session resumption.

   o  Connection mobility.

   o  DoS mitigation (cookie-based).  ESP

   o  Record confidentiality and integrity.

   o  Record replay protection.

4.4.3.  Protocol dependencies  IKEv2

   o  Availability of UDP to negotiate, or implementation support for

   o  Some EAP authentication types require accessing a hardware device,
      such as a SIM card; or interacting with a user, such as password
      prompting.  ESP

   o  Since ESP is below transport protocols, it does not have any
      dependencies on the transports themselves, other than on UDP or
      TCP where encapsulation is employed.

4.5.  Secure RTP (with DTLS)

   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].

4.5.1.  Protocol description

   SRTP adds confidentiality and optional integrity protection to RTP
   data packets, and adds confidentially and mandatory integrity
   protection to RTCP packets.  For RTP data packets, this is done by
   encrypting the payload section of the packet and optionally appending
   an authentication tag (MAC) as a packet trailer, with the RTP header
   authenticated but not encrypted (the RTP header was left unencrypted
   to enable RTP header compression [RFC2508] [RFC3545]).  For RTCP
   packets, the first packet in the compound RTCP packet is partially
   encrypted, leaving the first eight octets of the header as clear-text
   to allow identification of the packet as RTCP, while the remainder of

Pauly, et al.            Expires January 1, 2019               [Page 14]

Internet-Draft          transport security survey              June 2018

   the compound packet is fully encrypted.  The entire RTCP packet is
   then authenticated by appending a MAC as packet trailer.

   Packets are encrypted using session keys, which are ultimately
   derived from a master key and an additional master salt and session
   salt.  SRTP packets carry a 2-byte sequence number to partially
   identify the unique packet index.  SRTP peers maintain a separate
   roll-over counter (ROC) for RTP data packets that is incremented
   whenever the sequence number wraps.  The sequence number and ROC
   together determine the packet index.  RTCP packets have a similar,
   yet differently named, field called the RTCP index which serves the
   same purpose.

   Numerous encryption modes are supported.  For popular modes of
   operation, e.g., AES-CTR, the (unique) initialization vector (IV)
   used for each encryption mode is a function of the RTP SSRC
   (synchronization source), packet index, and session "salting key".

   SRTP offers replay detection by keeping a replay list of already seen
   and processed packet indices.  If a packet arrives with an index that
   matches one in the replay list, it is silently discarded.

   DTLS [RFC5764] is commonly used to perform mutual authentication and
   key agreement for SRTP [RFC5763].  Peers use DTLS to perform mutual
   certificate-based authentication on the media path, and to generate
   the SRTP master key.  Peer certificates can be issued and signed by a
   certificate authority.  Alternatively, certificates used in the DTLS
   exchange can be self-signed.  If they are self-signed, certificate
   fingerprints are included in the signalling exchange (e.g., in SIP or
   WebRTC), and used to bind the DTLS key exchange in the media plane to
   the signaling plane.  The combination of a mutually authenticated
   DTLS key exchange on the media path and a fingerprint sent in the
   signalling channel protects against active attacks on the media,
   provided the signalling can be trusted.  Signalling needs to be
   protected as described in, for example, SIP [RFC3261] Authenticated
   Identity Management [RFC4474] or the WebRTC security architecture
   [I-D.ietf-rtcweb-security-arch], to provide complete system security.

4.5.2.  Protocol features

   o  Forward-secure key establishment.

   o  Cryptographic algorithm negotiation.

   o  Mutual authentication.

   o  Partial datagram confidentiality.  (Packet headers are not

Pauly, et al.            Expires January 1, 2019               [Page 15]

Internet-Draft          transport security survey              June 2018

   o  Optional authentication of data packets.

   o  Mandatory authentication of control packets.

   o  Out-of-order record receipt.

4.5.3.  Protocol dependencies

   o  External key derivation and management protocol, e.g., DTLS

   o  External identity management protocol, e.g., SIP Authenticated
      Identity Management [RFC4474], WebRTC Security Architecture

4.5.4.  Variant: ZRTP for Media Path Key Agreement

   ZRTP [RFC6189] is an alternative key agreement protocol for SRTP.  It
   uses standard SRTP to protect RTP data packets and RTCP packets, but
   provides alternative key agreement and identity management protocols.

   Key agreement is performed using a Diffie-Hellman key exchange that
   runs on the media path.  This generates a shared secret that is then
   used to generate the master key and salt for SRTP.

   ZRTP does not rely on a PKI or external identity management system.
   Rather, it uses an ephemeral Diffie-Hellman key exchange with hash
   commitment to allow detection of man-in-the-middle attacks.  This
   requires endpoints to display a short authentication string that the
   users must read and verbally compare to validate the hashes and
   ensure security.  Endpoints cache some key material after the first
   call to use in subsequent calls; this is mixed in with the Diffie-
   Hellman shared secret, so the short authentication string need only
   be checked once for a given user.  This gives key continuity
   properties analogous to the secure shell (ssh) [RFC4253].

4.6.  tcpcrypt

   Tcpcrypt is a lightweight extension to the TCP protocol to enable
   opportunistic encryption with hooks available to the application
   layer for implementation of endpoint authentication.

4.6.1.  Protocol Description

   Tcpcrypt extends TCP to enable opportunistic encryption between the
   two ends of a TCP connection [I-D.ietf-tcpinc-tcpcrypt].  It is a
   family of TCP encryption protocols (TEP), distinguished by key
   exchange algorithm.  The use of a TEP is negotiated with a TCP option

Pauly, et al.            Expires January 1, 2019               [Page 16]

Internet-Draft          transport security survey              June 2018

   during the initial TCP handshake via the mechanism described by TCP
   Encryption Negotiation Option (ENO) [I-D.ietf-tcpinc-tcpeno].  In the
   case of initial session establishment, once a tcpcrypt TEP has been
   negotiated the key exchange occurs within the data segments of the
   first few packets exchanged after the handshake completes.  The
   initiator of a connection sends a list of supported AEAD algorithms,
   a random nonce, and an ephemeral public key share.  The responder
   typically chooses a mutually-supported AEAD algorithm and replies
   with this choice, its own nonce, and ephemeral key share.  An initial
   shared secret is derived from the ENO handshake, the tcpcrypt
   handshake, and the initial keying material resulting from the key
   exchange.  The traffic encryption keys on the initial connection are
   derived from the shared secret.  Connections can be re-keyed before
   the natural AEAD limit for a single set of traffic encryption keys is

   Each tcpcrypt session is associated with a ladder of resumption IDs,
   each derived from the respective entry in a ladder of shared secrets.
   These resumption IDs can be used to negotiate a stateful resumption
   of the session in a subsequent connection, resulting in use of a new
   shared secret and traffic encryption keys without requiring a new key
   exchange.  Willingness to resume a session is signaled via the ENO
   option during the TCP handshake.  Given the length constraints
   imposed by TCP options, unlike stateless resumption mechanisms (such
   as that provided by session tickets in TLS) resumption in tcpcrypt
   requires the maintenance of state on the server, and so successful
   resumption across a pool of servers implies shared state.

   Owing to middlebox ossification issues, tcpcrypt only protects the
   payload portion of a TCP packet.  It does not encrypt any header
   information, such as the TCP sequence number.

   Tcpcrypt exposes a universally-unique connection-specific session ID
   to the application, suitable for application-level endpoint
   authentication either in-band or out-of-band.

4.6.2.  Protocol Features

   o  Forward-secure key establishment.

   o  Record (channel) confidentiality and integrity.

   o  Stateful cross-connection session resumption.

   o  Connection re-keying.

   o  Application authentication delegation.

Pauly, et al.            Expires January 1, 2019               [Page 17]

Internet-Draft          transport security survey              June 2018

4.6.3.  Protocol Dependencies

   o  TCP

   o  TCP Encryption Negotiation Option (ENO)

4.7.  WireGuard

   WireGuard is a layer 3 protocol designed to complement or replace
   IPsec [WireGuard].  Unlike most transport security protocols, which
   rely on PKI for peer authentication, WireGuard authenticates peers
   using pre-shared public keys delivered out-of-band, each of which is
   bound to one or more IP addresses.  Moreover, as a protocol suited
   for VPNs, WireGuard offers no extensibility, negotiation, or
   cryptographic agility.

4.7.1.  Protocol description

   WireGuard is a simple VPN protocol that binds a pre-shared public key
   to one or more IP addresses.  Users configure WireGuard by
   associating peer public keys with IP addresses.  These mappings are
   stored in a CryptoKey Routing Table.  (See Section 2 of [WireGuard]
   for more details and sample configurations.)  These keys are used
   upon WireGuard packet transmission and reception.  For example, upon
   receipt of a Handshake Initiation message, receivers use the static
   public key in their CryptoKey routing table to perform necessary
   cryptographic computations.

   WireGuard builds on Noise [Noise] for 1-RTT key exchange with
   identity hiding.  The handshake hides peer identities as per the
   SIGMA construction [SIGMA].  As a consequence of using Noise,
   WireGuard comes with a fixed set of cryptographic algorithms:

   o  x25519 [Curve25519] and HKDF [RFC5869] for ECDH and key

   o  ChaCha20+Poly1305 [RFC7539] for packet authenticated encryption.

   o  BLAKE2s [BLAKE2] for hashing.

   There is no cryptographic agility.  If weaknesses are found in any of
   these algorithms, new message types using new algorithms must be

   WireGuard is designed to be entirely stateless, modulo the CryptoKey
   routing table, which has size linear with the number of trusted
   peers.  If a WireGuard receiver is under heavy load and cannot
   process a packet, e.g., cannot spare CPU cycles for point

Pauly, et al.            Expires January 1, 2019               [Page 18]

Internet-Draft          transport security survey              June 2018

   multiplication, it can reply with a cookie similar to DTLS and IKEv2.
   This cookie only proves IP address ownership.  Any rate limiting
   scheme can be applied to packets coming from non-spoofed addresses.

4.7.2.  Protocol features

   o  Forward-secure key establishment.

   o  Peer authentication (Public-key and PSK).

   o  Mutual authentication.

   o  Record replay prevention (Stateful, timestamp-based).

   o  DoS mitigation (cookie-based).

4.7.3.  Protocol dependencies

   o  Datagram transport.

   o  Out-of-band key distribution and management.

4.8.  MinimalT

   MinimalT is a UDP-based transport security protocol designed to offer
   confidentiality, mutual authentication, DoS prevention, and
   connection mobility [MinimalT].  One major goal of the protocol is to
   leverage existing protocols to obtain server-side configuration
   information used to more quickly bootstrap a connection.  MinimalT
   uses a variant of TCP's congestion control algorithm.

4.8.1.  Protocol Description

   MinimalT is a secure transport protocol built on top of a widespread
   directory service.  Clients and servers interact with local directory
   services to (a) resolve server information and (b) public ephemeral
   state information, respectively.  Clients connect to a local resolver
   once at boot time.  Through this resolver they recover the IP
   address(es) and public key(s) of each server to which they want to

   Connections are instances of user-authenticated, mobile sessions
   between two endpoints.  Connections run within tunnels between hosts.
   A tunnel is a server-authenticated container that multiplexes
   multiple connections between the same hosts.  All connections in a
   tunnel share the same transport state machine and encryption.  Each
   tunnel has a dedicated control connection used to configure and
   manage the tunnel over time.  Moreover, since tunnels are independent

Pauly, et al.            Expires January 1, 2019               [Page 19]

Internet-Draft          transport security survey              June 2018

   of the network address information, they may be reused as both ends
   of the tunnel move about the network.  This does however imply that
   the connection establishment and packet encryption mechanisms are

   Before a client connects to a remote service, it must first establish
   a tunnel to the host providing or offering the service.  Tunnels are
   established in 1-RTT using an ephemeral key obtained from the
   directory service.  Tunnel initiators provide their own ephemeral key
   and, optionally, a DoS puzzle solution such that the recipient
   (server) can verify the authenticity of the request and derive a
   shared secret.  Within a tunnel, new connections to services may be

4.8.2.  Protocol Features

   o  Forward-secure key establishment.

   o  DoS mitigation (puzzle-based).

   o  Connection mobility (tunnel-based).

   Additional (orthogonal) transport features include: connection
   multiplexing between hosts across shared tunnels, and congestion
   control state is shared across connections between the same host

4.8.3.  Protocol Dependencies

   o  A DNS-like resolution service to obtain location information (an
      IP address) and ephemeral keys.

   o  A PKI trust store for certificate validation.

4.9.  CurveCP

   CurveCP [CurveCP] is a UDP-based transport security protocol from
   Daniel J.  Bernstein.  Unlike other transport security protocols, it
   is based entirely upon highly efficient public key algorithms.  This
   removes many pitfalls associated with nonce reuse and key

4.9.1.  Protocol Description

   CurveCP is a UDP-based transport security protocol.  It is built on
   three principal features: exclusive use of public key authenticated
   encryption of packets, server-chosen cookies to prohibit memory and

Pauly, et al.            Expires January 1, 2019               [Page 20]

Internet-Draft          transport security survey              June 2018

   computation DoS at the server, and connection mobility with a client-
   chosen ephemeral identifier.

   There are two rounds in CurveCP.  In the first round, the client
   sends its first initialization packet to the server, carrying its
   (possibly fresh) ephemeral public key C', with zero-padding encrypted
   under the server's long-term public key.  The server replies with a
   cookie and its own ephemeral key S' and a cookie that is to be used
   by the client.  Upon receipt, the client then generates its second
   initialization packet carrying: the ephemeral key C', cookie, and an
   encryption of C', the server's domain name, and, optionally, some
   message data.  The server verifies the cookie and the encrypted
   payload and, if valid, proceeds to send data in return.  At this
   point, the connection is established and the two parties can

   The use of only public-key encryption and authentication, or
   "boxing", is done to simplify problems that come with symmetric key
   management and synchronization.  For example, it allows the sender of
   a message to be in complete control of each message's nonce.  It does
   not require either end to share secret keying material.  Furthermore,
   it allows connections (or sessions) to be associated with unique
   ephemeral public keys as a mechanism for enabling forward secrecy
   given the risk of long-term private key compromise.

   The client and server do not perform a standard key exchange.
   Instead, in the initial exchange of packets, each party provides its
   own ephemeral key to the other end.  The client can choose a new
   ephemeral key for every new connection.  However, the server must
   rotate these keys on a slower basis.  Otherwise, it would be trivial
   for an attacker to force the server to create and store ephemeral
   keys with a fake client initialization packet.

   Unlike TCP, the server employs cookies to enable source validation.
   After receiving the client's initial packet, encrypted under the
   server's long-term public key, the server generates and returns a
   stateless cookie that must be echoed back in the client's following
   message.  This cookie is encrypted under the client's ephemeral
   public key.  This stateless technique prevents attackers from
   hijacking client initialization packets to obtain cookie values to
   flood clients.  (A client would detect the duplicate cookies and
   reject the flooded packets.)  Similarly, replaying the client's
   second packet, carrying the cookie, will be detected by the server.

   CurveCP supports a weak form of client authentication.  Clients are
   permitted to send their long-term public keys in the second
   initialization packet.  A server can verify this public key and, if
   untrusted, drop the connection and subsequent data.

Pauly, et al.            Expires January 1, 2019               [Page 21]

Internet-Draft          transport security survey              June 2018

   Unlike some other protocols, CurveCP data packets leave only the
   ephemeral public key, the connection ID, and the per-message nonce in
   the clear.  Everything else is encrypted.

4.9.2.  Protocol Features

   o  Datagram confidentiality and integrity (via public key

   o  1-RTT session bootstrapping.

   o  Connection mobility (based on a client-chosen ephemeral

   o  Optional length-hiding and anti-amplification padding.

4.9.3.  Protocol Dependencies

   o  An unreliable transport protocol such as UDP.

5.  Security Features and Transport Dependencies

   There exists a common set of features shared across the transport
   protocols surveyed in this document.  Mandatory features constitute a
   baseline of functionality that an application may assume for any TAPS
   implementation.  Optional features by contrast may vary from
   implementation to implementation, and so an application cannot simply
   assume they are available.  Applications learn of and use optional
   features by querying for their presence and support.  Optional
   features may not be implemented, or may be disabled if their presence
   impacts transport services or if a necessary transport service is

5.1.  Mandatory Features

   o  Segment or datagram encryption and authentication: Transit data
      must be protected with an authenticated encryption algorithm.

   o  Forward-secure key establishment: Negotiated keying material must
      come from an authenticated, forward-secure key exchange protocol.

   o  Public-key (raw or certificate) based authentication:
      Authentication based on public key signatures is commonplace for
      many transport security protocols.

   o  Responder authentication: The endpoint (receiver) of a new
      connection must be authenticated before any data is sent to said

Pauly, et al.            Expires January 1, 2019               [Page 22]

Internet-Draft          transport security survey              June 2018

   o  Pre-shared key support: A security protocol must be able to use a
      pre-shared key established out-of-band or from a prior session to
      encrypt individual messages, packets, or datagrams.

5.2.  Optional Features

   o  Cryptographic algorithm negotiation (AN): Transport security
      protocols should permit applications to configure supported or
      enabled cryptographic algorithms.

      *  Transport dependency: None.

      *  Application dependency: Application awareness of supported or
         desired algorithms.

   o  Application authentication delegation (AD): Some protocols may
      completely defer endpoint authentication to applications, e.g., to
      reduce online protocol complexity.

      *  Transport dependency: None.

      *  Application dependency: Application opt-in and policy for
         endpoint authentication

   o  Mutual authentication (MA): Transport security protocols should
      allow each endpoint to authenticate the other if required by the

      *  Transport dependency: None.

      *  Application dependency: Mutual authentication required for
         application support.

   o  DoS mitigation (DM): Transport security protocols may need to
      support volumetric DoS prevention via, e.g., cookies or initiator-
      side puzzles.

      *  Transport dependency: None.

      *  Application dependency: None.

   o  Connection mobility (CM): Sessions should not be bound to a
      network connection (or 5-tuple).  This allows cryptographic key
      material and other state information to be reused in the event of
      a connection change.  Examples of this include a NAT rebinding
      that occurs without a client's knowledge.

Pauly, et al.            Expires January 1, 2019               [Page 23]

Internet-Draft          transport security survey              June 2018

      *  Transport dependency: Connections are unreliable or can change
         due to unpredictable network events, e.g., NAT re-bindings.

      *  Application dependency: None.

   o  Source validation (SV): Source validation must be provided to
      mitigate server-targeted DoS attacks.  This can be done with
      puzzles or cookies.

      *  Transport dependency: Packets may arrive as datagrams instead
         of streams from unauthenticated sources.

      *  Application dependency: None.

   o  Application-layer feature negotiation (AFN): The type of
      application using a transport security protocol often requires
      features configured at the connection establishment layer, e.g.,
      ALPN [RFC7301].  Moreover, application-layer features may often be
      used to offload the session to another server which can better
      handle the request.  (The TLS SNI is one example of such a
      feature.)  As such, transport security protocols should provide a
      generic mechanism to allow for such application-specific features
      and options to be configured or otherwise negotiated.

      *  Transport dependency: None.

      *  Application dependency: Specification of application-layer
         features or functionality.

   o  Configuration extensions (CX): The protocol negotiation should be
      extensible with addition of new configuration options.

      *  Transport dependency: None.

      *  Application dependency: Specification of application-specific

   o  Session caching and management (SC): Sessions should be cacheable
      to enable reuse and amortize the cost of performing session
      establishment handshakes.

      *  Transport dependency: None.

      *  Application dependency: None.

   o  Length-hiding padding (LHP): Applications may wish to defer
      traffic padding to the security protocol to deter traffic analysis

Pauly, et al.            Expires January 1, 2019               [Page 24]

Internet-Draft          transport security survey              June 2018

      *  Transport dependency: None.

      *  Application dependency: Knowledge of desired padding policies.

5.3.  Optional Feature Availability

   The following table lists the availability of the above-listed
   optional features in each of the analyzed protocols.  "Mandatory"
   indicates that the feature is intrinsic to the protocol and cannot be
   disabled.  "Supported" indicates that the feature is optionally
   provided natively or through a (standardized, where applicable)

    | Protocol  | AN | AD | MA |  DM | CM | SV | AFN | CX | SC | LHP |
    | TLS       | S  | S  | S  |  S  | U* | M  |  S  | S  | S  |  S  |
    |           |    |    |    |     |    |    |     |    |    |     |
    | DTLS      | S  | S  | S  |  S  | S  | M  |  S  | S  | S  |  S  |
    |           |    |    |    |     |    |    |     |    |    |     |
    | IETF QUIC | S  | S  | S  |  S  | S  | M  |  S  | S  | S  |  S  |
    |           |    |    |    |     |    |    |     |    |    |     |
    | IKEv2+ESP | S  | S  | M  |  S  | S  | M  |  S  | S  | S  |  S  |
    |           |    |    |    |     |    |    |     |    |    |     |
    | SRTP+DTLS | S  | S  | S  |  S  | U  | M  |  S  | S  | S  |  U  |
    |           |    |    |    |     |    |    |     |    |    |     |
    | tcpcrypt  | S  | M  | U  | U** | U* | M  |  U  | U  | S  |  U  |
    |           |    |    |    |     |    |    |     |    |    |     |
    | WireGuard | U  | S  | M  |  S  | U  | M  |  U  | U  | U  |  S+ |
    |           |    |    |    |     |    |    |     |    |    |     |
    | MinimalT  | U  | U  | M  |  S  | M  | M  |  U  | U  | U  |  S  |
    |           |    |    |    |     |    |    |     |    |    |     |
    | CurveCP   | U  | U  | S  |  S  | M  | M  |  U  | U  | U  |  S  |

   S=Supported but not required
   *=On TCP; MPTCP would provide this ability
   **=TCP provides SYN cookies natively, but these are not
   cryptographically strong
   +=For transport packets only

6.  Transport Security Protocol Interfaces

   This section describes the interface surface exposed by the security
   protocols described above.  Note that not all protocols support each

Pauly, et al.            Expires January 1, 2019               [Page 25]

Internet-Draft          transport security survey              June 2018

   interface.  We partition these interfaces into pre-connection
   (configuration), connection, and post-connection interfaces.

6.1.  Pre-Connection Interfaces

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

   o  Identity and Private Keys
      The application can provide its identities (certificates) and
      private keys, or mechanisms to access these, to the security
      protocol to use during handshakes.
      Protocols: TLS, DTLS, QUIC + TLS, MinimalT, CurveCP, IKEv2,
      WireGuard, SRTP

   o  Supported Algorithms (Key Exchange, Signatures, and Ciphersuites)
      The application can choose the algorithms that are supported for
      key exchange, signatures, and ciphersuites.
      Protocols: TLS, DTLS, QUIC + TLS, MinimalT, tcpcrypt, IKEv2, SRTP

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

   o  Authentication Delegation
      The application provides access to a separate module that will
      provide authentication, using EAP for example.
      Protocols: IKEv2, SRTP

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

      *  Explict import: QUIC, ESP

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

      *  Non-importable: CurveCP

Pauly, et al.            Expires January 1, 2019               [Page 26]

Internet-Draft          transport security survey              June 2018

6.2.  Connection Interfaces

   o  Identity Validation
      During a handshake, the security protocol will conduct identity
      validation of the peer.  This can call into the application to
      offload validation.  Protocols: All (TLS, DTLS, QUIC + TLS,
      MinimalT, CurveCP, IKEv2, WireGuard, SRTP (DTLS))

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

6.3.  Post-Connection Interfaces

   o  Connection Termination The security protocol may be instructed to
      tear down its connection and session information.  This is needed
      by some protocols to prevent application data truncation attacks.
      Protocols: TLS, DTLS, QUIC + TLS, MinimalT, tcpcrypt, IKEv2

   o  Key Update
      The handshake protocol may be instructed to update its keying
      material, either by the application directly or by the record
      protocol sending a key expiration event.
      Protocols: TLS, DTLS, QUIC + TLS, MinimalT, tcpcrypt, IKEv2

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

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

      *  Direct export: TLS, DTLS, MinimalT

      *  Non-exportable: CurveCP

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

Pauly, et al.            Expires January 1, 2019               [Page 27]

Internet-Draft          transport security survey              June 2018

      Protocols: ESP ((Editor's note: One may consider TLS/DTLS to also
      have this interface))

   o  Connection mobility
      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.
      Protocols: QUIC, MinimalT, CurveCP, ESP, WireGuard (roaming)

7.  IANA Considerations

   This document has no request to IANA.

8.  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

9.  Acknowledgments

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

10.  Normative References

   [ALTS]     "Application Layer Transport Security", n.d..

   [BLAKE2]   "BLAKE2 -- simpler, smaller, fast as MD5", n.d..

              "Curve25519 - new Diffie-Hellman speed records", n.d..

   [CurveCP]  "CurveCP -- Usable security for the Internet", n.d..

              Thomson, M. and S. Turner, "Using Transport Layer Security
              (TLS) to Secure QUIC", draft-ietf-quic-tls-13 (work in
              progress), June 2018.

Pauly, et al.            Expires January 1, 2019               [Page 28]

Internet-Draft          transport security survey              June 2018

              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-13 (work
              in progress), June 2018.

              Rescorla, E., "WebRTC Security Architecture", draft-ietf-
              rtcweb-security-arch-14 (work in progress), March 2018.

              Pauly, T., Trammell, B., Brunstrom, A., Fairhurst, G.,
              Perkins, C., Tiesel, P., and C. Wood, "An Architecture for
              Transport Services", draft-ietf-taps-arch-00 (work in
              progress), April 2018.

              Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
              Q., and E. Smith, "Cryptographic protection of TCP Streams
              (tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-12 (work in
              progress), June 2018.

              Bittau, A., Giffin, D., Handley, M., Mazieres, D., and E.
              Smith, "TCP-ENO: Encryption Negotiation Option", draft-
              ietf-tcpinc-tcpeno-19 (work in progress), June 2018.

              Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom,
              "The Datagram Transport Layer Security (DTLS) Connection
              Identifier", draft-ietf-tls-dtls-connection-id-00 (work in
              progress), December 2017.

              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", draft-ietf-tls-dtls13-26 (work in progress), March

              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-28 (work in progress),
              March 2018.

              "MinimaLT -- Minimal-latency Networking Through Better
              Security", n.d..

   [Noise]    "The Noise Protocol Framework", n.d..

Pauly, et al.            Expires January 1, 2019               [Page 29]

Internet-Draft          transport security survey              June 2018

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
              1998, <>.

   [RFC2508]  Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP
              Headers for Low-Speed Serial Links", RFC 2508,
              DOI 10.17487/RFC2508, February 1999,

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,

   [RFC3545]  Koren, T., Casner, S., Geevarghese, J., Thompson, B., and
              P. Ruddy, "Enhanced Compressed RTP (CRTP) for Links with
              High Delay, Packet Loss and Reordering", RFC 3545,
              DOI 10.17487/RFC3545, July 2003,

   [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,

   [RFC3948]  Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
              Stenberg, "UDP Encapsulation of IPsec ESP Packets",
              RFC 3948, DOI 10.17487/RFC3948, January 2005,

   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
              January 2006, <>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474,
              DOI 10.17487/RFC4474, August 2006,

Pauly, et al.            Expires January 1, 2019               [Page 30]

Internet-Draft          transport security survey              June 2018

   [RFC4555]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol
              (MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,

   [RFC5723]  Sheffer, Y. and H. Tschofenig, "Internet Key Exchange
              Protocol Version 2 (IKEv2) Session Resumption", RFC 5723,
              DOI 10.17487/RFC5723, January 2010,

   [RFC5763]  Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
              for Establishing a Secure Real-time Transport Protocol
              (SRTP) Security Context Using Datagram Transport Layer
              Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May
              2010, <>.

   [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,

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5869,
              DOI 10.17487/RFC5869, May 2010,

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <>.

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066,
              DOI 10.17487/RFC6066, January 2011,

   [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,

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <>.

Pauly, et al.            Expires January 1, 2019               [Page 31]

Internet-Draft          transport security survey              June 2018

   [RFC7250]  Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
              Weiler, S., and T. Kivinen, "Using Raw Public Keys in
              Transport Layer Security (TLS) and Datagram Transport
              Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
              June 2014, <>.

   [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, <>.

   [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, <>.

   [RFC7539]  Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
              Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,

   [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,

   [RFC8229]  Pauly, T., Touati, S., and R. Mantha, "TCP Encapsulation
              of IKE and IPsec Packets", RFC 8229, DOI 10.17487/RFC8229,
              August 2017, <>.

   [SIGMA]    "SIGMA -- The 'SIGn-and-MAc' Approach to Authenticated
              Diffie-Hellman and Its Use in the IKE-Protocols", n.d..

              "WireGuard -- Next Generation Kernel Network Tunnel",

Authors' Addresses

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


Pauly, et al.            Expires January 1, 2019               [Page 32]

Internet-Draft          transport security survey              June 2018

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


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


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


Pauly, et al.            Expires January 1, 2019               [Page 33]