Network Working Group C. Wood, Ed.
Internet-Draft Apple Inc.
Intended status: Informational T. Enghardt
Expires: August 30, 2019 TU Berlin
T. Pauly
Apple Inc.
C. Perkins
University of Glasgow
K. Rose
Akamai Technologies, Inc.
February 26, 2019
A Survey of Transport Security Protocols
draft-ietf-taps-transport-security-05
Abstract
This document provides a survey of commonly used or notable network
security protocols, with a focus on how they interact and integrate
with applications and transport protocols. Its goal is to supplement
efforts to define and catalog transport services [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), tcpcrypt, Internet Key Exchange with Encapsulating Security
Protocol (IKEv2 + ESP), SRTP (with DTLS), WireGuard, CurveCP,
MinimalT. 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 https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 30, 2019.
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Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
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. Security Features . . . . . . . . . . . . . . . . . . 8
4.1.3. Protocol Dependencies . . . . . . . . . . . . . . . . 9
4.2. DTLS . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2.1. Protocol Description . . . . . . . . . . . . . . . . 9
4.2.2. Security Features . . . . . . . . . . . . . . . . . . 10
4.2.3. Protocol Dependencies . . . . . . . . . . . . . . . . 10
4.3. (IETF) QUIC with TLS . . . . . . . . . . . . . . . . . . 11
4.3.1. Protocol Description . . . . . . . . . . . . . . . . 11
4.3.2. Security Features . . . . . . . . . . . . . . . . . . 11
4.3.3. Protocol Dependencies . . . . . . . . . . . . . . . . 12
4.3.4. Variant: Google QUIC . . . . . . . . . . . . . . . . 12
4.4. IKEv2 with ESP . . . . . . . . . . . . . . . . . . . . . 12
4.4.1. Protocol descriptions . . . . . . . . . . . . . . . . 12
4.4.2. Security Features . . . . . . . . . . . . . . . . . . 14
4.4.3. Protocol Dependencies . . . . . . . . . . . . . . . . 14
4.5. Secure RTP (with DTLS) . . . . . . . . . . . . . . . . . 15
4.5.1. Protocol description . . . . . . . . . . . . . . . . 15
4.5.2. Security Features . . . . . . . . . . . . . . . . . . 16
4.5.3. Protocol Dependencies . . . . . . . . . . . . . . . . 16
4.5.4. Variant: ZRTP for Media Path Key Agreement . . . . . 16
4.6. tcpcrypt . . . . . . . . . . . . . . . . . . . . . . . . 17
4.6.1. Protocol Description . . . . . . . . . . . . . . . . 17
4.6.2. Security Features . . . . . . . . . . . . . . . . . . 18
4.6.3. Protocol Dependencies . . . . . . . . . . . . . . . . 18
4.7. WireGuard . . . . . . . . . . . . . . . . . . . . . . . . 18
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4.7.1. Protocol description . . . . . . . . . . . . . . . . 18
4.7.2. Security Features . . . . . . . . . . . . . . . . . . 19
4.7.3. Protocol Dependencies . . . . . . . . . . . . . . . . 19
4.8. CurveCP . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.8.1. Protocol Description . . . . . . . . . . . . . . . . 20
4.8.2. Protocol Features . . . . . . . . . . . . . . . . . . 21
4.8.3. Protocol Dependencies . . . . . . . . . . . . . . . . 21
4.9. MinimalT . . . . . . . . . . . . . . . . . . . . . . . . 21
4.9.1. Protocol Description . . . . . . . . . . . . . . . . 22
4.9.2. Protocol Features . . . . . . . . . . . . . . . . . . 22
4.9.3. Protocol Dependencies . . . . . . . . . . . . . . . . 23
4.10. OpenVPN . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.10.1. Protocol Description . . . . . . . . . . . . . . . . 23
4.10.2. Protocol Features . . . . . . . . . . . . . . . . . 24
4.10.3. Protocol Dependencies . . . . . . . . . . . . . . . 24
5. Security Features and Application Dependencies . . . . . . . 24
5.1. Mandatory Features . . . . . . . . . . . . . . . . . . . 25
5.2. Optional Features . . . . . . . . . . . . . . . . . . . . 25
5.3. Optional Feature Availability . . . . . . . . . . . . . . 27
6. Transport Security Protocol Interfaces . . . . . . . . . . . 29
6.1. Pre-Connection Interfaces . . . . . . . . . . . . . . . . 29
6.2. Connection Interfaces . . . . . . . . . . . . . . . . . . 30
6.3. Post-Connection Interfaces . . . . . . . . . . . . . . . 30
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
8. Security Considerations . . . . . . . . . . . . . . . . . . . 31
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 31
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 31
11. Normative References . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
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), tcpcrypt, Internet Key Exchange with Encapsulating Security
Protocol (IKEv2 + ESP), SRTP (with DTLS), WireGuard, CurveCP, and
MinimalT. For each protocol, this document provides a brief
description, the 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.
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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
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.
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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.
Security Features extend the set of Transport Features described
in [RFC8095] and provided by Transport Services implementations.
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: Framed protocol messages.
o Record Protocol: a security protocol that allows data to be
divided into manageable blocks and protected using shared
cryptographic context.
o Session: an ephemeral security association between applications.
o 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 Peer: an endpoint application party to a session.
o Client: the peer responsible for initiating a session.
o Server: the peer responsible for responding to a session
initiation.
3. Security Features
In this section, we enumerate Security Features exposed by protocols
discussed in the remainder of this document. Protocol security (and
privacy) 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.
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o Forward-secure session key establishment: Cryptographic key
establishment with forward secure properties.
o Cryptographic algorithm negotiation: Negotiate support of protocol
algorithms, including: encryption, hash, MAC (PRF), and digital
signature algorithms.
o Session caching and management: Manage session state cache used
for subsequent connections aimed towards amortizing connection
establishment costs.
o Peer authentication (certificate, raw public key, pre-shared key,
or EAP-based): Peer authentication using select or protocol-
specific mechanisms.
o Unilateral responder authentication: Required authentication for
the responder of a connection.
o Mutual authentication: Connection establishment wherein both
endpoints are authenticated.
o Application authentication delegation: Out-of-band peer
authentication performed by applications outside of the connection
establishment.
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
records.
o Optional record integrity: Optional authentication of certain
records.
o Record replay prevention: Protocol detection and defense against
record replays, e.g., due to in-network retransmissions.
o Early data support (starting with TLS 1.3): Transmission of
application data prior to connection (handshake) establishment.
o Connection mobility: a property of a connection that allows it to
be multihomed or resilient across network interface or address
changes, e.g., NAT rebindings that occur without an endpoint's
knowledge. Mobility allows cryptographic key material and other
state information to be reused in the event of a connection
change.
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o Application-layer feature negotiation: Securely negotiate
application-specific functionality, including those necessary for
connection handling and management, e.g., the TLS parent
connection protocol type via ALPN [RFC7301] or desired application
identity via SNI [RFC6066].
o Configuration extensions: Add protocol features via extensions or
configuration options. TLS extensions are a primary example of
this feature.
o Out-of-order record receipt: Processing of records received out-
of-order.
o Source validation (cookie or puzzle based): Peer source validation
and DoS mitigation via explicit proof of origin (cookie) or work
mechanisms (puzzles).
o Length-hiding 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
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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.
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] and record size limit
[I-D.ietf-tls-record-limit].
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. Security Features
o Forward-secure session key establishment.
o Cryptographic algorithm negotiation.
o Stateful and stateless cross-connection session resumption.
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o Session caching and management.
o Peer authentication (Certificate, raw public key, and pre-shared
key).
o Unilateral responder authentication.
o Mutual authentication.
o Application authentication delegation.
o Record (channel) confidentiality and integrity.
o Record replay prevention.
o Application-layer feature negotiation.
o Configuration extensions.
o Early data support (starting with TLS 1.3).
o Optional record-layer 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
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message loss is remedied by sender retransmission after a
configurable period in which the expected response has not yet been
received.
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}.)
Since datagrams can be replayed, DTLS provides optional anti-replay
detection based on a window of acceptable sequence numbers [RFC6347].
4.2.2. Security 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 DTLS relies on UDP.
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.
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o For the handshake: Reliable, in-order transport. DTLS provides
its own reliability.
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
functions:
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. QUIC implements a record protocol for TLS handshake
messages to establish a connection. These messages are sent in
special INITIAL and CRYPTO frames [I-D.ietf-quic-transport], types of
which are encrypted using different keys. INITIAL frames are
encrypted using "fixed" keys derived from the QUIC version and public
packet information (Connection ID). CRYPTO frames are encrypted
using TLS handshake secrets. Once TLS completes, QUIC uses the
resultant traffic secrets to for the QUIC connection to protect the
rest of the streams. QUIC supports 0-RTT (early) data using
previously negotiated connection secrets. Early data is sent in
0-RTT packets, which may be included in the same datagram as the
Initial and Handshake packets.
4.3.2. Security Features
o DoS mitigation (cookie-based).
See also the properties of TLS.
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4.3.3. Protocol Dependencies
o QUIC transport relies on UDP.
o QUIC transport relies on TLS 1.3 for key exchange, peer
authentication, and shared secret derivation.
o For the handshake: Reliable, in-order transport. QUIC provides
its own reliability.
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
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 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.
4.4.1. Protocol descriptions
4.4.1.1. IKEv2
IKEv2 is a control protocol that runs on UDP ports 500 or 4500 and
TCP port 4500. 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 4.4.1.2. 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. IKE then performs a phase of
authentication in which both peers present blobs signed by a shared
secret or private key that authenticates the entire IKE exchange and
the IKE identities. IKE then derives further sets of keys on demand,
which together with traffic policies are referred to as the "Child
SA". These Child SA keys are used by ESP.
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IKEv2 negotiates which protocols are acceptable to each peer for both
the IKE and Child SAs using "Proposals". Each proposal specifies an
encryption and authentication algorithm, or an AEAD 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 before expiration, which is
usually based either on time or number of bytes encrypted.
There is an extension to IKEv2 that allows session resumption
[RFC5723].
MOBIKE is a Mobility and Multihoming extension to IKEv2 that allows a
set of Security Associations to migrate over different outer IP
addresses and interfaces [RFC4555].
When UDP is not available or well-supported on a network, IKEv2 may
be encapsulated in TCP [RFC8229].
4.4.1.2. 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
confidentiality."
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.
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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
[RFC8229].
4.4.2. Security Features
4.4.2.1. IKEv2
o Forward-secure session key establishment.
o Cryptographic algorithm negotiation.
o Peer authentication (certificate, raw public key, pre-shared key,
and EAP).
o Unilateral responder authentication.
o Mutual authentication.
o Record (datagram) confidentiality and integrity.
o Session resumption.
o Connection mobility.
o DoS mitigation (cookie-based).
4.4.2.2. ESP
o Record confidentiality and integrity.
o Record replay protection.
4.4.3. Protocol Dependencies
4.4.3.1. IKEv2
o Availability of UDP to negotiate, or implementation support for
TCP-encapsulation.
o Some EAP authentication types require accessing a hardware device,
such as a SIM card; or interacting with a user, such as password
prompting.
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4.4.3.2. 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
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
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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. Security Features
o Forward-secure session key establishment.
o Cryptographic algorithm negotiation.
o Mutual authentication.
o Partial datagram confidentiality. (Packet headers are not
encrypted.)
o Optional authentication of data packets.
o Mandatory authentication of control packets.
o Out-of-order record receipt.
4.5.3. Protocol Dependencies
o Secure RTP can run over UDP or TCP.
o External key derivation and management protocol, e.g., DTLS
[RFC5763].
o External identity management protocol, e.g., SIP Authenticated
Identity Management [RFC4474], WebRTC Security Architecture
[I-D.ietf-rtcweb-security-arch].
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.
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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 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.
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
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
reached.
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
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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.
4.6.2. Security Features
o Forward-secure session key establishment.
o Record (channel) confidentiality and integrity.
o Stateful cross-connection session resumption.
o Session caching and management.
o Application authentication delegation.
4.6.3. Protocol Dependencies
o TCP.
o TCP Encryption Negotiation Option (ENO).
4.7. WireGuard
WireGuard is a layer 3 protocol designed as an alternative to IPsec
[WireGuard] for certain use cases. It uses UDP to encapsulate IP
datagrams between peers. Unlike most transport security protocols,
which rely on PKI for peer authentication, WireGuard authenticates
peers using pre-shared public keys delivered out-of-band, each of
which is bound to one or more IP addresses. Moreover, as a protocol
suited for VPNs, WireGuard offers no extensibility, negotiation, or
cryptographic agility.
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
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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
derivation.
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
introduced.
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
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. Security Features
o Forward-secure session 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.
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4.8. 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
synchronization.
4.8.1. 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
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
communicate.
The use of public-key encryption and authentication, or "boxing",
simplifies problems that come with symmetric key management and nonce
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.
Servers use cookies for source validation. After receiving a
client's initial packet, encrypted under the server's long-term
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public key, a 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 client authentication by allowing clients 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.
Unlike some other protocols, CurveCP data packets leave only the
ephemeral public key, connection ID, and per-message nonce in the
clear. All other data is encrypted.
4.8.2. Protocol Features
o Datagram confidentiality and integrity (via public key
encryption).
o Peer authentication (public-key).
o Unilateral responder authentication.
o Mutual authentication.
o Connection mobility (based on a client-chosen ephemeral
identifier).
o Optional length-hiding and anti-amplification padding.
o Source validation (cookie-based)
4.8.3. Protocol Dependencies
o An unreliable transport protocol such as UDP.
4.9. 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.
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4.9.1. 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) publish 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
connect.
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
of the network address information, they may be reused as both ends
of the tunnel move about the network. This does however imply that
connection establishment and packet encryption mechanisms are
coupled.
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
established.
Additional (orthogonal) transport features include: connection
multiplexing between hosts across shared tunnels, and congestion
control state is shared across connections between the same host
pairs.
4.9.2. Protocol Features
o Record or datagram confidentiality and integrity.
o Forward-secure session key establishment.
o Peer authentication (public-key).
o Unilateral responder authentication.
o DoS mitigation (puzzle-based).
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o Out-of-order receipt record.
o Connection mobility (based on tunnel identifiers).
4.9.3. Protocol Dependencies
o An unreliable transport protocol such as UDP.
o A DNS-like resolution service to obtain location information (an
IP address) and ephemeral keys.
o A PKI trust store for certificate validation.
4.10. OpenVPN
OpenVPN [OpenVPN] is a commonly used protocol designed as an
alternative to IPsec. A major goal of this protocol is to provide a
VPN that is simple to configure and works over a variety of
transports. OpenVPN encapsulates either IP packets or Ethernet
frames within a secure tunnel and can run over UDP or TCP.
4.10.1. Protocol Description
OpenVPN facilitates authentication using either a pre-shared static
key or using X.509 certificates and TLS. In pre-shared key mode,
OpenVPN derives keys for encryption and authentication directly from
one or multiple symmetric keys. In TLS mode, OpenVPN encapsulates a
TLS handshake, in which both peers must present a certificate for
authentication. After the handshake, both sides contribute random
source material to derive keys for encryption and authentication
using the TLS pseudo random function (PRF). OpenVPN provides the
possibility to authenticate and encrypt the TLS handshake itself
using a pre-shared key or passphrase. Furthermore, it supports
rekeying using TLS.
After authentication and key exchange, OpenVPN encrypts payload data,
i.e., IP packets or Ethernet frames, and signs the payload using an
HMAC function. The default cipher is BlowFish [BlowFish] and the
default message digest algorithm is SHA1, but an application can
select an arbitrary cipher, key size, and message digest algorithm
for the HMAC. OpenVPN peers support cipher negotiation (NCP) since
version 2.4, in which case they will upgrade the cipher to AES-
256-GCM by default.
OpenVPN can run over TCP or UDP. When running over UDP, OpenVPN
provides a simple reliability layer for control packets such as the
TLS handshake and key exchange. It assigns sequence numbers to
packets, acknowledges packets it receives, and retransmits packets it
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deems lost. Similar to DTLS, this reliability layer is not used for
data packets, which prevents the problem of two reliability
mechanisms being encapsulated within each other. When running over
TCP, OpenVPN includes the packet length in the header, which allows
the peer to deframe the TCP stream into messages.
For replay protection, OpenVPN assigns an identifier to each outgoing
packet, which is unique for the packet and the currently used key.
In pre-shared key mode or with a CFB or OFB mode cipher, OpenVPN
combines a timestamp with an incrementing sequence number into a
64-bit identifier. In TLS mode with CBC cipher mode, OpenVPN omits
the timestamp, so identifiers are only 32-bit. This is sufficient
since OpenVPN can guarantee the uniqueness of this identifier for
each key, as it can trigger rekeying if needed.
OpenVPN supports connection mobility by allowing a peer to change its
IP address during an ongoing session. When configured accordingly, a
host will accept authenticated packets for a session from any IP
address.
4.10.2. Protocol Features
o Peer authentication using certificates or pre-shared key.
o Mandatory mutual authentication.
o Connection mobility.
o Out-of-order record receipt.
o Length-hiding padding.
See also the properties of TLS.
4.10.3. Protocol Dependencies
o For control packets such as handshake and key exchange: Reliable,
in-order transport. Reliability is provided either by TCP, or by
OpenVPN's own reliability layer when using UDP.
5. Security Features and Application 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. They were selected on the basis that they are either
(a) required for any secure transport protocol or (b) nearly
ubiquitous amongst common secure transport protocols.
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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 or application
dependency is unavailable.
In this context, an application dependency is an aspect of the
security feature which can be exposed to the application. An
application dependency may be required for the security feature to
function, or it may provide additional information and control to the
application. For example, an application may need to provide
information such as keying material or authentication credentials, or
it may want to restrict which cryptographic algorithms to allow for
negotiation.
5.1. Mandatory Features
Mandatory features must be supported regardless of transport and
application services available. Note that not all mandatory features
are provided by each surveyed protocol above. For example, tcpcrypt
does not provide responder authentication and CurveCP does not
provide forward-secure session key establishment.
o Record or datagram confidentiality and integrity.
* Application dependency: None.
o Forward-secure session key establishment.
* Application dependency: None.
o Unilateral responder authentication.
* (Optional) Application dependency: Application-provided trust
information. System trust stores may also be used to
authenticate responders.
5.2. Optional Features
In this section we list optional features along with their necessary
application dependencies, if any.
o Pre-shared key support (PSK):
* Application dependency: Application provisioning and
distribution of pre-shared keys.
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o Mutual authentication (MA):
* Application dependency: Mutual authentication credentials
required.
o Cryptographic algorithm negotiation (AN):
* Application dependency: Application awareness of supported or
desired algorithms.
o Application authentication delegation (AD):
* Application dependency: Application opt-in and policy for
endpoint authentication.
o DoS mitigation (DM):
* Application dependency: None.
o Connection mobility (CM):
* Application dependency: None.
o Source validation (SV):
* Application dependency: None.
o Application-layer feature negotiation (AFN):
* Application dependency: Specification of application-layer
features or functionality.
o Configuration extensions (CX):
* Application dependency: Specification of application-specific
extensions.
o Session caching and management (SC):
* Application dependency: None.
o Length-hiding padding (LHP): (Optional) Application dependency:
Knowledge of desired padding policies. Some protocols, such as
IKE, can negotiate application-agnostic padding policies.
o Early data support (ED):
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* Application dependency: Anti-replay protections or hints of
data idempotency.
o Record replay prevention (RP):
* Application dependency: None.
o Out-of-order receipt record (OO):
* Application dependency: None.
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)
extension.
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+-----+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
| Pro | P | A | A | M | D | C | S | A | CX | SC | LH | ED | RP | OO |
| toc | S | N | D | A | M | M | V | F | | | P | | | |
| ol | K | | | | | | | N | | | | | | |
+-----+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
| TLS | S | S | S | S | S | U | M | S | S | S | S | S | U | U |
| | | | | | | * | | | | | | | | |
| | | | | | | | | | | | | | | |
| DTL | S | S | S | S | S | S | M | S | S | S | S | U | M | M |
| S | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
| IET | S | S | S | S | S | S | M | S | S | S | S | S | M | M |
| F Q | | | | | | | | | | | | | | |
| UIC | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
| IKE | S | S | S | M | S | S | M | S | S | S | S | U | M | M |
| v2+ | | | | | | | | | | | | | | |
| ESP | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
| SRT | S | S | S | S | S | U | M | S | S | S | U | U | M | M |
| P+D | | | | | | | | | | | | | | |
| TLS | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
| tcp | U | S | M | U | U | U | M | U | U | S | U | U | U | U |
| cry | | | | | * | * | | | | | | | | |
| pt | | | | | * | | | | | | | | | |
| | | | | | | | | | | | | | | |
| Wir | S | U | S | M | S | U | M | U | U | U | S+ | U | M | M |
| eGu | | | | | | | | | | | | | | |
| ard | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
| Min | U | U | U | M | S | M | M | U | U | U | S | U | U | U |
| ima | | | | | | | | | | | | | | |
| lT | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
| Cur | U | U | U | S | S | M | M | U | U | U | S | U | M | M |
| veC | | | | | | | | | | | | | | |
| P | | | | | | | | | | | | | | |
+-----+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
M=Mandatory S=Supported but not required U=Unsupported *=On TCP;
MPTCP would provide this ability **=TCP provides SYN cookies
natively, but these are not cryptographically strong +=For transport
packets only
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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
interface. We partition these interfaces into pre-connection
(configuration), connection, and post-connection interfaces,
following conventions in [I-D.ietf-taps-interface] and
[I-D.ietf-taps-arch].
6.1. Pre-Connection Interfaces
Configuration interfaces are used to configure the security protocols
before a handshake begins or the keys are negotiated.
o Identities and Private Keys The application can provide its
identities (certificates) and private keys, or mechanisms to
access these, to the security protocol to use during handshakes.
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 Extensions (Application-Layer Protocol Negotiation): The
application enables or configures extensions that are to be
negotiated by the security protocol, such as ALPN [RFC7301].
Protocols: TLS, DTLS, QUIC + TLS
o Session Cache Management The application provides the ability to
save and retrieve session state (such as tickets, keying material,
and server parameters) that may be used to resume the security
session. 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
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* Direct import: TLS, DTLS, MinimalT, tcpcrypt, WireGuard
* Non-importable: CurveCP
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, tcpcrypt, IKEv2, MinimalT
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, tcpcrypt, IKEv2, MinimalT
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
SRTP)
* 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. Protocols: ESP ((Editor's note:
One may consider TLS/DTLS to also have this interface))
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o Mobility Events The record protocol can be signaled that it is
being migrated to another transport or interface due to connection
mobility, which may reset address and state validation and induce
state changes such as use of a new Connection Identifier (CID).
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
implementation.
9. Privacy Considerations
Analysis of how features improve or degrade privacy is intentionally
omitted from this survey. All security protocols surveyed generally
improve privacy by reducing information leakage via encryption.
However, varying amounts of metadata remain in the clear across each
protocol. For example, client and server certificates are sent in
cleartext in TLS 1.2 [RFC5246], whereas they are encrypted in TLS 1.3
[RFC8446]. A survey of privacy features, or lack thereof, for
various security protocols could be addressed in a separate document.
10. Acknowledgments
The authors would like to thank Bob Bradley, Theresa Enghardt,
Frederic Jacobs, Mirja Kuehlewind, Yannick Sierra, and Brian Trammell
for their input and feedback on earlier versions of this draft.
11. Normative References
[ALTS] "Application Layer Transport Security", n.d..
[BLAKE2] "BLAKE2 -- simpler, smaller, fast as MD5", n.d..
[BlowFish]
"The Blowfish Encryption Algorithm", n.d..
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[Curve25519]
"Curve25519 - new Diffie-Hellman speed records", n.d..
[CurveCP] "CurveCP -- Usable security for the Internet", n.d..
[I-D.ietf-quic-tls]
Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
draft-ietf-quic-tls-18 (work in progress), January 2019.
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-18 (work
in progress), January 2019.
[I-D.ietf-rtcweb-security-arch]
Rescorla, E., "WebRTC Security Architecture", draft-ietf-
rtcweb-security-arch-18 (work in progress), February 2019.
[I-D.ietf-taps-arch]
Pauly, T., Trammell, B., Brunstrom, A., Fairhurst, G.,
Perkins, C., Tiesel, P., and C. Wood, "An Architecture for
Transport Services", draft-ietf-taps-arch-02 (work in
progress), October 2018.
[I-D.ietf-taps-interface]
Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G.,
Kuehlewind, M., Perkins, C., Tiesel, P., and C. Wood, "An
Abstract Application Layer Interface to Transport
Services", draft-ietf-taps-interface-02 (work in
progress), October 2018.
[I-D.ietf-tcpinc-tcpcrypt]
Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
Q., and E. Smith, "Cryptographic protection of TCP Streams
(tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-15 (work in
progress), December 2018.
[I-D.ietf-tcpinc-tcpeno]
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.
[I-D.ietf-tls-dtls-connection-id]
Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom,
"Connection Identifiers for DTLS 1.2", draft-ietf-tls-
dtls-connection-id-02 (work in progress), October 2018.
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[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-30 (work in progress),
November 2018.
[I-D.ietf-tls-record-limit]
Thomson, M., "Record Size Limit Extension for Transport
Layer Security (TLS)", draft-ietf-tls-record-limit-03
(work in progress), May 2018.
[I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-28 (work in progress),
March 2018.
[MinimalT]
"MinimaLT -- Minimal-latency Networking Through Better
Security", n.d..
[Noise] "The Noise Protocol Framework", n.d..
[OpenVPN] "OpenVPN cryptographic layer", n.d..
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
1998, <https://www.rfc-editor.org/info/rfc2385>.
[RFC2508] Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP
Headers for Low-Speed Serial Links", RFC 2508,
DOI 10.17487/RFC2508, February 1999,
<https://www.rfc-editor.org/info/rfc2508>.
[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,
<https://www.rfc-editor.org/info/rfc3261>.
[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,
<https://www.rfc-editor.org/info/rfc3545>.
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[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>.
[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,
<https://www.rfc-editor.org/info/rfc3948>.
[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
January 2006, <https://www.rfc-editor.org/info/rfc4253>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[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,
<https://www.rfc-editor.org/info/rfc4474>.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,
<https://www.rfc-editor.org/info/rfc4555>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5723] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange
Protocol Version 2 (IKEv2) Session Resumption", RFC 5723,
DOI 10.17487/RFC5723, January 2010,
<https://www.rfc-editor.org/info/rfc5723>.
[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, <https://www.rfc-editor.org/info/rfc5763>.
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[RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer
Security (DTLS) Extension to Establish Keys for the Secure
Real-time Transport Protocol (SRTP)", RFC 5764,
DOI 10.17487/RFC5764, May 2010,
<https://www.rfc-editor.org/info/rfc5764>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC6189] Zimmermann, P., Johnston, A., Ed., and J. Callas, "ZRTP:
Media Path Key Agreement for Unicast Secure RTP",
RFC 6189, DOI 10.17487/RFC6189, April 2011,
<https://www.rfc-editor.org/info/rfc6189>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[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, <https://www.rfc-editor.org/info/rfc7250>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[RFC7539] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
<https://www.rfc-editor.org/info/rfc7539>.
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[RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind,
Ed., "Services Provided by IETF Transport Protocols and
Congestion Control Mechanisms", RFC 8095,
DOI 10.17487/RFC8095, March 2017,
<https://www.rfc-editor.org/info/rfc8095>.
[RFC8229] Pauly, T., Touati, S., and R. Mantha, "TCP Encapsulation
of IKE and IPsec Packets", RFC 8229, DOI 10.17487/RFC8229,
August 2017, <https://www.rfc-editor.org/info/rfc8229>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[SIGMA] "SIGMA -- The 'SIGn-and-MAc' Approach to Authenticated
Diffie-Hellman and Its Use in the IKE-Protocols", n.d..
[WireGuard]
"WireGuard -- Next Generation Kernel Network Tunnel",
n.d..
Authors' Addresses
Christopher A. Wood (editor)
Apple Inc.
One Apple Park Way
Cupertino, California 95014
United States of America
Email: cawood@apple.com
Theresa Enghardt
TU Berlin
Marchstr. 23
10587 Berlin
Germany
Email: theresa@inet.tu-berlin.de
Tommy Pauly
Apple Inc.
One Apple Park Way
Cupertino, California 95014
United States of America
Email: tpauly@apple.com
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Colin Perkins
University of Glasgow
School of Computing Science
Glasgow G12 8QQ
United Kingdom
Email: csp@csperkins.org
Kyle Rose
Akamai Technologies, Inc.
150 Broadway
Cambridge, MA 02144
United States of America
Email: krose@krose.org
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