Internet DRAFT - draft-ietf-opsawg-mud-tls
draft-ietf-opsawg-mud-tls
OPSAWG WG T. Reddy
Internet-Draft Nokia
Intended status: Standards Track D. Wing
Expires: 26 July 2024 Citrix
B. Anderson
Cisco
23 January 2024
Manufacturer Usage Description (MUD) (D)TLS Profiles for IoT Devices
draft-ietf-opsawg-mud-tls-13
Abstract
This memo extends the Manufacturer Usage Description (MUD)
specification to incorporate (D)TLS profile parameters. This allows
a network security service to identify unexpected (D)TLS usage, which
can indicate the presence of unauthorized software or malware on an
endpoint.
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
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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 26 July 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview of MUD (D)TLS profiles for IoT devices . . . . . . . 5
4. (D)TLS 1.3 Handshake . . . . . . . . . . . . . . . . . . . . 6
4.1. Full (D)TLS 1.3 Handshake Inspection . . . . . . . . . . 7
4.2. Encrypted DNS . . . . . . . . . . . . . . . . . . . . . . 7
5. (D)TLS Profile of a IoT device . . . . . . . . . . . . . . . 8
5.1. Tree Structure of the (D)TLS profile Extension to the ACL
YANG Model . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. The (D)TLS profile Extension to the ACL YANG Model . . . 10
5.3. IANA (D)TLS profile YANG Module . . . . . . . . . . . . . 15
5.4. MUD (D)TLS Profile Extension . . . . . . . . . . . . . . 19
6. Processing of the MUD (D)TLS Profile . . . . . . . . . . . . 20
7. MUD File Example . . . . . . . . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 24
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
10.1. (D)TLS Profile YANG Modules . . . . . . . . . . . . . . 25
10.2. ACL TLS Version registry . . . . . . . . . . . . . . . . 27
10.3. ACL DTLS version registry . . . . . . . . . . . . . . . 27
10.4. ACL (D)TLS Parameters registry . . . . . . . . . . . . . 28
10.5. MUD Extensions registry . . . . . . . . . . . . . . . . 28
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
12.1. Normative References . . . . . . . . . . . . . . . . . . 29
12.2. Informative References . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
Encryption is necessary to enhance the privacy of end users using IoT
devices. TLS [RFC8446] and DTLS [RFC9147] are the dominant protocols
(counting all (D)TLS versions) providing encryption for IoT device
traffic. Unfortunately, in conjunction with IoT applications' rise
of encryption, malware authors are also using encryption which
thwarts network-based analysis such as deep packet inspection (DPI).
Other mechanisms are thus needed to help detecting malware running on
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an IoT device.
Malware frequently uses proprietary libraries for its activities, and
those libraries are reused much like any other software engineering
project. [malware] indicates that there are observable differences in
how malware uses encryption compared with how non-malware uses
encryption. There are several interesting findings specific to
(D)TLS which were found common to malware:
* Older and weaker cryptographic parameters (e.g.,
TLS_RSA_WITH_RC4_128_SHA).
* TLS server name indication (SNI) extension [RFC6066] and server
certificates are composed of subjects with characteristics of a
domain generation algorithm (DGA) (e.g., 'www.33mhwt2j.net').
* Higher use of self-signed certificates compared with typical
legitimate software.
* Discrepancies in the SNI TLS extension and the DNS names in the
SubjectAltName (SAN) X.509 extension in the server certificate
message.
* Discrepancies in the key exchange algorithm and the client public
key length in comparison with legitimate flows. As a reminder,
the Client Key Exchange message has been removed from TLS 1.3.
* Lower diversity in TLS client advertised extensions compared to
legitimate clients.
* Using privacy enhancing technologies like Tor, Psiphon, Ultrasurf
(see [malware-tls]), and evasion techniques such as ClientHello
randomization.
* Using DNS-over-HTTPS (DoH) [RFC8484] to avoid detection by malware
DNS filtering services [malware-doh]. Specifically, malware may
not use the DoH server provided by the local network.
If observable (D)TLS profile parameters are used, the following
functions are possible which have a positive impact on the local
network security:
* Permit intended DTLS or TLS use and block malicious DTLS or TLS
use. This is superior to the layers 3 and 4 ACLs of Manufacturer
Usage Description Specification (MUD) [RFC8520] which are not
suitable for broad communication patterns.
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* Ensure TLS certificates are valid. Several TLS deployments have
been vulnerable to active Man-In-The-Middle (MITM) attacks because
of the lack of certificate validation or vulnerability in the
certificate validation function (see [cryto-vulnerability]). By
observing (D)TLS profile parameters, a network element can detect
when the TLS SNI mismatches the SubjectAltName and when the
server's certificate is invalid. In (D)TLS 1.2
[RFC5246][RFC6347], the ClientHello, ServerHello and Certificate
messages are all sent in clear-text. This check is not possible
with (D)TLS 1.3, which encrypts the Certificate message thereby
hiding the server identity from any intermediary. In (D)TLS 1.3,
the server certificate validation functions should be executed
within an on-path (D)TLS proxy, if such a proxy exists.
* Support new communication patterns. An IoT device can learn a new
capability, and the new capability can change the way the IoT
device communicates with other devices located in the local
network and Internet. There would be an inaccurate policy if an
IoT device rapidly changes the IP addresses and domain names it
communicates with while the MUD ACLs were slower to update (see
[clear-as-mud]). In such a case, observable (D)TLS profile
parameters can be used to permit intended use and to block
malicious behavior from the IoT device.
The YANG module specified in Section 5.2 of this document is an
extension of YANG Data Model for Network Access Control Lists (ACLs)
[RFC8519] to enhance MUD [RFC8520] to model observable (D)TLS profile
parameters. Using these (D)TLS profile parameters, an active MUD-
enforcing network security service (e.g., firewall) can identify MUD
non-compliant (D)TLS behavior indicating outdated cryptography or
malware. This detection can prevent malware downloads, block access
to malicious domains, enforce use of strong ciphers, stop data
exfiltration, etc. In addition, organizations may have policies
around acceptable ciphers and certificates for the websites the IoT
devices connect to. Examples include no use of old and less secure
versions of TLS, no use of self-signed certificates, deny-list or
accept-list of Certificate Authorities, valid certificate expiration
time, etc. These policies can be enforced by observing the (D)TLS
profile parameters. Network security services can use the IoT
device's (D)TLS profile parameters to identify legitimate flows by
observing (D)TLS sessions, and can make inferences to permit
legitimate flows and to block malicious or insecure flows. The
proposed technique is also suitable in deployments where decryption
techniques are not ideal due to privacy concerns, non-cooperating
end-points, and expense.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
"(D)TLS" is used for statements that apply to both Transport Layer
Security [RFC8446] and Datagram Transport Layer Security [RFC6347].
Specific terms "TLS" and "DTLS" are used for any statement that
applies to either protocol alone.
'DoH/DoT' refers to DNS-over-HTTPS and/or DNS-over-TLS.
3. Overview of MUD (D)TLS profiles for IoT devices
In Enterprise networks, protection and detection are typically done
both on end hosts and in the network. Host security agents have deep
visibility on the devices where they are installed, whereas the
network has broader visibility. Installing host security agents may
not be a viable option on IoT devices, and network-based security is
an efficient means to protect such IoT devices. If the IoT device
supports a MUD (D)TLS profile, the (D)TLS profile parameters of the
IoT device can be used by a middlebox to detect and block malware
communication, while at the same time preserving the privacy of
legitimate uses of encryption. The middlebox need not proxy (D)TLS
but can passively observe the parameters of (D)TLS handshakes from
IoT devices and gain visibility into TLS 1.2 parameters and partial
visibility into TLS 1.3 parameters.
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Malicious agents can try to use the (D)TLS profile parameters of
legitimate agents to evade detection, but it becomes a challenge to
mimic the behavior of various IoT device types and IoT device models
from several manufacturers. In other words, malware developers will
have to develop malicious agents per IoT device type, manufacturer
and model, infect the device with the tailored malware agent and will
have keep up with updates to the device's (D)TLS profile parameters
over time. Furthermore, the malware's command and control server
certificates need to be signed by the same certifying authorities
trusted by the IoT devices. Typically, IoT devices have an
infrastructure that supports a rapid deployment of updates, and
malware agents will have a near-impossible task of similarly
deploying updates and continuing to mimic the TLS behavior of the IoT
device it has infected. However, if the IoT device has reached end-
of-life and the IoT manufacturer will not issue a firmware or
software update to the Thing or will not update the MUD file, the
"is-supported" attribute defined in Section 3.6 of [RFC8520] can be
used by the MUD manager to identify the IoT manufacturer no longer
supports the device.
The end-of-life of a device does not necessarily mean that it is
defective; rather, it denotes a need to replace and upgrade the
network to next-generation devices for additional functionality. The
network security service will have to rely on other techniques
discussed in Section 8 to identify malicious connections until the
device is replaced.
Compromised IoT devices are typically used for launching DDoS attacks
(Section 3 of [RFC8576]). For example, DDoS attacks like Slowloris
and Transport Layer Security (TLS) re-negotiation can be blocked if
the victim's server certificate is not be signed by the same
certifying authorities trusted by the IoT device.
4. (D)TLS 1.3 Handshake
In (D)TLS 1.3, full (D)TLS handshake inspection is not possible since
all (D)TLS handshake messages excluding the ClientHello message are
encrypted. (D)TLS 1.3 has introduced new extensions in the handshake
record layers called Encrypted Extensions. Using these extensions
handshake messages will be encrypted and network security services
(such as a firewall) are incapable of deciphering the handshake, and
thus cannot view the server certificate. However, the ClientHello
and ServerHello still have some fields visible, such as the list of
supported versions, named groups, cipher suites, signature algorithms
and extensions in ClientHello, and chosen cipher in the ServerHello.
For instance, if the malware uses evasion techniques like ClientHello
randomization, the observable list of cipher suites and extensions
offered by the malware agent in the ClientHello message will not
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match the list of cipher suites and extensions offered by the
legitimate client in the ClientHello message, and the middlebox can
block malicious flows without acting as a (D)TLS 1.3 proxy.
4.1. Full (D)TLS 1.3 Handshake Inspection
To obtain more visibility into negotiated TLS 1.3 parameters, a
middlebox can act as a (D)TLS 1.3 proxy. A middlebox can act as a
(D)TLS proxy for the IoT devices owned and managed by the IT team in
the Enterprise network and the (D)TLS proxy must meet the security
and privacy requirements of the organization. In other words, the
scope of middlebox acting as a (D)TLS proxy is restricted to
Enterprise network owning and managing the IoT devices. The
middlebox would have to follow the behaviour detailed in Section 9.3
of [RFC8446] to act as a compliant (D)TLS 1.3 proxy.
To further increase privacy, Encrypted Client Hello (ECH) extension
[I-D.ietf-tls-esni] prevents passive observation of the TLS Server
Name Indication extension and other potentially sensitive fields,
such as the ALPN [RFC7301]. To effectively provide that privacy
protection, ECH extension needs to be used in conjunction with DNS
encryption (e.g., DoH). A middlebox (e.g., firewall) passively
inspecting ECH extension cannot observe the encrypted SNI nor observe
the encrypted DNS traffic. The middlebox acting as a (D)TLS 1.3
proxy that does not support ECH extension will act as if connecting
to the public name and it follows the behaviour discussed in
Section 6.1.6 of [I-D.ietf-tls-esni] to securely signal the client to
disable ECH.
4.2. Encrypted DNS
A common usage pattern for certain type of IoT devices (e.g., light
bulb) is for it to "call home" to a service that resides on the
public Internet, where that service is referenced through a domain
name (A or AAAA record). As discussed in Manufacturer Usage
Description Specification [RFC8520], because these devices tend to
require access to very few sites, all other access should be
considered suspect. If an IoT device is pre-configured to use a DNS
resolver not signaled by the network, the MUD policy enforcement
point is moved to that resolver, which cannot enforce the MUD policy
based on domain names (Section 8 of [RFC8520]). If the DNS query is
not accessible for inspection, it becomes quite difficult for the
infrastructure to suspect anything. Thus the use of a DNS resolver
not signaled by the network is incompatible with MUD in general. A
network-designated DoH/DoT server is necessary to allow MUD policy
enforcement on the local network, for example, using the techniques
specified in DNR[RFC9463] and DDR [RFC9462].
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5. (D)TLS Profile of a IoT device
This document specifies a YANG module for representing (D)TLS
profile. The (D)TLS profile YANG module provides a method for
network security services to observe the (D)TLS profile parameters in
the (D)TLS handshake to permit intended use and to block malicious
behavior. This module uses the cryptographic types defined in
[I-D.ietf-netconf-crypto-types]. See [RFC7925] for (D)TLS 1.2 and
[I-D.ietf-uta-tls13-iot-profile] for DTLS 1.3 recommendations related
to IoT devices, and [RFC7525] for additional (D)TLS 1.2
recommendations.
A companion YANG module is defined to include a collection of (D)TLS
parameters and (D)TLS versions maintained by IANA: "iana-tls-profile"
(Section 5.3).
The (D)TLS parameters in each (D)TLS profile include the following:
* Profile name
* (D)TLS versions supported by the IoT device.
* List of supported cipher suites (Section 11 of [RFC8446]). For
(D)TLS1.2, [RFC7925] recommends AEAD ciphers for IoT devices.
* List of supported extension types
* List of trust anchor certificates used by the IoT device. If the
server certificate is signed by one of the trust anchors, the
middlebox continues with the connection as normal. Otherwise, the
middlebox will react as if the server certificate validation has
failed and takes appropriate action (e.g, block the (D)TLS
session). An IoT device can use a private trust anchor to
validate a server's certificate (e.g., the private trust anchor
can be preloaded at manufacturing time on the IoT device and the
IoT device fetches the firmware image from the Firmware server
whose certificate is signed by the private CA). This empowers the
middlebox to reject TLS sessions to servers that the IoT device
does not trust.
* List of pre-shared key exchange modes
* List of named groups (DHE or ECDHE) supported by the client
* List of signature algorithms the client can validate in X.509
server certificates
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* List of signature algorithms the client is willing to accept for
CertificateVerify message (Section 4.2.3 of [RFC8446]). For
example, a TLS client implementation can support different sets of
algorithms for certificates and in TLS to signal the capabilities
in "signature_algorithms_cert" and "signature_algorithms"
extensions.
* List of supported application protocols (e.g., h3, h2, http/1.1
etc.)
* List of certificate compression algorithms (defined in [RFC8879])
* List of the distinguished names [X501] of acceptable certificate
authorities, represented in DER-encoded format [X690] (defined in
Section 4.2.4 of [RFC8446])
GREASE [RFC8701] defines a mechanism for TLS peers to send random
values on TLS parameters to ensure future extensibility of TLS
extensions. Similar random values might be extended to other TLS
parameters. Thus, the (D)TLS profile parameters defined in the YANG
module by this document MUST NOT include the GREASE values for
extension types, named groups, signature algorithms, (D)TLS versions,
pre-shared key exchange modes, cipher suites and for any other TLS
parameters defined in future RFCs.
The (D)TLS profile does not include parameters like compression
methods for data compression, [RFC7525] recommends disabling TLS-
level compression to prevent compression-related attacks. In TLS
1.3, only the "null" compression method is allowed (Section 4.1.2 of
[RFC8446]).
5.1. Tree Structure of the (D)TLS profile Extension to the ACL YANG
Model
This document augments the "ietf-acl" ACL YANG module defined in
[RFC8519] for signaling the IoT device (D)TLS profile. This document
defines the YANG module "ietf-acl-tls". The meaning of the symbols
in the YANG tree diagram are defined in [RFC8340] and it has the
following tree structure:
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module: ietf-acl-tls
augment /acl:acls/acl:acl/acl:aces/acl:ace/acl:matches:
+--rw client-profiles {match-on-tls-dtls}?
+--rw tls-dtls-profile* [name]
+--rw name string
+--rw supported-tls-version* ianatp:tls-version
+--rw supported-dtls-version* ianatp:dtls-version
+--rw cipher-suite* ianatp:cipher-algorithm
+--rw extension-type*
| ianatp:extension-type
+--rw accept-list-ta-cert*
| ct:trust-anchor-cert-cms
+--rw psk-key-exchange-mode*
| ianatp:psk-key-exchange-mode
| {tls13 or dtls13}?
+--rw supported-groups*
| ianatp:supported-group
+--rw signature-algorithm-cert*
| ianatp:signature-algorithm
| {tls13 or dtls13}?
+--rw signature-algorithm*
| ianatp:signature-algorithm
+--rw application-protocol*
| ianatp:application-protocol
+--rw cert-compression-algorithm*
| ianatp:cert-compression-algorithm
| {tls13 or dtls13}?
+--rw certificate-authorities*
certificate-authority
{tls13 or dtls13}?
5.2. The (D)TLS profile Extension to the ACL YANG Model
<CODE BEGINS> file "ietf-acl-tls@2024-23-01.yang"
module ietf-acl-tls {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-acl-tls";
prefix acl-tls;
import iana-tls-profile {
prefix ianatp;
reference
"RFC XXXX: Manufacturer Usage Description (MUD) (D)TLS
Profiles for IoT Devices";
}
import ietf-crypto-types {
prefix ct;
reference
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"draft-ietf-netconf-crypto-types: YANG Data Types and Groupings
for Cryptography";
}
import ietf-access-control-list {
prefix acl;
reference
"RFC 8519: YANG Data Model for Network Access
Control Lists (ACLs)";
}
organization
"IETF OPSAWG (Operations and Management Area Working Group)";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: opsawg@ietf.org
Author: Konda, Tirumaleswar Reddy
kondtir@gmail.com
";
description
"This YANG module defines a component that augments the
IETF description of an access list to allow (D)TLS profile
as matching criteria.
Copyright (c) 2020 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Revised BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision 2022-10-10 {
description
"Initial revision";
reference
"RFC XXXX: Manufacturer Usage Description (MUD) (D)TLS
Profiles for IoT Devices";
}
feature tls12 {
description
"TLS Protocol Version 1.2 is supported.";
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reference
"RFC 5246: The Transport Layer Security (TLS) Protocol
Version 1.2";
}
feature tls13 {
description
"TLS Protocol Version 1.3 is supported.";
reference
"RFC 8446: The Transport Layer Security (TLS) Protocol
Version 1.3";
}
feature dtls12 {
description
"DTLS Protocol Version 1.2 is supported.";
reference
"RFC 6347: Datagram Transport Layer Security
Version 1.2";
}
feature dtls13 {
description
"DTLS Protocol Version 1.3 is supported.";
reference
"RFC 9147: Datagram Transport Layer
Security 1.3";
}
feature match-on-tls-dtls {
description
"The networking device can support matching on
(D)TLS parameters.";
}
typedef spki-pin-set {
type binary;
description
"Subject Public Key Info pin set as discussed in
Section 2.4 of RFC7469.";
}
typedef certificate-authority {
type string;
description
"Distinguished Name of Certificate authority as discussed
in Section 4.2.4 of RFC8446.";
}
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augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches" {
if-feature "match-on-tls-dtls";
description
"(D)TLS specific matches.";
container client-profiles {
description
"A grouping for (D)TLS profiles.";
list tls-dtls-profile {
key "name";
description
"A list of (D)TLS version profiles supported by
the client.";
leaf name {
type string {
length "1..64";
}
description
"The name of (D)TLS profile; space and special
characters are not allowed.";
}
leaf-list supported-tls-version {
type ianatp:tls-version;
description
"TLS versions supported by the client.";
}
leaf-list supported-dtls-version {
type ianatp:dtls-version;
description
"DTLS versions supported by the client.";
}
leaf-list cipher-suite {
type ianatp:cipher-algorithm;
description
"A list of Cipher Suites supported by the client.";
}
leaf-list extension-type {
type ianatp:extension-type;
description
"A list of Extension Types supported by the client.";
}
leaf-list accept-list-ta-cert {
type ct:trust-anchor-cert-cms;
description
"A list of trust anchor certificates used by the client.";
}
leaf-list psk-key-exchange-mode {
if-feature "tls13 or dtls13";
type ianatp:psk-key-exchange-mode;
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description
"pre-shared key exchange modes.";
}
leaf-list supported-group {
type ianatp:supported-group;
description
"A list of named groups supported by the client.";
}
leaf-list signature-algorithm-cert {
if-feature "tls13 or dtls13";
type ianatp:signature-algorithm;
description
"A list signature algorithms the client can validate
in X.509 certificates.";
}
leaf-list signature-algorithm {
type ianatp:signature-algorithm;
description
"A list signature algorithms the client can validate
in the CertificateVerify message.";
}
leaf-list application-protocol {
type ianatp:application-protocol;
description
"A list application protocols supported by the client.";
}
leaf-list cert-compression-algorithm {
if-feature "tls13 or dtls13";
type ianatp:cert-compression-algorithm;
description
"A list certificate compression algorithms
supported by the client.";
}
leaf-list certificate-authorities {
if-feature "tls13 or dtls13";
type certificate-authority;
description
"A list of the distinguished names of certificate authorities
acceptable to the client.";
}
}
}
}
}
<CODE ENDS>
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5.3. IANA (D)TLS profile YANG Module
The TLS and DTLS IANA registries are available from
https://www.iana.org/assignments/tls-parameters/tls-parameters.txt
and https://www.iana.org/assignments/tls-extensiontype-values/tls-
extensiontype-values.txt. Changes to TLS and DTLS related IANA
registries are discussed in [RFC8447].
The values for all the parameters in the "iana-tls-profile" YANG
module are defined in the TLS and DTLS IANA registries excluding the
tls-version, dtls-version, spki-pin-set, and certificate-authority
parameters. The values of spki-pin-set and certificate-authority
parameters will be specific to the IoT device.
The TLS and DTLS IANA registries do not maintain (D)TLS version
numbers. In (D)TLS 1.2 and below, "legacy_version" field in the
ClientHello message is used for version negotiation. However in
(D)TLS 1.3, the "supported_versions" extension is used by the client
to indicate which versions of (D)TLS it supports. TLS 1.3
ClientHello messages are identified as having a "legacy_version" of
0x0303 and a "supported_versions" extension present with 0x0304 as
the highest version. DTLS 1.3 ClientHello messages are identified as
having a "legacy_version" of 0xfefd and a "supported_versions"
extension present with 0x0304 as the highest version.
In order to ease updating the "iana-tls-profile" YANG module with
future (D)TLS versions, new (D)TLS version registries are defined in
Section 10.2 and Section 10.3. Whenever a new (D)TLS protocol
version is defined, the registry will be updated using expert review;
the "iana-tls-profile" YANG module will be automatically updated by
IANA.
Implementers or users of this specification must refer to the IANA-
maintained "iana-tls-profile" YANG module available at XXXX [Note to
RFC Editor to replace "XXXX" with the URL link of the IANA-maintained
"iana-tls-profile" YANG module].
The initial version of the "iana-tls-profile" YANG module is defined
as follows:
<CODE BEGINS> file "iana-tls-profile@2024-23-01.yang"
module iana-tls-profile {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:iana-tls-profile";
prefix ianatp;
organization
"IANA";
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contact
" Internet Assigned Numbers Authority
Postal: ICANN
12025 Waterfront Drive, Suite 300
Los Angeles, CA 90094-2536
United States
Tel: +1 310 301 5800
E-Mail: iana@iana.org>";
description
"This module contains YANG definition for the (D)TLS profile.
Copyright (c) 2020 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Revised BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision 2022-10-10 {
description
"Initial revision";
reference
"RFC XXXX: Manufacturer Usage Description (MUD) (D)TLS Profiles
for IoT Devices";
}
typedef extension-type {
type uint16;
description
"Extension type in the TLS ExtensionType Values registry as
defined in Section 7 of RFC8447.";
}
typedef supported-group {
type uint16;
description
"Supported Group in the TLS Supported Groups registry as
defined in Section 9 of RFC8447.";
}
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typedef signature-algorithm {
type uint16;
description
"Signature algorithm in the TLS SignatureScheme registry as
defined in Section 11 of RFC8446.";
}
typedef psk-key-exchange-mode {
type uint8;
description
"Pre-shared key exchange mode in the TLS PskKeyExchangeMode
registry as defined in Section 11 of RFC8446.";
}
typedef application-protocol {
type string;
description
"Application-Layer Protocol Negotiation (ALPN) Protocol ID
registry as defined in Section 6 of RFC7301.";
}
typedef cert-compression-algorithm {
type uint16;
description
"Certificate compression algorithm in TLS Certificate
Compression Algorithm IDs registry as defined in
Section 7.3 of RFC8879.";
}
typedef cipher-algorithm {
type uint16;
description
"Cipher suite in TLS Cipher Suites registry
as discussed in Section 11 of RFC8446.";
}
typedef tls-version {
type enumeration {
enum tls12 {
value 1;
description
"TLS Protocol Version 1.2.
TLS 1.2 ClientHello contains
0x0303 in 'legacy_version'.";
reference
"RFC 5246: The Transport Layer Security (TLS) Protocol
Version 1.2";
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}
enum tls13 {
value 2;
description
"TLS Protocol Version 1.3.
TLS 1.3 ClientHello contains a
supported_versions extension with 0x0304
contained in its body and the ClientHello contains
0x0303 in 'legacy_version'.";
reference
"RFC 8446: The Transport Layer Security (TLS) Protocol
Version 1.3";
}
}
description
"Indicates the TLS version.";
}
typedef dtls-version {
type enumeration {
enum dtls12 {
value 1;
description
"DTLS Protocol Version 1.2.
DTLS 1.2 ClientHello contains
0xfefd in 'legacy_version'.";
reference
"RFC 6347: Datagram Transport Layer Security 1.2";
}
enum dtls13 {
value 2;
description
"DTLS Protocol Version 1.3.
DTLS 1.3 ClientHello contains a
supported_versions extension with 0x0304
contained in its body and the ClientHello contains
0xfefd in 'legacy_version'.";
reference
"RFC 9147: Datagram Transport Layer Security 1.3";
}
}
description
"Indicates the DTLS version.";
}
}
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<CODE ENDS>
5.4. MUD (D)TLS Profile Extension
This document augments the "ietf-mud" MUD YANG module to indicate
whether the device supports (D)TLS profile. If the "ietf-mud-tls"
extension is supported by the device, MUD file is assumed to
implement the "match-on-tls-dtls" ACL model feature defined in this
specification. Furthermore, only "accept" or "drop" actions SHOULD
be included with the (D)TLS profile similar to the actions allowed in
Section 2 of [RFC8520].
This document defines the YANG module "ietf-mud-tls", which has the
following tree structure:
module: ietf-mud-tls
augment /ietf-mud:mud:
+--rw is-tls-dtls-profile-supported? boolean
The model is defined as follows:
<CODE BEGINS> file "ietf-mud-tls@2020-10-20.yang"
module ietf-mud-tls {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-mud-tls";
prefix ietf-mud-tls;
import ietf-mud {
prefix ietf-mud;
reference
"RFC 8520: Manufacturer Usage Description Specification";
}
organization
"IETF OPSAWG (Operations and Management Area Working Group)";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: opsawg@ietf.org
Author: Konda, Tirumaleswar Reddy
kondtir@gmail.com
";
description
"Extension to a MUD module to indicate (D)TLS
profile support.
Copyright (c) 2020 IETF Trust and the persons identified as
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authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Revised BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision 2022-10-10 {
description
"Initial revision.";
reference
"RFC XXXX: Manufacturer Usage Description (MUD) (D)TLS
Profiles for IoT Devices";
}
augment "/ietf-mud:mud" {
description
"This adds a extension for a manufacturer
to indicate whether (D)TLS profile is
is supported by a device.";
leaf is-tls-dtls-profile-supported {
type boolean;
default false;
description
"This value will equal 'true' if a device supports
(D)TLS profile.";
}
}
}
<CODE ENDS>
6. Processing of the MUD (D)TLS Profile
The following text outlines the rules for a network security service
(e.g., firewall) to follow to process the MUD (D)TLS Profile so as to
avoid ossification:
* If the (D)TLS parameter observed in a (D)TLS session is not
specified in the MUD (D)TLS profile and the parameter is
recognized by the firewall, it can identify unexpected (D)TLS
usage, which can indicate the presence of unauthorized software or
malware on an endpoint. The firewall can take several actions
like block the (D)TLS session or raise an alert to quarantine and
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remediate the compromised device. For example, if the cipher
suite TLS_RSA_WITH_AES_128_CBC_SHA in the ClientHello message is
not specified in the MUD (D)TLS profile and the cipher suite is
recognized by the firewall, it can identify unexpected TLS usage.
* If the (D)TLS parameter observed in a (D)TLS session is not
specified in the MUD (D)TLS profile and the (D)TLS parameter is
not recognized by the firewall, it can ignore the unrecognized
parameter and the correct behavior is not to block the (D)TLS
session. The behaviour is functionally equivalent to the
compliant TLS middlebox description in Section 9.3 of [RFC8446] to
ignore all unrecognized cipher suites, extensions, and other
parameters. For example, if the cipher suite
TLS_CHACHA20_POLY1305_SHA256 in the ClientHello message is not
specified in the MUD (D)TLS profile and the cipher suite is not
recognized by the firewall, it can ignore the unrecognized cipher
suite. This rule also ensures that the network security service
will ignore the GREASE values advertised by TLS peers and
interoperate with the implementations advertising GREASE values.
* Deployments update at different rates, so an updated MUD (D)TLS
profile may support newer parameters. If the firewall does not
recognize the newer parameters, an alert should be triggered to
the firewall vendor and the IoT device owner or administrator. A
firewall must be readily updatable, so that when new parameters in
the MUD (D)TLS profile are discovered that are not recognized by
the firewall, it can be updated quickly. Most importantly, if the
firewall is not readily updatable, its protection efficacy to
identify emerging malware will decrease with time. For example,
if the cipher suite TLS_AES_128_CCM_8_SHA256 specified in the MUD
(D)TLS profile is not recognized by the firewall, an alert will be
triggered. Similarly, if the (D)TLS version specified in the MUD
file is not recognized by the firewall, an alert will be
triggered.
7. MUD File Example
The example below contains (D)TLS profile parameters for a IoT device
used to reach servers listening on port 443 using TCP transport.
JSON encoding of YANG modelled data [RFC7951] is used to illustrate
the example.
{
"ietf-mud:mud": {
"mud-version": 1,
"mud-url": "https://example.com/IoTDevice",
"last-update": "2019-18-06T03:56:40.105+10:00",
"cache-validity": 100,
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"extensions": [
"ietf-mud-tls"
],
"ietf-mud-tls:is-tls-dtls-profile-supported": "true",
"is-supported": true,
"systeminfo": "IoT device name",
"from-device-policy": {
"access-lists": {
"access-list": [
{
"name": "mud-7500-profile"
}
]
}
},
"ietf-access-control-list:acls": {
"acl": [
{
"name": "mud-7500-profile",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-frdev",
"matches": {
"ipv6": {
"protocol": 6
},
"tcp": {
"ietf-mud:direction-initiated": "from-device",
"destination-port": {
"operator": "eq",
"port": 443
}
},
"ietf-acl-tls:client-profile" : {
"tls-dtls-profiles" : [
{
"name" : "profile1",
"supported-tls-versions" : ["tls13"],
"cipher-suite" : [4865, 4866],
"extension-types" : [10,11,13,16,24],
"supported-groups" : [29]
}
]
},
"actions": {
"forwarding": "accept"
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}
}
}
]
}
}
]
}
}
}
The following illustrates the example scenarios for processing the
above profile:
* If the extension type "encrypt_then_mac" (code point 22) [RFC7366]
in the ClientHello message is recognized by the firewall, it can
identify unexpected TLS usage.
* If the extension type "token_binding" (code point 24) [RFC8472] in
the MUD (D)TLS profile is not recognized by the firewall, it can
ignore the unrecognized extension. Because the extension type
"token_binding" is specified in the profile, an alert will be
triggered to the firewall vendor and the IoT device owner or
administrator to notify the firewall is not up to date.
* The two-byte values assigned by IANA for the cipher suites
TLS_AES_128_GCM_SHA256 and TLS_AES_256_GCM_SHA384 are represented
in decimal format.
8. Security Considerations
Security considerations in [RFC8520] need to be taken into
consideration. The middlebox must adhere to the invariants discussed
in Section 9.3 of [RFC8446] to act as a compliant proxy.
Although it is challenging for a malware to mimic the TLS behavior of
various IoT device types and IoT device models from several
manufacturers, malicious agents have a very low probability of using
the same (D)TLS profile parameters as legitimate agents on the IoT
device to evade detection. Network security services should also
rely on contextual network data to detect false negatives. In order
to detect such malicious flows, anomaly detection (deep learning
techniques on network data) can be used to detect malicious agents
using the same (D)TLS profile parameters as legitimate agent on the
IoT device. In anomaly detection, the main idea is to maintain
rigorous learning of "normal" behavior and where an "anomaly" (or an
attack) is identified and categorized based on the knowledge about
the normal behavior and a deviation from this normal behavior.
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Please note that the security considerations mentioned in Section 3.7
of [RFC8407] are not applicable in this case because the YANG
serialization is not intended to be accessed via NETCONF. However,
for those who try to instantiate this model in a network element via
the Network Configuration Protocol (NETCONF), all objects in each
model in this document exhibit similar security characteristics as
[RFC8519].
9. Privacy Considerations
Privacy considerations discussed in Section 16 of [RFC8520] to not
reveal the MUD URL to an attacker need to be taken into
consideration. The MUD URL can be stored in Trusted Execution
Environment (TEE) for secure operation, enhanced data security, and
prevent exposure to unauthorized software. The MUD URL MUST be
encrypted and shared only with the authorized components in the
network (see Section 1.5 and Section 1.8 of [RFC8520]) so that an on-
path attacker cannot read the MUD URL and identify the IoT device.
Otherwise, it provides the attacker with guidance on what
vulnerabilities may be present on the IoT device. Note that while
protecting the MUD URL is valuable as described above, a compromised
IoT device may be susceptible to malware performing vulnerability
analysis (and version mapping) of the legitimate software located in
memory or on non-volatile storage (e.g., disk, NVRAM). However, the
malware on the IoT device won't be able to establish a (D)TLS
connection with the C&C server to reveal this information because the
connection would be blocked by the network security service
supporting this specification.
Full handshake inspection (Section 4.1) requires a (D)TLS proxy
device which needs to decrypt traffic between the IoT device and its
server(s). There is a tradeoff between privacy of the data carried
inside (D)TLS (especially e.g., personally identifiable information
and protected health information) and efficacy of endpoint security.
It is strongly RECOMMENDED to avoid a (D)TLS proxy whenever possible.
For example, an enterprise firewall administrator can configure the
middlebox to bypass (D)TLS proxy functionality or payload inspection
for connections destined to specific well-known services.
Alternatively, a IoT device could be configured to reject all
sessions that involve proxy servers to specific well-known services.
In addition, mechanisms based on object security can be used by IoT
devices to enable end-to-end security and the middlebox will not have
any access to the packet data. For example, Object Security for
Constrained RESTful Environments (OSCORE) [RFC8613] is a proposal
that protects CoAP messages by wrapping them in the COSE format
[RFC8152].
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10. IANA Considerations
10.1. (D)TLS Profile YANG Modules
This document requests IANA to register the following URIs in the
"ns" subregistry within the "IETF XML Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:iana-tls-profile
Registrant Contact: IANA.
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-acl-tls
Registrant Contact: IESG.
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-mud-tls
Registrant Contact: IESG.
XML: N/A; the requested URI is an XML namespace.
IANA is requested to create an IANA-maintained YANG Module called
"iana-tls-profile", based on the contents of Section 5.3, which will
allow for new (D)TLS parameters and (D)TLS versions to be added to
"client-profile". The registration procedure will be Expert Review,
as defined by [RFC8126]. The designated expert allows new (D)TLS
parameters to be added to the YANG Module provided they were added to
the TLS and DTLS IANA registries and if the new (D)TLS parameters can
be used by a middlebox to identify a MUD non-compliant (D)TLS
behavior. The designated expert allows new (D)TLS version to be
added to the YANG Module provided the new (D)TLS version
specification is adopted by the TLS WG.
This document requests IANA to register the following YANG modules in
the "YANG Module Names" subregistry [RFC6020] within the "YANG
Parameters" registry.
name: iana-tls-profile
namespace: urn:ietf:params:xml:ns:yang:iana-tls-profile
maintained by IANA: Y
prefix: ianatp
reference: RFC XXXX
name: ietf-acl-tls
namespace: urn:ietf:params:xml:ns:yang:ietf-acl-tls
maintained by IANA: N
prefix: ietf-acl-tls
reference: RFC XXXX
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name: ietf-mud-tls
namespace: urn:ietf:params:xml:ns:yang:ietf-mud-tls
maintained by IANA: N
prefix: ietf-mud-tls
reference: RFC XXXX
IANA is requested to create an the initial version of the IANA-
maintained YANG Module called "iana-tls-profile", based on the
contents of Section 5.3, which will allow for new (D)TLS parameters
and (D)TLS versions to be added. IANA is requested to add this note:
* tls-version and dtls-version values must not be directly added to
the iana-tls-profile YANG module. They must instead be
respectively added to the "ACL TLS Version Codes", and "ACL DTLS
Version Codes" registries.
* (D)TLS parameters must not be directly added to the iana-tls-
profile YANG module. They must instead be added to the "ACL
(D)TLS Parameters" registry.
When a 'tls-version' or 'dtls-version' value is respectively added to
the "ACL TLS Version Codes" or "ACL DTLS Version Codes" registry, a
new "enum" statement must be added to the iana-tls-profile YANG
module. The following "enum" statement, and substatements thereof,
should be defined:
"enum": Replicates the label from the registry.
"value": Contains the IANA-assigned value corresponding to the
'tls-version' or 'dtls-version'.
"description": Replicates the description from the registry.
"reference": Replicates the reference from the registry and adds
the title of the document.
When a (D)TLS parameter is added to "ACL (D)TLS Parameters" registry,
a new "type" statement must be added to the iana-tls-profile YANG
module. The following "type" statement, and substatements thereof,
should be defined:
"derived type": Replicates the parameter name from the registry.
"built-in type": Contains the built-in YANG type.
"description": Replicates the description from the registry.
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When the iana-tls-profile YANG module is updated, a new "revision"
statement must be added in front of the existing revision statements.
IANA is requested to add this note to "ACL TLS Version Codes", "ACL
DTLS Version Codes", and "ACL (D)TLS Parameters" registries:
When this registry is modified, the YANG module iana-tls-profile
must be updated as defined in [RFCXXXX].
The registration procedure for "ietf-acl-tls" YANG module will be
Specification Required, as defined by [RFC8126].
10.2. ACL TLS Version registry
IANA is requested to create a new registry titled "ACL TLS Version
Codes". Codes in this registry are used as valid values of 'tls-
version' parameter. Further assignments are to be made through
Expert Review [RFC8126].
+-------+---------+-----------------+-----------+
| Value | Label | Description | Reference |
| | | | |
| | | | |
+-------+---------+-----------------+-----------+
| 1 | tls12 | TLS Version 1.2 | [RFC5246] |
+-------+---------+-----------------+-----------+
| 2 | tls13 | TLS Version 1.3 | [RFC8446] |
+-------+---------+-----------------+-----------+
10.3. ACL DTLS version registry
IANA is requested to create a new registry titled "ACL DTLS Version
Codes". Codes in this registry are used as valid values of 'dtls-
version' parameter. Further assignments are to be made through
Expert Review [RFC8126].
+-------+---------+----------------+-----------------------+
| Value | Label | Description | Reference |
| | | | |
| | | | |
+-------+---------+----------------+-----------------------+
| 1 |dtls12 |DTLS Version 1.2| [RFC6347] |
+-------+---------+----------------+-----------------------+
| 2 |dtls13 |DTLS Version 1.3| [RFC9147| |
+-------+---------+----------------+-----------------------+
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10.4. ACL (D)TLS Parameters registry
IANA is requested to create a new registry titled "ACL (D)TLS
parameters".
The values for all the (D)TLS parameters in the registry are defined
in the TLS and DTLS IANA registries
(https://www.iana.org/assignments/tls-parameters/tls-parameters.txt
and https://www.iana.org/assignments/tls-extensiontype-values/tls-
extensiontype-values.txt) excluding the tls-version and dtls-version
parameters. Further assignments are to be made through Expert Review
[RFC8126]. The registry is initially populated with the following
parameters:
+----------------------------+-------------+--------+---------------------------------------------+
| Parameter Name | YANG | JSON | |
| | Type | Type | Description |
| | | | |
+----------------------------+-------------+--------+---------------------------------------------+
| extension-type | uint16 | Number | Extension type |
+----------------------------+-------------+--------+---------------------------------------------+
| supported-group | uint16 | Number | Supported group |
+----------------------------+-------------+--------+---------------------------------------------+
| signature-algorithm | uint16 | Number | Signature algorithm |
+----------------------------+-------------+--------+---------------------------------------------+
| psk-key-exchange-mode | uint8 | Number | pre-shared key exchange mode |
+----------------------------+-------------+--------+---------------------------------------------+
| application-protocol | string | String | Application protocol |
+----------------------------+-------------+--------+---------------------------------------------+
| cert-compression-algorithm | uint16 | Number | Certificate compression algorithm |
+----------------------------+-------------+--------+---------------------------------------------+
| cipher-algorithm | uint16 | Number | Cipher Suite |
+----------------------------+-------------+--------+---------------------------------------------+
| tls-version | enumeration | String | TLS version |
+----------------------------+-------------+--------+---------------------------------------------+
| dtls-version | enumeration | String | DTLS version |
+----------------------------+-------------+--------+---------------------------------------------+
10.5. MUD Extensions registry
IANA is requested to create a new MUD Extension Name "ietf-mud-tls"
in the MUD Extensions IANA registry
https://www.iana.org/assignments/mud/mud.xhtml.
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11. Acknowledgments
Thanks to Flemming Andreasen, Shashank Jain, Michael Richardson,
Piyush Joshi, Eliot Lear, Harsha Joshi, Qin Wu, Mohamed Boucadair,
Ben Schwartz, Eric Rescorla, Panwei William, Nick Lamb, Tom Petch,
Paul Wouters and Nick Harper for the discussion and comments.
Thanks to Xufeng Liu for YANGDOCTOR review. Thanks to Linda Dunbar
for SECDIR review.
12. References
12.1. Normative References
[I-D.ietf-netconf-crypto-types]
Watsen, K., "YANG Data Types and Groupings for
Cryptography", Work in Progress, Internet-Draft, draft-
ietf-netconf-crypto-types-28, 28 December 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
crypto-types-28>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[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>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[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>.
[RFC8519] Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
"YANG Data Model for Network Access Control Lists (ACLs)",
RFC 8519, DOI 10.17487/RFC8519, March 2019,
<https://www.rfc-editor.org/info/rfc8519>.
[RFC8520] Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
Description Specification", RFC 8520,
DOI 10.17487/RFC8520, March 2019,
<https://www.rfc-editor.org/info/rfc8520>.
[RFC8701] Benjamin, D., "Applying Generate Random Extensions And
Sustain Extensibility (GREASE) to TLS Extensibility",
RFC 8701, DOI 10.17487/RFC8701, January 2020,
<https://www.rfc-editor.org/info/rfc8701>.
[RFC8879] Ghedini, A. and V. Vasiliev, "TLS Certificate
Compression", RFC 8879, DOI 10.17487/RFC8879, December
2020, <https://www.rfc-editor.org/info/rfc8879>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/info/rfc9147>.
[X690] ITU-T, "Information technology - ASN.1 encoding Rules:
Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", ISO/IEC 8825-1:2002, 2002.
12.2. Informative References
[clear-as-mud]
"Clear as MUD: Generating, Validating and Applying IoT
Behaviorial Profiles", October 2019,
<https://arxiv.org/pdf/1804.04358.pdf>.
[cryto-vulnerability]
Perez, B., "Exploiting the Windows CryptoAPI
Vulnerability", January 2020,
<https://media.defense.gov/2020/Jan/14/2002234275/-1/-1/0/
CSA-WINDOWS-10-CRYPT-LIB-20190114.PDF>.
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[I-D.ietf-tls-esni]
Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS
Encrypted Client Hello", Work in Progress, Internet-Draft,
draft-ietf-tls-esni-17, 9 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
esni-17>.
[I-D.ietf-uta-tls13-iot-profile]
Tschofenig, H., Fossati, T., and M. Richardson, "TLS/DTLS
1.3 Profiles for the Internet of Things", Work in
Progress, Internet-Draft, draft-ietf-uta-tls13-iot-
profile-08, 22 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-uta-
tls13-iot-profile-08>.
[malware] Anderson, B., Paul, S., and D. McGrew, "Deciphering
Malware's use of TLS (without Decryption)", July 2016,
<https://arxiv.org/abs/1607.01639>.
[malware-doh]
Cimpanu, C., "First-ever malware strain spotted abusing
new DoH (DNS over HTTPS) protocol", July 2019,
<https://www.zdnet.com/article/first-ever-malware-strain-
spotted-abusing-new-doh-dns-over-https-protocol/>.
[malware-tls]
Anderson, B. and D. McGrew, "TLS Beyond the Browser:
Combining End Host and Network Data to Understand
Application Behavior", October 2019,
<https://dl.acm.org/citation.cfm?id=3355601>.
[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>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[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>.
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[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>.
[RFC7366] Gutmann, P., "Encrypt-then-MAC for Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", RFC 7366, DOI 10.17487/RFC7366, September 2014,
<https://www.rfc-editor.org/info/rfc7366>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", RFC 7525, DOI 10.17487/RFC7525, May 2015,
<https://www.rfc-editor.org/info/rfc7525>.
[RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer
Security (TLS) / Datagram Transport Layer Security (DTLS)
Profiles for the Internet of Things", RFC 7925,
DOI 10.17487/RFC7925, July 2016,
<https://www.rfc-editor.org/info/rfc7925>.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<https://www.rfc-editor.org/info/rfc7951>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
[RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", BCP 216, RFC 8407,
DOI 10.17487/RFC8407, October 2018,
<https://www.rfc-editor.org/info/rfc8407>.
[RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
<https://www.rfc-editor.org/info/rfc8447>.
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[RFC8472] Popov, A., Ed., Nystroem, M., and D. Balfanz, "Transport
Layer Security (TLS) Extension for Token Binding Protocol
Negotiation", RFC 8472, DOI 10.17487/RFC8472, October
2018, <https://www.rfc-editor.org/info/rfc8472>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
[RFC8576] Garcia-Morchon, O., Kumar, S., and M. Sethi, "Internet of
Things (IoT) Security: State of the Art and Challenges",
RFC 8576, DOI 10.17487/RFC8576, April 2019,
<https://www.rfc-editor.org/info/rfc8576>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
[RFC9462] Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
Jensen, "Discovery of Designated Resolvers", RFC 9462,
DOI 10.17487/RFC9462, November 2023,
<https://www.rfc-editor.org/info/rfc9462>.
[RFC9463] Boucadair, M., Ed., Reddy.K, T., Ed., Wing, D., Cook, N.,
and T. Jensen, "DHCP and Router Advertisement Options for
the Discovery of Network-designated Resolvers (DNR)",
RFC 9463, DOI 10.17487/RFC9463, November 2023,
<https://www.rfc-editor.org/info/rfc9463>.
[X501] "Information Technology - Open Systems Interconnection -
The Directory: Models", ITU-T X.501, 1993.
Authors' Addresses
Tirumaleswar Reddy
Nokia
India
Email: kondtir@gmail.com
Dan Wing
Citrix Systems, Inc.
4988 Great America Pkwy
Santa Clara, CA 95054
United States of America
Email: danwing@gmail.com
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Blake Anderson
Cisco Systems, Inc.
170 West Tasman Dr
San Jose, CA 95134
United States of America
Email: blake.anderson@cisco.com
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