Internet DRAFT - draft-wilson-dance-architecture
draft-wilson-dance-architecture
DANCE A. Wilson
Internet-Draft Valimail
Intended status: Informational S. Huque
Expires: 25 November 2022 Salesforce
O. Johansson
Edvina.net
24 May 2022
An Architecture for DNS-Bound Client and Sender Identities
draft-wilson-dance-architecture-02
Abstract
This architecture document defines terminology, interaction, and
authentication patterns, related to the use of DANE DNS records for
TLS client and messaging peer identity, within the context of
existing object security and TLS-based protocols.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the DANE Authentication
for Network Clients Everywhere Working Group mailing list
(dance@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/dance/.
Source for this draft and an issue tracker can be found at
https://github.com/ashdwilson/draft-dance-architecture.
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 25 November 2022.
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Copyright Notice
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Communication Patterns . . . . . . . . . . . . . . . . . . . 5
3.1. Client/Server . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Peer2peer . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Decoupled . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Mutual TLS Authentication . . . . . . . . . . . . . . . . 7
4.1.1. Example 1: TLS authentication for HTTPS API
interaction, DANE preauthorization . . . . . . . . . 7
4.1.2. IoT: Device to cloud . . . . . . . . . . . . . . . . 8
4.1.3. Oauth2 . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.4. Edge Computing . . . . . . . . . . . . . . . . . . . 9
4.1.5. SIP and WebRTC inter-domain privacy . . . . . . . . . 9
4.1.6. DNS over TLS client authentication . . . . . . . . . 9
4.1.7. SMTP, STARTTLS . . . . . . . . . . . . . . . . . . . 9
4.1.8. SSH client . . . . . . . . . . . . . . . . . . . . . 9
4.1.9. Network Access . . . . . . . . . . . . . . . . . . . 9
4.1.10. LoRaWAN . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Object Security . . . . . . . . . . . . . . . . . . . . . 11
4.2.1. Structured data messages: JOSE/COSE . . . . . . . . . 11
4.3. Operational anomaly reporting . . . . . . . . . . . . . . 11
4.3.1. MUD reporting for improper provisioning . . . . . . . 11
4.3.2. XARF for abuse reporting . . . . . . . . . . . . . . 11
4.4. Adjacent Ecosystem Components . . . . . . . . . . . . . . 11
4.4.1. Certification Authority . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5.1. Confidentiality . . . . . . . . . . . . . . . . . . . . . 11
5.2. Integrity . . . . . . . . . . . . . . . . . . . . . . . . 11
5.3. Availability . . . . . . . . . . . . . . . . . . . . . . 12
5.4. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.4.1. DNS Scalability . . . . . . . . . . . . . . . . . . . 12
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5.4.2. Change of ownership . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. Normative References . . . . . . . . . . . . . . . . . . . . 13
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
A digital identity, in an abstract sense, possesses at least two
features: an identifier (or name), and a means of proving ownership
of the identifier. One of the most resilient mechanisms for tying an
identifier to a method for proving ownership of the identifier is the
digital certificate, issued by a well-run Certification Authority
(CA). The CA acts as a mutually trusted third party, a root of
trust.
Certificate-based identities are limited in scope by the issuing CA,
or by the namespace of the application responsible for issuing or
validating the identity.
An example of this limitation is well-illustrated by organizational
Public Key Infrastructure (PKI). Organizational PKI is very often
coupled with email and LDAP systems, and can be used for associating
a human or machine identity identifier with a public key. Within the
organization, authentication systems already agree on the roots of
trust for validating entity certificates issued by organizational
PKI.
Attempting to use organizational PKI outside the organization can be
challenging. In order to authenticate a certificate, the
certificate's CA must be trusted. CAs have no way of controlling
identifiers in certificates issued by other CAs. Consequently,
trusting multiple CAs at the same time can enable entity identifier
collisions. Asking an entity to trust your CA implies trust in
anything that your CA signs. This is why many organizations operate
a private CA, and require devices connecting to the organization's
networks or applications to possess certificates issued by the
organization's CA.
These limitations make the implementation and ongoing maintenance of
a PKI costly, and have a chilling effect on the broader adoption of
certificate-based IoT device identity. If certificate-based device
identity were easier to manage, more broadly trusted, and less
operationally expensive, more organizations and applications would be
able to use it.
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The lack of trust between PKI domains has lead to a lack of simple
and globally scalable solutions for secure end-to-end inter-domain
communication between entities, such as SIP phones, email and chat
accounts and IoT devices belonging to different organizations.
DANCE seeks to make PKI-based IoT device identity universally
discoverable, more broadly recognized, and less expensive to maintain
by using DNS as the constraining namespace and lookup mechanism.
DANCE builds on patterns established by the original DANE RFCs to
enable client and sending entity certificate, public key, and trust
anchor discovery. DANCE allows entities to possess a first-class
identity, which, thanks to DNS, may be trusted by any application
also trusting the DNS. A first-class identity is an application-
independent identity.
2. Conventions and Definitions
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.
*This section will be interesting to define. We have great examples
of identity terminology in the https://datatracker.ietf.org/doc/html/
draft-sarikaya-t2trg-sbootstrapping-06 document, but this document
also admits that there is semantic drift on terms like
"bootstrapping", depending on who's talking.*
*Identity provisioning:* This refers to the set of tasks required to
securely provision an asymmetric key pair for the device, sign the
certificate (if the public credential is not simply a raw public
key), and publish the public key or certificate in DNS. Under some
circumstances, these steps are not all performed by the same party or
organization. A manufacturer may instantiate the key pair, and a
systems integrator may be responsible for issuing (and publishing)
the device certificate in DNS. In some circumstances, a manufacturer
may also publish device identity records in DNS. In this case, the
system integrator needs to perform network and application access
configuration, since the identity already exists in DNS.
*Security Domain:* DNS-bound client identity allows the device to
establish secure communications with any server with a DNS-bound
identity, as long as a network path exists, the entity is configured
to trust its communicating peer by name, and agreement on protocols
can be achieved. The act of joining a security domain, in the past,
may have involved certificate provisioning. Now, it can be as simple
as using a manufacturer-provisioned identity to join the device to
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the network and application. [Is the security domain defined by how
broadly the identity is recognized, or by the breadth of the
application or network access policy?]
*Client:* This architecture document adopts the definition of
"Client" from RFC 8446: "The endpoint initiating the TLS connection"
*Server:* This architecture document adopts the definition of
"Server" from RFC 8446: "The endpoint that did not initiate the TLS
connection"
*Sending agent:* Software which encodes and transmits messages. A
sending agent may perform tasks related to generating cryptographic
signatures and/or encrypting messages before transmission.
*Receiving agent:* Software which interprets and processes messages.
A receiving agent may perform tasks related to the decryption of
messages, and verification of message signatures.
*Store-and-forward system:* A message handling system in-path between
the sending agent and the receiving agent.
*Hardware supplier role:* The entity which manufactures or assembles
the physical device. In many situations, multiple hardware suppliers
are involved in producing a given device. In some cases, the
hardware supplier may provision an asymmetric key pair for the device
and establish the device identity in DNS. In some cases, the
hardware supplier may ship a device with software pre-installed.
*Systems integrator:* The party responsible for configuration and
deployment of application components. In some cases, the systems
integrator also installs the software onto the device, and may
provision the device identity in DNS.
*Consumer:* The entity or organization which pays for the value
provided by the application, and defines the success criteria for the
output of the application.
3. Communication Patterns
3.1. Client/Server
Client/server communication patterns imply a direct connection
between an entity which provides a service (the server), and an
entity which initiates a connection to the server, called a client.
A secure implementation of this pattern includes a TLS-protected
session directly between the client and the server. A secure
implementation may also include public key-based mutual
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authentication.
Extending DANE to include client identity allows the server to
authenticate clients independent of the private PKI used to issue the
client certificate. This reduces the complexity of managing the CA
certificate collection, and mitigates the possibility of client
identifier collision.
3.2. Peer2peer
The extension also allows an application to find an application
identity and set up a secure communication channel directly. This
pattern can be used in mesh networking, IoT and in many communication
protocols for multimedia sessions, chat and messaging.
3.3. Decoupled
Decoupled architecture, frequently incorporating store-and-forward
systems, provides no direct connection between the producer and
consumer of information. The producer (or sending agent) and
consumer (or receiving agent) are typically separated by at least one
layer of messaging-oriented middleware. The Messaging-oriented
middleware components may act as a server for the purpose of
establishing TLS sessions for the producer and consumer. This allows
the assertion of identity between the middleware and sending agent,
and the middleware and receiving agent. The trust relationship
between the sending agent and receiving agent is based on the
presumed trustworthiness of the middleware, unless an identity can be
attached to the message itself, independent of transport and
middleware components.
Within many existing store-and-forward protocols, certificates may be
transmitted within the signed message itself. An example of this is
S/MIME. Within IoT applications, we find that networks may be more
constrained. Including certificates in message payloads can present
an unnecessary overhead on constrained network links. Decoupled
applications benefit from an out-of-band public key discovery
mechanism, which may enable the retrieval of certificates only when
needed, and sometimes using a less expensive network connection.
4. Use Cases
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4.1. Mutual TLS Authentication
Using DNS to convey certificate information for authenticating TLS
clients gives a not-yet-authenticated client the ability to trigger a
DNS lookup on the server side of the TLS connection. An opportunity
for DDOS may exist when malicious clients can trigger arbitrary DNS
lookups. For instance, an authoritative DNS server which has been
configured to respond slowly, may cause a high concurrency of in-
flight TLS authentication processes as well as open connections to
upstream resolvers. This sort of attack (of type slowloris) could
have a performance or availability impact on the TLS server.
4.1.1. Example 1: TLS authentication for HTTPS API interaction, DANE
preauthorization
* The client initiates a TLS connection to the server.
* The TLS server compares the dane_clientid (conveyed via the DANE
Client Identity extension) to a list of allowed client domains.
* If the dane_clientid is allowed, the TLS server then performs a
DNS lookup for the client's TLSA record. If the dane_clientid is
not allowed, authentication fails.
* If the client's TLSA record matches the presented certificate or
public key, the TLS handshake completes successfully and the
authenticated dane_clientid is presented to the web application in
the (TBD) header field.
This pattern has the following advantages:
* This pattern translates well to TLS/TCP load balancers, by using a
TCP TLV instead of an HTTP header.
* No traffic reaches the application behind the load balancer unless
DANE client authentication is successful.
4.1.1.1. Example 2: TLS authentication for HTTPS API interaction, DANE
matching in web application
* The client initiates a TLS connection to the server.
* The TLS server accepts any certificate for which the client can
prove possession of the corresponding private key.
* The TLS server passes the certificate to the web application in
(TBD) header field.
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* The HTTP request body contains the dane_clientid, and is passed to
the web application.
* The web application compares the dane_clientid to a list of
allowed clients or client domains.
* If the dane_clientid is allowed, the web application makes the DNS
query for the TLSA records for dane_clientid
* If the presented certificate (which was authenticated by the TLS
server) matches at least one TLSA record for dane_clientid,
authentication succeeds.
This pattern has the following advantages:
* In a web application where a TLS-terminating load balancer sits in
front of a web application, the authentication logic in the load
balancer remains simple.
* The web application ultimately decides whether to make the DNS
query to support DANE authentication. This allows the web
application to reject clients with identifiers which are not
allowed, before making a DNS query for TLSA retrieval and
comparison. No need to manage an allow-list in the load balancer.
* This can be implemented with no changes to the TLS handshake.
4.1.2. IoT: Device to cloud
Direct device-to-cloud communication is common in simple IoT
applications. Authentication in these applications is usually
accomplished using shared credentials like API keys, or using client
certificates. Client certificate authentication frequently requires
the consumer to maintain a CA. The CA trust anchor certificate is
installed into the cloud application, and used in the TLS
authentication process.
Using DANE for device identity can allow parties other than the
implementer to operate the CA. A hardware manufacturer can provide a
pre-established identity, with the certificate or public key already
published in DNS. This makes PKI-based identity more approachable
for small organizations which currently lack the resources to operate
an organizational CA.
4.1.3. Oauth2
[This can be a broad topic. Should we include, or wait until a re-
chartering to update?]
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4.1.4. Edge Computing
https://datatracker.ietf.org/doc/html/draft-hong-t2trg-iot-edge-
computing-01 (Edge Computing) may require devices to mutually
authenticate in the field. A practical example of this pattern is
the edge computing in construction use case
[https://datatracker.ietf.org/doc/html/draft-hong-t2trg-iot-edge-
computing-01#section-6.2.1]. Using traditional certificate-based
identity, the sensor and the gateway may have certificates issued by
the same organizational PKI. By using DANE for client and sender
identity, the sensor and the gateway may have identities represented
by the equipment supplier, and still be able to mutually
authenticate. Important sensor measurements forwarded by the gateway
to the cloud may bear the DNS name and signature of the originating
sensor, and the cloud application may authenticate the measurement
independent of the gateway which forwarded the information to the
application.
4.1.5. SIP and WebRTC inter-domain privacy
End to end security in SIP is currently based on a classical S/MIME
model which has not received much implementation. There are also SIP
standards that build upon a trust chained anchored on the HTTP trust
chain (SIP identity, STIR). WebRTC has a trust model between the web
browser and the servers using TLS, but no inter-domain trust
infrastructure. WebRTC lacks a definition of namespace to map to
DNS, where SIP is based on an email-style addressing scheme. For
WebRTC the application developer needs to define the name space and
mapping to DNS.
By using DNS as a shared root of trust SIP and WebRTC end points can
anchor the keys used for DTLS/SRTP media channel setup. In addition,
SIP devices can establish security in the SIP messaging by using DNS
to find the callee's and the callers digital identity.
[https://datatracker.ietf.org/doc/html/draft-johansson-sipcore-dane-
sip]
*NOTE: include reference to earlier drafts for SIP + DANE*
4.1.6. DNS over TLS client authentication
4.1.7. SMTP, STARTTLS
4.1.8. SSH client
4.1.9. Network Access
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4.1.9.1. EAP-TLS with RADIUS
4.1.9.1.1. Terminology
*Supplicant:* The entity which acts as the TLS client in the EAP-TLS
authentication protocol. This term is defined in IEEE 802.1x. The
suppliant acts as a client in the EAPOL (EAP over LAN) protocol,
which is terminated at the authenticator (defined below).
*Authentication server:* The entity which acts as the TLS server in
the EAP-TLS protocol. RADIUS (RFC 2865) is a frequently-used
authentication server protocol.
*Authenticator:* The authenticator is the device which acts as a
server the EAPOL (EAP over LAN) protocol, and is a client of the
authentication server. The authenticator is responsible for passing
EAP messages between the supplicant and the authentication server,
and for ensuring that only authenticated supplicants gain access to
the network.
https://datatracker.ietf.org/doc/html/rfc5216 (EAP-TLS) is a mature
and widely-used protocol for network authentication, for IoT and IT
equipment. IEEE 802.1x defines the encapsulation of EAP over LAN
access technologies, like IEEE 802.11 wireless and IEEE 802.3
ethernet. RADIUS is a protocol and server technology frequently used
for supporting the server side of EAP-TLS authentication. Guidance
for implementing RADIUS strongly encourages the use of a single
common CA for all supplicants, to mitigate the possibility of
identifier collisions across PKIs. The use of DANE for client
identity can allow the safe use of any number of CAs. DNS acts as a
constraining namespace, which prevents two unrelated CAs from issuing
valid certificates bearing the same identifier. Certificates
represented in DNS are valid, and all others are un-trusted.
4.1.9.2. RADSEC
The RADIUS protocol has a few recognized security problems.
https://datatracker.ietf.org/doc/html/rfc6614 (RADSEC) addresses the
challenges related to the weakness of MD5-based authentication and
confidentiality over untrusted networks by establishing a TLS session
between the RADIUS protocol client and the RADIUS protocol server.
RADIUS datagrams are then transmitted between the authenticator and
authentication server within the TLS session. Updating the RADSEC
standard to include the use of DANE for client and server identity
would allow a RADIUS server and client to mutually authenticate,
independent of the client's and server's issuing CAs. The benefit
for this use case is that a hosted RADIUS service may mutually
authenticate any client device, like a WiFi access point or ethernet
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switch, via RADSEC, without requiring the distribution of CA
certificates.
4.1.10. LoRaWAN
*We should ask S. if he wants to contribute to this section*
4.2. Object Security
4.2.1. Structured data messages: JOSE/COSE
JOSE and COSE provide formats for exchanging authenticated and
encrypted structured data. JOSE defines the x5u field in
https://datatracker.ietf.org/doc/html/rfc7515#section-4.1.5
(RFC7515), and COSE defines a field of the same name in
https://datatracker.ietf.org/doc/html/draft-ietf-cose-
x509-08#section-2 (draft-ietf-cose-x509) which can be used for out-
of-band x.509 certificate discovery. By adopting DANE for out-of-
band certificate discovery, CBOR and JSON data may be authenticated,
even if the originating sending agent not have IP connectivity,
provided that the sending agent's certificate is discoverable in DNS
and the receiving agent has access to DNS.
4.3. Operational anomaly reporting
4.3.1. MUD reporting for improper provisioning
4.3.2. XARF for abuse reporting
4.4. Adjacent Ecosystem Components
4.4.1. Certification Authority
5. Security Considerations
5.1. Confidentiality
DNS clients should use DNS over TLS with trusted DNS resolvers to
protect the identity of authenticating peers.
5.2. Integrity
The integrity of public keys represented in DNS is most important.
An altered public key can enable device impersonation, and the denial
of existence for a valid identity can cause devices to become un-
trusted by the network or the application. DNS records should be
validated by the DNS stub resolver, using the DNSSEC protocol.
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Compartmentalizing failure domains within an application is a well-
known architectural best practice. Within the context of protecting
DNS-based identities, this compartmentalization may manifest by
hosting an identity zone on a DNS server which only supports the
resource record types essential for representing device identities.
This can prevent a compromised identity zone DNS server from
presenting records essential for impersonating web sites under the
organization's domain name.
The naming pattern suggested in
https://datatracker.ietf.org/doc/html/draft-huque-dane-client-cert
(https://datatracker.ietf.org/doc/html/draft-huque-dane-client-cert)
includes an underscore label (_device) which also prevents the
issuance of Web PKI-validating certificates in the event a DNS server
hosting a client identity zone, which is capable of presenting A and
AAAA records, is compromised.
5.3. Availability
5.4. Privacy
If the name of the identity proven by a certificate is directly or
indirectly relatable to a person, privacy needs to be considered when
forming the name of the DNS resource record for the certificate.
When creating the name of the RR, effects of DNS zone walking and
possible harvesting of identities in the DNS zone will have to be
considered. The name of the RR may note have to have a direct
relation to the name of the subject of the certificate.
Further work has do be done in this area.
AW: Consider if an approach like the email local-part hashing used in
SMIMEA https://datatracker.ietf.org/doc/html/rfc8162
(https://datatracker.ietf.org/doc/html/rfc8162) might work for this.
If the identifier/local-part is hashed and the certificate
association is a SHA256 or SHA512 hash, the effort required to walk a
zone would not produce much useful information.
5.4.1. DNS Scalability
In the use case for IoT an implementation must be scalable to a large
amount of devices. In many cases, identities may also be very short
lived as revocation is performed by simply removing a DNS record. A
zone will have to manage a large amount of changes as devices are
constantly added and de-activated.
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In these cases it is important to consider the architecture of the
DNS zone and when possible use a tree-like structure with many
subdomain parts, much like reverse DNS records or how telephone
numbers are represented in the ENUM standard (RFC 6116).
If an authoritative resolver were configured to respond quite slowly
(think slow loris), is it possible to cause a DoS on the TLS server
via complete exhaustion of TCP connections?
The availability of a client identity zone is essential to permitting
clients to authenticate. If the DNS infrastructure hosting client
identities becomes unavailable, then the clients represented by that
zone cannot be authenticated.
*OEJ: We may want to have a discussion with the IETF DNS directorate.
The scalability section above is from a discussion with one of the
members...*
5.4.2. Change of ownership
What happens if an organization owning the client identity goes out
of business? What's the best way to transfer an identifier to
another zone? <note: there may be an opportunity here to take
advantage of EST, or another protocol supporting certificate renewal,
to allow client devices to rotate to another zone>
6. IANA Considerations
This document has no IANA actions.
7. Normative References
[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/rfc/rfc2119>.
[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/rfc/rfc8174>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
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Ash Wilson
Valimail
Email: ash.d.wilson@gmail.com
Shumon Huque
Salesforce
Email: shuque@gmail.com
Olle Johansson
Edvina.net
Email: oej@edvina.net
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