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An Architecture for DNS-Bound Client and Sender Identities
draft-wilson-dance-architecture-00

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Ash Wilson , Shumon Huque , Olle E. Johansson
Last updated 2021-10-22
Replaced by draft-ietf-dance-architecture
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draft-wilson-dance-architecture-00
DANCE                                                          A. Wilson
Internet-Draft                                                  Valimail
Intended status: Informational                                  S. Huque
Expires: 25 April 2022                                        Salesforce
                                                            O. Johansson
                                                              Edvina.net
                                                         22 October 2021

       An Architecture for DNS-Bound Client and Sender Identities
                    draft-wilson-dance-architecture-00

Abstract

   TODO

Status of This Memo

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   This Internet-Draft will expire on 25 April 2022.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Communication Patterns  . . . . . . . . . . . . . . . . . . .   4
     3.1.  Client/Server . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Peer2peer . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Decoupled . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Mutual TLS Authentication . . . . . . . . . . . . . . . .   5
       4.1.1.  Device to cloud . . . . . . . . . . . . . . . . . . .   5
       4.1.2.  Oauth2  . . . . . . . . . . . . . . . . . . . . . . .   6
       4.1.3.  Edge Computing  . . . . . . . . . . . . . . . . . . .   6
       4.1.4.  SIP and WebRTC inter-domain privacy . . . . . . . . .   6
       4.1.5.  DNS over TLS client authentication  . . . . . . . . .   7
       4.1.6.  SMTP, STARTTLS  . . . . . . . . . . . . . . . . . . .   7
       4.1.7.  Network Access  . . . . . . . . . . . . . . . . . . .   7
       4.1.8.  LoRaWAN . . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Object Security . . . . . . . . . . . . . . . . . . . . .   7
       4.2.1.  Structured data messages: JOSE/COSE . . . . . . . . .   8
     4.3.  Operational anomaly reporting . . . . . . . . . . . . . .   8
       4.3.1.  MUD reporting for improper provisioning . . . . . . .   8
       4.3.2.  XARF for abuse reporting  . . . . . . . . . . . . . .   8
     4.4.  Adjacent Ecosystem Components . . . . . . . . . . . . . .   8
       4.4.1.  Certification Authority . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
     5.1.  Confidentiality . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Availability  . . . . . . . . . . . . . . . . . . . . . .   9
       5.2.1.  DNS Scalability . . . . . . . . . . . . . . . . . . .   9
       5.2.2.  Change of ownership . . . . . . . . . . . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

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.

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   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.

   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

   {::boilerplate bcp14-tagged}

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   *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
   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?

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
   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.

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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, sometimes referred to as store-and-forward,
   provides no direct connection between the producer and consumer of
   information.  The producer and consumer 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 producer, and
   the middleware and consumer.  The trust relationship between the
   producer and consumer 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

4.1.  Mutual TLS Authentication

4.1.1.  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 requires the
   implementer to manage a certification authority.  The CA trust anchor
   certificate is installed into the cloud application, and used in the
   TLS authentication process.

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   Using DANE for device identity can allow parties other than the
   implementer to operate the CA.  A hardware secure element provider
   can provide a pre-established identity, with the certificate or
   public key already published in DNS.  This can make PKI-based
   identity more approachable for small organizations which currently
   lack the resources to operate an organizational CA.

4.1.2.  Oauth2

   [This can be a broad topic.  Should we include, or wait until a re-
   chartering to update?]

4.1.3.  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.

4.1.4.  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.

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   [https://datatracker.ietf.org/doc/html/draft-johansson-sipcore-dane-
   sip]

   *NOTE: include reference to earlier drafts for SIP + DANE*

4.1.5.  DNS over TLS client authentication

4.1.6.  SMTP, STARTTLS

4.1.7.  Network Access

4.1.7.1.  EAP-TLS

   https://datatracker.ietf.org/doc/html/rfc5216 (EAP-TLS) is frequently
   used for network authentication, for IoT and traditional IT
   equipment.  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.  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.

4.1.7.2.  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 client and the RADIUS server.  RADIUS datagrams are then
   transmitted 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 switch, via RADSEC,
   without requiring the distribution of CA certificates.

4.1.8.  LoRaWAN

   *We should ask S. if he wants to contribute to this section*

4.2.  Object Security

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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 entity does not have IP connectivity,
   provided that the originating entity's certificate is discoverable in
   DNS and the authenticating system has access to the 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.  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.

   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.

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   The naming pattern suggested in (client identity draft) 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.

5.2.  Availability

5.2.1.  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.

   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...*

5.2.2.  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.

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Appendix A.  Acknowledgments

   TODO acknowledge.

Authors' Addresses

   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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