An Architecture for DNS-Bound Client and Sender Identities
draft-ietf-dance-architecture-10

DANCE                                                          A. Wilson
Internet-Draft                                                  Valimail
Intended status: Informational                                  S. Huque
Expires: 6 June 2026                                          Salesforce
                                                            O. Johansson
                                                              Edvina.net
                                                           M. Richardson
                                            Sandelman Software Works Inc
                                                         3 December 2025

       An Architecture for DNS-Bound Client and Sender Identities
                    draft-ietf-dance-architecture-10

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 6 June 2026.

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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.  Peer to peer  . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Decoupled . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Client authentication . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Overview - DANCE usage examples . . . . . . . . . . . . .   6
       4.1.1.  Example 1: TLS authentication for HTTPS API
               interaction, DANE pattern assurance . . . . . . . . .   7
       4.1.2.  Example 2: TLS authentication for HTTPS API
               interaction, DANE matching in web application . . . .   8
       4.1.3.  Example 3: TLS user authentication for an LDAP
               query . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.1.4.  Example 4: IoT: Device to cloud . . . . . . . . . . .   9
       4.1.5.  Example 5: LoRaWAN  . . . . . . . . . . . . . . . . .  10
       4.1.6.  Example 6: Edge Computing . . . . . . . . . . . . . .  10
       4.1.7.  Example 7: Domain Users . . . . . . . . . . . . . . .  10
       4.1.8.  Example 8: SIP and WebRTC inter-domain privacy  . . .  11
       4.1.9.  Example 9: DNS over TLS client authentication . . . .  11
       4.1.10. Example 10: SMTP, STARTTLS  . . . . . . . . . . . . .  12
       4.1.11. Example 11: SSH client  . . . . . . . . . . . . . . .  12
       4.1.12. Example 12: Network Access  . . . . . . . . . . . . .  13
       4.1.13. Example 13: Structured data messages: JOSE/COSE . . .  15
   5.  Protocol implementations  . . . . . . . . . . . . . . . . . .  15
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
     6.1.  Confidentiality . . . . . . . . . . . . . . . . . . . . .  15
     6.2.  Integrity . . . . . . . . . . . . . . . . . . . . . . . .  16
     6.3.  Availability  . . . . . . . . . . . . . . . . . . . . . .  16
     6.4.  TLS Server availability . . . . . . . . . . . . . . . . .  17

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     6.5.  Privacy . . . . . . . . . . . . . . . . . . . . . . . . .  17
       6.5.1.  DNS Scalability . . . . . . . . . . . . . . . . . . .  17
       6.5.2.  Change of ownership for IoT devices . . . . . . . . .  18
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

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.

   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.  In the browser-anchored "WebPKI" this is a serious
   concern with noteable events such as [comodogate], which has led to
   the IETF Public Notary Transparency WG:trans, [RFC6962] and later
   [RFC9162].

   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 users and 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 and user identity.  If
   certificate-based device and user 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 user and 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 DNSSEC, may be trusted by any
   application also trusting the DNS.  A first-class identity is an
   application-independent identity.

2.  Conventions and Definitions

   *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.  These steps
   not necessarily performed by the same party or organization.
   Examples:

   *  A device manufacturer may instantiate the key pair, and a systems
      integrator may be responsible for issuing (and publishing) the
      device certificate in DNS.

   *  A device manufacturer may publish the device identity records in
      DNS.  The system integrator needs to perform network and
      application access configuration, since the identity already
      exists in DNS.

   *  A user may instantiate a key pair, based upon which an
      organization's CA may produce a certificate after internally
      assuring the user identity, and the systems integrator may publish
      the CA root certificate in DNS.

   *DANCE protocol:* A DANCE protocol is protocol that has been taught
   to use DANE client mchanisms..

   *Client:* This architecture document adopts the definition of
   "Client" from RFC 8446: "The endpoint initiating the TLS connection"

   *User:* A client whose name consists of a user identity and a DNS
   owner name prefixed with a _user label.

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   *Server:* This architecture document adopts the definition of
   "Server" from RFC 8446: "The endpoint that did not initiate the TLS
   connection"

   *Store-and-forward system:* A message handling system in-path between
   the sending agent and the receiving agent.

   *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
   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: the client identity is always a DNS name, no
   matter what is in the certificate, so no impersonation is possible.

   In many cases the client is not a user specific device (like a laptop
   or smartphone), but rather an enterprise or residential device with a
   non-user specific name.

   When the client is a user device, then additional precautions may be
   necessary to avoid divulging personally identitiable information in
   the DNS.  Mechanisms like SASL EXTERNAL [RFC4422] can be used to
   integrate more abstract user identities with specific authorizations
   that need to be more personal.

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3.2.  Peer to peer

   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, where each
   endpoint may represent a device or a user.

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
   host running 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.  Client authentication

4.1.  Overview - DANCE usage examples

   A client system sets up a TLS connection to a server, attaching a
   client certificate with a subjectAltName dNSName indicating the DNS
   owner name of the client [RFC5280].  When the client is a user, then
   their user identity is a subjectAltName extension containing either
   an otherName type with uid attribute [RFC4519] or email address
   [RFC9598].

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   In the TLS connection the DANE-client-id
   [I-D.ietf-dance-tls-clientid] extension is used to tell the server to
   use the certificate dNSName to find a DANE record including the
   public key of the certificate to be able to validate.  If the server
   can validate the DNSSEC response, the server validates the
   certificate and completes the TLS connection setup.

   Using DANE 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.

   Without the use of the DANE-client-id extension, a server can not
   know if the DNS lookup will result in a useful result, and the server
   then winds up doing needless and potentially privacy violating DNS
   lookups.

   For instance, an authoritative DNS server [RFC9499] 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
        pattern assurance

   *  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
      a header field.

   This pattern has the following advantages:

   *  This pattern translates well to TLS/TCP load balancers, by using a
      TLS TLV instead of an HTTP header.

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   *  No traffic reaches the application behind the TLS terminating
      proxy (and load balancer) unless DANE client authentication is
      successful.

4.1.2.  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 a
      header field.

   *  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.

4.1.3.  Example 3: TLS user authentication for an LDAP query

   *  The LDAP client initiates a TLS connection to the server,
      conveying the user's domain via the DANE Client Identity
      extension.

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   *  If the dane_clientid is allowed and begins with a _user label, the
      TLS server then performs a DNS lookup for TLSA records holding the
      user's CA, and includes them when requesting a client certificate.

   *  If the client's certificate is signed by a CA found in the TLSA
      records and the certificate's dNSName prefixed with a _user label
      matches the dane_clientid then the client identity is
      authenticated to consist of the lowercase uid in the certificate,
      an "@" symbol and the lowercase UTF-8 representation of the
      certificate's dNSName (which lacks the "_user." prefix).

   *  The LDAP server responds to SASL EXTERNAL authentication by
      obtaining the authenticated user identity in userid@domain.name
      form and, if so requested, attempts to change to an authorization
      identity.

   This pattern has the following advantages:

   *  SASL authentication under TLS encryption is common to many
      protocols, including new ones.

   *  This LDAP example demonstrates the potential of authentication
      with realm crossover support as a precursor to fine access control
      to possibly sensitive data.

   *  User identities cannot be iterated in DNS; TLS 1.3 conceals the
      client certificate; TLS in general conceals the user's choice of
      authorization identity during SASL EXTERNAL.

   *  This can be implemented with no changes to the TLS handshake.

4.1.4.  Example 4: 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.  Before client DANE, the CA trust
   anchor certificate would be installed into the cloud application, and
   used in the TLS authentication process.

   Using client 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.

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4.1.5.  Example 5: LoRaWAN

   For the end-device onboarding in LoRaWAN, the "network server" and
   the "join server" [RFC8376] needs to establish mutual TLS
   authentication in order to exchange configuration parameters.
   Certificate Authority based mutual TLS authentication doesn't work in
   LoRaWAN due to the non availability of the CA trust store in the
   LoRaWAN network stack.  Self-signed certificate based mutual-TLS
   authentication method is the alternative solution.

   DANE based client identity allows the server to authenticate clients
   during the TLS handhsake.  Thus, independent of the private PKI used
   to issue the client's self-signed certificate, the "network server"
   and the "join server" could be mutually authenticated.

4.1.6.  Example 6: Edge Computing

   [I-D.hong-t2trg-iot-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
   [I-D.hong-t2trg-iot-edge-computing], 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 owner 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.

4.1.7.  Example 7: Domain Users

   The allocation of user identities is the prerogative of a domain, in
   line with the nesting suggested in URI notation.  Domains may even
   choose to assign domain user identities to services, possibly with
   easily recognised identities like +mail+archive@domain.name.  Domains
   who publish TLSA records for a CA under a _user name underneath their
   domain allow the validation of user identities as mentioned in a
   certificate as TLS client or peer identities.  This mechanism is not
   restricted to domain-internal users, but can be used to validate
   users under any domain.

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   Since ENUM maps telephone numbers to DNS owner names, it is possible
   to employ these same mechanisms for telephone number users.  Any
   DANCE protocol may however define alternate derivation procedures to
   obtain the DNS owner name for a phone number from specialised PKIX or
   LDAP attributes such as telephoneNumber, telexNumber, homePhone,
   mobile and pager.

   There is no reason why other uses, such as store-and-forward with S/
   MIME, could not benefit from this DNS-based PKI, as long as they
   remain mindful that anything in the certificate is the prerogative of
   the domain publishing the TLSA record, and the only reliable identity
   statements are for resources underneath the domain -- notably, the
   assignment of uid names.

4.1.8.  Example 8: 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 chain 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.

   For an example, read [I-D.johansson-sipcore-dane-sip](SIPDANE).

4.1.9.  Example 9: DNS over TLS client authentication

   DNS-over-TLS client authentication is applicable to most portions of
   the transport segments of the DNS infrastructure.  Current best
   practise for authentication between DNS infrastructure tends to be
   based upon a shared secret in the form of TSIG.

   From authoritative to authoritative secondary, it can be applied to
   XFR-over-TLS ("XoT") as an upgrade to TSIG, removing the need for
   out-of-band communication of shared secrets, currently a weak point
   in that portion of the infrastructure.

   From authoritative servers to recursive servers [RFC9499], in
   situations in which both are part of a common trust-group or have
   access to the same non-public or split-horizon zone data, client

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   authentication allows authoritative servers to give selective access
   to specific recursive servers.  Alternatively, some recursive servers
   could authenticate in order to gain access to non-content-related
   special services, such as a higher query rate-limit quota than is
   publicly available.

   Between recursive resolvers and caching/forwarding or stub resolvers
   [RFC9499], authentication can be used to gain access to special
   services, such as subscription-based malware blocking, or visibility
   of corporate split-horizon internal zone, or to distinguish between
   subscribers to different performance tiers.

   In the ideal implementation, client and server would bidirectionally
   authenticate, using DANE client certificates to bootstrap TLS
   transport security.

4.1.10.  Example 10: SMTP, STARTTLS

   SMTP has included the ability to upgrade in-protocol to TLS using the
   STARTTLS [RFC7817] command.  When upgrading the connection, the
   client checks the server certificate using the DNS-ID mechanisms
   described in [RFC9525].  Support for this is very common and most
   email on the Internet is transmitted in this way.

   The use of client TLS certificates has not yet become common, in part
   because it is unclear how or what the server would check the
   certificate against.

   For mail-transfer-agent (MTA) to MTA communications, the use of a
   TLSA RR as described in [I-D.ietf-dance-client-auth] permits the SMTP
   server to check the identity of the parties trying to send email.
   There are many use cases, but a major one is often dealing with
   authenticated relaying of email.

4.1.11.  Example 11: SSH client

   SSH servers have for some time been able to put their host keys into
   DNS using [RFC4255].

   In many SSH server implementations the list of users that is
   authorized to login to an account is given by listing their public
   keys in a per-user file ("authorized_keys").  The file provides both
   authorization (who may login), and authentication (how they prove
   their identity).  While this is an implementation detail, doing both
   in one place has been one of Secure Shell's major reason for success.

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   However, there are downsides to this: a user can not easily replace
   their key without visiting every host they are authorized to access
   and update the key on that host.  Separation of authorization and
   authentication in this case would involve putting the key material in
   a third place, such as in a DANE record in DNS, and then listing only
   the DNS owner name in the authorization file:

   *  A user who wants to update their key need only update DNS in that
      case.

   *  A user who has lost access to their key, but can still update DNS
      (or can have a colleague update it) would more easily be able to
      recover.

   *  An administrator who controls the domain would be able to remove a
      departing user's key from DNS, preventing the user from
      authenticating in the future.

   The DNS record used could be TLSA, but it is possible with some
   protocol work that it could instead be SSHFP.  Since SSH can trust CA
   certificates from X.509 [RFC6187], those may be published for user
   authentication.

4.1.12.  Example 12: Network Access

   Network access refers to an authentication process by which a node is
   admitted securely onto network infrastructure.  This is most common
   for wireless networks (wifi, 802.15.4), but has also routinely been
   done for wired infrastructure using 802.1X mechanisms with EAPOL.

   While there are EAP protocols that do not involve certificates, such
   as EAPSIM [RFC4186], the use of symmetric key mechanisms as the
   "network key" [WPAPSK] (is common in many homes.  The use of
   certificate based mechanisms are expected to increase, due to
   challenges, such as Randomized and Changing MAC addresses (RCM), as
   described in [I-D.ietf-madinas-use-cases].

4.1.12.1.  EAP-TLS with RADIUS

   Enterprise EAP methods use a version of TLS to form a secure
   transport.  Client and server-side certificates are used as
   credentials.  EAP-TLS [EAP-TLS] does not run over TCP, but rather
   over a reliable transport provided by EAP.  To keep it simple the EAP
   "window" is always one, and there are various amounts of overhead
   that needs to be accounted for, and the EAP segment size is often
   noticeably smaller than the normal ethernet 1500 bytes.  [RFC3748]
   does guarantee a minimum payload of 1020 bytes.

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   The client side certificates are often larger than 1500 bytes and can
   take two or three round trip times to transport from the supplicant
   to the authenticator (see [EAP-TLS] and [RFC5126] for terminology).
   In worst case scenarios, which are common with eduroam [RFC7593], the
   EAP packets are transported some distance, easily across the entire
   planet.  The authenticating system (the "authentication server" in
   EAP terms) is a system at the institute that issued the client side
   certificate, and so already has access to the entire client
   certificate.  Transferring the client certificate is redundant.  That
   is, the authenticator already has access to the entire certificate,
   but the client does not know this to the case, so it sends the entire
   certificate anyway.

   The use of DANE Client IDs in TLS as described in
   [I-D.ietf-dance-tls-clientid] reduces the redundant bytes of
   certificate sent.  If the client can assume that the server will be
   able to lookup it's client certificate in DNS, then it need never
   send it.  For the eduroam case, where it was never needed, so this
   significantly reduces the packet size.  For the non-eduroam cases,
   the client can be assured that omitting an inline certificate chain
   will not result in failure.

   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.

4.1.12.2.  RADSEC

   Note that EAP-TLS lives within a number of protocols, including
   RADIUS, but this section refers to the outer layer, while the above
   was about the inner portion.

   The RADIUS protocol has a few recognized security problems.  [RADSEC]
   and [I-D.ietf-radext-radiusdtls-bis] 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.  The use of client-
   side certificates has been encouraged by the recent work.  There are
   no protocol or specification changes required to put client-side
   certificates into DNS.  The use of the [I-D.ietf-dance-tls-clientid]
   with the created TLS connectio should suffice.  Note that this use
   cases addresses the security of the hop-by-hop RADIUS protocol, not
   the security of the end-to-end EAP(-TLS) session that might be
   carried within.

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4.1.13.  Example 13: Structured data messages: JOSE/COSE

   JOSE and COSE provide formats for exchanging authenticated and
   encrypted structured data.  JOSE defines the x5u field in [RFC7515],
   Section 4.1.5, and COSE defines a field of the same name in
   [I-D.ietf-cose-x509], Section 2.

   However, this URL field points to where the key can be found.  There
   is, as yet, no URI scheme which says that the key can be found via
   the DNS lookup itself.

   In order to make use of x5u, a DANCE protocol would have to define a
   new URI scheme that explained how to get the right key from DNS.

5.  Protocol implementations

   For each protocol implementation, a specific usage document needs to
   be published.  In this document, the DANCE protocol requirements and
   usage needs to be specified (this is refered above as the "How to
   DANCE" document).  These documents should as a minimum contain the
   following sections:

   *  Specifics on naming: How the name of the client is defined and how
      this is related to the name in a DNS zone.  This defines the
      organization of the related DNS zone.  Whether a flat namespace is
      used, or a way to use a DNS Zone hierarchy is applied to this
      usage. (see notes above on DNS zone design)

   *  Privacy: If the subject name is a personal identifier, how to
      protect that name from being exposed in the DNS zone.  [RFC7929]
      describes one way to handle privacy for personal identifiers in
      DNS.

   *  TTL: Recommended TTL settings for records in this usage

   *  Security: Security considerations for this usage

6.  Security Considerations

6.1.  Confidentiality

   DNS clients should use DNS over TLS with trusted DNS resolvers to
   protect the identity of authenticating peers.

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6.2.  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 using the DNSSEC protocol.  When using a DNS stub resolver
   [RFC9499] rather than doing local validation, then the connection to
   the validating DNS resolver needs to be secured.

   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 [I-D.ietf-dance-client-auth] includes
   an underscore label (_device).  The underscore is not a valid
   character for names used in the Web PKI.  This prevents the issuance
   of any Web PKI-validating certificates for these names.

   This means that even were the authoritative DNS server compromised,
   it would not be possible to issue Web PKI certificates using, for
   instance, the [RFC8555] DNS-01 challenge.

   An alternative underscore label _user separates the TLSA records with
   the domain CA from the TLSA records for devices.

6.3.  Availability

   One of the advantages of DNS is that it has more than fourty years of
   demonstrated scaling.  It is a distributed database with a caching
   mechanism, and properly configured, it has proven resilient to many
   kinds of outages and attacks.

   A key part of this availability is the proper use of Time To Live
   (TTL) values for resource records.  A cache is allowed to hang on to
   the data for a set time, the TTL, after which it must do a new query
   to find out if the data has changed, or perhaps been deleted.

   There is therefore a tension between resilience (higher TTL values),
   and agility (lower TTL values).  A lower TTL value allows for
   revocation or replacement of a key to become known much faster.  This
   allows for a more agile security posture.

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   The TTL value is not enforced, which may lead to unexpected
   responses, like a malicious server caching responses for a long time
   after the TTL for the record has expired.  This may lead to a
   situation where a revocation by removing the record from DNS doesn't
   come in to effect as expected.

   On the other hand, lower TTLs cause the queries to occur more often,
   which may reveal more information to an observer about which devices
   are active.  Encrypted transports like DoT/DoH/DoQ make these queries
   far less visible.  In addition to the on-path observer being able to
   see more, the resolver logs also may be a source of information.  It
   also allows for more opportunities for an attacker to affect the
   response time of the queries.

6.4.  TLS Server availability

   TLS servers supporting DANCE should implement a list of domains that
   are valid for client authentication, in order not to be open to DDOS
   attacks where a large number of clients force the server to do random
   DNS lookups.  More implementation details are to be found in the
   protocol specific documents.

6.5.  Privacy

   If the DNS owner 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.  This privacy is implied for domain users inasfar as the
   domain CA does not mention users.  When creating the DNS owner name,
   effects of DNS zone walking and possible harvesting of identities in
   the DNS zone will have to be considered.  The DNS owner name may not
   have to have a direct relation to the name of the subject or the
   subjectAltName of the certificate.  If there is such a relation, a
   DANCE protocol may specify support for CA certificates, stored under
   a wildcard in DNS.

   Further work has do be done in this area.

6.5.1.  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
   using TCP, (for instance, a [slowloris] attack), it possible that
   this would cause a TLS server to exhaust all it's TCP sockets.

   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.

6.5.2.  Change of ownership for IoT devices

   One of the significant use cases is where the devices are identified
   by their manufacturer assigned identities.  A significant savings was
   that enterprises would not have to run their own (private) PKI
   systems, sometimes even one system per device type.  But, with this
   usage style for DANCE there is no private PKI to run, and as a result
   there is no change of ownership required.  The device continues to
   use the manufacturer assigned identity.

   The device OwnerOperator is therefore at risk if the device's
   manufacturer goes out of business, or decides that they no longer
   wish to manufacturer that device.  Should that happen then the
   OwnerOperator of the device may be in trouble, and may find
   themselves having to replace the devices.

   [RFC8995], Section 10.4 (BRSKI) deals with concerns about
   manufacturers influence on devices.  In the case of BRSKI, the
   concern was limited to when the device ownership transfer was
   performed (the BRSKI transaction itself).  There was no concern once
   the OwnerOperator had taken control over the device through an
   [RFC8366] voucher.

   In the case of DANCE, the manufacturer is continuously involved with
   the day to day operation of the device.

   If this is of concern, then the OwnerOperator should perform some
   kind of transfer of ownership, such as using DPP, [RFC8995](BRSKI),
   [RFC9140](EAP-NOOB), and others yet to come.

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   The DANCE method of using manufacturer assigned identities would
   therefore seem to be best used for devices which have a short
   lifetime: one much smaller than the uncertainty about the anticipated
   lifespan of the manufacturer.  For instance, some kind of battery
   operated sensor which might be used in a large quantity at a
   construction site, and which can not be recharged.

7.  IANA Considerations

   This document has no IANA actions.

8.  References

8.1.  Normative References

   [I-D.ietf-dance-client-auth]
              Huque, S. and V. Dukhovni, "TLS Client Authentication via
              DANE TLSA records", Work in Progress, Internet-Draft,
              draft-ietf-dance-client-auth-09, 19 September 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-dance-
              client-auth-09>.

   [I-D.ietf-dance-tls-clientid]
              Huque, S. and V. Dukhovni, "TLS Extension for DANE Client
              Identity", Work in Progress, Internet-Draft, draft-ietf-
              dance-tls-clientid-07, 17 September 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-dance-
              tls-clientid-07>.

   [RFC9525]  Saint-Andre, P. and R. Salz, "Service Identity in TLS",
              RFC 9525, DOI 10.17487/RFC9525, November 2023,
              <https://www.rfc-editor.org/rfc/rfc9525>.

8.2.  Informative References

   [comodogate]
              Schneier, B., "Comodo Group Issues Bogus SSL
              Certificates", 31 March 2011,
              <https://www.schneier.com/blog/archives/2011/03/
              comodo_group_is.html>.

   [EAP-TLS]  Preuß Mattsson, J. and M. Sethi, "EAP-TLS 1.3: Using the
              Extensible Authentication Protocol with TLS 1.3",
              RFC 9190, DOI 10.17487/RFC9190, February 2022,
              <https://www.rfc-editor.org/rfc/rfc9190>.

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   [I-D.hong-t2trg-iot-edge-computing]
              Hong, J., Hong, Y., de Foy, X., Kovatsch, M., Schooler,
              E., and D. KUTSCHER, "IoT Edge Challenges and Functions",
              Work in Progress, Internet-Draft, draft-hong-t2trg-iot-
              edge-computing-05, 13 July 2020,
              <https://datatracker.ietf.org/doc/html/draft-hong-t2trg-
              iot-edge-computing-05>.

   [I-D.ietf-cose-x509]
              Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Header Parameters for Carrying and Referencing X.509
              Certificates", Work in Progress, Internet-Draft, draft-
              ietf-cose-x509-09, 13 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-cose-
              x509-09>.

   [I-D.ietf-madinas-use-cases]
              Henry, J. and Y. Lee, "Randomized and Changing MAC
              Address: Context, Network Impacts, and Use Cases", Work in
              Progress, Internet-Draft, draft-ietf-madinas-use-cases-19,
              20 December 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-madinas-use-cases-19>.

   [I-D.ietf-radext-radiusdtls-bis]
              Rieckers, J. and S. Winter, "RadSec: RADIUS over Transport
              Layer Security (TLS) and Datagram Transport Layer Security
              (DTLS)", Work in Progress, Internet-Draft, draft-ietf-
              radext-radiusdtls-bis-11, 21 November 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-radext-
              radiusdtls-bis-11>.

   [I-D.johansson-sipcore-dane-sip]
              Johansson, O. E., "TLS sessions in SIP using DNS-based
              Authentication of Named Entities (DANE) TLSA records",
              Work in Progress, Internet-Draft, draft-johansson-sipcore-
              dane-sip-00, 6 October 2014,
              <https://datatracker.ietf.org/doc/html/draft-johansson-
              sipcore-dane-sip-00>.

   [pkiiot]   Balakrichenan, S., Ayoub, I., and B. Ampeau, "PKI for IoT
              using the DNS infrastructure", IEEE, 2022 IEEE
              International Conference on Public Key Infrastructure and
              its Applications (PKIA) pp. 1-8,
              DOI 10.1109/pkia56009.2022.9952253, September 2022,
              <https://doi.org/10.1109/pkia56009.2022.9952253>.

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   [RADSEC]   Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
              "Transport Layer Security (TLS) Encryption for RADIUS",
              RFC 6614, DOI 10.17487/RFC6614, May 2012,
              <https://www.rfc-editor.org/rfc/rfc6614>.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, Ed., "Extensible Authentication Protocol
              (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
              <https://www.rfc-editor.org/rfc/rfc3748>.

   [RFC4186]  Haverinen, H., Ed. and J. Salowey, Ed., "Extensible
              Authentication Protocol Method for Global System for
              Mobile Communications (GSM) Subscriber Identity Modules
              (EAP-SIM)", RFC 4186, DOI 10.17487/RFC4186, January 2006,
              <https://www.rfc-editor.org/rfc/rfc4186>.

   [RFC4255]  Schlyter, J. and W. Griffin, "Using DNS to Securely
              Publish Secure Shell (SSH) Key Fingerprints", RFC 4255,
              DOI 10.17487/RFC4255, January 2006,
              <https://www.rfc-editor.org/rfc/rfc4255>.

   [RFC4422]  Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
              Authentication and Security Layer (SASL)", RFC 4422,
              DOI 10.17487/RFC4422, June 2006,
              <https://www.rfc-editor.org/rfc/rfc4422>.

   [RFC4519]  Sciberras, A., Ed., "Lightweight Directory Access Protocol
              (LDAP): Schema for User Applications", RFC 4519,
              DOI 10.17487/RFC4519, June 2006,
              <https://www.rfc-editor.org/rfc/rfc4519>.

   [RFC5126]  Pinkas, D., Pope, N., and J. Ross, "CMS Advanced
              Electronic Signatures (CAdES)", RFC 5126,
              DOI 10.17487/RFC5126, March 2008,
              <https://www.rfc-editor.org/rfc/rfc5126>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/rfc/rfc5280>.

   [RFC6187]  Igoe, K. and D. Stebila, "X.509v3 Certificates for Secure
              Shell Authentication", RFC 6187, DOI 10.17487/RFC6187,
              March 2011, <https://www.rfc-editor.org/rfc/rfc6187>.

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   [RFC6962]  Laurie, B., Langley, A., and E. Kasper, "Certificate
              Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013,
              <https://www.rfc-editor.org/rfc/rfc6962>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/rfc/rfc7515>.

   [RFC7593]  Wierenga, K., Winter, S., and T. Wolniewicz, "The eduroam
              Architecture for Network Roaming", RFC 7593,
              DOI 10.17487/RFC7593, September 2015,
              <https://www.rfc-editor.org/rfc/rfc7593>.

   [RFC7817]  Melnikov, A., "Updated Transport Layer Security (TLS)
              Server Identity Check Procedure for Email-Related
              Protocols", RFC 7817, DOI 10.17487/RFC7817, March 2016,
              <https://www.rfc-editor.org/rfc/rfc7817>.

   [RFC7929]  Wouters, P., "DNS-Based Authentication of Named Entities
              (DANE) Bindings for OpenPGP", RFC 7929,
              DOI 10.17487/RFC7929, August 2016,
              <https://www.rfc-editor.org/rfc/rfc7929>.

   [RFC8366]  Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
              "A Voucher Artifact for Bootstrapping Protocols",
              RFC 8366, DOI 10.17487/RFC8366, May 2018,
              <https://www.rfc-editor.org/rfc/rfc8366>.

   [RFC8376]  Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN)
              Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018,
              <https://www.rfc-editor.org/rfc/rfc8376>.

   [RFC8555]  Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
              Kasten, "Automatic Certificate Management Environment
              (ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
              <https://www.rfc-editor.org/rfc/rfc8555>.

   [RFC8995]  Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
              May 2021, <https://www.rfc-editor.org/rfc/rfc8995>.

   [RFC9140]  Aura, T., Sethi, M., and A. Peltonen, "Nimble Out-of-Band
              Authentication for EAP (EAP-NOOB)", RFC 9140,
              DOI 10.17487/RFC9140, December 2021,
              <https://www.rfc-editor.org/rfc/rfc9140>.

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   [RFC9162]  Laurie, B., Messeri, E., and R. Stradling, "Certificate
              Transparency Version 2.0", RFC 9162, DOI 10.17487/RFC9162,
              December 2021, <https://www.rfc-editor.org/rfc/rfc9162>.

   [RFC9499]  Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
              RFC 9499, DOI 10.17487/RFC9499, March 2024,
              <https://www.rfc-editor.org/rfc/rfc9499>.

   [RFC9598]  Melnikov, A., Chuang, W., and C. Bonnell,
              "Internationalized Email Addresses in X.509 Certificates",
              RFC 9598, DOI 10.17487/RFC9598, May 2024,
              <https://www.rfc-editor.org/rfc/rfc9598>.

   [slowloris]
              "Slowloris Attack", 15 August 2024,
              <https://en.wikipedia.org/wiki/
              Slowloris_(computer_security)>.

   [WPAPSK]   The Wi-Fi Alliance, "WPA (Wi-Fi Protected Access). v3.1
              2004", 20 October 2025, <https://www.wi-
              fi.org/system/files/WPA_80211_v3_1_090922.pdf>.

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

   Michael Richardson
   Sandelman Software Works Inc
   Email: mcr+ietf@sandelman.ca

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