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Internet Engineering Task Force (IETF)                         M. MillerRequest for Comments: 7711                           Cisco Systems, Inc.Category: Standards Track                                 P. Saint-AndreISSN: 2070-1721                                                     &yet                                                           November 2015PKIX over Secure HTTP (POSH)Abstract   Experience has shown that it is difficult to deploy proper PKIX   certificates for Transport Layer Security (TLS) in multi-tenanted   environments.  As a result, domains hosted in such environments often   deploy applications using certificates that identify the hosting   service, not the hosted domain.  Such deployments force end users and   peer services to accept a certificate with an improper identifier,   resulting in degraded security.  This document defines methods that   make it easier to deploy certificates for proper server identity   checking in non-HTTP application protocols.  Although these methods   were developed for use in the Extensible Messaging and Presence   Protocol (XMPP) as a Domain Name Association (DNA) prooftype, they   might also be usable in other non-HTTP application protocols.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7711.Miller & Saint-Andre         Standards Track                    [Page 1]

RFC 7711                          POSH                     November 2015Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1. Introduction ....................................................32. Terminology .....................................................43. Obtaining Verification Material .................................53.1. Source Domain Possesses PKIX Certificate Information .......63.2. Source Domain References PKIX Certificate ..................83.3. Performing Verification ....................................94. Secure Delegation ...............................................95. Order of Operations ............................................106. Caching Results ................................................117. Guidance for Server Operators ..................................128. Guidance for Protocol Authors ..................................129. IANA Considerations ............................................139.1. Well-Known URI ............................................139.2. POSH Service Names ........................................1310. Security Considerations .......................................1411. References ....................................................1511.1. Normative References .....................................1511.2. Informative References ...................................16   Acknowledgements ..................................................18   Authors' Addresses ................................................18Miller & Saint-Andre         Standards Track                    [Page 2]

RFC 7711                          POSH                     November 20151.  Introduction   We begin with a thought experiment.   Imagine that you work on the operations team of a hosting company   that provides instances of the hypothetical "Secure Protocol for   Internet Content Exchange" (SPICE) service for ten thousand different   customer organizations.  Each customer wants their instance to be   identified by the customer's domain name (e.g., bar.example.com), not   the hosting company's domain name (e.g., hosting.example.net).   In order to properly secure each customer's SPICE instance via   Transport Layer Security (TLS) [RFC5246], you need to obtain and   deploy PKIX certificates [RFC5280] containing identifiers such as   bar.example.com, as explained in the "CertID" specification   [RFC6125].  Unfortunately, you can't obtain and deploy such   certificates because:   o  Certification authorities won't issue such certificates to you      because you work for the hosting company, not the customer      organization.   o  Customers won't obtain such certificates and then give them (plus      the associated private keys) to you because their legal department      is worried about liability.   o  You don't want to install such certificates (plus the associated      private keys) on your servers because your legal department is      worried about liability, too.   o  Even if your legal department is happy, this still means managing      one certificate for each customer across the infrastructure,      contributing to a large administrative load.   Given your inability to obtain and deploy public keys / certificates   containing the right identifiers, your back-up approach has always   been to use a certificate containing hosting.example.net as the   identifier.  However, more and more customers and end users are   complaining about warning messages in user agents and the inherent   security issues involved with taking a "leap of faith" to accept the   identity mismatch between the source domain (bar.example.com) and the   delegated domain (hosting.example.net) [RFC6125].   This situation is both insecure and unsustainable.  You have   investigated the possibility of using DNS Security [RFC4033] and   DNS-Based Authentication of Named Entities (DANE) [RFC6698] to solve   the problem.  However, your customers and your operations team have   told you that it will be several years before they will be able toMiller & Saint-Andre         Standards Track                    [Page 3]

RFC 7711                          POSH                     November 2015   deploy DNSSEC and DANE for all of your customers (because of tooling   updates, slow deployment of DNSSEC at some top-level domains, etc.).   The product managers in your company are pushing you to find a method   that can be deployed more quickly to overcome the lack of proper   server identity checking for your hosted customers.   One possible approach that your team has investigated is to ask each   customer to provide the public key / certificate for its SPICE   service at a special HTTPS URI on their website   ("https://bar.example.com/.well-known/posh/spice.json" is one   possibility).  This could be a public key that you generate for the   customer, but because the customer hosts it via HTTPS, any user agent   can find that public key and check it against the public key you   provide during TLS negotiation for the SPICE service (as one added   benefit, the customer never needs to hand you a private key).   Alternatively, the customer can redirect requests for that special   HTTPS URI to an HTTPS URI at your own website, thus making it   explicit that they have delegated the SPICE service to you.   The approach sketched out above, called POSH ("PKIX over Secure   HTTP"), is explained in the remainder of this document.  Although   this approach was developed for use in the Extensible Messaging and   Presence Protocol (XMPP) as a prooftype for Domain Name Associations   (DNA) [RFC7712], it might be usable by any non-HTTP application   protocol.2.  Terminology   This document inherits security terminology from [RFC5280].  The   terms "source domain", "delegated domain", "derived domain", and   "reference identifier" are used as defined in the "CertID"   specification [RFC6125].   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   [RFC2119].   Additionally, this document uses the following terms:   POSH client:  A client that uses the application service and that      uses POSH to obtain material for verifying the service's identity.   POSH server:  A server that hosts the application service and that      uses POSH to provide material for verifying its identity.Miller & Saint-Andre         Standards Track                    [Page 4]

RFC 7711                          POSH                     November 20153.  Obtaining Verification Material   Server identity checking (see [RFC6125]) involves three different   aspects:   1.  A proof of the POSH server's identity (in PKIX, this takes the       form of a PKIX end-entity certificate [RFC5280]).   2.  Rules for checking the certificate (which vary by application       protocol, although [RFC6125] attempts to harmonize those rules).   3.  The material that a POSH client uses to verify the POSH server's       identity or check the POSH server's proof (in PKIX, this takes       the form of chaining the end-entity certificate back to a trusted       root and performing all validity checks as described in       [RFC5280], [RFC6125], and the relevant application protocol       specification).   When POSH is used, the first two aspects remain the same: the POSH   server proves its identity by presenting a PKIX certificate   [RFC5280], and the certificate is checked according to the rules   defined in the appropriate application protocol specification (such   as [RFC6120] for XMPP).  However, the POSH client obtains the   material it will use to verify the server's proof by retrieving a   JSON document [RFC7159] containing hashes of the PKIX certificate   over HTTPS ([RFC7230] and [RFC2818]) from a well-known URI [RFC5785]   at the source domain.  POSH servers MUST use HTTPS.  This means that   the POSH client MUST verify the certificate of the HTTPS service at   the source domain in order to securely "bootstrap" into the use of   POSH; specifically, the rules of [RFC2818] apply to this   "bootstrapping" step to provide a secure basis for all subsequent   POSH operations.   A PKIX certificate is retrieved over secure HTTP in the   following way:   1.  The POSH client performs an HTTPS GET request at the source       domain to the path "/.well-known/posh/{servicedesc}.json".  The       value of "{servicedesc}" is application-specific; seeSection 8       of this document for more details.  For example, if the       application protocol is the hypothetical SPICE service, then       "{servicedesc}" could be "spice"; thus, if an application client       were to use POSH to verify an application server for the source       domain "bar.example.com", the HTTPS GET request would be as       follows:       GET /.well-known/posh/spice.json HTTP/1.1       Host: bar.example.comMiller & Saint-Andre         Standards Track                    [Page 5]

RFC 7711                          POSH                     November 2015   2.  The source domain HTTPS server responds in one of three ways:       *  If it possesses PKIX certificate information for the requested          path, it responds as detailed inSection 3.1.       *  If it has a reference to where the PKIX certificate          information can be obtained, it responds as detailed inSection 3.2.       *  If it does not have any PKIX certificate information or a          reference to such information for the requested path, it          responds with an HTTP 404 Not Found status code [RFC7231].3.1.  Source Domain Possesses PKIX Certificate Information   If the source domain HTTPS server possesses the certificate   information, it responds to the HTTPS GET request with a success   status code and the message body set to a JSON document [RFC7159];   the document is a "fingerprints document", i.e., a JSON object with   the following members:   o  A "fingerprints" member whose value is a JSON array of fingerprint      descriptors (the member MUST include at least one fingerprint      descriptor).   o  An "expires" member whose value is a JSON number specifying the      number of seconds after which the POSH client ought to consider      the keying material to be stale (further explained underSection 6).   The JSON document returned MUST NOT contain a "url" member, as   described inSection 3.2.   Each included fingerprint descriptor is a JSON object, where each   member name is the textual name of a hash function (as listed in   [HASH-NAMES]) and its associated value is the base64-encoded   fingerprint hash generated using the named hash function (where the   encoding adheres to the definition inSection 4 of [RFC4648] and   where the padding bits are set to zero).   The fingerprint hash for a given hash algorithm is generated by   performing the named hash function over the DER encoding of the PKIX   X.509 certificate.  (This implies that if the certificate expires or   is revoked, the fingerprint value will be out of date.)Miller & Saint-Andre         Standards Track                    [Page 6]

RFC 7711                          POSH                     November 2015   As an example of the fingerprint format, the "sha-256" and "sha-512"   fingerprints are generated by performing the SHA-256 and SHA-512 hash   functions, respectively, over the DER encoding of the PKIX   certificate, as illustrated below.  Note that for readability   whitespace has been added to the content portion of the HTTP response   shown below but is not reflected in the Content-Length.   Example Fingerprints Response   HTTP/1.1 200 OK   Content-Type: application/json   Content-Length: 195   {     "fingerprints": [       {         "sha-256": "4/mggdlVx8A3pvHAWW5sD+qJyMtUHgiRuPjVC48N0XQ=",         "sha-512": "25N+1hB2Vo42l9lSGqw+n3BKFhDHsyork8ou+D9B43TXeJ                     1J81mdQEDqm39oR/EHkPBDDG1y5+AG94Kec0xVqA=="       }     ],     "expires": 604800   }   The "expires" value is a hint regarding the expiration of the keying   material.  It MUST be a non-negative integer.  If the "expires"   member has a value of 0 (zero), a POSH client MUST consider the   verification material to be invalid.  SeeSection 6 for how to   reconcile this "expires" member with the reference's "expires"   member.Miller & Saint-Andre         Standards Track                    [Page 7]

RFC 7711                          POSH                     November 2015   To indicate alternate PKIX certificates (such as when an existing   certificate will soon expire), the returned fingerprints member MAY   contain multiple fingerprint descriptors.  The fingerprints SHOULD be   ordered with the most relevant certificate first as determined by the   application service operator (e.g., the renewed certificate),   followed by the next most relevant certificate (e.g., the certificate   soonest to expire).  Here is an example (note that whitespace is   added for readability):   {     "fingerprints": [       {         "sha-256": "4/mggdlVx8A3pvHAWW5sD+qJyMtUHgiRuPjVC48N0XQ",         "sha-512": "25N+1hB2Vo42l9lSGqw+n3BKFhDHsyork8ou+D9B43TXe                     J1J81mdQEDqm39oR/EHkPBDDG1y5+AG94Kec0xVqA=="       },       {         "sha-256": "otyLADSKjRDjVpj8X7/hmCAD5C7Qe+PedcmYV7cUncE=",         "sha-512": "MbBD+ausTGJisEXKSynROWrMfHP2xvBnmI79Pr/KXnDyLN                     +13Jof8/Uq9fj5HZG8Rk1E2fclcivpGdijUsvHRg=="       }     ],     "expires": 806400   }   Matching on any of these fingerprints is acceptable.   Rolling over from one hosting provider to another is best handled by   updating the relevant SRV records, not primarily by updating the POSH   documents themselves.3.2.  Source Domain References PKIX Certificate   If the source domain HTTPS server has a reference to the certificate   information, it responds to the HTTPS GET request with a success   status code and message body set to a JSON document.  The document is   a "reference document", i.e., a JSON object with the following   members:   o  A "url" member whose value is a JSON string specifying the HTTPS      URI where POSH clients can obtain the actual certificate      information.  The URI can be a well-known POSH URI as described inSection 8, but it need not be.  (For historical reasons, the      member name is "url", not "uri".)   o  An "expires" member whose value is a JSON number specifying the      number of seconds after which the POSH client ought to consider      the delegation to be stale (further explained underSection 6).Miller & Saint-Andre         Standards Track                    [Page 8]

RFC 7711                          POSH                     November 2015   Example Reference Response   HTTP/1.1 200 OK   Content-Type: application/json   Content-Length: 82   {     "url":"https://hosting.example.net/.well-known/posh/spice.json",     "expires":86400   }   In order to process a reference response, the client performs an   HTTPS GET request for the URI specified in the "url" member value.   The HTTPS server for the URI to which the client has been referred   responds to the request with a JSON document containing fingerprints   as described inSection 3.1.  The document retrieved from the   location specified by the "url" member MUST NOT itself be a reference   document (i.e., containing a "url" member instead of a "fingerprints"   member), in order to prevent circular delegations.      Note: SeeSection 10 for discussion about HTTPS redirects.   The "expires" value is a hint regarding the expiration of the source   domain's delegation of service to the delegated domain.  It MUST be a   non-negative integer.  If the "expires" member has a value of 0   (zero), a POSH client MUST consider the delegation invalid.  SeeSection 6 for guidelines about reconciling this "expires" member with   the "expires" member of the fingerprints document.3.3.  Performing Verification   The POSH client compares the PKIX information presented by the POSH   server against each fingerprint descriptor object in the POSH   fingerprints document, until a match is found using the hash   functions that the client supports, or until the collection of POSH   verification material is exhausted.  If none of the fingerprint   descriptor objects match the POSH server PKIX information, the POSH   client SHOULD reject the connection (however, the POSH client might   still accept the connection if other verification methods are   successful, such as DANE [RFC6698]).4.  Secure Delegation   The delegation from the source domain to the delegated domain can be   considered secure if the credentials offered by the POSH server match   the verification material obtained by the client, regardless of how   the material was obtained.Miller & Saint-Andre         Standards Track                    [Page 9]

RFC 7711                          POSH                     November 20155.  Order of Operations   In order for the POSH client to perform verification of reference   identifiers without potentially compromising data, POSH operations   MUST be complete before any application-layer data is exchanged for   the source domain.  In cases where the POSH client initiates an   application-layer connection, the client SHOULD perform all POSH   retrievals before initiating a connection (naturally, this is not   possible in cases where the POSH client receives instead of initiates   an application-layer connection).  For application protocols that use   DNS SRV (including queries for TLSA records in concert with SRV   records as described in [RFC7673]), the POSH operations ideally ought   to be done in parallel with resolving the SRV records and the   addresses of any targets, similar to the "Happy Eyeballs" approach   for IPv4 and IPv6 [RFC6555].   The following diagram illustrates the possession flow:    POSH                      Source                      POSH   Client                     Domain                     Server   ------                     ------                     ------     |                          |                          |     |      POSH Request        |                          |     |------------------------->|                          |     |                          |                          |     | Return POSH fingerprints |                          |     |<-------------------------|                          |     |                                                     |     |                  Service TLS Handshake              |     |<===================================================>|     |                                                     |     |                     Service Data                    |     |<===================================================>|     |                                                     |               Figure 1: Order of Events for Possession FlowMiller & Saint-Andre         Standards Track                   [Page 10]

RFC 7711                          POSH                     November 2015   While the following diagram illustrates the reference flow:    POSH              Source       Delegated              POSH   Client             Domain         Domain              Server   ------             ------         ------              ------     |                  |              |                   |     |  POSH Request    |              |                   |     |----------------->|              |                   |     |                  |              |                   |     | Return POSH url  |              |                   |     |<-----------------|              |                   |     |                                 |                   |     |            POSH Request         |                   |     |-------------------------------->|                   |     |                                 |                   |     |     Return POSH fingerprints    |                   |     |<--------------------------------|                   |     |                                                     |     |                 Service TLS Handshake               |     |<===================================================>|     |                                                     |     |                     Service Data                    |     |<===================================================>|     |                                                     |               Figure 2: Order of Events for Reference Flow6.  Caching Results   The POSH client MUST NOT cache results (reference or fingerprints)   indefinitely.  If the source domain returns a reference, the POSH   client MUST use the lower of the two "expires" values when   determining how long to cache results (i.e., if the reference   "expires" value is lower than the fingerprints "expires" value, honor   the reference "expires" value).  Once the POSH client considers the   results stale, it needs to perform the entire POSH operation again,   starting with the HTTPS GET request to the source domain.  The POSH   client MAY use a lower value than any provided in the "expires"   member(s), or not cache results at all.   The foregoing considerations apply to the handling of the "expires"   values in POSH documents; naturally, a POSH client MUST NOT consider   an expired PKIX certificate to be valid, in accordance with   [RFC5280].Miller & Saint-Andre         Standards Track                   [Page 11]

RFC 7711                          POSH                     November 2015   The POSH client SHOULD NOT rely on HTTP caching mechanisms, instead   using the expiration hints provided in the POSH reference document or   fingerprints document.  To that end, the HTTPS servers for source   domains and derived domains SHOULD specify a 'Cache-Control' header   indicating a very short duration (e.g., max-age=60) or "no-cache" to   indicate that the response (redirect, reference, or fingerprints) is   not appropriate to cache at the HTTP layer.7.  Guidance for Server Operators   POSH is intended to ease the operational burden of securing   application services, especially in multi-tenanted environments.  It   does so by obviating the need to obtain certificates for hosted   domains, so that an operator can obtain a certificate only for its   hosting service (naturally, this certificate needs to be valid   according to [RFC5280] and contain the proper identifier(s) in   accordance with [RFC6125] and the relevant application protocol   specification).   However, in order to use POSH, an operator does need to coordinate   with its customers so that the appropriate POSH documents are   provided via HTTPS at a well-known URI at each customer's domain   (i.e., at the source domain), thus ensuring delegation to the   operator's hosting service (i.e., the delegated domain).  Because   correct hosting of the POSH document at the source domain is   essential for successful functioning of the POSH "chain", errors at   the source domain will result in authentication problems, certificate   warnings, and other operational issues.   Furthermore, if the POSH document is a reference document instead of   a fingerprints document, the operational burden is further decreased   because the operator does not need to provision its customers with   updated POSH documents when the certificate for the delegated domain   expires or is replaced.8.  Guidance for Protocol Authors   Protocols that use POSH are expected to register with the "POSH   Service Names" registry defined underSection 9.2.   For POSH-using protocols that rely on DNS SRV records [RFC2782], the   service name SHOULD be the same as the DNS SRV "Service".  As an   example, the POSH service name for XMPP server-to-server connections   would be "xmpp-server" because [RFC6120] registers a DNS SRV   "Service" of "xmpp-server".  One example of the resulting well-known   URI would be "https://example.com/.well-known/posh/xmpp-server.json".Miller & Saint-Andre         Standards Track                   [Page 12]

RFC 7711                          POSH                     November 2015   For other POSH-using protocols, the service name MAY be any unique   string or identifier for the protocol; for example, it might be a   service name registered with the IANA in accordance with [RFC6335],   or it might be an unregistered name.  As an example, the well-known   URI for the hypothetical SPICE application might be "spice".9.  IANA Considerations9.1.  Well-Known URI   IANA has registered "posh" in the "Well-Known URIs" registry as   defined by [RFC5785].  The completed template follows.   URI suffix:  posh   Change controller:  IETF   Specification:RFC 7711 (this document)   Related information:  The suffix "posh" is expected to be followed by      an additional path component consisting of a service name (say,      "spice") and a file extension of ".json", resulting in a full path      of, for instance, "/.well-known/posh/spice.json".  Registration of      service names shall be requested by developers of the relevant      application protocols.9.2.  POSH Service Names   IANA has established the "POSH Service Names" registry within the   "Uniform Resource Identifier (URI) Schemes" group of registries.   The IANA registration policy [RFC5226] is Expert Review or IETF   Review (this was chosen instead of the more liberal policy of First   Come First Served to help ensure that POSH services are defined in   ways that are consistent with this specification).  One or more   Designated Experts are to be appointed by the IESG or their delegate.   Registration requests are to be sent to the posh@ietf.org mailing   list for review and comment, with an appropriate subject (e.g.,   "Request for POSH service name: example").   Before a period of 14 days has passed, the Designated Expert(s) will   either approve or deny the registration request, communicating this   decision both to the review list and to IANA.  Denials should include   an explanation and, if applicable, suggestions as to how to make the   request successful.  Registration requests that are undetermined for   a period longer than 21 days can be brought to the IESG's attention   (using the iesg@iesg.org mailing list) for resolution.Miller & Saint-Andre         Standards Track                   [Page 13]

RFC 7711                          POSH                     November 20159.2.1.  Registration Template   Service name:  The name requested, relative to "/.well-known/posh/";      e.g., a service name of "example" would result in a well-known URI      such as "https://example.com/.well-known/posh/example.json".   Change controller:  For Standards Track RFCs, state "IETF".  In all      other cases, provide the name and email address of the responsible      party.  Other details (e.g., postal address or website URI) may      also be included.   Definition and usage:  A brief description that defines the service      name and mentions where and how it is used (e.g., in the context      of a particular application protocol).   Specification:  Optionally, reference to a document that specifies      the service or application protocol that uses the service name,      preferably including a URI that can be used to retrieve a copy of      the document.  An indication of the relevant sections may also be      included but is not required.10.  Security Considerations   This document supplements but does not supersede the security   considerations provided in specifications for application protocols   that decide to use POSH (e.g., [RFC6120] and [RFC6125] for XMPP).   Specifically, the security of requests and responses sent via HTTPS   depends on checking the identity of the HTTP server in accordance   with [RFC2818] as well as following the most modern best practices   for TLS as specified in [RFC7525].  Additionally, the security of   POSH can benefit from other HTTP-hardening protocols, such as HTTP   Strict Transport Security (HSTS) [RFC6797] and key pinning [RFC7469],   especially if the POSH client shares some information with a common   HTTPS implementation (e.g., a platform-default web browser).   Note well that POSH is used by a POSH client to obtain the public key   of a POSH server to which it might connect for a particular   application protocol such as IMAP or XMPP.  POSH does not enable a   hosted domain to transfer private keys to a hosting service via   HTTPS.  POSH also does not enable a POSH server to engage in   certificate enrollment with a certification authority via HTTPS, as   is done in Enrollment over Secure Transport [RFC7030].   A web server at the source domain might redirect an HTTPS request to   another HTTPS URI.  The location provided in the redirect response   MUST specify an HTTPS URI.  Source domains SHOULD use only temporary   redirect mechanisms, such as HTTP status codes 302 (Found) and 307   (Temporary Redirect) [RFC7231].  Clients MAY treat any redirect asMiller & Saint-Andre         Standards Track                   [Page 14]

RFC 7711                          POSH                     November 2015   temporary, ignoring the specific semantics for 301 (Moved   Permanently) [RFC7231] and 308 (Permanent Redirect) [RFC7538].  To   protect against circular references, it is RECOMMENDED that POSH   clients follow no more than 10 redirects, although applications or   implementations can require that fewer redirects be followed.   Hash function agility is an important quality to ensure secure   operations in the face of attacks against the fingerprints obtained   within verification material.  Because POSH verification material is   relatively short-lived compared to long-lived credentials such as   PKIX end-entity certificates (at least as typically deployed),   entities that deploy POSH are advised to swap out POSH documents if   the hash functions are found to be subject to practical attacks   [RFC4270].11.  References11.1.  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,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC2818]  Rescorla, E., "HTTP Over TLS",RFC 2818,              DOI 10.17487/RFC2818, May 2000,              <http://www.rfc-editor.org/info/rfc2818>.   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data              Encodings",RFC 4648, DOI 10.17487/RFC4648, October 2006,              <http://www.rfc-editor.org/info/rfc4648>.   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security              (TLS) Protocol Version 1.2",RFC 5246,              DOI 10.17487/RFC5246, August 2008,              <http://www.rfc-editor.org/info/rfc5246>.   [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,              <http://www.rfc-editor.org/info/rfc5280>.   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known              Uniform Resource Identifiers (URIs)",RFC 5785,              DOI 10.17487/RFC5785, April 2010,              <http://www.rfc-editor.org/info/rfc5785>.Miller & Saint-Andre         Standards Track                   [Page 15]

RFC 7711                          POSH                     November 2015   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and              Verification of Domain-Based Application Service Identity              within Internet Public Key Infrastructure Using X.509              (PKIX) Certificates in the Context of Transport Layer              Security (TLS)",RFC 6125, DOI 10.17487/RFC6125,              March 2011, <http://www.rfc-editor.org/info/rfc6125>.   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data              Interchange Format",RFC 7159, DOI 10.17487/RFC7159,              March 2014, <http://www.rfc-editor.org/info/rfc7159>.   [RFC7230]  Fielding, R., Ed., and J. Reschke, Ed., "Hypertext              Transfer Protocol (HTTP/1.1): Message Syntax and Routing",RFC 7230, DOI 10.17487/RFC7230, June 2014,              <http://www.rfc-editor.org/info/rfc7230>.   [RFC7231]  Fielding, R., Ed., and J. Reschke, Ed., "Hypertext              Transfer Protocol (HTTP/1.1): Semantics and Content",RFC 7231, DOI 10.17487/RFC7231, June 2014,              <http://www.rfc-editor.org/info/rfc7231>.   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,              "Recommendations for Secure Use of Transport Layer              Security (TLS) and Datagram Transport Layer Security              (DTLS)",BCP 195,RFC 7525, DOI 10.17487/RFC7525,              May 2015, <http://www.rfc-editor.org/info/rfc7525>.11.2.  Informative References   [HASH-NAMES]              "Hash Function Textual Names",              <http://www.iana.org/assignments/hash-function-text-names>.   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for              specifying the location of services (DNS SRV)",RFC 2782,              DOI 10.17487/RFC2782, February 2000,              <http://www.rfc-editor.org/info/rfc2782>.   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.              Rose, "DNS Security Introduction and Requirements",RFC 4033, DOI 10.17487/RFC4033, March 2005,              <http://www.rfc-editor.org/info/rfc4033>.   [RFC4270]  Hoffman, P. and B. Schneier, "Attacks on Cryptographic              Hashes in Internet Protocols",RFC 4270,              DOI 10.17487/RFC4270, November 2005,              <http://www.rfc-editor.org/info/rfc4270>.Miller & Saint-Andre         Standards Track                   [Page 16]

RFC 7711                          POSH                     November 2015   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an              IANA Considerations Section in RFCs",BCP 26,RFC 5226,              DOI 10.17487/RFC5226, May 2008,              <http://www.rfc-editor.org/info/rfc5226>.   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence              Protocol (XMPP): Core",RFC 6120, DOI 10.17487/RFC6120,              March 2011, <http://www.rfc-editor.org/info/rfc6120>.   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.              Cheshire, "Internet Assigned Numbers Authority (IANA)              Procedures for the Management of the Service Name and              Transport Protocol Port Number Registry",BCP 165,RFC 6335, DOI 10.17487/RFC6335, August 2011,              <http://www.rfc-editor.org/info/rfc6335>.   [RFC6555]  Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with              Dual-Stack Hosts",RFC 6555, DOI 10.17487/RFC6555,              April 2012, <http://www.rfc-editor.org/info/rfc6555>.   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication              of Named Entities (DANE) Transport Layer Security (TLS)              Protocol: TLSA",RFC 6698, DOI 10.17487/RFC6698,              August 2012, <http://www.rfc-editor.org/info/rfc6698>.   [RFC6797]  Hodges, J., Jackson, C., and A. Barth, "HTTP Strict              Transport Security (HSTS)",RFC 6797,              DOI 10.17487/RFC6797, November 2012,              <http://www.rfc-editor.org/info/rfc6797>.   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,              "Enrollment over Secure Transport",RFC 7030,              DOI 10.17487/RFC7030, October 2013,              <http://www.rfc-editor.org/info/rfc7030>.   [RFC7469]  Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning              Extension for HTTP",RFC 7469, DOI 10.17487/RFC7469,              April 2015, <http://www.rfc-editor.org/info/rfc7469>.   [RFC7538]  Reschke, J., "The Hypertext Transfer Protocol Status              Code 308 (Permanent Redirect)",RFC 7538,              DOI 10.17487/RFC7538, April 2015,              <http://www.rfc-editor.org/info/rfc7538>.Miller & Saint-Andre         Standards Track                   [Page 17]

RFC 7711                          POSH                     November 2015   [RFC7673]  Finch, T., Miller, M., and P. Saint-Andre, "Using              DNS-Based Authentication of Named Entities (DANE) TLSA              Records with SRV Records",RFC 7673, DOI 10.17487/RFC7673,              October 2015, <http://www.rfc-editor.org/info/rfc7673>.   [RFC7712]  Saint-Andre, P., Miller, M., and P. Hancke, "Domain Name              Associations (DNA) in the Extensible Messaging and              Presence Protocol (XMPP)",RFC 7712, DOI 10.17487/RFC7712,              November 2015, <http://www.rfc-editor.org/info/rfc7712>.Acknowledgements   Thanks to Thijs Alkemade, Philipp Hancke, Joe Hildebrand, and Tobias   Markmann for their implementation feedback, and to Dave Cridland,   Chris Newton, Max Pritikin, and Joe Salowey for their input on the   specification.   During IESG review, Stephen Farrell, Barry Leiba, and Kathleen   Moriarty provided helpful input that resulted in improvements in the   document.   Thanks also to Dave Cridland as document shepherd, Joe Hildebrand as   working group chair, and Ben Campbell as area director.   Peter Saint-Andre wishes to acknowledge Cisco Systems, Inc., for   employing him during his work on earlier draft versions of this   document.Authors' Addresses   Matthew Miller   Cisco Systems, Inc.   1899 Wynkoop Street, Suite 600   Denver, CO  80202   United States   Email: mamille2@cisco.com   Peter Saint-Andre   &yet   Email: peter@andyet.com   URI:https://andyet.com/Miller & Saint-Andre         Standards Track                   [Page 18]