draft-ietf-xmpp-posh-02.txt   draft-ietf-xmpp-posh-03.txt 
XMPP Working Group M. Miller XMPP Working Group M. Miller
Internet-Draft Cisco Systems, Inc. Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track P. Saint-Andre Intended status: Standards Track P. Saint-Andre
Expires: April 13, 2015 &yet Expires: July 30, 2015 &yet
October 10, 2014 January 26, 2015
PKIX over Secure HTTP (POSH) PKIX over Secure HTTP (POSH)
draft-ietf-xmpp-posh-02 draft-ietf-xmpp-posh-03
Abstract Abstract
Experience has shown that it is extremely difficult to deploy proper Experience has shown that it is extremely difficult to deploy proper
PKIX certificates for TLS in multi-tenanted environments, since PKIX certificates for TLS in multi-tenanted environments. As a
certification authorities will not issue certificates for hosted result, domains hosted in such environments often deploy applications
domains to hosting services, hosted domains do not want hosting using certificates that identify the hosting service, not the hosted
services to hold their private keys, and hosting services wish to domain. Such deployments force end users and peer services to accept
avoid liability for holding those keys. As a result, domains hosted a certificate with an improper identifier, resulting in obvious
in multi-tenanted environments often deploy non-HTTP applications security implications. This document defines two methods that make
such as email and instant messaging using certificates that identify it easier to deploy certificates for proper server identity checking
the hosting service, not the hosted domain. Such deployments force in non-HTTP application protocols. While these methods developed for
end users and peer services to accept a certificate with an improper use in the Extensible Messaging and Presence Protocol (XMPP) as a
identifier, resulting in obvious security implications. This Domain Name Association (DNA) prooftype, they might also be usable in
document defines two methods that make it easier to deploy other non-HTTP application protocols.
certificates for proper server identity checking in non-HTTP
application protocols. The first method enables the TLS client
associated with a user agent or peer application server to obtain the
end-entity certificate of a hosted domain over secure HTTP as an
alternative to standard PKIX techniques. The second method enables a
hosted domain to securely delegate a non-HTTP application to a
hosting service using redirects provided by HTTPS itself or by a
pointer in a file served over HTTPS at the hosted domain. While this
approach was developed for use in the Extensible Messaging and
Presence Protocol (XMPP) as a Domain Name Association prooftype, it
can be applied to any non-HTTP application protocol.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 13, 2015. This Internet-Draft will expire on July 30, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 46 skipping to change at page 2, line 37
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12 10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 13 10.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 14 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
We start with a thought experiment. We begin with a thought experiment.
Imagine that you work on the operations team of a hosting company Imagine that you work on the operations team of a hosting company
that provides the "foo" service (or email or instant messaging or that provides the "foo" service (or email or instant messaging or
social networking service) for ten thousand different customer social networking service) for ten thousand different customer
organizations. Each customer wants their service to be identified by organizations. Each customer wants their service to be identified by
the customer's domain name (e.g., foo.example.com), not the hosting the customer's domain name (e.g., bar.example.com), not the hosting
company's domain name (e.g., hosting.example.net). company's domain name (e.g., hosting.example.net).
In order to properly secure each customer's "foo" service via In order to properly secure each customer's "foo" service via
Transport Layer Security (TLS) [RFC5246], you need to obtain PKIX Transport Layer Security (TLS) [RFC5246], you need to obtain PKIX
certificates [RFC5280] containing identifiers such as certificates [RFC5280] containing identifiers such as
foo.example.com, as explained in the "CertID" specification bar.example.com, as explained in the "CertID" specification
[RFC6125]. Unfortunately, you can't obtain such certificates [RFC6125]. Unfortunately, you can't obtain such certificates
because: because:
o Certification authorities won't issue such certificates to you o Certification authorities won't issue such certificates to you
because you work for the hosting company, not the customer because you work for the hosting company, not the customer
organization. organization.
o Customers won't obtain such certificates and then give them (plus o Customers won't obtain such certificates and then give them (plus
the associated private keys) to you because their legal department the associated private keys) to you because their legal department
is worried about liability. is worried about liability.
o You don't want to install such certificates (plus the associated o You don't want to install such certificates (plus the associated
private keys) on your servers anyway because your legal department private keys) on your servers anyway because your legal department
is worried about liability, too. 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 deploy public keys / certificates containing Given your inability to deploy public keys / certificates containing
the right identifiers, your back-up approach has always been to use a the right identifiers, your back-up approach has always been to use a
certificate containing hosting.example.net as the identifier. certificate containing hosting.example.net as the identifier.
However, more and more customers and end users are complaining about However, more and more customers and end users are complaining about
warning messages in user agents and the inherent security issues warning messages in user agents and the inherent security issues
involved with taking a "leap of faith" to accept the identity involved with taking a "leap of faith" to accept the identity
mismatch between the source domain (foo.example.com) and the mismatch between what [RFC6125] calls the Source Domain
delegated domain (hosting.example.net). (bar.example.com) and the Delegated Domain (hosting.example.net).
This situation is both insecure and unsustainable. You have This situation is both insecure and unsustainable. You have
investigated the possibility of using DNS Security [RFC4033] and DNS- investigated the possibility of using DNS Security [RFC4033] and DNS-
Based Authentication of Named Entities (DANE) [RFC6698] to solve the Based Authentication of Named Entities (DANE) [RFC6698] to solve the
problem. However, your customers and your operations team have told problem. However, your customers and your operations team have told
you that it will be several years before they will be able to deploy you that it will be several years before they will be able to deploy
DNSSEC and DANE for all of your customers (because of tooling DNSSEC and DANE for all of your customers (because of tooling
updates, slow deployment of DNSSEC at some top-level domains, etc.). updates, slow deployment of DNSSEC at some top-level domains, etc.).
The product managers in your company are pushing you to find a method 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 that can be deployed more quickly to overcome the lack of proper
server identity checking for your hosted customers. server identity checking for your hosted customers.
One possible approach that your team has investigated is to ask each One possible approach that your team has investigated is to ask each
customer to provide the public key / certificate for the "foo" customer to provide the public key / certificate for the "foo"
service at a special HTTPS URL on their website service at a special HTTPS URL on their website
("https://foo.example.com/.well-known/posh.foo.json" is one ("https://bar.example.com/.well-known/posh.foo.json" is one
possibility). This could be a public key that you generate for the possibility). This could be a public key that you generate for the
customer, but because the customer hosts it via HTTPS, any user agent 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 can find that public key and check it against the public key you
provide during TLS negotiation for the "foo" service (as one added provide during TLS negotiation for the "foo" service (as one added
benefit, the customer never needs to hand you a private key). benefit, the customer never needs to hand you a private key).
Alternatively, the customer can redirect requests for that special Alternatively, the customer can redirect requests for that special
HTTPS URL to an HTTPS URL at your own website, thus making it HTTPS URL to an HTTPS URL at your own website, thus making it
explicit that they have delegated the "foo" service to you. explicit that they have delegated the "foo" service to you.
The approach sketched out above, called POSH ("PKIX Over Secure The approach sketched out above, called POSH ("PKIX Over Secure
HTTP"), is explained in the remainder of this document. While this HTTP"), is explained in the remainder of this document. While this
approach was developed for use in the Extensible Messaging and approach was developed for use in the Extensible Messaging and
Presence Protocol (XMPP) as a prooftype for Domain Name Associations Presence Protocol (XMPP) as a prooftype for Domain Name Associations
(DNA) [I-D.ietf-xmpp-dna], it can be applied to any non-HTTP (DNA) [I-D.ietf-xmpp-dna], it can be applied to any non-HTTP
application protocol. application protocol.
2. Terminology 2. Terminology
This document inherits security terminology from [RFC5280]. The This document inherits security terminology from [RFC5280]. The
terms "source domain", "derived domain", "reference identifier", and terms "Source Domain", "Delegated Domain", "Derived Domain", and
"presented identifier" are used as defined in the "CertID" "Reference Identifier" are used as defined in the "CertID"
specification [RFC6125]. specification [RFC6125].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
3. Obtaining Verification Materials 3. Obtaining Verification Materials
Server identity checking (see [RFC6125]) involves three different Server identity checking (see [RFC6125]) involves three different
aspects: aspects:
1. A proof of the TLS server's identity (in PKIX, this takes the 1. A proof of the POSH server's identity (in PKIX, this takes the
form of a PKIX certificate [RFC5280]). form of a PKIX end-entity certificate [RFC5280]).
2. Rules for checking the certificate (which vary by application 2. Rules for checking the certificate (which vary by application
protocol, although [RFC6125] attempts to harmonize those rules). protocol, although [RFC6125] attempts to harmonize those rules).
3. The materials that a TLS client uses to verify the TLS server's 3. The materials that a POSH client uses to verify the POSH server's
identity or check the TLS server's proof (in PKIX, this takes the identity or check the POSH server's proof (in PKIX, this takes
form of chaining the end-entity certificate back to a trusted the form of chaining the end-entity certificate back to a trusted
root and performing all validity checks as described in root and performing all validity checks as described in
[RFC5280], [RFC6125], and the relevant application protocol [RFC5280], [RFC6125], and the relevant application protocol
specification). specification).
When POSH is used, the first two aspects remain the same: the TLS When POSH is used, the first two aspects remain the same: the POSH
server proves it identity by presenting a PKIX certificate [RFC5280] server proves it identity by presenting a PKIX certificate [RFC5280]
and the certificate is checked according to the rules defined in the and the certificate is checked according to the rules defined in the
appropriate application protocol specification (such as [RFC6120] for appropriate application protocol specification (such as [RFC6120] for
XMPP). However, the TLS client obtains the materials it will use to XMPP). However, the POSH client obtains the materials it will use to
verify the server's proof by retrieving a JSON document [RFC7159] verify the server's proof by retrieving a JSON document [RFC7159]
containing hashes of the PKIX certificate over HTTPS ([RFC7230] and containing hashes of the PKIX certificate over HTTPS ([RFC7230] and
[RFC2818]) from a well-known URI [RFC5785]. [RFC2818]) from a well-known URI [RFC5785] at the Source Domain.
(This means that the POSH client needs to 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 processing.)
The process for retrieving a PKIX certificate over secure HTTP is as The process for retrieving a PKIX certificate over secure HTTP is as
follows. follows.
1. The TLS client performs an HTTPS GET at the source domain to the 1. The POSH client performs an HTTPS GET request at the Source
path "/.well-known/posh.{servicedesc}.json". The value of Domain to the path "/.well-known/posh.{servicedesc}.json". The
"{servicedesc}" is application-specific; see Section 8 of this value of "{servicedesc}" is application-specific; see Section 8
document for more details. For example, if the application of this document for more details. For example, if the
protocol is some hypothetical "Foo" service, then "{servicedesc}" application protocol is some hypothetical "foo" service, then
could be "foo"; thus if a Foo client were to use POSH to verify a "{servicedesc}" could be "foo"; thus if an application client
Foo server for the domain "foo.example.com", the HTTPS GET were to use POSH to verify an application server for the Source
request would be as follows: Domain "bar.example.com", the HTTPS GET request would be as
follows:
GET /.well-known/posh.foo.json HTTP/1.1 GET /.well-known/posh.foo.json HTTP/1.1
Host: foo.example.com Host: bar.example.com
2. The source domain HTTPS server responds in one of three ways: 2. The Source Domain HTTPS server responds in one of three ways:
* If it possesses PKIX certificate information for the requested * If it possesses PKIX certificate information for the requested
path, it responds as detailed in Section 3.1. path, it responds as detailed in Section 3.1.
* If it has a reference to where the PKIX certificate * If it has a reference to where the PKIX certificate
information can be obtained, it responds as detailed in information can be obtained, it responds as detailed in
Section 3.2. Section 3.2.
* If it does not have any PKIX certificate information or a * If it does not have any PKIX certificate information or a
reference to such information for the requested path, it reference to such information for the requested path, it
responds with an HTTP client error status code (e.g., 404). responds with an HTTP client error status code (e.g., 404).
3.1. Source Domain Possesses PKIX Certificate Information 3.1. Source Domain Possesses PKIX Certificate Information
If the source domain HTTPS server possesses the certificate If the Source Domain HTTPS server possesses the certificate
information, it responds to the HTTPS GET with a success status code information, it responds to the HTTPS GET request with a success
and the message body set to a JSON document [RFC7159]; the document status code and the message body set to a JSON document [RFC7159];
is a JSON object which MUST have the following: the document is a JSON object which MUST have the following:
o A "fingerprints" field whose value is a JSON array of fingerprint o A "fingerprints" field whose value is a JSON array of fingerprint
descriptors. descriptors.
o An "expires" field whose value is a JSON number specifying the o An "expires" field whose value is a JSON number specifying the
number of seconds after which the TLS client ought to consider the number of seconds after which the POSH client ought to consider
key information to be stale (further explained under Section 6). the key information to be stale (further explained under
Section 6).
Each included fingerprint descriptor is a JSON object, where each Each included fingerprint descriptor is a JSON object, where each
member name is the textual name of a hash function (as listed in member name is the textual name of a hash function (as listed in
[HASH-NAMES]) and its associated value is the base 64 encoded [HASH-NAMES]) and its associated value is the base 64 encoded
fingerprint hash generated using the named hash function (where the fingerprint hash generated using the named hash function (where the
encoding adheres to the definition in Section 4 of [RFC4648] and encoding adheres to the definition in Section 4 of [RFC4648] and
where the padding bits are set to zero). Each fingerprint descriptor where the padding bits are set to zero). Each fingerprint descriptor
MUST possess at least one named hash function. MUST possess at least one named hash function.
The fingerprint hash for a given hash algorithm is generated by The fingerprint hash for a given hash algorithm is generated by
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{ {
"sha-1":"UpjRI/A3afKE8/AIeTZ5o1dECTY=", "sha-1":"UpjRI/A3afKE8/AIeTZ5o1dECTY=",
"sha-256":"4/mggdlVx8A3pvHAWW5sD+qJyMtUHgiRuPjVC48N0XQ=" "sha-256":"4/mggdlVx8A3pvHAWW5sD+qJyMtUHgiRuPjVC48N0XQ="
} }
], ],
"expires": 604800 "expires": 604800
} }
The "expires" value is a hint regarding the expiration of the keying The "expires" value is a hint regarding the expiration of the keying
materials. It MUST be a non-negative integer. If no "expires" field materials. It MUST be a non-negative integer. If no "expires" field
is included or its value is equal to 0, a TLS client SHOULD consider is included or its value is equal to 0, a POSH client SHOULD consider
these verification materials invalid. See Section 6 for how to these verification materials invalid. See Section 6 for how to
reconcile this "expires" field with the reference's "expires" field. reconcile this "expires" field with the reference's "expires" field.
3.2. Source Domain References PKIX Certificate 3.2. Source Domain References PKIX Certificate
If the source domain HTTPS server has a reference to the certificate If the Source Domain HTTPS server has a reference to the certificate
information, it responds to the HTTPS GET with a success status code information, it responds to the HTTPS GET request with a success
and message body set to a JSON document. The document is a JSON status code and message body set to a JSON document. The document is
object which MUST contain the following: a JSON object which MUST contain the following:
o A "url" field whose value is a JSON string specifying the HTTPS o A "url" field whose value is a JSON string specifying the HTTPS
URL where TLS clients can obtain the actual certificate URL where POSH clients can obtain the actual certificate
information. information.
o An "expires" field whose value is a JSON number specifying the o An "expires" field whose value is a JSON number specifying the
number of seconds after which the TLS client ought to consider the number of seconds after which the POSH client ought to consider
delegation to be stale (further explained under Section 6). the delegation to be stale (further explained under Section 6).
Example Reference Response Example Reference Response
HTTP/1.1 200 Ok HTTP/1.1 200 Ok
Content-Type: application/json Content-Type: application/json
Content-Length: 79 Content-Length: 79
{ {
"url":"https://hosting.example.net/.well-known/posh.foo.json", "url":"https://hosting.example.net/.well-known/posh.foo.json",
"expires":86400 "expires":86400
} }
The client performs an HTTPS GET for the URL specified in the "url" The client performs an HTTPS GET request for the URL specified in the
field value. The HTTPS server for the URL to which the client has "url" field value. The HTTPS server for the URL to which the client
been redirected responds to the request with a JSON document has been redirected responds to the request with a JSON document
containing fingerprints as described in Section 3.1. The content containing fingerprints as described in Section 3.1. The content
retrieved from the "url" location MUST NOT itself be a reference retrieved from the "url" location MUST NOT itself be a reference
(i.e., containing a "url" field instead of a "fingerprints" field), (i.e., containing a "url" field instead of a "fingerprints" field),
in order to prevent circular delegations. in order to prevent circular delegations.
Note: The JSON document returned by the source domain HTTPS server Note: The JSON document returned by the Source Domain HTTPS server
MUST contain either a reference or a fingerprints document, but MUST contain either a reference or a fingerprints document, but
MUST NOT contain both. MUST NOT contain both.
Note: See Section 9 for discussion about HTTPS redirects. Note: See Section 9 for discussion about HTTPS redirects.
The "expires" value is a hint regarding the expiration of the source 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 Domain's delegation of service to the Delegated Domain. It MUST be a
non-negative integer. If no "expires" field is included or its value non-negative integer. If no "expires" field is included or its value
is equal to 0, a TLS client SHOULD consider the delegation invalid. is equal to 0, a POSH client SHOULD consider the delegation invalid.
See Section 6 for guidelines about reconciling this "expires" field See Section 6 for guidelines about reconciling this "expires" field
with the "expires" field of the fingerprints document. with the "expires" field of the fingerprints document.
3.3. Performing Verification 3.3. Performing Verification
The TLS client compares the PKIX information obtained from the TLS The POSH client compares the PKIX information obtained from the POSH
server against each fingerprint descriptor object in the POSH server against each fingerprint descriptor object in the POSH
results, until a match is found or the collection of POSH results, until a match is found using the hash functions that the
verification materials is exhausted. If none of the fingerprint client suports, or until the collection of POSH verification
descriptor objects match the TLS server PKIX information, the TLS materials is exhausted. If none of the fingerprint descriptor
client SHOULD reject the connection (however, the TLS client might objects match the POSH server PKIX information, the POSH client
still accept the connection if other verification schemes are SHOULD reject the connection (however, the POSH client might still
successful). accept the connection if other verification schemes are successful).
4. Secure Delegation 4. Secure Delegation
The delegation from the source domain to the delegated domain can be The delegation from the Source Domain to the Delegated Domain can be
considered secure if the certificate offered by the TLS server considered secure if the credentials offered by the POSH server match
matches the POSH certificate, regardless of how the POSH certificate the verification materials possessed by the client, regardless of how
is obtained. those materials are obtained.
5. Order of Operations 5. Order of Operations
In order for the TLS client to perform verification of reference In order for the POSH client to perform verification of Reference
identifiers without potentially compromising data, POSH processes Identifiers without potentially compromising data, POSH processes
MUST be complete before any application-level data is exchanged for MUST be complete before any application-layer data is exchanged for
the source domain. The TLS client SHOULD perform all POSH retrievals the Source Domain. In cases where the POSH client initiates an
before opening any socket connections to the application protocol application-layer connection, the client SHOULD perform all POSH
server. For application protocols that use DNS SRV (including retrievals before initiating a connection (naturally this is not
possible in cases where the POSH client receives an application-layer
connection). For application protocols that use DNS SRV (including
queries for TLSA records in concert with SRV records as described in queries for TLSA records in concert with SRV records as described in
[I-D.ietf-dane-srv]), the POSH processes ideally ought to be done in [I-D.ietf-dane-srv]), the POSH processes ideally ought to be done in
parallel with resolving the SRV records and the addresses of any parallel with resolving the SRV records and the addresses of any
targets, similar to the "happy eyeballs" approach for IPv4 and IPv6 targets, similar to the "happy eyeballs" approach for IPv4 and IPv6
[RFC6555]. [RFC6555].
The following diagram illustrates the possession flow: The following diagram illustrates the possession flow:
Client Domain Server Client Domain Server
------ ------ ------ ------ ------ ------
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|<===================================================>| |<===================================================>|
| | | | | |
| Service Data | | Service Data |
|<===================================================>| |<===================================================>|
| | | | | |
Figure 2: Order of Events for Reference Flow Figure 2: Order of Events for Reference Flow
6. Caching Results 6. Caching Results
The TLS client MUST NOT cache results (reference or fingerprints) The POSH client MUST NOT cache results (reference or fingerprints)
indefinitely. If the source domain returns a reference, the TLS indefinitely. If the Source Domain returns a reference, the POSH
client MUST use the lower of the two "expires" values when client MUST use the lower of the two "expires" values when
determining how long to cache results (i.e., if the reference determining how long to cache results (i.e., if the reference
"expires" value is lower than the fingerprints "expires" value, honor "expires" value is lower than the fingerprints "expires" value, honor
the reference "expires" value). Once the TLS client considers the the reference "expires" value). Once the POSH client considers the
results stale, it needs to perform the entire POSH process again results stale, it needs to perform the entire POSH process again
starting with the HTTPS GET to the source domain. The TLS client MAY starting with the HTTPS GET request to the Source Domain. The POSH
use a lower value than any provided in the "expires" field(s), or not client MAY use a lower value than any provided in the "expires"
cache results at all. field(s), or not cache results at all.
The TLS client SHOULD NOT rely on HTTP caching mechanisms, instead The POSH client SHOULD NOT rely on HTTP caching mechanisms, instead
using the expiration hints provided in the POSH reference document or using the expiration hints provided in the POSH reference document or
fingerprints documents. To that end, the HTTPS servers for source fingerprints documents. To that end, the HTTPS servers for Source
domains and derived domains SHOULD specify a 'Cache-Control' header Domains and Derived Domains SHOULD specify a 'Cache-Control' header
indicating a very short duration (e.g., max-age=60) or "no-cache" to indicating a very short duration (e.g., max-age=60) or "no-cache" to
indicate that the response (redirect, reference, or content) is not indicate that the response (redirect, reference, or content) is not
appropriate to cache at the HTTP level. appropriate to cache at the HTTP layer.
7. Alternates and Roll-over 7. Alternates and Roll-over
To indicate alternate PKIX certificates (such as when an existing To indicate alternate PKIX certificates (such as when an existing
certificate will soon expire), the returned fingerprints document MAY certificate will soon expire), the returned fingerprints document MAY
contain multiple fingerprint descriptors. The fingerprints SHOULD be contain multiple fingerprint descriptors. The fingerprints SHOULD be
ordered with the most relevant certificate first as determined by the ordered with the most relevant certificate first as determined by the
application service operator (e.g., the renewed certificate), application service operator (e.g., the renewed certificate),
followed by the next most relevant certificate (e.g., the certificate followed by the next most relevant certificate (e.g., the certificate
soonest to expire). Here is an example: soonest to expire). Here is an example:
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"sha-256":"4/mggdlVx8A3pvHAWW5sD+qJyMtUHgiRuPjVC48N0XQ" "sha-256":"4/mggdlVx8A3pvHAWW5sD+qJyMtUHgiRuPjVC48N0XQ"
}, },
{ {
"sha-1":"T29tGO9d7kxbfWnUaac8+5+ICLM=", "sha-1":"T29tGO9d7kxbfWnUaac8+5+ICLM=",
"sha-256":"otyLADSKjRDjVpj8X7/hmCAD5C7Qe+PedcmYV7cUncE=" "sha-256":"otyLADSKjRDjVpj8X7/hmCAD5C7Qe+PedcmYV7cUncE="
} }
], ],
"expires": 806400 "expires": 806400
} }
Rolling over from one hosting provider to another is best handled by
updating the relevant SRV records, not primarily by updating the POSH
files themselves.
8. IANA Considerations 8. IANA Considerations
This document registers a well-known URI [RFC5785] for protocols that This document registers a well-known URI [RFC5785] for protocols that
use POSH. The completed template follows. use POSH. The completed template follows.
URI suffix: posh. URI suffix: posh.
Change controller: IETF Change controller: IETF
Specification document: [[ this document ]] Specification document: [[ this document ]]
skipping to change at page 11, line 21 skipping to change at page 11, line 24
DNS SRV "Proto" also prepended by the underscore character "_". As DNS SRV "Proto" also prepended by the underscore character "_". As
an example, the well-known URI for XMPP server-to-server connections an example, the well-known URI for XMPP server-to-server connections
would be "posh._xmpp-server._tcp.json" since XMPP [RFC6120] registers would be "posh._xmpp-server._tcp.json" since XMPP [RFC6120] registers
a service name of "xmpp-server" and uses TCP as the underlying a service name of "xmpp-server" and uses TCP as the underlying
transport protocol. transport protocol.
For other POSH-using protocols, the "{servicedesc}" part of the well- For other POSH-using protocols, the "{servicedesc}" part of the well-
known URI can be any unique string or identifier for the protocol, known URI can be any unique string or identifier for the protocol,
which might be a service name registered with the IANA in accordance which might be a service name registered with the IANA in accordance
with [RFC6335] or which might be an unregistered name. As an with [RFC6335] or which might be an unregistered name. As an
example, the well-known URI for the mythical "Foo" service could be example, the well-known URI for the mythical "foo" service could be
"posh.foo.json". "posh.foo.json".
Note: As explained in [RFC5785], the IANA registration policy Note: As explained in [RFC5785], the IANA registration policy
[RFC5226] for well-known URIs is Specification Required. [RFC5226] for well-known URIs is Specification Required.
9. Security Considerations 9. Security Considerations
This document supplements but does not supersede the security This document supplements but does not supersede the security
considerations provided in specifications for application protocols considerations provided in specifications for application protocols
that decide to use POSH (e.g., [RFC6120] and [RFC6125] for XMPP). that decide to use POSH (e.g., [RFC6120] and [RFC6125] for XMPP).
Specifically, the security of requests and responses sent via HTTPS Specifically, the security of requests and responses sent via HTTPS
depends on checking the identity of the HTTP server in accordance depends on checking the identity of the HTTP server in accordance
with [RFC2818]. Additionally, the security of POSH can benefit from with [RFC2818]. Additionally, the security of POSH can benefit from
other HTTP hardening protocols, such as HSTS [RFC6797] and key other HTTP hardening protocols, such as HSTS [RFC6797] and key
pinning [I-D.ietf-websec-key-pinning], especially if the TLS client pinning [I-D.ietf-websec-key-pinning], especially if the POSH client
shares some information with a common HTTPS implementation (e.g., shares some information with a common HTTPS implementation (e.g.,
platform-default web browser). platform-default web browser).
Note well that POSH is used by a TLS client to obtain the public key Note well that POSH is used by a POSH client to obtain the public key
of a TLS server to which it might connect for a particular of a POSH server to which it might connect for a particular
application protocol such as IMAP or XMPP. POSH does not enable a application protocol such as IMAP or XMPP. POSH does not enable a
hosted domain to transfer private keys to a hosting service via hosted domain to transfer private keys to a hosting service via
HTTPS. POSH also does not enable a TLS server to engage in HTTPS. POSH also does not enable a POSH server to engage in
certificate enrollment with a certification authority via HTTPS, as certificate enrollment with a certification authority via HTTPS, as
is done in Enrollment over Secure Transport [RFC7030]. is done in Enrollment over Secure Transport [RFC7030].
A web server at the source domain might redirect an HTTPS request to A web server at the Source Domain might redirect an HTTPS request to
another URL. The location provided in the redirect response MUST another URL. The location provided in the redirect response MUST
specify an HTTPS URL. Source domains SHOULD use only temporary specify an HTTPS URL. Source domains SHOULD use only temporary
redirect mechanisms, such as HTTP status codes 302 (Found) and 307 redirect mechanisms, such as HTTP status codes 302 (Found) and 307
(Temporary Redirect). Clients MAY treat any redirect as temporary, (Temporary Redirect). Clients MAY treat any redirect as temporary,
ignoring the specific semantics for 301 (Moved Permanently) and 308 ignoring the specific semantics for 301 (Moved Permanently) and 308
(Permanent Redirect) [RFC7238]. To protect against circular (Permanent Redirect) [RFC7238]. To protect against circular
references, clients MUST NOT follow an infinite number of redirects. references, clients MUST NOT follow an infinite number of redirects.
It is RECOMMENDED that clients follow no more than 10 redirects, It is RECOMMENDED that clients follow no more than 10 redirects,
although applications or implementations can require that fewer although applications or implementations can require that fewer
redirects be followed. 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 materials. Because POSH verification materials
are 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 files if the
hash functions in use are found to be subject to realistic attacks.
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
skipping to change at page 14, line 39 skipping to change at page 15, line 4
Authors' Addresses Authors' Addresses
Matthew Miller Matthew Miller
Cisco Systems, Inc. Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600 1899 Wynkoop Street, Suite 600
Denver, CO 80202 Denver, CO 80202
USA USA
Email: mamille2@cisco.com Email: mamille2@cisco.com
Peter Saint-Andre Peter Saint-Andre
&yet &yet
P.O. Box 787
Parker, CO 80134
USA
Email: peter@andyet.com Email: peter@andyet.com
URI: https://andyet.com/
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