draft-ietf-xmpp-dna-03.txt   draft-ietf-xmpp-dna-04.txt 
Network Working Group P. Saint-Andre Network Working Group P. Saint-Andre
Internet-Draft M. Miller Internet-Draft M. Miller
Intended status: Standards Track Cisco Systems, Inc. Intended status: Standards Track Cisco Systems, Inc.
Expires: March 10, 2014 September 6, 2013 Expires: April 23, 2014 October 20, 2013
Domain Name Associations (DNA) in the Extensible Messaging and Presence Domain Name Associations (DNA) in the Extensible Messaging and Presence
Protocol (XMPP) Protocol (XMPP)
draft-ietf-xmpp-dna-03 draft-ietf-xmpp-dna-04
Abstract Abstract
This document improves the security of the Extensible Messaging and This document improves the security of the Extensible Messaging and
Presence Protocol (XMPP) in two ways. First, it specifies how Presence Protocol (XMPP) in two ways. First, it specifies how
"prooftypes" can establish a strong association between a domain name "prooftypes" can establish a strong association between a domain name
and an XML stream. Second, it describes how to securely delegate a and an XML stream. Second, it describes how to securely delegate a
source domain to a derived domain, which is especially important in source domain to a derived domain, which is especially important in
virtual hosting environments. virtual hosting environments.
Status of this Memo Status of This Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. A Simple Scenario . . . . . . . . . . . . . . . . . . . . . . 6 4. A Simple Scenario . . . . . . . . . . . . . . . . . . . . . . 6
5. One-Way Authentication . . . . . . . . . . . . . . . . . . . . 7 5. One-Way Authentication . . . . . . . . . . . . . . . . . . . 7
6. Piggybacking . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. Piggybacking . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Assertion . . . . . . . . . . . . . . . . . . . . . . . . 8 6.1. Assertion . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Supposition . . . . . . . . . . . . . . . . . . . . . . . 9 6.2. Supposition . . . . . . . . . . . . . . . . . . . . . . . 9
7. Alternative Prooftypes . . . . . . . . . . . . . . . . . . . . 10 7. Alternative Prooftypes . . . . . . . . . . . . . . . . . . . 11
7.1. DANE . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. DANE . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.2. POSH . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.2. POSH . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. Secure Delegation and Multi-Tenancy . . . . . . . . . . . . . 11 8. Secure Delegation and Multi-Tenancy . . . . . . . . . . . . . 12
9. Prooftype Model . . . . . . . . . . . . . . . . . . . . . . . 12 9. Prooftype Model . . . . . . . . . . . . . . . . . . . . . . . 13
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10.1. Well-Known URI for xmpp-client Service . . . . . . . . . . 12 10.1. Well-Known URI for xmpp-client Service . . . . . . . . . 13
10.2. Well-Known URI for xmpp-server Service . . . . . . . . . . 13 10.2. Well-Known URI for xmpp-server Service . . . . . . . . . 14
11. Security Considerations . . . . . . . . . . . . . . . . . . . 13 11. Security Considerations . . . . . . . . . . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . . 13 12.1. Normative References . . . . . . . . . . . . . . . . . . 14
12.2. Informative References . . . . . . . . . . . . . . . . . . 14 12.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
The need to establish a strong association between a domain name and The need to establish a strong association between a domain name and
an XML stream arises in both client-to-server and server-to-server an XML stream arises in both client-to-server and server-to-server
communication using the Extensible Messaging and Presence Protocol communication using the Extensible Messaging and Presence Protocol
(XMPP), because XMPP servers are typically identified by DNS domain (XMPP) [RFC6120]. Because XMPP servers are typically identified by
names. However, a client or peer server needs to verify the identity DNS domain names, a client or peer server needs to verify the
of a server to which it connects. To date, such verification has identity of a server to which it connects.
been established based on information obtained from the Domain Name
System (DNS), the Public Key Infrastructure (PKI), or similar
sources. This document (1) generalizes the model currently in use so
that additional prooftypes can be defined, (2) provides a basis for
modernizing some prooftypes to reflect progress in underlying
technologies such as DNS Security [RFC4033], and (3) describes the
flow of operations for establishing a domain name association.
Furthermore, the process for resolving the domain name of an XMPP To date, such verification has been established based on information
service into the IP address at which an XML stream will be negotiated obtained from the Domain Name System (DNS), the Public Key
(defined in [RFC6120]) can involve delegation of a source domain Infrastructure (PKI), or similar sources. In relation to such
(say, example.com) to a derived domain (say, hosting.example.net). associations, this document does the following:
If such delegation is not done in a secure manner, then the domain
name association cannot be authenticated. Therefore, this document 1. Generalizes the model currently in use so that additional
provides guidelines for defining secure delegation methods. prooftypes can be defined
2. Provides a basis for modernizing some prooftypes to reflect
progress in underlying technologies such as DNS Security
[RFC4033]
3. Describes the flow of operations for establishing a domain name
association (DNA)
This document also provides guidelines for secure delegation. The
need for secure delegation arises because the process for resolving
the domain name of an XMPP service into the IP address at which an
XML stream will be negotiated (defined in [RFC6120]) can involve
delegation of a source domain (say, example.com) to a derived domain
(say, hosting.example.net) using technologies such as DNS SRV records
[RFC2782]. If such delegation is not done in a secure manner, then
the domain name association cannot be authenticated.
2. Terminology 2. Terminology
This document inherits XMPP terminology from [RFC6120] and This document inherits XMPP terminology from [RFC6120] and
[XEP-0220], DNS terminology from [RFC1034], [RFC1035], [RFC2782] and [XEP-0220], DNS terminology from [RFC1034], [RFC1035], [RFC2782] and
[RFC4033], and security terminology from [RFC4949] and [RFC5280]. [RFC4033], and security terminology from [RFC4949] and [RFC5280].
The terms "source domain", "derived domain", "reference identity", The terms "source domain", "derived domain", "reference identity",
and "presented identity" are used as defined in the "CertID" and "presented identity" are used as defined in the "CertID"
specification [RFC6125]. The terms "permissive federation", specification [RFC6125]. The terms "permissive federation",
"verified federation", and "encrypted federation" are derived from "verified federation", and "encrypted federation" are derived from
[XEP-0238], although we substitute the term "authenticated [XEP-0238], although we substitute the term "authenticated
federation" for the term "trusted federation" from that document. federation" for the term "trusted federation" from that document.
3. Flow Chart 3. Flow Chart
The following flow chart illustrates the protocol flow for The following flow chart illustrates the protocol flow for
establishing domain name associations between Server A and Server B, establishing domain name associations between Server 1 and Server 2,
as described in the remaining sections of this document. as described in the remaining sections of this document.
| |
| |
(Section 4: A Simple Scenario) (Section 4: A Simple Scenario)
| |
| |
DNS RESOLUTION ETC. DNS RESOLUTION ETC.
| |
+-------------STREAM HEADERS--------------------+ +-------------STREAM HEADERS--------------------+
skipping to change at page 6, line 25 skipping to change at page 6, line 11
| B: <db:result from='rooms.a.example' | | B: <db:result from='rooms.a.example' |
| to='c.example' | | to='c.example' |
| type='valid'/> | | type='valid'/> |
| | | |
+-----------------------------------------------+ +-----------------------------------------------+
4. A Simple Scenario 4. A Simple Scenario
To illustrate the problem, consider the simplified order of events To illustrate the problem, consider the simplified order of events
(see [RFC6120] for details) in establishing an XML stream between (see [RFC6120] for details) in establishing an XML stream between
Server A (a.example) and Server B (b.example): Server 1 (a.example) and Server 2 (b.example):
1. Server A resolves the DNS domain name b.example. 1. Server 1 resolves the DNS domain name b.example.
2. Server A opens a TCP connection to the resolved IP address.
3. Server A sends an initial stream header to Server B, asserting 2. Server 1 opens a TCP connection to the resolved IP address.
3. Server 1 sends an initial stream header to Server 2, asserting
that it is a.example: that it is a.example:
<stream:stream from='a.example' to='b.example'> <stream:stream from='a.example' to='b.example'>
4. Server B sends a response stream header to Server A, asserting 4. Server 2 sends a response stream header to Server 1, asserting
that it is b.example: that it is b.example:
<stream:stream from='b.example' to='a.example'> <stream:stream from='b.example' to='a.example'>
5. The servers attempt TLS negotiation, during which Server B 5. The servers attempt TLS negotiation, during which Server 2
(acting as a TLS server) presents a PKIX certificate proving that (acting as a TLS server) presents a PKIX certificate proving that
it is b.example and Server A (acting as a TLS client) presents a it is b.example and Server 1 (acting as a TLS client) presents a
PKIX certificate proving that it is a.example. PKIX certificate proving that it is a.example.
6. Server A checks the PKIX certificate that Server B provided and
Server B checks the PKIX certificate that Server A provided; if 6. Server 1 checks the PKIX certificate that Server 2 provided and
Server 2 checks the PKIX certificate that Server 1 provided; if
these proofs are consistent with the XMPP profile of the matching these proofs are consistent with the XMPP profile of the matching
rules from [RFC6125], each server accepts that there is a strong rules from [RFC6125], each server accepts that there is a strong
domain name association between its stream to the other party and domain name association between its stream to the other party and
the DNS domain name of the other party. the DNS domain name of the other party.
Several simplifying assumptions underlie the happy scenario just Several simplifying assumptions underlie the happy scenario just
outlined: outlined:
o Server A presents a PKIX certificate during TLS negotiation, which o Server 1 presents a PKIX certificate during TLS negotiation, which
enables the parties to complete mutual authentication. enables the parties to complete mutual authentication.
o There are no additional domains associated with Server A and
Server B (say, a subdomain rooms.a.example on Server A or a second o There are no additional domains associated with Server 1 and
domain c.example on Server B). Server 2 (say, a subdomain rooms.a.example on Server 1 or a second
domain c.example on Server 2).
o The server administrators are able to obtain PKIX certificates in o The server administrators are able to obtain PKIX certificates in
the first place. the first place.
o The server administrators are running their own XMPP servers, o The server administrators are running their own XMPP servers,
rather than using hosting services. rather than using hosting services.
Let's consider each of these "wrinkles" in turn. Let's consider each of these "wrinkles" in turn.
5. One-Way Authentication 5. One-Way Authentication
If Server A does not present its PKIX certificate during TLS If Server 1 does not present its PKIX certificate during TLS
negotiation (perhaps because it wishes to verify the identity of negotiation (perhaps because it wishes to verify the identity of
Server B before presenting its own credentials), Server B is unable Server 2 before presenting its own credentials), Server 2 is unable
to mutually authenticate Server A. Therefore, Server B needs to to mutually authenticate Server 1. Therefore, Server 2 needs to
negotiate and authenticate a stream to Server A, just as Server A has negotiate and authenticate a stream to Server 1, just as Server 1 has
done: done:
1. Server B resolves the DNS domain name a.example. 1. Server 2 resolves the DNS domain name a.example.
2. Server B opens a TCP connection to the resolved IP address.
3. Server B sends an initial stream header to Server A, asserting 2. Server 2 opens a TCP connection to the resolved IP address.
3. Server 2 sends an initial stream header to Server 1, asserting
that it is b.example: that it is b.example:
<stream:stream from='b.example' to='a.example'> <stream:stream from='b.example' to='a.example'>
4. Server A sends a response stream header to Server B, asserting
4. Server 1 sends a response stream header to Server 2, asserting
that it is a.example: that it is a.example:
<stream:stream from='a.example' to='b.example'> <stream:stream from='a.example' to='b.example'>
5. The servers attempt TLS negotiation, during which Server A
5. The servers attempt TLS negotiation, during which Server 1
(acting as a TLS server) presents a PKIX certificate proving that (acting as a TLS server) presents a PKIX certificate proving that
it is a.example. it is a.example.
6. Server B checks the PKIX certificate that Server A provided; if
it is consistent with the XMPP profile of the matching rules from
[RFC6125], Server B accepts that there is a strong domain name
association between its stream to Server A and the DNS domain
name a.example.
Unfortunately, now the servers are using two TCP connections instead 6. Server 2 checks the PKIX certificate that Server 1 provided; if
of one, which is somewhat wasteful. However, there are ways to tie it is consistent with the XMPP profile [RFC6120] of the matching
the authentication achieved on the second TCP connection to the first rules from [RFC6125], Server 2 accepts that there is a strong
TCP connection; see [XEP-0288] for further discussion. domain name association between its stream to Server 1 and the
DNS domain name a.example.
At this point the servers are using two TCP connections instead of
one, which is somewhat wasteful. However, there are ways to tie the
authentication achieved on the second TCP connection to the first TCP
connection; see [XEP-0288] for further discussion.
6. Piggybacking 6. Piggybacking
6.1. Assertion 6.1. Assertion
Consider the common scenario in which Server B hosts not only Consider the common scenario in which Server 2 hosts not only
b.example but also a second domain c.example. If a user of Server B b.example but also a second domain c.example (a "multi-tenanted"
associated with c.example wishes to communicate with a friend at environment). If a user of Server 2 associated with c.example wishes
a.example, Server B needs to send XMPP stanzas from the domain to communicate with a friend at a.example, Server 2 needs to send
c.example rather than b.example. Although Server B could open an new XMPP stanzas from the domain c.example rather than b.example.
TCP connection and negotiate new XML streams for the domain pair of Although Server 2 could open an new TCP connection and negotiate new
c.example and a.example, that too is wasteful. Server B already has XML streams for the domain pair of c.example and a.example, that too
a connection to a.example, so how can it assert that it would like to is wasteful. Server 2 already has a connection to a.example, so how
add a new domain pair to the existing connection? can it assert that it would like to add a new domain pair to the
existing connection?
The traditional method for doing so is the Server Dialback protocol, The traditional method for doing so is the Server Dialback protocol,
first specified in [RFC3920] and since moved to [XEP-0220]. Here, first specified in [RFC3920] and since moved to [XEP-0220]. Here,
Server B can send a <db:result/> element for the new domain pair over Server 2 can send a <db:result/> element for the new domain pair over
the existing stream. the existing stream.
<db:result from='c.example' to='a.example'> <db:result from='c.example' to='a.example'>
some-dialback-key some-dialback-key
</db:result> </db:result>
This element functions as Server B's assertion that it is (also) This element functions as Server 2's assertion that it is (also)
c.example, and thus is functionally equivalent to the 'from' address c.example, and thus is functionally equivalent to the 'from' address
of an initial stream header as previously described. of an initial stream header as previously described.
In response to this assertion, Server A needs to obtain some kind of In response to this assertion, Server 1 needs to obtain some kind of
proof that Server B really is also c.example. It can do the same proof that Server 2 really is also c.example. It can do the same
thing that it did before: thing that it did before:
1. Server A resolves the DNS domain name c.example. 1. Server 1 resolves the DNS domain name c.example.
2. Server A opens a TCP connection to the resolved IP address (which
2. Server 1 opens a TCP connection to the resolved IP address (which
might be the same IP address as for b.example). might be the same IP address as for b.example).
3. Server A sends an initial stream header to Server B, asserting
3. Server 1 sends an initial stream header to Server 2, asserting
that it is a.example: that it is a.example:
<stream:stream from='a.example' to='c.example'> <stream:stream from='a.example' to='c.example'>
4. Server B sends a response stream header to Server A, asserting
4. Server 2 sends a response stream header to Server 1, asserting
that it is c.example: that it is c.example:
<stream:stream from='c.example' to='a.example'> <stream:stream from='c.example' to='a.example'>
5. The servers attempt TLS negotiation, during which Server B
5. The servers attempt TLS negotiation, during which Server 2
(acting as a TLS server) presents a PKIX certificate proving that (acting as a TLS server) presents a PKIX certificate proving that
it is c.example. it is c.example.
6. Server A checks the PKIX certificate that Server B provided; if
it is consistent with the XMPP profile of the matching rules from
[RFC6125], Server A accepts that there is a strong domain name
association between its stream to Server B and the DNS domain
name c.example.
Now that Server A accepts the domain name association, it informs 6. Server 1 checks the PKIX certificate that Server 2 provided; if
Server B of that fact: it is consistent with the XMPP profile [RFC6120] of the matching
rules from [RFC6125], Server 1 accepts that there is a strong
domain name association between its stream to Server 2 and the
DNS domain name c.example.
<db:result from='a.example' to='c.example' type='valid'/> Now that Server 1 accepts the domain name association, it informs
Server 2 of that fact:
<db:result from='a.example' to='c.example' type='valid'/>
The parties can then terminate the second connection, since it was The parties can then terminate the second connection, since it was
used only for Server A to associate a stream over the same IP:port used only for Server 1 to associate a stream over the same IP:port
combination with the domain name c.example (dialback key links the combination with the domain name c.example (the dialback key links
original stream to the new association). the original stream to the new association).
6.2. Supposition 6.2. Supposition
Piggybacking can also occur in the other direction. Consider the Piggybacking can also occur in the other direction. Consider the
common scenario in which Server A provides XMPP services not only for common scenario in which Server 1 provides XMPP services not only for
a.example but also for a subdomain such as a groupchat service at a.example but also for a subdomain such as a groupchat service at
rooms.a.example (see [XEP-0045]). If a user from c.example at Server rooms.a.example (see [XEP-0045]). If a user from c.example at Server
B wishes to join a room on the groupchat sevice, Server B needs to 2 wishes to join a room on the groupchat sevice, Server 2 needs to
send XMPP stanzas from the domain c.example to the domain send XMPP stanzas from the domain c.example to the domain
rooms.a.example rather than a.example. Therefore, Server B needs to rooms.a.example rather than a.example. Therefore, Server 2 needs to
negotiate and authenticate a stream to rooms.a.example: negotiate and authenticate a stream to rooms.a.example:
1. Server B resolves the DNS domain name rooms.a.example. 1. Server 2 resolves the DNS domain name rooms.a.example.
2. Server B opens a TCP connection to the resolved IP address.
3. Server B sends an initial stream header to Server A acting as 2. Server 2 opens a TCP connection to the resolved IP address.
3. Server 2 sends an initial stream header to Server 1 acting as
rooms.a.example, asserting that it is b.example: rooms.a.example, asserting that it is b.example:
<stream:stream from='b.example' to='rooms.a.example'> <stream:stream from='b.example' to='rooms.a.example'>
4. Server A sends a response stream header to Server B, asserting
4. Server 1 sends a response stream header to Server 2, asserting
that it is rooms.a.example: that it is rooms.a.example:
<stream:stream from='rooms.a.example' to='b.example'> <stream:stream from='rooms.a.example' to='b.example'>
5. The servers attempt TLS negotiation, during which Server A
5. The servers attempt TLS negotiation, during which Server 1
(acting as a TLS server) presents a PKIX certificate proving that (acting as a TLS server) presents a PKIX certificate proving that
it is rooms.a.example. it is rooms.a.example.
6. Server B checks the PKIX certificate that Server A provided; if
it is consistent with the XMPP profile of the matching rules from 6. Server 2 checks the PKIX certificate that Server 1 provided; if
[RFC6125], Server B accepts that there is a strong domain name it is consistent with the XMPP profile [RFC6120] of the matching
association between its stream to Server A and the DNS domain rules from [RFC6125], Server 2 accepts that there is a strong
name rooms.a.example. domain name association between its stream to Server 1 and the
DNS domain name rooms.a.example.
As before, the parties now have two TCP connections open. So that As before, the parties now have two TCP connections open. So that
they can close the now-redundant connection, Server B sends a they can close the now-redundant connection, Server 2 sends a
dialback key to Server A over the new connection. dialback key to Server 1 over the new connection.
<db:result from='c.example' to='rooms.a.example'> <db:result from='c.example' to='rooms.a.example'>
some-dialback-key some-dialback-key
</db:result> </db:result>
Server A then informs Server B that it accepts the domain name Server 1 then informs Server 2 that it accepts the domain name
association: association:
<db:result from='rooms.a.example' to='c.example' type='valid'/> <db:result from='rooms.a.example' to='c.example' type='valid'/>
Server B can now close the connection over which it tested the domain Server 2 can now close the connection over which it tested the domain
name association for rooms.a.example. name association for rooms.a.example.
7. Alternative Prooftypes 7. Alternative Prooftypes
The foregoing protocol flows assumed that domain name associations The foregoing protocol flows assumed that domain name associations
were proved using the standard PKI prooftype specified in [RFC6120]: were proved using the standard PKI prooftype specified in [RFC6120]:
that is, the server's proof consists of a PKIX certificate that is that is, the server's proof consists of a PKIX certificate that is
checked according to a profile of the matching rules from [RFC6125], checked according to the XMPP profile [RFC6120] of the matching rules
the client's verification material is obtained out of band in the from [RFC6125], the client's verification material is obtained out of
form of a trusted root, and secure DNS is not necessary. band in the form of a trusted root, and secure DNS is not necessary.
However, sometimes XMPP server administrators are unable or unwilling However, sometimes XMPP server administrators are unable or unwilling
to obtain valid PKIX certificates for their servers (e.g., the to obtain valid PKIX certificates for their servers. As one example,
administrator of im.cs.podunk.example can't receive certification a certificate authority (CA) might try to send email messages to
authority verification messages sent to authoritative mailbox names [RFC2142], but the administrator of a
mailto:hostmaster@podunk.example, or hosting.example.net does not subsidiary service such as im.cs.podunk.example can't receive email
want to take on the liability of holding the certificate and private sent to mailto:hostmaster@podunk.example. As another example, a
key for example.com). In these circumstances, prooftypes other than hosting provider such as hosting.example.net might not want to take
PKIX are desirable. Two alternatives have been defined so far: DANE on the liability of holding the certificate and private key for a
and POSH. tenant such as example.com (or the tenant might not want the hosting
provider to hold its certificate and private key). In these
circumstances, prooftypes other than PKIX are desirable. As
described below, two alternatives have been defined so far: DNS-Based
Authentication of Named Entities (DANE) and and PKIX Over Secure HTTP
(POSH).
7.1. DANE 7.1. DANE
In the DANE prooftype, the server's proof consists of a PKIX In the DANE prooftype, the server's proof consists of a PKIX
certificate that is compared as an exact match or a hash of either certificate that is compared as an exact match or a hash of either
the SubjectPublicKeyInfo or the full certificate, and the client's the SubjectPublicKeyInfo or the full certificate, and the client's
verification material is obtained via secure DNS. verification material is obtained via secure DNS.
The DANE prooftype is based on [I-D.ietf-dane-srv]. For XMPP The DANE prooftype makes use of the DNS-Based Authentication of Named
purposes, the following rules apply: Entities [RFC6698], specifically the use of DANE with DNS SRV records
[I-D.ietf-dane-srv]. For XMPP purposes, the following rules apply:
o If there is no SRV resource record, pursue the fallback methods o If there is no SRV resource record, pursue the fallback methods
described in [RFC6120]. described in [RFC6120].
o Use the 'to' address of the initial stream header to determine the o Use the 'to' address of the initial stream header to determine the
domain name of the TLS client's reference identifier (since use of domain name of the TLS client's reference identifier (since use of
the TLS Server Name Indication is purely discretionary in XMPP, as the TLS Server Name Indication is purely discretionary in XMPP, as
mentioned in [RFC6120]). mentioned in [RFC6120]).
7.2. POSH 7.2. POSH
In the POSH (PKIX Over Secure HTTP) prooftype, the server's proof In the POSH prooftype, the server's proof consists of a PKIX
consists of a PKIX certificate that is checked according to the rules certificate that is checked according to the rules from [RFC6120] and
from [RFC6120] and [RFC6125], the client's verification material is [RFC6125], the client's verification material is obtained by
obtained by retrieving the PKIK certificate over HTTPS at a well- retrieving the PKIK certificate over HTTPS at a well-known URI
known URI [RFC5785], and secure DNS is not necessary since the HTTPS [RFC5785], and secure DNS is not necessary since the HTTPS retrieval
retrieval mechanism relies on the chain of trust from the public key mechanism relies on the chain of trust from the public key
infrastructure. infrastructure.
POSH is defined in [I-D.miller-posh]. For XMPP purposes, the well- POSH is defined in [I-D.miller-posh]. For XMPP purposes, the well-
known URIs [RFC5785] to be used are: known URIs [RFC5785] to be used are:
o "/.well-known/posh._xmpp-client._tcp.json" for client-to-server o "/.well-known/posh._xmpp-client._tcp.json" for client-to-server
connections connections
o "/.well-known/posh._xmpp-server._tcp.json" for server-to-server o "/.well-known/posh._xmpp-server._tcp.json" for server-to-server
connections connections
8. Secure Delegation and Multi-Tenancy 8. Secure Delegation and Multi-Tenancy
One common method for deploying XMPP services is multi-tenancy or One common method for deploying XMPP services is multi-tenancy or
virtual hosting: e.g., the XMPP service for example.com is actually virtual hosting: e.g., the XMPP service for example.com is actually
hosted at hosting.example.net. Such an arrangement is relatively hosted at hosting.example.net. Such an arrangement is relatively
convenient in XMPP given the use of DNS SRV records [RFC2782], such convenient in XMPP given the use of DNS SRV records [RFC2782], such
as the following pointer from example.com to hosting.example.net: as the following pointer from example.com to hosting.example.net:
skipping to change at page 11, line 38 skipping to change at page 12, line 39
convenient in XMPP given the use of DNS SRV records [RFC2782], such convenient in XMPP given the use of DNS SRV records [RFC2782], such
as the following pointer from example.com to hosting.example.net: as the following pointer from example.com to hosting.example.net:
_xmpp-server._tcp.example.com. 0 IN SRV 0 0 5269 hosting.example.net _xmpp-server._tcp.example.com. 0 IN SRV 0 0 5269 hosting.example.net
Secure connections with multi-tenancy can work using the PKIX Secure connections with multi-tenancy can work using the PKIX
prooftype on a small scale if the provider itself wishes to host prooftype on a small scale if the provider itself wishes to host
several domains (e.g., several related domains such as jabber- several domains (e.g., several related domains such as jabber-
de.example and jabber-ch.example). However, in practice the security de.example and jabber-ch.example). However, in practice the security
of multi-tenancy has been found to be unwieldy when the provider of multi-tenancy has been found to be unwieldy when the provider
hosts large numbers of XMPP services on behalf of multiple customers. hosts large numbers of XMPP services on behalf of multiple tenants.
Typically there are two main reasons for this state of affairs: the Typically there are two main reasons for this state of affairs: the
service provider (say, hosting.example.net) wishes to limit its service provider (say, hosting.example.net) wishes to limit its
liability and therefore does not wish to hold the certificate and liability and therefore does not wish to hold the certificate and
private key for the customer (say, example.com) and the customer private key for the tenant (say, example.com) and the tenant wishes
wishes to improve the security of the service and therefore does not to improve the security of the service and therefore does not wish to
wish to share its certificate and private key with service provider. share its certificate and private key with service provider. As a
As a result, server-to-server communications to example.com go result, server-to-server communications to example.com go unencrypted
unencrypted or the communications are TLS-encrypted but the or the communications are TLS-encrypted but the certificates are not
certificates are not checked (which is functionally equivalent to a checked (which is functionally equivalent to a connection using an
connection using an anonymous key exchange). This is also true of anonymous key exchange). This is also true of client-to-server
client-to-server communications, forcing end users to override communications, forcing end users to override certificate warnings or
certificate warnings or configure their clients to accept configure their clients to accept certificates for
certificates for hosting.example.net instead of example.com. The hosting.example.net instead of example.com. The fundamental problem
fundamental problem here is that if DNSSEC is not used then the act here is that if DNSSEC is not used then the act of delegation via DNS
of delegation via DNS SRV records is inherently insecure. SRV records is inherently insecure.
The specification for use of SRV and MX records with DANE
[I-D.ietf-dane-srv] explains how to use DNSSEC for secure delegation [I-D.ietf-dane-srv] explains how to use DNSSEC for secure delegation
with the DANE prooftype and [I-D.miller-posh] explains how to use with the DANE prooftype, and the POSH specification [I-D.miller-posh]
HTTPS redirects for secure delegation with the POSH prooftype. explains how to use HTTPS redirects for secure delegation with the
POSH prooftype.
9. Prooftype Model 9. Prooftype Model
In general, a DNA prooftype conforms to the following definition: In general, a domain name association (DNA) prooftype conforms to the
following definition:
prooftype: A mechanism for proving an association between a domain prooftype: A mechanism for proving an association between a domain
name and an XML stream, where the mechanism defines (1) the nature name and an XML stream, where the mechanism defines (1) the nature
of the server's proof, (2) the matching rules for comparing the of the server's proof, (2) the matching rules for comparing the
client's verification material against the server's proof, (3) how client's verification material against the server's proof, (3) how
the client obtains its verification material, and (4) whether the the client obtains its verification material, and (4) whether the
mechanism depends on secure DNS. mechanism depends on secure DNS.
The PKI, DANE, and POSH prooftypes adhere to this model. In The PKI, DANE, and POSH prooftypes adhere to this model. In
addition, other prooftypes are possible (examples might include PGP addition, other prooftypes are possible (examples might include PGP
keys rather than PKIX certificates, or a token mechanism such as keys rather than PKIX certificates, or a token mechanism such as
Kerberos or OAuth). Kerberos or OAuth).
Some prooftypes depend on (or are enhanced by) secure DNS and Some prooftypes depend on (or are enhanced by) secure DNS and thus
therefore also need to describe how secure delegation occurs for that also need to describe how they ensure secure delegation.
prooftype.
10. IANA Considerations 10. IANA Considerations
The POSH specification [I-D.miller-posh] defines a registry for well- The POSH specification [I-D.miller-posh] provides guidelines for
known URIs [RFC5785] of protocols that make use of POSH. This registering the well-known URIs [RFC5785] of protocols that make use
specification registers two such URIs, for which the completed of POSH. This specification registers two such URIs, for which the
registration templates follow. completed registration templates follow.
10.1. Well-Known URI for xmpp-client Service 10.1. Well-Known URI for xmpp-client Service
This specification registers the "posh._xmpp-client._tcp.json" well- This specification registers the well-known URI "posh._xmpp-
known URI in the Well-Known URI Registry as defined by [RFC5785]. client._tcp.json" in the Well-Known URI Registry as defined by
[RFC5785].
URI suffix: posh._xmpp-client._tcp.json URI suffix: posh._xmpp-client._tcp.json
Change controller: IETF Change controller: IETF
Specification document(s): [[ this document ]] Specification document(s): [[ this document ]]
10.2. Well-Known URI for xmpp-server Service 10.2. Well-Known URI for xmpp-server Service
This specification registers the "posh._xmpp-server._tcp.json" well- This specification registers the well-known URI "posh._xmpp-
known URI in the Well-Known URI Registry as defined by [RFC5785]. server._tcp.json" in the Well-Known URI Registry as defined by
[RFC5785].
URI suffix: posh._xmpp-server._tcp.json URI suffix: posh._xmpp-server._tcp.json
Change controller: IETF Change controller: IETF
Specification document(s): [[ this document ]] Specification document(s): [[ this document ]]
11. Security Considerations 11. Security Considerations
This document supplements but does not supersede the security This document supplements but does not supersede the security
skipping to change at page 13, line 34 skipping to change at page 14, line 35
12.1. Normative References 12.1. Normative References
[I-D.ietf-dane-srv] [I-D.ietf-dane-srv]
Finch, T., "Using DNS-Based Authentication of Named Finch, T., "Using DNS-Based Authentication of Named
Entities (DANE) TLSA records with SRV and MX records.", Entities (DANE) TLSA records with SRV and MX records.",
draft-ietf-dane-srv-02 (work in progress), February 2013. draft-ietf-dane-srv-02 (work in progress), February 2013.
[I-D.miller-posh] [I-D.miller-posh]
Miller, M. and P. Saint-Andre, "PKIX over Secure HTTP Miller, M. and P. Saint-Andre, "PKIX over Secure HTTP
(POSH)", draft-miller-posh-01 (work in progress), (POSH)", draft-miller-posh-02 (work in progress),
September 2013. September 2013.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
February 2000. February 2000.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", Rose, "DNS Security Introduction and Requirements", RFC
RFC 4033, May 2005. 4033, May 2005.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
RFC 4949, August 2007. 4949, August 2007.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008. (CRL) Profile", RFC 5280, May 2008.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785, Uniform Resource Identifiers (URIs)", RFC 5785, April
April 2010. 2010.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011. Protocol (XMPP): Core", RFC 6120, March 2011.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011. Security (TLS)", RFC 6125, March 2011.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, August 2012.
[XEP-0220] [XEP-0220]
Miller, J., Saint-Andre, P., and P. Hancke, "Server Miller, J., Saint-Andre, P., and P. Hancke, "Server
Dialback", XSF XEP 0220, August 2013. Dialback", XSF XEP 0220, September 2013.
12.2. Informative References 12.2. Informative References
[RFC2142] Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND
FUNCTIONS", RFC 2142, May 1997.
[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence [RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004. Protocol (XMPP): Core", RFC 3920, October 2004.
[XEP-0045] [XEP-0045]
Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February
February 2012. 2012.
[XEP-0238] [XEP-0238]
Saint-Andre, P., "XMPP Protocol Flows for Inter-Domain Saint-Andre, P., "XMPP Protocol Flows for Inter-Domain
Federation", XSF XEP 0238, March 2008. Federation", XSF XEP 0238, March 2008.
[XEP-0288] [XEP-0288]
Hancke, P. and D. Cridland, "Bidirectional Server-to- Hancke, P. and D. Cridland, "Bidirectional Server-to-
Server Connections", XSF XEP 0288, August 2012. Server Connections", XSF XEP 0288, September 2013.
Authors' Addresses Authors' Addresses
Peter Saint-Andre Peter Saint-Andre
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: psaintan@cisco.com Email: psaintan@cisco.com
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