draft-ietf-dane-use-cases-01.txt   draft-ietf-dane-use-cases-02.txt 
DANE R. Barnes DANE R. Barnes
Internet-Draft BBN Technologies Internet-Draft BBN Technologies
Intended status: Informational April 22, 2011 Intended status: Informational April 29, 2011
Expires: October 24, 2011 Expires: October 31, 2011
Use Cases and Requirements for DNS-based Authentication of Named Use Cases and Requirements for DNS-based Authentication of Named
Entities (DANE) Entities (DANE)
draft-ietf-dane-use-cases-01.txt draft-ietf-dane-use-cases-02.txt
Abstract Abstract
Many current applications use the certificate-based authentication Many current applications use the certificate-based authentication
features in TLS to allow clients to verify that a connected server features in TLS to allow clients to verify that a connected server
properly represents a desired domain name. Traditionally, this properly represents a desired domain name. Traditionally, this
authentication has been based on PKIX trust hierarchies, rooted in authentication has been based on PKIX trust hierarchies, rooted in
well-known CAs, but additional information can be provided via the well-known CAs, but additional information can be provided via the
DNS itself. This document describes a set of use cases in which the DNS itself. This document describes a set of use cases in which the
DNS and DNSSEC could be used to make assertions that support the TLS DNS and DNSSEC could be used to make assertions that support the TLS
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This Internet-Draft will expire on October 24, 2011. This Internet-Draft will expire on October 31, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. CA Constraints . . . . . . . . . . . . . . . . . . . . . . 4 3.1. CA Constraints . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Certificate Constraints . . . . . . . . . . . . . . . . . . 5 3.2. Certificate Constraints . . . . . . . . . . . . . . . . . 5
3.3. Domain-Issued Certificates . . . . . . . . . . . . . . . . 5 3.3. Domain-Issued Certificates . . . . . . . . . . . . . . . . 6
4. Other Requirements . . . . . . . . . . . . . . . . . . . . . . 6 3.4. Delegated Services . . . . . . . . . . . . . . . . . . . . 7
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 3.5. Opportunistic Security . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 3.6. Web Services . . . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 8 4. Other Requirements . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction 1. Introduction
Transport-Layer Security or TLS is used as the basis for security Transport-Layer Security or TLS is used as the basis for security
features in many modern Internet applications [RFC5246]. It features in many modern Internet applications [RFC5246]. It
underlies secure HTTP and secure email [RFC2818][RFC2595][RFC3207], underlies secure HTTP and secure email [RFC2818][RFC2595][RFC3207],
and provides hop-by-hop security in real-time multimedia and instant- and provides hop-by-hop security in real-time multimedia and instant-
messaging protocols [RFC3261][RFC6120]. messaging protocols [RFC3261][RFC6120].
One feature that is common to most uses of TLS is the use of One feature that is common to most uses of TLS is the use of
certificates to authenticate domain names for services. The TLS certificates to authenticate domain names for services. The TLS
client begins the TLS connection process with the goal of connecting client begins the TLS connection process with the goal of connecting
to a server with a specific domain name. After locating the server to a server with a specific domain name. (The process of obtaining
via an A or AAAA record, the client conducts a TLS handshake with the this domain name is application-specific. It could be entered by a
user or found through an automated discovery process, e.g., via an
SRV or NAPTR record.) After obtaining the address of the server via
an A or AAAA record, the client conducts a TLS handshake with the
server, during which the server presents a PKIX certificate for server, during which the server presents a PKIX certificate for
itself [RFC5280]. Based on this certificate, the client decides itself [RFC5280]. Based on this certificate, the client decides
whether the server properly represents the desired domain name, and whether the server properly represents the desired domain name, and
thus whether to proceed with the TLS connection or not. thus whether to proceed with the TLS connection or not.
In most current applications, this decision process is based on PKIX In most current applications, this decision process is based on PKIX
validation and name matching. The client validates that the validation and application-specific name matching. The client
certificate chains to a trust anchor [RFC5280], and that the desired validates that the certificate chains to a trust anchor [RFC5280],
domain name is contained in the certificate [RFC6125]. Within this and that the desired domain name is contained in the certificate
framework, bindings between public keys and domain names are asserted [RFC6125]. Within this framework, bindings between public keys and
by PKIX CAs. Authentication decisions based on these bindings rely domain names are asserted by PKIX CAs. Authentication decisions
on the authority of these CAs. based on these bindings rely on the authority of these CAs.
The DNS is built to provide information about domain names, and with The DNS is built to provide information about domain names, and with
the advent of DNSSEC [RFC1034][RFC4033], it is possible for this the advent of DNSSEC [RFC1034][RFC4033], it is possible for this
information to be provided securely, in the sense that clients can information to be provided securely, in the sense that clients can
verify that DNS information was provided by the domain owner. The verify that DNS information was provided by the domain owner. The
goal of technologies for DNS-based Authentication of Named Entities goal of technologies for DNS-based Authentication of Named Entities
(DANE) is to use the DNS and DNSSEC to provide additional information (DANE) is to use the DNS and DNSSEC to provide additional information
to inform the TLS domain authentication process. This document to inform the TLS domain authentication process. This document
describes a set of use cases that capture specific goals for using describes a set of use cases that capture specific goals for using
the DNS in this way, and a set of requirements that the ultimate DANE the DNS in this way, and a set of requirements that the ultimate DANE
mechanism should satisfy. mechanism should satisfy.
2. Definitions 2. Definitions
This document also makes use of standard PKIX, DNSSEC, and TLS This document also makes use of standard PKIX, DNSSEC, and TLS
terminology. See RFC 5280 [RFC5280], RFC 4033 [RFC4033], and RFC terminology. See RFC 5280 [RFC5280], RFC 4033 [RFC4033], and RFC
5246 [RFC5246], respectively, for these terms. 5246 [RFC5246], respectively, for these terms.
Note in particular that the term "server" in this document refers to
the server role in TLS, rather than to a host. Multiple servers of
this type may be co-located on a single physical host, using
different ports, and each of these can use different certificates.
3. Use Cases 3. Use Cases
In this section, we describe the major use cases that the DANE In this section, we describe the major use cases that the DANE
mechanism should support. This list is not intended to represent all mechanism should support. This list is not intended to represent all
possible ways that the DNS can be used to support TLS authentication. possible ways that the DNS can be used to support TLS authentication.
Rather it represents the specific cases that comprise the initial Rather it represents the specific cases that comprise the initial
goal for DANE. goal for DANE.
In the below use cases, we will refer to the following dramatis In the below use cases, we will refer to the following dramatis
personae: personae:
Alice The operator of a TLS-protected service on the host Alice The operator of a TLS-protected service on the host
alice.example.com, and administrator of the corresponding DNS alice.example.com, and administrator of the corresponding DNS
zone. zone.
Bob A client connecting to alice.example.com Bob A client connecting to alice.example.com
Charlie A well-known CA that issues certificates with domain names Charlie A well-known CA that issues certificates with domain names
as identifiers as identifiers
Oscar An outsourcing provider that operates TLS-protected services
on behalf of customers
Trent A CA that issues certificates with domain names as
identifiers, but is not generally well-known.
These use cases are framed in terms of adding protections to TLS These use cases are framed in terms of adding protections to TLS
server certificates, since the use of these certificates to server certificates, since the use of these certificates to
authenticate server domain names is very common. In applications authenticate server domain names is very common. In applications
where TLS clients are also identified by domain names (e.g., XMPP where TLS clients are also identified by domain names (e.g., XMPP
server-to-server connections), the same considerations and use cases server-to-server connections), the same considerations and use cases
can also be applied to TLS client certificates. can also be applied to TLS client certificates.
3.1. CA Constraints 3.1. CA Constraints
Alice runs a website on alice.example.com and has obtained a Alice runs a website on alice.example.com and has obtained a
certificate from the well-known CA Charlie. She is concerned that certificate from the well-known CA Charlie. She is concerned that
other well-known CAs might issue certificates for alice.example.com other well-known CAs might issue certificates for alice.example.com
without her authorization, which clients would accept. Alice would without her authorization, which clients would accept. Alice would
like to provide a mechanism for visitors to her site to know that like to provide a mechanism for visitors to her site to know that
they should expect alice.example.com to use a certificate issued they should expect alice.example.com to use a certificate issued
under the CA that she uses (Charlie) and not another CA. under the CA that she uses (Charlie) and not another CA. In TLS
terms, Alice is letting Bob know that Charlie's certificate must
appear somewhere in the server Certificate message's certificate_list
structure.
When Bob connects to alice.example.com, he uses this mechanism to When Bob connects to alice.example.com, he uses this mechanism to
verify that that the certificate presented by the server was issued verify that that the certificate presented by the server was issued
under the proper CA, Charlie. Bob also performs the normal PKIX under the proper CA, Charlie. Bob also performs the normal PKIX
validation procedure for this certificate, in particular verifying validation procedure for this certificate, in particular verifying
that the certificate chains to a trust anchor. that the certificate chains to a trust anchor.
Because these constraints do not increase the scope of PKIX-based Because these constraints do not increase the scope of PKIX-based
assertions about domains, there is not a strict requirement for assertions about domains, there is not a strict requirement for
DNSSEC. Deletion of records removes the protection provided by this DNSSEC. Deletion of records removes the protection provided by this
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target server unless it can also obtain a certificate for the target target server unless it can also obtain a certificate for the target
domain. domain.
3.2. Certificate Constraints 3.2. Certificate Constraints
Alice runs a website on alice.example.com and has obtained a Alice runs a website on alice.example.com and has obtained a
certificate from the well-known CA Charlie. She is concerned about certificate from the well-known CA Charlie. She is concerned about
additional, unauthorized certificates being issued by Charlie as well additional, unauthorized certificates being issued by Charlie as well
as by other CAs. She would like to provide a way for visitors to her as by other CAs. She would like to provide a way for visitors to her
site to know that they should expect alice.example.com to present the site to know that they should expect alice.example.com to present the
specific certificate issued by Charlie. specific certificate issued by Charlie. In TLS terms, Alice is
letting Bob know that this specific certificate must be the first
certificate in the server Certificate message's certificate_list
structure.
When Bob connects to alice.example.com, he uses this mechanism to When Bob connects to alice.example.com, he uses this mechanism to
verify that that the certificate presented by the server is the verify that that the certificate presented by the server is the
correct certificate. Bob also performs the normal PKIX validation correct certificate. Bob also performs the normal PKIX validation
procedure for this certificate, in particular verifying that the procedure for this certificate, in particular verifying that the
certificate chains to a trust anchor. certificate chains to a trust anchor.
The security considerations for this case are the same as for the "CA As in Section 3.1., Alice's assertions about server certificates can
Constraints" case above. be used to constrain the behavior of an outsourcing provider Oscar as
well as the CA Charlie and other CAs. Such a certificate constraint
requires Oscar to present the specified certificate to clients and
not another.
The other security considerations for this case are the same as for
the "CA Constraints" case above.
3.3. Domain-Issued Certificates 3.3. Domain-Issued Certificates
Alice would like to be able to use generate and use certificates for Alice would like to be able to use generate and use certificates for
her website on alice.example.com without involving an external CA at her website on alice.example.com without involving an external CA at
all. Alice can generate her own certificates today, making self- all. Alice can generate her own certificates today, making self-
signed certificates and possibly certificates subordinate to those signed certificates and possibly certificates subordinate to those
certificates. When Bob receives such a certificate, however, he certificates. When Bob receives such a certificate, however, he
doesn't have a way to verify that the issuer of the certificate is doesn't have a way to verify that the issuer of the certificate is
actually Alice. This concerns him because an attacker could present actually Alice. This concerns him because an attacker could present
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Alice would thus like to have a mechanism for visitors to her site to Alice would thus like to have a mechanism for visitors to her site to
know that the certificates she issues are actually hers. When Bob know that the certificates she issues are actually hers. When Bob
connects to alice.example.com, he uses this mechanism to verify that connects to alice.example.com, he uses this mechanism to verify that
the certificate presented by the server was issued by Alice. Since the certificate presented by the server was issued by Alice. Since
Bob can bind certificates to Alice in this way, he can use Alice's CA Bob can bind certificates to Alice in this way, he can use Alice's CA
as a trust anchor for purposes of validating certificates for as a trust anchor for purposes of validating certificates for
alice.example.com. Alice can additionally recommend that clients alice.example.com. Alice can additionally recommend that clients
accept only her certificates using the CA constraints described accept only her certificates using the CA constraints described
above. above.
This use case is functionally equivalent to the case where Alice
doesn't issue her own certificates, but uses a CA Trent that is not
well-known. In this case, Alice would be advising Bob that he should
treat Trent as a trust anchor for purposes of validating Alice's
certificates, rather than a CA operated by Alice herself.
Alice's advertising of trust anchor material in this way does not
guarantee that Bob will accept the advertised trust anchor. For
example, Bob might have out-of-band information (such as a pre-
existing local policy) that indicates that the CA Trent advertised by
Alice is not trustworthy, which would lead him to decide not to
accept Trent as a TA, and thus to reject Alice's certificate if it is
issued under Trent.
Providing trust anchor material in this way clearly requires DNSSEC, Providing trust anchor material in this way clearly requires DNSSEC,
since corrupted or injected records could be used by an attacker to since corrupted or injected records could be used by an attacker to
cause clients to trust an attacker's certificate. Deleted records cause clients to trust an attacker's certificate. Deleted records
will only result in connection failure and denial of service, will only result in connection failure and denial of service,
although this could result in clients re-connecting without TLS (a although this could result in clients re-connecting without TLS (a
downgrade attack), depending on the application. Therefore, in order downgrade attack), depending on the application. Therefore, in order
for this use case to be safe, applications must forbid clients from for this use case to be safe, applications must forbid clients from
falling back to unsecured channels when records appear to have been falling back to unsecured channels when records appear to have been
deleted (e.g., when a missing record has no NSEC or NSEC3 record). deleted (e.g., when a missing record has no NSEC or NSEC3 record).
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This is not a significant incremental risk, however, relative to the This is not a significant incremental risk, however, relative to the
current PKIX-based system. In the current system, CAs need to verify current PKIX-based system. In the current system, CAs need to verify
that an entity requesting a certificate for a domain is actually the that an entity requesting a certificate for a domain is actually the
legitimate holder of that domain. Typically this is done using legitimate holder of that domain. Typically this is done using
information published about that domain, such as WHOIS email information published about that domain, such as WHOIS email
addresses or special records inserted into a domain. By manipulating addresses or special records inserted into a domain. By manipulating
these values, it is possible for DNS operators to obtain certificates these values, it is possible for DNS operators to obtain certificates
from some well-known certificate authorities today without from some well-known certificate authorities today without
authorization from the true domain owner. authorization from the true domain owner.
3.4. Delegated Services
In addition to guarding against CA mis-issue, CA constraints and
certificate constraints can also be used to constrain the set of
certificates that can be used by an outsourcing provider. Suppose
that Oscar operates alice.example.com on behalf of Alice. In
particular, Oscar then has de facto control over what certificates to
present in TLS handshakes for alice.example.com. In such cases,
there are few ways that DNS-based information about TLS certificates
could be configured, for example:
1. Alice has the A/AAAA records in her DNS and can sign them along
with the DANE record, but Oscar and Alice now need to have tight
coordination if the addresses and/or the certificates change.
2. Alice refers to Oscar's DNS by delegating a sub-domain name to
Oscar, and has no control over the A/AAAA, DANE or any other
pieces under Oscar's control.
3. Alice can put DANE records into her DNS server, but delegate the
address records to Diane's DNS server. This means that Alice can
control the usage of certificates but Diane is free to move the
servers around as needed. The only coordination needed is when
the certificates change, and then it would depend on how the DANE
record is setup (i.e. a CA or an EE certificate pointer).
Which of these deployment patterns is used in a given deployment will
determine what sort of constraints can be made. In cases where Alice
controls DANE records (1 and 3), she can use CA and certificate
constraints to control what certificates Oscar presents for Alice's
services. For instance, Alice might require Oscar to use
certificates under a given set of CAs. This control, however,
requires that Alice update DANE records when Oscar needs to change
certificates. Cases where Oscar controls DANE records allow Oscar to
maintain more autonomy from Alice, but by the same token, Alice
cannot make any requirements on the certificates that Oscar uses.
3.5. Opportunistic Security
Alice would like to to publish a web site so that Bob will always
have the benefit of the best security his client is capable of,
without resulting in a negative user experience when using a legacy
browser. For example, suppose that Bob uses two browsers on
different machines, one is a legacy browser that does not support
DANE and cannot be updated, the other is a browser that has full
support for DANE. In this case, the legacy browser should continue
to work as before, while the new browser should be able to discover
DANE support. In general, the DANE mechanism must allow a clients to
determine whether DANE security is available for a site.
3.6. Web Services
A web service is an HTTP-based Internet protocol designed to support
direct machine-to-machine communication without the intervention of a
human operator or other form of supervisor. Since web services are
application protocols, the one aspect of Internet architecture that
is essential as far as a Web Service is concerned is that the DNS be
used as the naming system for service discovery. Web Services
typically evolve over time. A service provider must frequently
support legacy clients alongside new and in many cases multiple
versions of each protocol. Discovering the certificates or keys to
be used to secure the connection to the Web service represents merely
one aspect of the more general problem of Web Service property
discovery.
4. Other Requirements 4. Other Requirements
In addition to supporting the above use cases, the DANE mechanism In addition to supporting the above use cases, the DANE mechanism
must satisfy several lower-level operational and protocol must satisfy several lower-level operational and protocol
requirements and goals. requirements and goals.
Multiple Ports: DANE should be able to support multiple services Multiple Ports: DANE should be able to support multiple services
with different credentials on the same named host, distinguished with different credentials on the same named host, distinguished
by port number. by port number.
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