DANE R. Barnes
Internet-Draft BBN Technologies
Intended status: Informational April 19, 2011
Expires: October 21, 2011
Use Cases and Requirements for DNS-based Authentication of Named
Entities
draft-ietf-dane-use-cases-00.txt
Abstract
Many current applications use the certificate-based authentication
features in TLS to allow clients to verify that a connected server
properly represents a desired domain name. Traditionally, this
authentication has been based on PKIX trust hierarchies, rooted in
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 and DNSSEC could be used to make assertions that support the TLS
authentication process.
Status of this Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on October 21, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. CA Constraints . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Certificate Constraints . . . . . . . . . . . . . . . . . . 5
3.3. Domain-Issued Certificates . . . . . . . . . . . . . . . . 5
4. Other Requirements . . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
Transport-Layer Security or TLS is used as the basis for security
features in many modern Internet applications [RFC5246]. It is used
as the basis for secure HTTP and secure email
[RFC2818][RFC2595][RFC3207], and provides hop-by-hop security in
real-time multimedia and instant-messaging protocols
[RFC3261][RFC6120].
One feature that is common to most uses of TLS is the use of
certificates to authenticate domain names for services. The TLS
client begins the TLS connection process with the goal of connecting
to a server with a specific domain name. After locating 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
itself [RFC5280]. Based on this certificate, the client decides
whether the server properly represents the desired domain name, and
thus whether to proceed with the TLS connection or not.
In most current applications, this decision process is based on PKIX
validation and name matching. The client validates that the
certificate chains to a trust anchor [RFC5280], and that the desired
domain name is contained in the certificate [RFC6125]. Within this
framework, bindings between public keys and domain names are asserted
by PKIX CAs. Authentication decisions based on these bindings rely
on the authority of these CAs.
The DNS is built to provide information about domain names, and with
the advent of DNSSEC [RFC1034][RFC4033], it is possible for this
information to be provided securely (in the sense that clients can
verify that DNS information was provided by the domain owner). One
of the goals of the current DANE working group is to develop
technologies for using the DNS to provide additional information to
inform the TLS domain authentication process. This document
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
mechanism should satisfy.
2. Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
This document also makes use of standard PKIX, DNSSEC, and TLS
terminology. See RFC 5280 [RFC5280], RFC 4033 [RFC4033], and RFC
5246 [RFC5246], respectively, for these terms.
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3. Use Cases
In this section, we describe the two major use cases that the DANE
mechanism should support. This list is not intended to represent all
possible ways that the DNS can be used to support TLS authentication.
Rather it represents the specific cases that comprise the initial
goal for DANE.
In the below use cases, we will refer to the following dramatis
personae:
Alice The operator of a TLS-based service on the host
alice.example.com, and administrator of the corresponding DNS
zone.
Bob A client connecting to alice.example.com
Charlie A well-known CA that issues certificates with domain names
as identifiers
3.1. CA Constraints
Alice runs a website on alice.example.com and has obtained a
certificate from the well-known CA Charlie. She is concerned about
mis-issued certificates and would like to provide a mechanism for
visitors to her site to know that they should expect
alice.example.com to use a certificate issued by the CA that she uses
(Charlie) and not another CA.
When Bob connects to alice.example.com, he uses this mechanism to
verify that that the certificate presented by the server was issued
by the proper CA, Charlie. Bob also performs the normal PKIX
validation procedure for this certificate, in particular verifying
that the certificate chains to a trust anchor.
Because these constraints do not increase the scope of PKIX-based
assertions about domains, there is not a strict requirement for
DNSSEC. Deletion of records removes the protection provided by this
constraint, but the client is still protected by CA practices (as
now). Injected or modified false records are not useful unless the
attacker can also obtain an unauthorized certificate. In the worst
case, tampering with these constraints degrades security to the level
that is now standard.
Continuing to require PKIX validation also limits the degree to which
DNS operators can interfere with TLS authentication through this
mechanism. As above, even if a DNS operator falsifies DANE records,
it cannot masquerade as the target server unless it can also obtain
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an unauthorized certificate.
3.2. Certificate Constraints
Alice runs a website on alice.example.com and has obtained a
certificate from the well-known CA Charlie. She is concerned about
certificates being issued by Charlie as well as 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 specific certificate
issued by Charlie.
When Bob connects to alice.example.com, he uses this mechanism to
verify that that the certificate presented by the server is the
correct certificate. Bob also performs the normal PKIX validation
procedure for this certificate, in particular verifying that the
certificate chains to a trust anchor.
The security considerations for this case are the same as for the "CA
Constraints" case above.
3.3. Domain-Issued Certificates
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
all. Alice can generate her own certificates today, making self-
signed certificates and possibly certificates subordinate to those
certificates. When Bob receives such a certificate, however, he
doesn't have a way to verify that the issuer of the certificate is
actually Alice. This concerns him as an attacker could present a
different certificate and perform a man in the middle attack. Bob
would like to protect against this.
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
connects to alice.example.com, he uses this mechanism to verify that
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
as a trust anchor for purposes of validating certificates for
alice.example.com. Alice can additionally recommend that clients
accept only her certificates using the CA constraints described
above.
Providing trust anchor material in this way clearly requires DNSSEC,
since corrupted or injected records could be used by an attacker to
cause clients to trust an attacker's certificate. Deleted records
will only result in connection failure and denial of service,
although this could result on a bid-down to an unsecured protocol,
depending on the application.
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By the same token, this use case puts the most power in the hands of
DNS operators. Since the operator of the appropriate DNS zone has de
facto control over the content and signing of the zone, he can create
false DANE records that bind a malicious party's certificate to a
domain. This is not a significant incremental risk relative to the
current PKIX-based system, however, since it is possible for domain
operators to obtain certificates for domains under some well-known
certificate authorities today.
4. Other Requirements
In addition to supporting the above use cases, the DANE mechanism
must satisfy several lower-level operational and protocol
requirements and goals.
Multiple Ports: DANE should be able to support multiple services
with different credentials on the same named host, distinguished
by port number.
Simple Key Management: DANE must have a mode in which the domain
owner only needs to maintain a single long-lived public/private
key pair.
Hard Failure: Clients must be required to refuse to proceed with a
connection to a site if DANE indicates a security error.
Encapsulation: If there is a DANE record for the name
alice.example.com, it must only affect services hosted at
alice.example.com.
Predictability: Client behavior in response to DANE records must be
spelled out in the DANE specification as precisely as possible.
Minimal Dependencies: It should be possible for a site to deploy
DANE without also deploying anything else, except DNSSEC.
Minimal Options: Ideally, DANE should have only one operating mode.
Practically, DANE should have as few operating modes as possible.
Wild Cards and CNAME: The mechanism for DANE record distribution
should be compatible with the use of DNS wild cards and CNAME
records for setting default properties for domains and redirecting
services.
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5. Acknowledgements
Thanks to Eric Rescorla for the initial formulation of the use cases,
Zack Weinberg and Phillip Hallam-Baker for contributing other
requirements, and the whole DANE working group for helpful comments
on the mailing list.
6. IANA Considerations
This document makes no request of IANA.
7. Security Considerations
The primary focus of this document is the enhancement of TLS
authentication procedures using the DNS. The general effect of such
mechanisms is to increase the role of DNS operators in authentication
processes, either in place of or in addition to traditional third-
party actors such as commercial certificate authorities. The
specific security implications of the respective use cases are
discussed in their respective sections above.
8. References
8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
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8.2. Informative References
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
Author's Address
Richard Barnes
BBN Technologies
9861 Broken Land Parkway
Columbia, MD 21046
US
Phone: +1 410 290 6169
Email: rbarnes@bbn.com
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