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Versions: (draft-miller-posh) 00 01 02 03 04
05 06 RFC 7711
XMPP Working Group M. Miller
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track P. Saint-Andre
Expires: August 27, 2015 &yet
February 23, 2015
PKIX over Secure HTTP (POSH)
draft-ietf-xmpp-posh-04
Abstract
Experience has shown that it is extremely difficult to deploy proper
PKIX certificates for TLS in multi-tenanted environments. As a
result, domains hosted in such environments often deploy applications
using certificates that identify the hosting service, not the hosted
domain. Such deployments force end users and peer services to accept
a certificate with an improper identifier, resulting in obvious
security implications. This document defines two methods that make
it easier to deploy certificates for proper server identity checking
in non-HTTP application protocols. While these methods developed for
use in the Extensible Messaging and Presence Protocol (XMPP) as a
Domain Name Association (DNA) prooftype, they might also be usable in
other non-HTTP application protocols.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 27, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Obtaining Verification Materials . . . . . . . . . . . . . . 4
3.1. Source Domain Possesses PKIX Certificate Information . . 5
3.2. Source Domain References PKIX Certificate . . . . . . . . 7
3.3. Performing Verification . . . . . . . . . . . . . . . . . 8
4. Secure Delegation . . . . . . . . . . . . . . . . . . . . . . 8
5. Order of Operations . . . . . . . . . . . . . . . . . . . . . 8
6. Caching Results . . . . . . . . . . . . . . . . . . . . . . . 10
7. Alternates and Roll-over . . . . . . . . . . . . . . . . . . 10
8. Guidelines for Protocols that Use POSH . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Security Considerations . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
We begin with a thought experiment.
Imagine that you work on the operations team of a hosting company
that provides the "SPICE" service (or email or instant messaging or
social networking service) for ten thousand different customer
organizations. Each customer wants their service to be identified by
the customer's domain name (e.g., bar.example.com), not the hosting
company's domain name (e.g., hosting.example.net).
In order to properly secure each customer's "SPICE" service via
Transport Layer Security (TLS) [RFC5246], you need to obtain PKIX
certificates [RFC5280] containing identifiers such as
bar.example.com, as explained in the "CertID" specification
[RFC6125]. Unfortunately, you can't obtain such certificates
because:
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o Certification authorities won't issue such certificates to you
because you work for the hosting company, not the customer
organization.
o Customers won't obtain such certificates and then give them (plus
the associated private keys) to you because their legal department
is worried about liability.
o You don't want to install such certificates (plus the associated
private keys) on your servers anyway because your legal department
is worried about liability, too.
o Even if your legal department is happy, this still means managing
one certificate for each customer across the infrastructure,
contributing to a large administrative load.
Given your inability to deploy public keys / certificates containing
the right identifiers, your back-up approach has always been to use a
certificate containing hosting.example.net as the identifier.
However, more and more customers and end users are complaining about
warning messages in user agents and the inherent security issues
involved with taking a "leap of faith" to accept the identity
mismatch between what [RFC6125] calls the Source Domain
(bar.example.com) and the Delegated Domain (hosting.example.net).
This situation is both insecure and unsustainable. You have
investigated the possibility of using DNS Security [RFC4033] and DNS-
Based Authentication of Named Entities (DANE) [RFC6698] to solve the
problem. However, your customers and your operations team have told
you that it will be several years before they will be able to deploy
DNSSEC and DANE for all of your customers (because of tooling
updates, slow deployment of DNSSEC at some top-level domains, etc.).
The product managers in your company are pushing you to find a method
that can be deployed more quickly to overcome the lack of proper
server identity checking for your hosted customers.
One possible approach that your team has investigated is to ask each
customer to provide the public key / certificate for the "SPICE"
service at a special HTTPS URL on their website
("https://bar.example.com/.well-known/posh.spice.json" is one
possibility). This could be a public key that you generate for the
customer, but because the customer hosts it via HTTPS, any user agent
can find that public key and check it against the public key you
provide during TLS negotiation for the "SPICE" service (as one added
benefit, the customer never needs to hand you a private key).
Alternatively, the customer can redirect requests for that special
HTTPS URL to an HTTPS URL at your own website, thus making it
explicit that they have delegated the "SPICE" service to you.
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The approach sketched out above, called POSH ("PKIX Over Secure
HTTP"), is explained in the remainder of this document. While this
approach was developed for use in the Extensible Messaging and
Presence Protocol (XMPP) as a prooftype for Domain Name Associations
(DNA) [I-D.ietf-xmpp-dna], it can be applied to any non-HTTP
application protocol.
2. Terminology
This document inherits security terminology from [RFC5280]. The
terms "Source Domain", "Delegated Domain", "Derived Domain", and
"Reference Identifier" are used as defined in the "CertID"
specification [RFC6125].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
Additionally, this document uses the following terms:
POSH client: The client utilizing the application service (e.g., an
XMPP client). It relies on the protocol defined herein to verify
the POSH server's identity.
POSH server: The server hosting the application service (e.g., an
XMPP server). It expects clients to rely on the protocol defined
herein to verify its identity.
3. Obtaining Verification Materials
Server identity checking (see [RFC6125]) involves three different
aspects:
1. A proof of the POSH server's identity (in PKIX, this takes the
form of a PKIX end-entity certificate [RFC5280]).
2. Rules for checking the certificate (which vary by application
protocol, although [RFC6125] attempts to harmonize those rules).
3. The materials that a POSH client uses to verify the POSH server's
identity or check the POSH server's proof (in PKIX, this takes
the form of chaining the end-entity certificate back to a trusted
root and performing all validity checks as described in
[RFC5280], [RFC6125], and the relevant application protocol
specification).
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When POSH is used, the first two aspects remain the same: the POSH
server proves it identity by presenting a PKIX certificate [RFC5280]
and the certificate is checked according to the rules defined in the
appropriate application protocol specification (such as [RFC6120] for
XMPP). However, the POSH client obtains the materials it will use to
verify the server's proof by retrieving a JSON document [RFC7159]
containing hashes of the PKIX certificate over HTTPS ([RFC7230] and
[RFC2818]) from a well-known URI [RFC5785] at the Source Domain.
(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
follows.
1. The POSH client performs an HTTPS GET request at the Source
Domain to the path "/.well-known/posh.{servicedesc}.json". The
value of "{servicedesc}" is application-specific; see Section 9
of this document for more details. For example, if the
application protocol is some hypothetical "SPICE" service, then
"{servicedesc}" could be "spice"; thus if an application client
were to use POSH to verify an application server for the Source
Domain "bar.example.com", the HTTPS GET request would be as
follows:
GET /.well-known/posh.spice.json HTTP/1.1
Host: bar.example.com
2. The Source Domain HTTPS server responds in one of three ways:
* If it possesses PKIX certificate information for the requested
path, it responds as detailed in Section 3.1.
* If it has a reference to where the PKIX certificate
information can be obtained, it responds as detailed in
Section 3.2.
* If it does not have any PKIX certificate information or a
reference to such information for the requested path, it
responds with an HTTP client error status code (e.g., 404).
3.1. Source Domain Possesses PKIX Certificate Information
If the Source Domain HTTPS server possesses the certificate
information, it responds to the HTTPS GET request with a success
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status code and the message body set to a JSON document [RFC7159];
the document is a JSON object which MUST have the following:
o A "fingerprints" field whose value is a JSON array of fingerprint
descriptors.
o An "expires" field whose value is a JSON number specifying the
number of seconds after which the POSH client ought to consider
the key information to be stale (further explained under
Section 6).
The JSON document returned MUST NOT contain a "url" field as
described in Section 3.2.
Each included fingerprint descriptor is a JSON object, where each
member name is the textual name of a hash function (as listed in
[HASH-NAMES]) and its associated value is the base 64 encoded
fingerprint hash generated using the named hash function (where the
encoding adheres to the definition in Section 4 of [RFC4648] and
where the padding bits are set to zero). Each fingerprint descriptor
MUST possess at least one named hash function.
The fingerprint hash for a given hash algorithm is generated by
performing the named hash function over the DER encoding of the PKIX
X.509 certifiate; for example, a "sha-1" fingerprint is generated by
performing the SHA-1 hash function over the DER encoding of the PKIX
certificate.
The following example illustrates the usage described above.
Example Content Response
HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 134
{
"fingerprints": [
{
"sha-1":"UpjRI/A3afKE8/AIeTZ5o1dECTY=",
"sha-256":"4/mggdlVx8A3pvHAWW5sD+qJyMtUHgiRuPjVC48N0XQ="
}
],
"expires": 604800
}
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The "expires" value is a hint regarding the expiration of the keying
materials. It MUST be a non-negative integer. If no "expires" field
is included or its value is equal to 0, a POSH client SHOULD consider
these verification materials invalid. See Section 6 for how to
reconcile this "expires" field with the reference's "expires" field.
3.2. Source Domain References PKIX Certificate
If the Source Domain HTTPS server has a reference to the certificate
information, it responds to the HTTPS GET request with a success
status code and message body set to a JSON document. The document is
a JSON object which MUST contain the following:
o A "url" field whose value is a JSON string specifying the HTTPS
URL where POSH clients can obtain the actual certificate
information.
o An "expires" field whose value is a JSON number specifying the
number of seconds after which the POSH client ought to consider
the delegation to be stale (further explained under Section 6).
Example Reference Response
HTTP/1.1 200 Ok
Content-Type: application/json
Content-Length: 79
{
"url":"https://hosting.example.net/.well-known/posh.spice.json",
"expires":86400
}
The client performs an HTTPS GET request for the URL specified in the
"url" field value. The HTTPS server for the URL to which the client
has been redirected responds to the request with a JSON document
containing fingerprints as described in Section 3.1. The content
retrieved from the "url" location MUST NOT itself be a reference
(i.e., containing a "url" field instead of a "fingerprints" field),
in order to prevent circular delegations.
Note: See Section 10 for discussion about HTTPS redirects.
The "expires" value is a hint regarding the expiration of the Source
Domain's delegation of service to the Delegated Domain. It MUST be a
non-negative integer. If no "expires" field is included or its value
is equal to 0, a POSH client SHOULD consider the delegation invalid.
See Section 6 for guidelines about reconciling this "expires" field
with the "expires" field of the fingerprints document.
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3.3. Performing Verification
The POSH client compares the PKIX information obtained from the POSH
server against each fingerprint descriptor object in the POSH
results, until a match is found using the hash functions that the
client suports, or until the collection of POSH verification
materials is exhausted. If none of the fingerprint descriptor
objects match the POSH server PKIX information, the POSH client
SHOULD reject the connection (however, the POSH client might still
accept the connection if other verification schemes are successful).
4. Secure Delegation
The delegation from the Source Domain to the Delegated Domain can be
considered secure if the credentials offered by the POSH server match
the verification materials possessed by the client, regardless of how
those materials are obtained.
5. Order of Operations
In order for the POSH client to perform verification of Reference
Identifiers without potentially compromising data, POSH processes
MUST be complete before any application-layer data is exchanged for
the Source Domain. In cases where the POSH client initiates an
application-layer connection, the client SHOULD perform all POSH
retrievals before initiating a connection (naturally this is not
possible in cases where the POSH client receives an application-layer
connection). For application protocols that use DNS SRV (including
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
parallel with resolving the SRV records and the addresses of any
targets, similar to the "happy eyeballs" approach for IPv4 and IPv6
[RFC6555].
The following diagram illustrates the possession flow:
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Client Domain Server
------ ------ ------
| | |
| Request POSH | |
|------------------------->| |
| | |
| Return POSH fingerprints | |
|<-------------------------| |
| | |
| Service TLS Handshake |
|<===================================================>|
| | |
| Service Data |
|<===================================================>|
| | |
Figure 1: Order of Events for Possession Flow
While the following diagram illustrates the reference flow:
Client Domain Server
------ ------ ------
| | |
| Request POSH | |
|------------------------->| |
| | |
| Return POSH url | |
|<-------------------------| |
| | |
| Request POSH |
|---------------------------------------------------->|
| | |
| Return POSH fingerprints |
|<----------------------------------------------------|
| | |
| Service TLS Handshake |
|<===================================================>|
| | |
| Service Data |
|<===================================================>|
| | |
Figure 2: Order of Events for Reference Flow
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6. Caching Results
The POSH client MUST NOT cache results (reference or fingerprints)
indefinitely. If the Source Domain returns a reference, the POSH
client MUST use the lower of the two "expires" values when
determining how long to cache results (i.e., if the reference
"expires" value is lower than the fingerprints "expires" value, honor
the reference "expires" value). Once the POSH client considers the
results stale, it needs to perform the entire POSH process again
starting with the HTTPS GET request to the Source Domain. The POSH
client MAY use a lower value than any provided in the "expires"
field(s), or not cache results at all.
The POSH client SHOULD NOT rely on HTTP caching mechanisms, instead
using the expiration hints provided in the POSH reference document or
fingerprints documents. To that end, the HTTPS servers for Source
Domains and Derived Domains SHOULD specify a 'Cache-Control' header
indicating a very short duration (e.g., max-age=60) or "no-cache" to
indicate that the response (redirect, reference, or content) is not
appropriate to cache at the HTTP layer.
7. Alternates and Roll-over
To indicate alternate PKIX certificates (such as when an existing
certificate will soon expire), the returned fingerprints document MAY
contain multiple fingerprint descriptors. The fingerprints SHOULD be
ordered with the most relevant certificate first as determined by the
application service operator (e.g., the renewed certificate),
followed by the next most relevant certificate (e.g., the certificate
soonest to expire). Here is an example:
{
"fingerprints": [
{
"sha-1":"UpjRI/A3afKE8/AIeTZ5o1dECTY=",
"sha-256":"4/mggdlVx8A3pvHAWW5sD+qJyMtUHgiRuPjVC48N0XQ"
},
{
"sha-1":"T29tGO9d7kxbfWnUaac8+5+ICLM=",
"sha-256":"otyLADSKjRDjVpj8X7/hmCAD5C7Qe+PedcmYV7cUncE="
}
],
"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.
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8. Guidelines for Protocols that Use POSH
Protocols that use POSH will need to register well-known URIs wth the
IANA in accordance with [RFC5785] (the IANA registration policy
[RFC5226] for well-known URIs is Specification Required).
For the sake of consistency, it would be best if the URIs registered
by such protocols match the URI template [RFC6570] path "/.well-
known/posh.{servicedesc}.json"; that is, begin with "posh." and end
with ".json" (indicating a media type of application/json [RFC7159]).
For POSH-using protocols that rely on DNS SRV records [RFC2782], it
would be best if the "{servicedesc}" part of the well-known URI is
"{service}.{proto}", where the "{service}" is the DNS SRV "Service"
prepended by the underscore character "_" and the "{proto}" is the
DNS SRV "Proto" also prepended by the underscore character "_". As
an example, the well-known URI for XMPP server-to-server connections
would be "posh._xmpp-server._tcp.json" since XMPP [RFC6120] registers
a service name of "xmpp-server" and uses TCP as the underlying
transport protocol.
For other POSH-using protocols, the "{servicedesc}" part of the well-
known URI can be any unique string or identifier for the protocol,
which might be a service name registered with the IANA in accordance
with [RFC6335] or which might be an unregistered name. As an
example, the well-known URI for a hypothetical "SPICE" application
could be "posh.spice.json".
9. IANA Considerations
This document requests no actions of IANA. [Note to RFC Editor:
please remove this section before publication.]
10. Security Considerations
This document supplements but does not supersede the security
considerations provided in specifications for application protocols
that decide to use POSH (e.g., [RFC6120] and [RFC6125] for XMPP).
Specifically, the security of requests and responses sent via HTTPS
depends on checking the identity of the HTTP server in accordance
with [RFC2818]. Additionally, the security of POSH can benefit from
other HTTP hardening protocols, such as HSTS [RFC6797] and key
pinning [I-D.ietf-websec-key-pinning], especially if the POSH client
shares some information with a common HTTPS implementation (e.g.,
platform-default web browser).
Note well that POSH is used by a POSH client to obtain the public key
of a POSH server to which it might connect for a particular
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application protocol such as IMAP or XMPP. POSH does not enable a
hosted domain to transfer private keys to a hosting service via
HTTPS. POSH also does not enable a POSH server to engage in
certificate enrollment with a certification authority via HTTPS, as
is done in Enrollment over Secure Transport [RFC7030].
A web server at the Source Domain might redirect an HTTPS request to
another URL. The location provided in the redirect response MUST
specify an HTTPS URL. Source domains SHOULD use only temporary
redirect mechanisms, such as HTTP status codes 302 (Found) and 307
(Temporary Redirect). Clients MAY treat any redirect as temporary,
ignoring the specific semantics for 301 (Moved Permanently) and 308
(Permanent Redirect) [RFC7238]. To protect against circular
references, it is RECOMMENDED that POSH clients follow no more than
10 redirects, although applications or implementations can require
that fewer redirects be followed.
Hash function agility is an important quality to ensure secure
operations in the face of attacks against the fingerprints obtained
within verification 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.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[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.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785, April
2010.
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[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.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, June
2014.
11.2. Informative References
[I-D.ietf-dane-srv]
Finch, T., Miller, M., and P. Saint-Andre, "Using DNS-
Based Authentication of Named Entities (DANE) TLSA Records
with SRV Records", draft-ietf-dane-srv-11 (work in
progress), February 2015.
[I-D.ietf-websec-key-pinning]
Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
Extension for HTTP", draft-ietf-websec-key-pinning-21
(work in progress), October 2014.
[I-D.ietf-xmpp-dna]
Saint-Andre, P., Miller, M., and P. Hancke, "Domain Name
Associations (DNA) in the Extensible Messaging and
Presence Protocol (XMPP)", draft-ietf-xmpp-dna-09 (work in
progress), February 2015.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
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[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165, RFC
6335, August 2011.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570, March 2012.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, August 2012.
[RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)", RFC 6797, November 2012.
[RFC7030] Pritikin, M., Yee, P., and D. Harkins, "Enrollment over
Secure Transport", RFC 7030, October 2013.
[RFC7238] Reschke, J., "The Hypertext Transfer Protocol Status Code
308 (Permanent Redirect)", RFC 7238, June 2014.
[HASH-NAMES]
"Hash Function Textual Names",
<http://www.iana.org/assignments/hash-function-text-names/
hash-function-text-names.xhtml>.
Appendix A. Acknowledgements
Many thanks to Thijs Alkemade, Philipp Hancke, Joe Hildebrand, and
Tobias Markmann for their implementation feedback. Thanks also to
Dave Cridland, Chris Newton, Max Pritikin, and Joe Salowey for their
input on the specification.
Authors' Addresses
Matthew Miller
Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600
Denver, CO 80202
USA
Email: mamille2@cisco.com
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Internet-Draft POSH February 2015
Peter Saint-Andre
&yet
Email: peter@andyet.com
URI: https://andyet.com/
Miller & Saint-Andre Expires August 27, 2015 [Page 15]
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