Internet DRAFT - draft-ietf-httpbis-client-hints
draft-ietf-httpbis-client-hints
HTTP Working Group I. Grigorik
Internet-Draft Y. Weiss
Intended status: Experimental Google
Expires: January 4, 2021 July 3, 2020
HTTP Client Hints
draft-ietf-httpbis-client-hints-15
Abstract
HTTP defines proactive content negotiation to allow servers to select
the appropriate response for a given request, based upon the user
agent's characteristics, as expressed in request headers. In
practice, user agents are often unwilling to send those request
headers, because it is not clear whether they will be used, and
sending them impacts both performance and privacy.
This document defines an Accept-CH response header that servers can
use to advertise their use of request headers for proactive content
negotiation, along with a set of guidelines for the creation of such
headers, colloquially known as "Client Hints."
Note to Readers
Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/ [1].
Working Group information can be found at http://httpwg.github.io/
[2]; source code and issues list for this draft can be found at
https://github.com/httpwg/http-extensions/labels/client-hints [3].
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 https://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."
Grigorik & Weiss Expires January 4, 2021 [Page 1]
Internet-Draft HTTP Client Hints July 2020
This Internet-Draft will expire on January 4, 2021.
Copyright Notice
Copyright (c) 2020 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
Provisions Relating to IETF Documents
(https://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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 4
2. Client Hint Request Header Fields . . . . . . . . . . . . . . 4
2.1. Sending Client Hints . . . . . . . . . . . . . . . . . . 4
2.2. Server Processing of Client Hints . . . . . . . . . . . . 5
3. Advertising Server Support . . . . . . . . . . . . . . . . . 5
3.1. The Accept-CH Response Header Field . . . . . . . . . . . 5
3.2. Interaction with Caches . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
4.1. Information Exposure . . . . . . . . . . . . . . . . . . 7
4.2. Deployment and Security Risks . . . . . . . . . . . . . . 9
4.3. Abuse Detection . . . . . . . . . . . . . . . . . . . . . 9
5. Cost of Sending Hints . . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. Accept-CH . . . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . 11
A.1. Since -00 . . . . . . . . . . . . . . . . . . . . . . . . 11
A.2. Since -01 . . . . . . . . . . . . . . . . . . . . . . . . 12
A.3. Since -02 . . . . . . . . . . . . . . . . . . . . . . . . 12
A.4. Since -03 . . . . . . . . . . . . . . . . . . . . . . . . 12
A.5. Since -04 . . . . . . . . . . . . . . . . . . . . . . . . 12
A.6. Since -05 . . . . . . . . . . . . . . . . . . . . . . . . 12
A.7. Since -06 . . . . . . . . . . . . . . . . . . . . . . . . 12
A.8. Since -07 . . . . . . . . . . . . . . . . . . . . . . . . 12
A.9. Since -08 . . . . . . . . . . . . . . . . . . . . . . . . 13
Grigorik & Weiss Expires January 4, 2021 [Page 2]
Internet-Draft HTTP Client Hints July 2020
A.10. Since -09 . . . . . . . . . . . . . . . . . . . . . . . . 13
A.11. Since -10 . . . . . . . . . . . . . . . . . . . . . . . . 13
A.12. Since -11 . . . . . . . . . . . . . . . . . . . . . . . . 13
A.13. Since -12 . . . . . . . . . . . . . . . . . . . . . . . . 13
A.14. Since -13 . . . . . . . . . . . . . . . . . . . . . . . . 13
A.15. Since -14 . . . . . . . . . . . . . . . . . . . . . . . . 13
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
There are thousands of different devices accessing the web, each with
different device capabilities and preference information. These
device capabilities include hardware and software characteristics, as
well as dynamic user and user agent preferences. Historically,
applications that wanted the server to optimize content delivery and
user experience based on such capabilities had to rely on passive
identification (e.g., by matching the User-Agent header field
(Section 5.5.3 of [RFC7231]) against an established database of user
agent signatures), use HTTP cookies [RFC6265] and URL parameters, or
use some combination of these and similar mechanisms to enable ad hoc
content negotiation.
Such techniques are expensive to set up and maintain, and are not
portable across both applications and servers. They also make it
hard for both user agent and server to understand which data are
required and is in use during the negotiation:
o User agent detection cannot reliably identify all static
variables, cannot infer dynamic user agent preferences, requires
an external device database, is not cache friendly, and is reliant
on a passive fingerprinting surface.
o Cookie-based approaches are not portable across applications and
servers, impose additional client-side latency by requiring
JavaScript execution, and are not cache friendly.
o URL parameters, similar to cookie-based approaches, suffer from
lack of portability, and are hard to deploy due to a requirement
to encode content negotiation data inside of the URL of each
resource.
Proactive content negotiation (Section 3.4.1 of [RFC7231]) offers an
alternative approach; user agents use specified, well-defined request
headers to advertise their capabilities and characteristics, so that
servers can select (or formulate) an appropriate response based on
those request headers (or on other, implicit characteristics).
However, traditional proactive content negotiation techniques often
mean that user agents send these request headers prolifically. This
Grigorik & Weiss Expires January 4, 2021 [Page 3]
Internet-Draft HTTP Client Hints July 2020
causes performance concerns (because it creates "bloat" in requests),
as well as privacy issues; passively providing such information
allows servers to silently fingerprint the user.
This document defines Client Hints, a framework that enables servers
to opt-in to specific proactive content negotiation features,
adapting their content accordingly, as well as guidelines for content
negotiation mechanisms that use the framework. This document also
defines a new response header, Accept-CH, that allows an origin
server to explicitly ask that user agents send these headers in
requests.
Client Hints mitigate performance concerns by assuring that user
agents will only send the request headers when they're actually going
to be used, and privacy concerns of passive fingerprinting by
requiring explicit opt-in and disclosure of required headers by the
server through the use of the Accept-CH response header, turning
passive fingerprinting vectors into active ones.
The document does not define specific usages of Client Hints. Such
usages need to be defined in their respective specifications.
One example of such usage is the User Agent Client Hints [UA-CH].
1.1. Notational Conventions
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the Augmented Backus-Naur Form (ABNF) notation of
[RFC5234].
2. Client Hint Request Header Fields
A Client Hint request header field is a HTTP header field that is
used by HTTP user agents to indicate data that can be used by the
server to select an appropriate response. Each one conveys user
agent preferences that the server can use to adapt and optimize the
response.
2.1. Sending Client Hints
User agents choose what Client Hints to send in a request based on
their default settings, user configuration, and server preferences
expressed in "Accept-CH". The user agent and server can use an opt-
Grigorik & Weiss Expires January 4, 2021 [Page 4]
Internet-Draft HTTP Client Hints July 2020
in mechanism outlined below to negotiate which header fields need to
be sent to allow for efficient content adaption, and optionally use
additional mechanisms (e.g., as outlined in
[CLIENT-HINTS-INFRASTRUCTURE]) to negotiate delegation policies that
control access of third parties to those same header fields. User
agents SHOULD require an opt-in to send any hints that are not listed
in the low-entropy hint table at [CLIENT-HINTS-INFRASTRUCTURE].
Implementers need to be aware of the fingerprinting implications when
implementing support for Client Hints, and follow the considerations
outlined in the Security Considerations (Section 4) section of this
document.
2.2. Server Processing of Client Hints
When presented with a request that contains one or more Client Hint
header fields, servers can optimize the response based upon the
information in them. When doing so, and if the resource is
cacheable, the server MUST also generate a Vary response header field
(Section 7.1.4 of [RFC7231]) to indicate which hints can affect the
selected response and whether the selected response is appropriate
for a later request.
Servers MUST ignore hints they do not understand nor support. There
is no mechanism for servers to indicate to user agents that hints
were ignored.
Furthermore, the server can generate additional response header
fields (as specified by the hint or hints in use) that convey related
values to aid client processing.
3. Advertising Server Support
Servers can advertise support for Client Hints using the mechanism
described below.
3.1. The Accept-CH Response Header Field
The Accept-CH response header field indicates server support for the
hints indicated in its value. Servers wishing to receive user agent
information through Client Hints SHOULD add Accept-CH response header
to their responses as early as possible.
Accept-CH is a Structured Header [I-D.ietf-httpbis-header-structure].
Its value MUST be an sf-list (Section 3.1 of
[I-D.ietf-httpbis-header-structure]) whose members are tokens
(Section 3.3.4 of [I-D.ietf-httpbis-header-structure]). Its ABNF is:
Grigorik & Weiss Expires January 4, 2021 [Page 5]
Internet-Draft HTTP Client Hints July 2020
Accept-CH = sf-list
For example:
Accept-CH: Sec-CH-Example, Sec-CH-Example-2
When a user agent receives an HTTP response containing "Accept-CH",
that indicates that the origin opts-in to receive the indicated
request header fields for subsequent same-origin requests. The opt-
in MUST be ignored if delivered over non-secure transport (using a
scheme different from HTTPS). It SHOULD be persisted and bound to
the origin to enable delivery of Client Hints on subsequent requests
to the server's origin, for the duration of the user's session (as
defined by the user agent). An opt-in overrides previous persisted
opt-in values and SHOULD be persisted in its stead.
Based on the Accept-CH example above, which is received in response
to a user agent navigating to "https://site.example", and delivered
over a secure transport, persisted Accept-CH preferences will be
bound to "https://site.example". It will then use it for navigations
to e.g., "https://site.example/foobar.html", but not to e.g.,
"https://foobar.site.example/". It will similarly use the preference
for any same-origin resource requests (e.g., to
"https://site.example/image.jpg") initiated by the page constructed
from the navigation's response, but not to cross-origin resource
requests (e.g., "https://thirdparty.example/resource.js"). This
preference will not extend to resource requests initiated to
"https://site.example" from other origins (e.g., from navigations to
"https://other.example/").
3.2. Interaction with Caches
When selecting a response based on one or more Client Hints, and if
the resource is cacheable, the server needs to generate a Vary
response header field ([RFC7234]) to indicate which hints can affect
the selected response and whether the selected response is
appropriate for a later request.
Vary: Sec-CH-Example
The above example indicates that the cache key needs to include the
Sec-CH-Example header field.
Vary: Sec-CH-Example, Sec-CH-Example-2
The above example indicates that the cache key needs to include the
Sec-CH-Example and Sec-CH-Example-2 header fields.
Grigorik & Weiss Expires January 4, 2021 [Page 6]
Internet-Draft HTTP Client Hints July 2020
4. Security Considerations
4.1. Information Exposure
Request header fields used in features relying on this document
expose information about the user's environment to enable privacy-
preserving proactive content negotiation, and avoid exposing passive
fingerprinting vectors. However, implementers need to bear in mind
that in the worst case, uncontrolled and unmonitored active
fingerprinting is not better than passive fingerprinting. In order
to provide user privacy benefits, user agents need to apply further
policies that prevent abuse of the information exposed by features
using Client Hints.
The information exposed by features might reveal new information
about the user and implementers ought to consider the following
considerations, recommendations, and best practices.
The underlying assumption is that exposing information about the user
as a request header is equivalent (from a security perspective) to
exposing this information by other means. (For example, if the
request's origin can access that information using JavaScript APIs,
and transmit it to its servers).
Because Client Hints is an explicit opt-in mechanism, that means that
servers that want access to information about the user's environment
need to actively ask for it, enabling clients and privacy researchers
to keep track of which origins collect that data, and potentially act
upon it. The header-based opt-in means that removal of passive
fingerprinting vectors is possible, such as the User-Agent string
(enabling active access to that information through User-Agent Client
Hints ([UA-CH]) or otherwise expose information already available
through script (e.g., the Save-Data Client Hint [4]), without
increasing the passive fingerprinting surface. User agents
supporting Client Hints features which send certain information to
opted-in servers SHOULD avoid sending the equivalent information
passively.
Therefore, features relying on this document to define Client Hint
headers MUST NOT provide new information that is otherwise not made
available to the application by the user agent, such as existing
request headers, HTML, CSS, or JavaScript.
Such features need to take into account the following aspects of the
information exposed:
o Entropy - Exposing highly granular data can be used to help
identify users across multiple requests to different origins.
Grigorik & Weiss Expires January 4, 2021 [Page 7]
Internet-Draft HTTP Client Hints July 2020
Reducing the set of header field values that can be expressed, or
restricting them to an enumerated range where the advertised value
is close to but is not an exact representation of the current
value, can improve privacy and reduce risk of linkability by
ensuring that the same value is sent by multiple users.
o Sensitivity - The feature SHOULD NOT expose user-sensitive
information. To that end, information available to the
application, but gated behind specific user actions (e.g., a
permission prompt or user activation) SHOULD NOT be exposed as a
Client Hint.
o Change over time - The feature SHOULD NOT expose user information
that changes over time, unless the state change itself is also
exposed (e.g., through JavaScript callbacks).
Different features will be positioned in different points in the
space between low-entropy, non-sensitive and static information
(e.g., user agent information), and high-entropy, sensitive and
dynamic information (e.g., geolocation). User agents need to
consider the value provided by a particular feature vs these
considerations, and may wish to have different policies regarding
that tradeoff on a per-feature or other fine-grained basis.
Implementers ought to consider both user- and server- controlled
mechanisms and policies to control which Client Hints header fields
are advertised:
o Implementers SHOULD restrict delivery of some or all Client Hints
header fields to the opt-in origin only, unless the opt-in origin
has explicitly delegated permission to another origin to request
Client Hints header fields.
o Implementers considering providing user choice mechanisms that
allow users to balance privacy concerns against bandwidth
limitations need to also consider that explaining to users the
privacy implications involved, such as the risks of passive
fingerprinting, may be challenging or even impractical.
o Implementations specific to certain use cases or threat models MAY
avoid transmitting some or all of Client Hints header fields. For
example, avoid transmission of header fields that can carry higher
risks of linkability.
User agents MUST clear persisted opt-in preferences when any one of
site data, browsing history, browsing cache, cookies, or similar, are
cleared.
Grigorik & Weiss Expires January 4, 2021 [Page 8]
Internet-Draft HTTP Client Hints July 2020
4.2. Deployment and Security Risks
Deployment of new request headers requires several considerations:
o Potential conflicts due to existing use of header field name
o Properties of the data communicated in header field value
Authors of new Client Hints are advised to carefully consider whether
they need to be able to be added by client-side content (e.g.,
scripts), or whether they need to be exclusively set by the user
agent. In the latter case, the Sec- prefix on the header field name
has the effect of preventing scripts and other application content
from setting them in user agents. Using the "Sec-" prefix signals to
servers that the user agent - and not application content - generated
the values. See [FETCH] for more information.
By convention, request headers that are Client Hints are encouraged
to use a CH- prefix, to make them easier to identify as using this
framework; for example, CH-Foo or, with a "Sec-" prefix, Sec-CH-Foo.
Doing so makes them easier to identify programmatically (e.g., for
stripping unrecognised hints from requests by privacy filters).
A Client Hints request header negotiated using the Accept-CH opt-in
mechanism MUST have a field name that matches sf-token (Section 3.3.4
of [I-D.ietf-httpbis-header-structure]).
4.3. Abuse Detection
A user agent that tracks access to active fingerprinting information
SHOULD consider emission of Client Hints headers similarly to the way
it would consider access to the equivalent API.
Research into abuse of Client Hints might look at how HTTP responses
to requests that contain Client Hints differ from those with
different values, and from those without. This might be used to
reveal which Client Hints are in use, allowing researchers to further
analyze that use.
5. Cost of Sending Hints
Sending Client Hints to the server incurs an increase in request byte
size. Some of this increase can be mitigated by HTTP header
compression schemes, but each new hint sent will still lead to some
increased bandwidth usage. Servers SHOULD take that into account
when opting in to receive Client Hints, and SHOULD NOT opt-in to
receive hints unless they are to be used for content adaptation
purposes.
Grigorik & Weiss Expires January 4, 2021 [Page 9]
Internet-Draft HTTP Client Hints July 2020
Due to request byte size increase, features relying on this document
to define Client Hints MAY consider restricting sending those hints
to certain request destinations [FETCH], where they are more likely
to be useful.
6. IANA Considerations
Features relying on this document are expected to register added
request header fields in the Permanent Message Header Fields registry
([RFC3864]).
This document defines the "Accept-CH" HTTP response header field, and
registers it in the same registry.
6.1. Accept-CH
o Header field name: Accept-CH
o Applicable protocol: HTTP
o Status: experimental
o Author/Change controller: IETF
o Specification document(s): Section 3.1 of this document
o Related information: for Client Hints
7. References
7.1. Normative References
[CLIENT-HINTS-INFRASTRUCTURE]
Weiss, Y., "Client Hints Infrastructure", n.d.,
<https://wicg.github.io/client-hints-infrastructure/>.
[I-D.ietf-httpbis-header-structure]
Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", draft-ietf-httpbis-header-structure-19 (work in
progress), June 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
DOI 10.17487/RFC3864, September 2004,
<https://www.rfc-editor.org/info/rfc3864>.
Grigorik & Weiss Expires January 4, 2021 [Page 10]
Internet-Draft HTTP Client Hints July 2020
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<https://www.rfc-editor.org/info/rfc7234>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[FETCH] van Kesteren, A., "Fetch", n.d.,
<https://fetch.spec.whatwg.org/>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>.
[UA-CH] West, M. and Y. Weiss, "User Agent Client Hints", n.d.,
<https://wicg.github.io/ua-client-hints/>.
7.3. URIs
[1] https://lists.w3.org/Archives/Public/ietf-http-wg/
[2] http://httpwg.github.io/
[3] https://github.com/httpwg/http-extensions/labels/client-hints
[4] https://wicg.github.io/savedata/#save-data-request-header-field
Appendix A. Changes
A.1. Since -00
o Issue 168 (make Save-Data extensible) updated ABNF.
o Issue 163 (CH review feedback) editorial feedback from httpwg
list.
Grigorik & Weiss Expires January 4, 2021 [Page 11]
Internet-Draft HTTP Client Hints July 2020
o Issue 153 (NetInfo API citation) added normative reference.
A.2. Since -01
o Issue 200: Moved Key reference to informative.
o Issue 215: Extended passive fingerprinting and mitigation
considerations.
o Changed document status to experimental.
A.3. Since -02
o Issue 239: Updated reference to CR-css-values-3
o Issue 240: Updated reference for Network Information API
o Issue 241: Consistency in IANA considerations
o Issue 250: Clarified Accept-CH
A.4. Since -03
o Issue 284: Extended guidance for Accept-CH
o Issue 308: Editorial cleanup
o Issue 306: Define Accept-CH-Lifetime
A.5. Since -04
o Issue 361: Removed Downlink
o Issue 361: Moved Key to appendix, plus other editorial feedback
A.6. Since -05
o Issue 372: Scoped CH opt-in and delivery to secure transports
o Issue 373: Bind CH opt-in to origin
A.7. Since -06
o Issue 524: Save-Data is now defined by NetInfo spec, dropping
o PR 775: Removed specific features to be defined in other
specifications
A.8. Since -07
o Issue 761: Clarified that the defined headers are response
headers.
o Issue 730: Replaced Key reference with Variants.
o Issue 700: Replaced ABNF with structured headers.
o PR 878: Removed Accept-CH-Lifetime based on feedback at IETF 105
Grigorik & Weiss Expires January 4, 2021 [Page 12]
Internet-Draft HTTP Client Hints July 2020
A.9. Since -08
o PR 985: Describe the bytesize cost of hints.
o PR 776: Add Sec- and CH- prefix considerations.
o PR 1001: Clear CH persistence when cookies are cleared.
A.10. Since -09
o PR 1064: Fix merge issues with "cost of sending hints".
A.11. Since -10
o PR 1072: LC feedback from Julian Reschke.
o PR 1080: Improve list style.
o PR 1082: Remove section mentioning Variants.
o PR 1097: Editorial feedback from mnot.
o PR 1131: Remove unused references.
o PR 1132: Remove nested list.
A.12. Since -11
o PR 1134: Re-insert back section.
A.13. Since -12
o PR 1160: AD review.
A.14. Since -13
o PR 1171: Genart review.
A.15. Since -14
o PR 1220: AD review.
Acknowledgements
Thanks to Mark Nottingham, Julian Reschke, Chris Bentzel, Ben
Greenstein, Tarun Bansal, Roy Fielding, Vasiliy Faronov, Ted Hardie,
Jonas Sicking, Martin Thomson, and numerous other members of the IETF
HTTP Working Group for invaluable help and feedback.
Authors' Addresses
Grigorik & Weiss Expires January 4, 2021 [Page 13]
Internet-Draft HTTP Client Hints July 2020
Ilya Grigorik
Google
Email: ilya@igvita.com
URI: https://www.igvita.com/
Yoav Weiss
Google
Email: yoav@yoav.ws
URI: https://blog.yoav.ws/
Grigorik & Weiss Expires January 4, 2021 [Page 14]
