Use Cases and Requirements for Web Packages
draft-yasskin-webpackage-use-cases-00
The information below is for an old version of the document.
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|---|---|---|---|
| Author | Jeffrey Yasskin | ||
| Last updated | 2017-08-30 | ||
| Replaced by | draft-yasskin-wpack-use-cases | ||
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draft-yasskin-webpackage-use-cases-00
dispatch J. Yasskin
Internet-Draft Google
Intended status: Informational August 30, 2017
Expires: March 3, 2018
Use Cases and Requirements for Web Packages
draft-yasskin-webpackage-use-cases-00
Abstract
This document lists use cases for signing and/or bundling collections
of web pages, and extracts a set of requirements from them.
Note to Readers
Discussion of this draft takes place on the ART area mailing list
(art@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/search/?email_list=art.
The source code and issues list for this draft can be found in
https://github.com/WICG/webpackage.
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 March 3, 2018.
Copyright Notice
Copyright (c) 2017 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
(http://trustee.ietf.org/license-info) in effect on the date of
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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
2. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Essential . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1. Offline installation . . . . . . . . . . . . . . . . 3
2.1.2. Offline browsing . . . . . . . . . . . . . . . . . . 5
2.1.3. Save and share a web page . . . . . . . . . . . . . . 5
2.2. Nice-to-have . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1. Packaged Web Publications . . . . . . . . . . . . . . 6
2.2.2. Third-party security review . . . . . . . . . . . . . 7
2.2.3. Building packages from multiple libraries . . . . . . 7
2.2.4. CDNs . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.5. Installation from a self-extracting executable . . . 8
2.2.6. Ergonomic replacement for HTTP/2 PUSH . . . . . . . . 9
2.2.7. Packages in version control . . . . . . . . . . . . . 9
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Essential . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.1. Indexed by URL . . . . . . . . . . . . . . . . . . . 10
3.1.2. Request headers . . . . . . . . . . . . . . . . . . . 10
3.1.3. Response headers . . . . . . . . . . . . . . . . . . 10
3.1.4. Signing as an origin . . . . . . . . . . . . . . . . 10
3.1.5. Random access . . . . . . . . . . . . . . . . . . . . 11
3.1.6. Resources from multiple origins in a package . . . . 11
3.1.7. Cryptographic agility . . . . . . . . . . . . . . . . 11
3.1.8. Unsigned content . . . . . . . . . . . . . . . . . . 11
3.1.9. Certificate revocation . . . . . . . . . . . . . . . 11
3.1.10. Downgrade prevention . . . . . . . . . . . . . . . . 11
3.1.11. Metadata . . . . . . . . . . . . . . . . . . . . . . 11
3.1.12. Implementations are hard to get wrong . . . . . . . . 12
3.2. Nice to have . . . . . . . . . . . . . . . . . . . . . . 12
3.2.1. Streamed loading . . . . . . . . . . . . . . . . . . 12
3.2.2. Cross-signatures . . . . . . . . . . . . . . . . . . 12
3.2.3. Binary . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.4. Deduplication of diamond dependencies . . . . . . . . 12
3.2.5. Old crypto can be removed . . . . . . . . . . . . . . 12
3.2.6. Compress transfers . . . . . . . . . . . . . . . . . 13
3.2.7. Compress stored packages . . . . . . . . . . . . . . 13
3.2.8. Subsetting and reordering . . . . . . . . . . . . . . 13
3.2.9. Packaged validity information . . . . . . . . . . . . 13
3.2.10. Signing uses existing TLS certificates . . . . . . . 13
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3.2.11. External dependencies . . . . . . . . . . . . . . . . 13
3.2.12. Trailing length . . . . . . . . . . . . . . . . . . . 13
4. Non-goals . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Store confidential data . . . . . . . . . . . . . . . . . 14
4.2. Generate packages on the fly . . . . . . . . . . . . . . 14
4.3. Non-origin identity . . . . . . . . . . . . . . . . . . . 14
4.4. DRM . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Informative References . . . . . . . . . . . . . . . . . 15
7.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
People would like to use content offline and in other situations
where there isn't a direct connection to the server where the content
originates. However, it's difficult to distribute and verify the
authenticity of applications and content without a connection to the
network. The W3C has addressed running applications offline with
Service Workers ([ServiceWorkers]), but not the problem of
distribution.
Previous attempts at packaging web resources (e.g. Resource Packages
[3] and the W3C TAG's packaging proposal [4]) were motivated by
speeding up the download of resources from a single server, which is
probably better achieved through other mechanisms like HTTP/2 PUSH,
possibly augmented with a simple manifest of URLs a page plans to use
[5]. This attempt is instead motivated by avoiding a connection to
the origin server at all. It may still be useful for the earlier use
cases, so they're still listed, but they're not primary.
2. Use cases
These use cases are in rough descending priority order. If use cases
have conflicting requirements, the design should enable more
important use cases.
2.1. Essential
2.1.1. Offline installation
Alex can download a file containing a website (a PWA [6]) including a
Service Worker from origin "O", and transmit it to their peer Bailey,
and then Bailey can install the Service Worker with a proof that it
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came from "O". This saves Bailey the bandwidth costs of transferring
the website.
Associated requirements:
o Indexed by URL: Resources on the web are addressed by URL.
o Request headers: If Bailey's running a different browser from Alex
or has a different language configured, the "accept*" headers are
important for selecting which resource to use at each URL.
o Response headers: The meaning of a resource is heavily influenced
by its HTTP response headers.
o Signing as an origin: To prove that the file came from "O".
o Signing uses existing TLS certificates: So "O" doesn't have to
spend lots of money buying a specialized certificate.
o Resources from multiple origins in a package: So the site can be
built from multiple components (Section 2.2.3).
o Cryptographic agility: Today's algorithms will eventually be
obsolete and will need to be replaced.
o Certificate revocation: "O"'s certificate might be compromised or
mis-issued, and the attacker shouldn't then get an infinite
ability to mint packages.
o Downgrade prevention: "O"'s site might have an XSS vulnerability,
and attackers with an old signed package shouldn't be able to take
advantage of the XSS forever.
o Metadata: The browser needs to know which resource within a
package file to treat as its Service Worker and/or initial HTML
page.
2.1.1.1. Online use
Bailey may have an internet connection through which they can, in
real time, fetch updates to the package they received from Alex.
2.1.1.2. Fully offline use
Or Bailey may not have any internet connection a significant fraction
of the time, either because they have no internet at all, because
they turn off internet except when intentionally downloading content,
or because they use up their plan partway through each month.
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Associated requirements beyond Offline installation:
o Packaged validity information: Even without a direct internet
connection, Bailey should be able to check that their package is
still valid.
2.1.2. Offline browsing
Alex can download a file containing a large website (e.g. Wikipedia)
from its origin, save it to transferrable storage (e.g. an SD card),
and hand it to their peer Bailey. Then Bailey can browse the website
with a proof that it came from "O". Bailey may not have the storage
space to copy the website before browsing it.
Associated requirements beyond Offline installation:
o Random access: To avoid needing a long linear scan before using
the content.
o Compress stored packages: So that more content can fit on the same
storage device.
2.1.3. Save and share a web page
Casey is viewing a web page and wants to save it either for offline
use or to show it to their friend Dakota. Since Casey isn't the web
page's author, they don't have the private key needed to sign the
page. Browsers currently allow their users to save pages, but each
browser uses a different format (MHTML, Web Archive, or files in a
directory), so Dakota and Casey would need to be using the same
browser. Casey could also take a screenshot, at the cost of losing
links and accessibility.
Associated requirements:
o Unsigned content: A client can't sign content as another origin.
o Resources from multiple origins in a package: General web pages
include resources from multiple origins.
o Indexed by URL: Resources on the web are addressed by URL.
o Response headers: The meaning of a resource is heavily influenced
by its HTTP response headers.
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2.2. Nice-to-have
2.2.1. Packaged Web Publications
The W3C's Publishing Working Group [7], merged from the International
Digital Publishing Forum (IDPF) and in charge of EPUB maintenance,
wants to be able to create publications on the web and then let them
be copied to different servers or to other users via arbitrary
protocols. See their Packaged Web Publications use cases [8] for
more details.
Associated requirements:
o Indexed by URL: Resources on the web are addressed by URL.
o Signing as an origin: So that readers can be sure their copy is
authentic and so that copying the package preserves the URLs of
the content inside it.
o Downgrade prevention: An early version of a publication might
contain incorrect content, and a publisher should be able to
update that without worrying that an attacker can still show the
old content to users.
o Metadata: A publication can have copyright and licensing concerns;
a title, author, and cover image; an ISBN or DOI name; etc.; which
should be included when that publication is packaged.
Other requirements are similar to those from Offline installation:
o Random access: To avoid needing a long linear scan before using
the content.
o Compress stored packages: So that more content can fit on the same
storage device.
o Request headers: If different users' browsers have different
capabilities or preferences, the "accept*" headers are important
for selecting which resource to use at each URL.
o Response headers: The meaning of a resource is heavily influenced
by its HTTP response headers.
o Signing uses existing TLS certificates: So a publisher doesn't
have to spend lots of money buying a specialized certificate.
o Cryptographic agility: Today's algorithms will eventually be
obsolete and will need to be replaced.
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o Certificate revocation: The publisher's certificate might be
compromised or mis-issued, and an attacker shouldn't then get an
infinite ability to mint packages.
2.2.2. Third-party security review
Some users may want to grant certain permissions only to applications
that have been reviewed for security by a trusted third party. These
third parties could provide guarantees similar to those provided by
the iOS, Android, or ChromeOS app stores, which might allow browsers
to offer more powerful capabilities than have been deemed safe for
unaudited websites.
Binary transparency for websites is similar: like with Certificate
Transparency [RFC6962], the transparency logs would sign the content
of the package to provide assurance that experts had a chance to
audit the exact package a client received.
Associated requirements:
o Cross-signatures
2.2.3. Building packages from multiple libraries
Large programs are built from smaller components. In the case of the
web, components can be included either as Javascript files or as
"<iframe>"d subresources. In the first case, the packager could copy
the JS files to their own origin; but in the second, it may be
important for the "<iframe>"d resources to be able to make same-
origin [9] requests back to their own origin, for example to
implement federated sign-in.
Associated requirements:
o Resources from multiple origins in a package: Each component may
come from its own origin.
o Deduplication of diamond dependencies: If we have dependencies
A->B->D and A->C->D, it's important that a request for a D
resource resolves to a single resource that both B and C can
handle.
2.2.3.1. Shared libraries
In ecosystems like Electron [10] and Node [11], many packages may
share some common dependencies. The cost of downloading each package
can be greatly reduced if the package can merely point at other
dependencies to download instead of including them all inline.
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Associated requirements:
o External dependencies
2.2.4. CDNs
CDNs want to re-publish other origins' content so readers can access
it more quickly or more privately. Currently, to attribute that
content to the original origin, they need the full ability to publish
arbitrary content under that origin's name. There should be a way to
let them attribute only the exact content that the original origin
published.
Web Packages would allow CDNs to publish content as another site as
long as the user visited a URL explicitly mentioning the CDN.
CDNs want to serve only the bytes that most optimally represent the
content the current user needs, even though the origin needs to
provide representations for all users. Think PNG vs WebP and small
vs large resolutions.
Associated requirements:
o Streamed loading: To get optimal performance, the browser should
be able to start loading early resources before the CDN finishes
sending the whole package.
o Signing as an origin: To prove the content came from the original
origin.
o Subsetting and reordering: If a package includes both WebP and PNG
versions of an image, the CDN should be able to select the best
one to send to each client.
o Compress transfers
2.2.5. Installation from a self-extracting executable
The Node and Electron communities would like to install packages
using self-extracting executables. The traditional way to design a
self-extracting executable is to concatenate the package to the end
of the executable, have the executable look for a length at its own
end, and seek backwards from there for the start of the package.
Associated requirements:
o Trailing length
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2.2.6. Ergonomic replacement for HTTP/2 PUSH
HTTP/2 PUSH ([RFC7540], section 8.2) is hard for developers to
configure, and an explicit package format might be easier.
Trying to bundle resources in order to speed up page loads has a long
history, including Resource Packages [12] from 2010 and the W3C TAG's
packaging proposal [13] from 2015.
However, the HTTPWG is doing a lot of work to let servers optimize
the PUSHed data, and packaging would either have to re-do that or
accept lower performance. Accepting lower performance might be
worthwhile if it allows more developers to adopt the smaller
optimization.
Associated requirements:
o Streamed loading: If the whole package has to be downloaded before
the browser can load a piece, this will definitely be slower than
PUSH.
o Compress transfers: I believe PUSHed resources cannot keep a
single compression state across resource boundaries, so this might
be an advantage for packaging.
o Indexed by URL: Resources on the web are addressed by URL.
o Request headers: PUSH_PROMISE [14] ([RFC7540], section 6.6)
includes request headers.
o Response headers: PUSHed resources include their response headers.
2.2.7. Packages in version control
Once packages are generated, they should be stored in version
control. Many popular VC systems auto-detect text files in order to
"fix" their line endings. If the first bytes of a package look like
text, while later bytes store binary data, VC may break the package.
Associated requirements:
o Binary
3. Requirements
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3.1. Essential
3.1.1. Indexed by URL
Resources should be keyed by URLs, matching how browsers look
resources up over HTTP.
3.1.2. Request headers
Resource keys should include request headers like "accept" and
"accept-language", which allows content-negotiated resources to be
represented.
This would require an extension to [MHTML], which uses the "content-
location" response header to encode the requested URL, but has no way
to encode other request headers. MHTML also has no instructions for
handling multiple resources with the same "content-location".
This also requires an extension to [ZIP]: we'd need to encode the
request headers into ZIP's filename fields.
3.1.3. Response headers
Resources should include their HTTP response headers, like "content-
type", "content-encoding", "expires", "content-security-policy", etc.
This requires an extension to [ZIP]: we'd need something like [JAR]'s
"META-INF" directory to hold extra metadata beyond the resource's
body.
3.1.4. Signing as an origin
Resources within a package are provably from an entity with the
ability to serve HTTPS requests for those resources' origin
[RFC6454].
Resources within a package are provably from an entity with the
ability to serve HTTPS requests for those resources' origin
[RFC6454].
Note that previous attempts to sign HTTP messages
([I-D.thomson-http-content-signature], [I-D.burke-content-signature],
and [I-D.cavage-http-signatures]) omit a description of how a client
should use a signature to prove that a resource comes from a
particular origin, and they're probably not usable for that purpose.
This would require an extension to the [ZIP] format, similar to
[JAR]'s signatures.
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In any cryptographic system, the specification is responsible to make
correct implementations easier to deploy than incorrect
implementations (Section 3.1.12).
3.1.5. Random access
When a package is stored on disk, the browser can access arbitrary
resources without a linear scan.
[MHTML] would need to be extended with an index of the byte offsets
of each contained resource.
3.1.6. Resources from multiple origins in a package
A package from origin "A" can contain resources from origin "B"
authenticated at the same level as those from "A".
3.1.7. Cryptographic agility
Obsolete cryptographic algorithms can be replaced.
Planning to upgrade the cryptography also means we should include
some way to know when it's safe to remove old cryptography
(Section 3.2.5).
3.1.8. Unsigned content
Alex can create their own package without a CA-signed certificate,
and Bailey can view the content of the package.
3.1.9. Certificate revocation
When a package is signed by a revoked certificate, online browsers
can detect this reasonably quickly.
3.1.10. Downgrade prevention
Attackers can't cause a browser to trust an older, vulnerable version
of a package after the browser has seen a newer version.
3.1.11. Metadata
Metadata like that found in the W3C's Application Manifest
[W3C.WD-appmanifest-20170828] can help a client know how to load and
display a package.
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3.1.12. Implementations are hard to get wrong
The design should incorporate aspects that tend to cause incorrect
implementations to get noticed quickly, and avoid aspects that are
easy to implement incorrectly. For example:
o Explicitly specifying a cryptographic algorithm identifier in
[RFC7515] made it easy for implementations to trust that
algorithm, which caused vulnerabilities [15].
o [ZIP]'s duplicate specification of filenames makes it easy for
implementations to check the signature of one copy but use the
other [16].
o Following Langley's Law [17] when possible makes it hard to deploy
incorrect implementations.
3.2. Nice to have
3.2.1. Streamed loading
The browser can load a package as it downloads.
This conflicts with ZIP, since ZIP's index is at the end.
3.2.2. Cross-signatures
Third-parties can vouch for packages by signing them.
3.2.3. Binary
The format is identified as binary by tools that might try to "fix"
line endings.
This conflicts with using an [MHTML]-based format.
3.2.4. Deduplication of diamond dependencies
Nested packages that have multiple dependency routes to the same sub-
package, can be transmitted and stored with only one copy of that
sub-package.
3.2.5. Old crypto can be removed
The ecosystem can identify when an obsolete cryptographic algorithm
is no longer needed and can be removed.
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3.2.6. Compress transfers
Transferring a package over the network takes as few bytes as
possible. This is an easier problem than Compress stored packages
since it doesn't have to preserve Random access.
3.2.7. Compress stored packages
Storing a package on disk takes as few bytes as possible.
3.2.8. Subsetting and reordering
Resources can be removed from and reordered within a package, without
breaking signatures (Section 3.1.4).
3.2.9. Packaged validity information
Certificate revocation and Downgrade prevention information can
itself be packaged or included in other packages.
3.2.10. Signing uses existing TLS certificates
A "normal" TLS certificate can be used for signing packages.
Avoiding extra requirements like "code signing" certificates makes
packaging more accessible to all sites.
3.2.11. External dependencies
Sub-packages can be "external" to the main package, meaning the
browser will need to either fetch them separately or already have
them. (#35, App Installer Story [18])
3.2.12. Trailing length
The package's length in bytes appears a fixed offset from the end of
the package.
This conflicts with [MHTML].
4. Non-goals
Some features often come along with packaging and signing, and it's
important to explicitly note that they don't appear in the list of
Requirements.
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4.1. Store confidential data
Packages are designed to hold public information and to be shared to
people with whom the original author never has an interactive
connection. In that situation, there's no way to keep the contents
confidential: even if they were encrypted, to make the data public,
anyone would have to be able to get the decryption key.
It's possible to maintain something similar to confidentiality for
non-public packaged data, but doing so complicates the format design
and can give users a false sense of security.
We believe we'll cause fewer privacy breaches if we omit any
mechanism for encrypting data, than if we include something and try
to teach people when it's unsafe to use.
4.2. Generate packages on the fly
See discussion at WICG/webpackage#6 [19].
4.3. Non-origin identity
A package can be primarily identified as coming from something other
than a Web Origin [20].
4.4. DRM
Special support for blocking access to downloaded content based on
licensing. Note that DRM systems can be shipped inside the package
even if the packaging format doesn't specifically support them.
5. Security Considerations
The security considerations will depend on the solution designed to
satisfy the above requirements. See
[I-D.yasskin-dispatch-web-packaging] for one possible set of security
considerations.
6. IANA Considerations
This document has no actions for IANA.
7. References
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7.1. Informative References
[I-D.burke-content-signature]
Burke, B., "HTTP Header for digital signatures", draft-
burke-content-signature-00 (work in progress), March 2011.
[I-D.cavage-http-signatures]
Cavage, M. and M. Sporny, "Signing HTTP Messages", draft-
cavage-http-signatures-07 (work in progress), July 2017.
[I-D.thomson-http-content-signature]
Thomson, M., "Content-Signature Header Field for HTTP",
draft-thomson-http-content-signature-00 (work in
progress), July 2015.
[I-D.yasskin-dispatch-web-packaging]
Yasskin, J., "Web Packaging", draft-yasskin-dispatch-web-
packaging-00 (work in progress), June 2017.
[JAR] "JAR File Specification", 2014,
<https://docs.oracle.com/javase/7/docs/technotes/guides/
jar/jar.html>.
[MHTML] Palme, J., Hopmann, A., and N. Shelness, "MIME
Encapsulation of Aggregate Documents, such as HTML
(MHTML)", RFC 2557, DOI 10.17487/RFC2557, March 1999,
<https://www.rfc-editor.org/info/rfc2557>.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011, <https://www.rfc-
editor.org/info/rfc6454>.
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013,
<https://www.rfc-editor.org/info/rfc6962>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015, <https://www.rfc-
editor.org/info/rfc7540>.
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[ServiceWorkers]
Russell, A., Song, J., Archibald, J., and M.
Kruisselbrink, "Service Workers 1", World Wide Web
Consortium WD WD-service-workers-1-20161011, October 2016,
<https://www.w3.org/TR/2016/WD-service-workers-
1-20161011>.
[W3C.WD-appmanifest-20170828]
Caceres, M., Christiansen, K., Lamouri, M., Kostiainen,
A., and R. Dolin, "Web App Manifest", World Wide Web
Consortium WD WD-appmanifest-20170828, August 2017,
<https://www.w3.org/TR/2017/WD-appmanifest-20170828>.
[ZIP] "APPNOTE.TXT - .ZIP File Format Specification", October
2014, <https://pkware.cachefly.net/webdocs/casestudies/
APPNOTE.TXT>.
7.2. URIs
[1] https://www.mnot.net/blog/2010/02/18/resource_packages
[2] https://w3ctag.github.io/packaging-on-the-web/
[3] https://lists.w3.org/Archives/Public/public-web-
perf/2015Jan/0038.html
[4] https://developers.google.com/web/progressive-web-apps/checklist
[5] https://www.w3.org/publishing/groups/publ-wg/
[6] https://www.w3.org/TR/pwp-ucr/#pwp
[7] https://html.spec.whatwg.org/multipage/origin.html#same-origin
[8] https://electron.atom.io/
[9] https://nodejs.org/en/
[10] https://www.mnot.net/blog/2010/02/18/resource_packages
[11] https://w3ctag.github.io/packaging-on-the-web/
[12] http://httpwg.org/specs/rfc7540.html#PUSH_PROMISE
[13] https://paragonie.com/blog/2017/03/jwt-json-web-tokens-is-bad-
standard-that-everyone-should-avoid
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[14] https://nakedsecurity.sophos.com/2013/07/10/anatomy-of-a-
security-hole-googles-android-master-key-debacle-explained/
[15] https://blog.gerv.net/2016/09/introducing-deliberate-protocol-
errors-langleys-law/
[16] https://github.com/WICG/webpackage/issues/35
[17] https://github.com/WICG/webpackage/
issues/6#issuecomment-275746125
[18] https://html.spec.whatwg.org/multipage/browsers.html#concept-
origin
Appendix A. Acknowledgements
Author's Address
Jeffrey Yasskin
Google
Email: jyasskin@chromium.org
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