draft-ietf-httpbis-http2-encryption-06.txt   draft-ietf-httpbis-http2-encryption-07.txt 
HTTP Working Group M. Nottingham HTTP Working Group M. Nottingham
Internet-Draft Internet-Draft
Intended status: Experimental M. Thomson Intended status: Experimental M. Thomson
Expires: December 23, 2016 Mozilla Expires: April 7, 2017 Mozilla
June 21, 2016 October 4, 2016
Opportunistic Security for HTTP Opportunistic Security for HTTP
draft-ietf-httpbis-http2-encryption-06 draft-ietf-httpbis-http2-encryption-07
Abstract Abstract
This document describes how "http" URIs can be accessed using This document describes how "http" URIs can be accessed using
Transport Layer Security (TLS) to mitigate pervasive monitoring Transport Layer Security (TLS) to mitigate pervasive monitoring
attacks. attacks.
Note to Readers Note to Readers
Discussion of this draft takes place on the HTTP working group Discussion of this draft takes place on the HTTP working group
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 23, 2016. This Internet-Draft will expire on April 7, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Goals and Non-Goals . . . . . . . . . . . . . . . . . . . 3 1.1. Goals and Non-Goals . . . . . . . . . . . . . . . . . . . 3
1.2. Notational Conventions . . . . . . . . . . . . . . . . . 3 1.2. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Using HTTP URIs over TLS . . . . . . . . . . . . . . . . . . 3 2. Using HTTP URIs over TLS . . . . . . . . . . . . . . . . . . 3
3. Server Authentication . . . . . . . . . . . . . . . . . . . . 4 2.1. Alternative Server Opt-In . . . . . . . . . . . . . . . . 4
4. Interaction with "https" URIs . . . . . . . . . . . . . . . . 5 2.2. Interaction with "https" URIs . . . . . . . . . . . . . . 5
5. Requiring Use of TLS . . . . . . . . . . . . . . . . . . . . 6 2.3. The "http-opportunistic" well-known URI . . . . . . . . . 5
5.1. Opportunistic Commitment . . . . . . . . . . . . . . . . 6 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.2. Client Handling of A Commitment . . . . . . . . . . . . . 7 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5.3. Operational Considerations . . . . . . . . . . . . . . . 7 4.1. Security Indicators . . . . . . . . . . . . . . . . . . . 6
6. The "http-opportunistic" well-known URI . . . . . . . . . . . 8 4.2. Downgrade Attacks . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 4.3. Privacy Considerations . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 4.4. Confusion Regarding Request Scheme . . . . . . . . . . . 7
8.1. Security Indicators . . . . . . . . . . . . . . . . . . . 9 4.5. Server Controls . . . . . . . . . . . . . . . . . . . . . 7
8.2. Downgrade Attacks . . . . . . . . . . . . . . . . . . . . 9 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.3. Privacy Considerations . . . . . . . . . . . . . . . . . 9 5.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.4. Confusion Regarding Request Scheme . . . . . . . . . . . 9 5.2. Informative References . . . . . . . . . . . . . . . . . 8
8.5. Server Controls . . . . . . . . . . . . . . . . . . . . . 10 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
This document describes a use of HTTP Alternative Services [RFC7838] This document describes a use of HTTP Alternative Services [RFC7838]
to decouple the URI scheme from the use and configuration of to decouple the URI scheme from the use and configuration of
underlying encryption, allowing a "http" URI [RFC7230] to be accessed underlying encryption, allowing a "http" URI [RFC7230] to be accessed
using Transport Layer Security (TLS) [RFC5246] opportunistically. using Transport Layer Security (TLS) [RFC5246] opportunistically.
Serving "https" URIs require acquiring and configuring a valid Serving "https" URIs requires avoiding Mixed Content
certificate, which means that some deployments find supporting TLS [W3C.CR-mixed-content-20160802], which is problematic in many
difficult. This document describes a usage model whereby sites can deployments. This document describes a usage model whereby sites can
serve "http" URIs over TLS without being required to support strong serve "http" URIs over TLS, thereby avoiding these issues, while
server authentication. still providing protection against passive attacks.
Opportunistic Security [RFC7435] does not provide the same guarantees Opportunistic Security [RFC7435] does not provide the same guarantees
as using TLS with "https" URIs; it is vulnerable to active attacks, as using TLS with "https" URIs; it is vulnerable to active attacks,
and does not change the security context of the connection. and does not change the security context of the connection.
Normally, users will not be able to tell that it is in use (i.e., Normally, users will not be able to tell that it is in use (i.e.,
there will be no "lock icon"). there will be no "lock icon").
A mechanism for partially mitigating active attacks is described in
Section 5.
1.1. Goals and Non-Goals 1.1. Goals and Non-Goals
The immediate goal is to make the use of HTTP more robust in the face The immediate goal is to make the use of HTTP more robust in the face
of pervasive passive monitoring [RFC7258]. of pervasive passive monitoring [RFC7258].
A secondary goal is to limit the potential for active attacks. It is A secondary (but significant) goal is to provide for ease of
not intended to offer the same level of protection as afforded to
"https" URIs, but instead to increase the likelihood that an active
attack can be detected.
A final (but significant) goal is to provide for ease of
implementation, deployment and operation. This mechanism is expected implementation, deployment and operation. This mechanism is expected
to have a minimal impact upon performance, and require a trivial to have a minimal impact upon performance, and require a trivial
administrative effort to configure. administrative effort to configure.
Preventing active attacks (such as a Man-in-the-Middle) is a non-goal
for this specification. Furthermore, this specification is not
intended to replace or offer an alternative to "https", since it both
prevents active attacks and invokes a more stringent security model
in most clients.
1.2. Notational Conventions 1.2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Using HTTP URIs over TLS 2. Using HTTP URIs over TLS
An origin server that supports the resolution of "http" URIs can An origin server that supports the resolution of "http" URIs can
indicate support for this specification by providing an alternative indicate support for this specification by providing an alternative
service advertisement [RFC7838] for a protocol identifier that uses service advertisement [RFC7838] for a protocol identifier that uses
TLS, such as "h2" [RFC7540]. TLS, such as "h2" [RFC7540].
A client that receives such an advertisement MAY make future requests A client that receives such an advertisement MAY make future requests
intended for the associated origin ([RFC6454]) to the identified intended for the associated origin ([RFC6454]) to the identified
service (as specified by [RFC7838]). service (as specified by [RFC7838]), provided that the alternative
service opts in as described in Section 2.1.
A client that places the importance of protection against passive A client that places the importance of protection against passive
attacks over performance might choose to withhold requests until an attacks over performance might choose to withhold requests until an
encrypted connection is available. However, if such a connection encrypted connection is available. However, if such a connection
cannot be successfully established, the client can resume its use of cannot be successfully established, the client can resume its use of
the cleartext connection. the cleartext connection.
A client can also explicitly probe for an alternative service A client can also explicitly probe for an alternative service
advertisement by sending a request that bears little or no sensitive advertisement by sending a request that bears little or no sensitive
information, such as one with the OPTIONS method. Likewise, clients information, such as one with the OPTIONS method. Likewise, clients
with existing alternative services information could make such a with existing alternative services information could make such a
request before they expire, in order minimize the delays that might request before they expire, in order minimize the delays that might
be incurred. be incurred.
Client certificates are not meaningful for URLs with the "http" Client certificates are not meaningful for URLs with the "http"
scheme, and therefore clients creating new TLS connections to scheme, and therefore clients creating new TLS connections to
alternative services for the purposes of this specification MUST NOT alternative services for the purposes of this specification MUST NOT
present them. Established connections with client certificates MAY present them. Established connections with client certificates MAY
be reused, however. be reused, however.
3. Server Authentication 2.1. Alternative Server Opt-In
[RFC7838] requires that an alternative service only be used when
there are "reasonable assurances" that it is under control of and
valid for the whole origin.
As defined in that specification, a client can establish reasonable
assurances when using a TLS-based protocol with the certificate
checks defined in [RFC2818].
For the purposes of this specification, an additional way of
establishing reasonable assurances is available when the alternative
is on the same host as the origin, using the "http-opportunistic"
well-known URI defined in Section 6.
This allows deployment without the use of valid certificates, to It is possible that the server might become confused about whether
encourage deployment of opportunistic security. When it is in use, requests' URLs have a "http" or "https" scheme, for various reasons;
the alternative service can provide any certificate, or even select see Section 4.4. To ensure that the alternative service has opted
TLS cipher suites that do not include authentication. into serving "http" URLs over TLS, clients are required to perform
additional checks before directing "http" requests to it.
When a client has a valid http-opportunistic response for an origin Clients MUST NOT send "http" requests over a connection with the "h2"
(as per Section 6), it MAY consider there to be reasonable assurances protocol identifier, unless they have obtained a valid http-
as long as: opportunistic response for an origin (as per Section 2.3), and:
o The origin and alternative service's hostnames are the same when o The chosen alternative service presents a certificate that is
compared in a case-insensitive fashion, and valid for the origin, as per [RFC2818] (this also establishes
"reasonable assurances" for the purposes of {RFC7838}}), and
o The origin object of the http-opportunistic response has a `tls- o The origin object of the http-opportunistic response has a `tls-
ports' member, whose value is an array of numbers, one of which ports' member, whose value is an array of numbers, one of which
matches the port of the alternative service in question, and matches the port of the alternative service in question, and
o The chosen alternative service returns the same representation as o The chosen alternative service returns the same representation as
the origin did for the http-opportunistic resource. the origin did for the http-opportunistic resource.
For example, this request/response pair would constitute reasonable For example, this request/response pair would allow reqeusts for the
assurances for the origin "http://www.example.com" for an alternative origin "http://www.example.com" to be sent to an alternative service
service on port 443 or 8000 of the host "www.example.com": on port 443 or 8000 of the host "www.example.com":
GET /.well-known/http-opportunistic HTTP/1.1 GET /.well-known/http-opportunistic HTTP/1.1
Host: www.example.com Host: www.example.com
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Connection: close Connection: close
{ {
"http://www.example.com": { "http://www.example.com": {
"tls-ports": [443, 8000], "tls-ports": [443, 8000],
"lifetime": 2592000 "lifetime": 2592000
} }
} }
Note that this mechanism is only defined to establish reasonable 2.2. Interaction with "https" URIs
assurances for the purposes of this specification; it does not apply
to other uses of alternative services unless they explicitly invoke
it.
4. Interaction with "https" URIs
When using alternative services, requests for resources identified by When using alternative services, requests for resources identified by
both "http" and "https" URIs might use the same connection, because both "http" and "https" URIs might use the same connection, because
HTTP/2 permits requests for multiple origins on the same connection. HTTP/2 permits requests for multiple origins on the same connection.
Since "https" URIs rely on server authentication, a connection that
is initially created for "http" URIs without authenticating the
server cannot be used for "https" URIs until the server certificate
is successfully authenticated. Section 3.1 of [RFC2818] describes
the basic mechanism, though the authentication considerations in
Section 2.1 of [RFC7838] also apply.
Connections that are established without any means of server
authentication (for instance, the purely anonymous TLS cipher suites)
cannot be used for "https" URIs.
Because of the risk of server confusion about individual requests' Because of the risk of server confusion about individual requests'
schemes (see Section 8.4), clients MUST NOT mix "https" and "http" schemes (see Section 4.4), clients MUST NOT send "http" requests on a
requests on the same connection unless the http-opportunistic connection that has previously been used for "https" requests, unless
response's origin object Section 6 has a "mixed-scheme" member whose the http-opportunistic origin object Section 2.3 fetched over that
value is "true". connection has a "mixed-scheme" member whose value is "true".
5. Requiring Use of TLS
Even when the alternative service is strongly authenticated,
opportunistically upgrading cleartext HTTP connections to use TLS is
subject to active attacks. In particular:
o Because the original HTTP connection is in cleartext, it is
vulnerable to man-in-the-middle attacks, and
o By default, if clients cannot reach the alternative service, they
will fall back to using the original cleartext origin.
Given that the primary goal of this specification is to prevent
passive attacks, these are not critical failings (especially
considering the alternative - HTTP over cleartext). However, a
modest form of protection against active attacks can be provided for
clients on subsequent connections.
When an origin is able to commit to providing service for a
particular origin over TLS for a bounded period of time, clients can
choose to rely upon its availability, failing when it cannot be
contacted. Effectively, this makes the choice to use a secured
protocol "sticky".
5.1. Opportunistic Commitment
An origin can reduce the risk of attacks on opportunistically secured
connections by committing to provide a secured, authenticated
alternative service. This is done by including the optional "tls-
commit" member in the origin object of the http-opportunistic well-
known response (see Section 6).
This feature is optional due to the requirement for server
authentication and the potential risk entailed (see Section 5.3).
When the value of the "tls-commit" member is "true" ([RFC7159],
Section 3), it indicates that the origin makes such a commitment for
the duration of the origin object lifetime.
{
"http://www.example.com": {
"tls-ports": [443,8080],
"tls-commit": true,
"lifetime": 3600
}
}
Including "tls-commit" creates a commitment to provide a secured
alternative service for the advertised period. Clients that receive
this commitment can assume that a secured alternative service will be
available for the origin object lifetime. Clients might however
choose to limit this time (see Section 5.3).
5.2. Client Handling of A Commitment
The value of the "tls-commit" member MUST be ignored unless the
alternative service can be strongly authenticated. The same
authentication requirements that apply to "https://" resources SHOULD
be applied to authenticating the alternative. Minimum authentication
requirements for HTTP over TLS are described in Section 2.1 of
[RFC7838] and Section 3.1 of [RFC2818]. As noted in [RFC7838],
clients can impose other checks in addition to this minimum set. For
instance, a client might choose to apply key pinning [RFC7469].
A client that receives a commitment and that successfully
authenticates the alternative service can assume that a secured
alternative will remain available for the origin object lifetime.
A client SHOULD avoid sending requests via cleartext protocols or to
unauthenticated alternative services for the duration of the origin
object lifetime, except to discover new potential alternatives.
A commitment is not bound to a particular alternative service.
Clients are able to use alternative services that they become aware
of. However, once a valid and authenticated commitment has been
received, clients SHOULD NOT use an alternative service without both
reasonable assurances (see Section 3) and strong authentication.
Where there is an active commitment, clients SHOULD ignore
advertisements for unsecured alternative services.
A client MAY send requests to an unauthenticated origin in an attempt
to discover potential alternative services, but these requests SHOULD
be entirely generic and avoid including credentials.
5.3. Operational Considerations
Errors in configuration of commitments has the potential to render
even the unsecured origin inaccessible for the duration of a
commitment. Initial deployments are encouraged to use short duration
commitments so that errors can be detected without causing the origin
to become inaccessible to clients for extended periods.
To avoid situations where a commitment causes errors, clients MAY
limit the time over which a commitment is respected for a given
origin. A lower limit might be appropriate for initial commitments;
the certainty that a site has set a correct value - and the
corresponding limit on persistence - might increase as a commitment
is renewed multiple times.
6. The "http-opportunistic" well-known URI 2.3. The "http-opportunistic" well-known URI
This specification defines the "http-opportunistic" well-known URI This specification defines the "http-opportunistic" well-known URI
[RFC5785]. A client is said to have a valid http-opportunistic [RFC5785]. A client is said to have a valid http-opportunistic
response for a given origin when: response for a given origin when:
o The client has obtained a 200 (OK) response for the well-known URI o The client has obtained a 200 (OK) response for the well-known URI
from the origin, and it is fresh [RFC7234] (potentially through from the origin, and it is fresh [RFC7234] (potentially through
revalidation [RFC7232]), and revalidation [RFC7232]), and
o That response has the media type "application/json", and o That response has the media type "application/json", and
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o The origin object has a "lifetime" member, whose value is a number o The origin object has a "lifetime" member, whose value is a number
indicating the number of seconds which the origin object is valid indicating the number of seconds which the origin object is valid
for (hereafter, the "origin object lifetime"), and for (hereafter, the "origin object lifetime"), and
o The origin object lifetime is greater than the "current_age" (as o The origin object lifetime is greater than the "current_age" (as
per [RFC7234], Section 4.2.3). per [RFC7234], Section 4.2.3).
Note that origin object lifetime might differ from the freshness Note that origin object lifetime might differ from the freshness
lifetime of the response. lifetime of the response.
7. IANA Considerations 3. IANA Considerations
This specification registers a Well-Known URI [RFC5785]: This specification registers a Well-Known URI [RFC5785]:
o URI Suffix: http-opportunistic o URI Suffix: http-opportunistic
o Change Controller: IETF o Change Controller: IETF
o Specification Document(s): Section 6 of [this specification] o Specification Document(s): Section 2.3 of [this specification]
o Related Information: o Related Information:
8. Security Considerations 4. Security Considerations
8.1. Security Indicators 4.1. Security Indicators
User Agents MUST NOT provide any special security indicia when an User Agents MUST NOT provide any special security indicia when an
"http" resource is acquired using TLS. In particular, indicators "http" resource is acquired using TLS. In particular, indicators
that might suggest the same level of security as "https" MUST NOT be that might suggest the same level of security as "https" MUST NOT be
used (e.g., a "lock device"). used (e.g., a "lock device").
8.2. Downgrade Attacks 4.2. Downgrade Attacks
A downgrade attack against the negotiation for TLS is possible. With A downgrade attack against the negotiation for TLS is possible.
commitment (see Section 5), this is limited to occasions where
clients have no prior information (see Section 8.3), or when
persisted commitments have expired.
For example, because the "Alt-Svc" header field [RFC7838] likely For example, because the "Alt-Svc" header field [RFC7838] likely
appears in an unauthenticated and unencrypted channel, it is subject appears in an unauthenticated and unencrypted channel, it is subject
to downgrade by network attackers. In its simplest form, an attacker to downgrade by network attackers. In its simplest form, an attacker
that wants the connection to remain in the clear need only strip the that wants the connection to remain in the clear need only strip the
"Alt-Svc" header field from responses. "Alt-Svc" header field from responses.
Downgrade attacks can be partially mitigated using the "tls-commit" 4.3. Privacy Considerations
member of the http-opportunistic well-known resource, because when it
is used, a client can avoid using cleartext to contact a supporting
server. However, this only works when a previous connection has been
established without an active attacker present; a continuously
present active attacker can either prevent the client from ever using
TLS, or offer its own certificate.
8.3. Privacy Considerations
Cached alternative services can be used to track clients over time; Cached alternative services can be used to track clients over time;
e.g., using a user-specific hostname. Clearing the cache reduces the e.g., using a user-specific hostname. Clearing the cache reduces the
ability of servers to track clients; therefore clients MUST clear ability of servers to track clients; therefore clients MUST clear
cached alternative service information when clearing other origin- cached alternative service information when clearing other origin-
based state (i.e., cookies). based state (i.e., cookies).
8.4. Confusion Regarding Request Scheme 4.4. Confusion Regarding Request Scheme
HTTP implementations and applications sometimes use ambient signals HTTP implementations and applications sometimes use ambient signals
to determine if a request is for an "https" resource; for example, to determine if a request is for an "https" resource; for example,
they might look for TLS on the stack, or a server port number of 443. they might look for TLS on the stack, or a server port number of 443.
This might be due to limitations in the protocol (the most common This might be due to limitations in the protocol (the most common
HTTP/1.1 request form does not carry an explicit indication of the HTTP/1.1 request form does not carry an explicit indication of the
URI scheme), or it may be because how the server and application are URI scheme), or it may be because how the server and application are
implemented (often, they are two separate entities, with a variety of implemented (often, they are two separate entities, with a variety of
possible interfaces between them). possible interfaces between them).
Any security decisions based upon this information could be misled by Any security decisions based upon this information could be misled by
the deployment of this specification, because it violates the the deployment of this specification, because it violates the
assumption that the use of TLS (or port 443) means that the client is assumption that the use of TLS (or port 443) means that the client is
accessing a HTTPS URI, and operating in the security context implied accessing a HTTPS URI, and operating in the security context implied
by HTTPS. by HTTPS.
Therefore, servers need to carefully examine the use of such signals Therefore, servers need to carefully examine the use of such signals
before deploying this specification. before deploying this specification.
8.5. Server Controls 4.5. Server Controls
Because this specification allows "reasonable assurances" to be This specification requires that a server send both an Alternative
established by the content of a well-known URI, servers SHOULD take Service advertisement and host content in a well-known location to
suitable measures to assure that its content remains under their send HTTP requests over TLS. Servers SHOULD take suitable measures
control. Likewise, because the Alt-Svc header field is used to to ensure that the content of the well-known resource remains under
their control. Likewise, because the Alt-Svc header field is used to
describe policies across an entire origin, servers SHOULD NOT permit describe policies across an entire origin, servers SHOULD NOT permit
user content to set or modify the value of this header. user content to set or modify the value of this header.
9. References 5. References
9.1. Normative References 5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000, DOI 10.17487/RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>. <http://www.rfc-editor.org/info/rfc2818>.
skipping to change at page 11, line 33 skipping to change at page 8, line 42
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540, Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015, DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>. <http://www.rfc-editor.org/info/rfc7540>.
[RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP [RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Alternative Services", RFC 7838, DOI 10.17487/RFC7838, Alternative Services", RFC 7838, DOI 10.17487/RFC7838,
April 2016, <http://www.rfc-editor.org/info/rfc7838>. April 2016, <http://www.rfc-editor.org/info/rfc7838>.
9.2. Informative References 5.2. Informative References
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <http://www.rfc-editor.org/info/rfc7258>. 2014, <http://www.rfc-editor.org/info/rfc7258>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435, Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <http://www.rfc-editor.org/info/rfc7435>. December 2014, <http://www.rfc-editor.org/info/rfc7435>.
[RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning [RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April
2015, <http://www.rfc-editor.org/info/rfc7469>. 2015, <http://www.rfc-editor.org/info/rfc7469>.
[W3C.CR-mixed-content-20160802]
West, M., "Mixed Content", World Wide Web Consortium CR
CR-mixed-content-20160802, August 2016,
<https://www.w3.org/TR/2016/CR-mixed-content-20160802>.
Appendix A. Acknowledgements Appendix A. Acknowledgements
Mike Bishop contributed significant text to this document. Mike Bishop contributed significant text to this document.
Thanks to Patrick McManus, Stefan Eissing, Eliot Lear, Stephen Thanks to Patrick McManus, Stefan Eissing, Eliot Lear, Stephen
Farrell, Guy Podjarny, Stephen Ludin, Erik Nygren, Paul Hoffman, Adam Farrell, Guy Podjarny, Stephen Ludin, Erik Nygren, Paul Hoffman, Adam
Langley, Eric Rescorla, Julian Reschke, Kari Hurtta, and Richard Langley, Eric Rescorla, Julian Reschke, Kari Hurtta, and Richard
Barnes for their feedback and suggestions. Barnes for their feedback and suggestions.
Authors' Addresses Authors' Addresses
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