draft-ietf-httpbis-http2-encryption-11.txt   draft-ietf-httpbis-http2-encryption-latest.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: September 18, 2017 Mozilla Expires: December 2, 2017 Mozilla
March 17, 2017 May 31, 2017
Opportunistic Security for HTTP/2 Opportunistic Security for HTTP/2
draft-ietf-httpbis-http2-encryption-11 draft-ietf-httpbis-http2-encryption-latest
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) and HTTP/2 to mitigate pervasive Transport Layer Security (TLS) and HTTP/2 to mitigate pervasive
monitoring attacks. This mechanism not a replacement for "https" monitoring attacks. This mechanism not a replacement for "https"
URIs; it is vulnerable to active attacks. URIs; it is vulnerable to active attacks.
Status of This Memo Status of This Memo
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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 September 18, 2017. This Internet-Draft will expire on December 2, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 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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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 . . . . . . . . . . . . . . . . . . . 2 1.1. Goals and Non-Goals . . . . . . . . . . . . . . . . . . . 2
1.2. Notational Conventions . . . . . . . . . . . . . . . . . 3 1.2. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Using HTTP URIs over TLS . . . . . . . . . . . . . . . . . . 3 2. Using HTTP URIs over TLS . . . . . . . . . . . . . . . . . . 3
2.1. Alternative Server Opt-In . . . . . . . . . . . . . . . . 4 2.1. Alternative Server Opt-In . . . . . . . . . . . . . . . . 4
2.2. Interaction with "https" URIs . . . . . . . . . . . . . . 5 2.2. Interaction with “https” URIs . . . . . . . . . . . . . . 5
2.3. The "http-opportunistic" well-known URI . . . . . . . . . 5 2.3. The “http-opportunistic” well-known URI . . . . . . . . . 5
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
4.1. Security Indicators . . . . . . . . . . . . . . . . . . . 6 4.1. Security Indicators . . . . . . . . . . . . . . . . . . . 6
4.2. Downgrade Attacks . . . . . . . . . . . . . . . . . . . . 6 4.2. Downgrade Attacks . . . . . . . . . . . . . . . . . . . . 6
4.3. Privacy Considerations . . . . . . . . . . . . . . . . . 6 4.3. Privacy Considerations . . . . . . . . . . . . . . . . . 6
4.4. Confusion Regarding Request Scheme . . . . . . . . . . . 7 4.4. Confusion Regarding Request Scheme . . . . . . . . . . . 7
4.5. Server Controls . . . . . . . . . . . . . . . . . . . . . 7 4.5. Server Controls . . . . . . . . . . . . . . . . . . . . . 7
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Normative References . . . . . . . . . . . . . . . . . . 7 5.1. Normative References . . . . . . . . . . . . . . . . . . 7
5.2. Informative References . . . . . . . . . . . . . . . . . 8 5.2. Informative References . . . . . . . . . . . . . . . . . 8
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This document describes a usage model whereby sites can serve "http" This document describes a usage model whereby sites can serve "http"
URIs over TLS, thereby avoiding the problem of serving Mixed Content URIs over TLS, thereby avoiding the problem of serving Mixed Content
(described in [W3C.CR-mixed-content-20160802]) while still providing (described in [W3C.CR-mixed-content-20160802]) while still providing
protection against passive attacks. protection against passive attacks.
Opportunistic Security does not provide the same guarantees as using Opportunistic Security does not provide the same guarantees as using
TLS with "https" URIs, because it is vulnerable to active attacks, TLS with "https" URIs, because 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”).
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 (but significant) goal is to provide for ease of A secondary (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 Preventing active attacks (such as a Man-in-the-Middle) is a non-goal
for this specification. Furthermore, this specification is not for this specification. Furthermore, this specification is not
intended to replace or offer an alternative to "https", since "https" intended to replace or offer an alternative to "https", since "https"
both prevents active attacks and invokes a more stringent security both prevents active attacks and invokes a more stringent security
model in most clients. 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]. Such a protocol MUST include an TLS, such as "h2" [RFC7540]. Such a protocol MUST include an
explicit indication of the scheme of the resource. This excludes explicit indication of the scheme of the resource. This excludes
HTTP/1.1; HTTP/1.1 clients are forbidden from including the absolute HTTP/1.1; HTTP/1.1 clients are forbidden from including the absolute
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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. A server that also provides "https" resources on the present them. A server that also provides "https" resources on the
same port can request a certificate during the TLS handshake, but it same port can request a certificate during the TLS handshake, but it
MUST NOT abort the handshake if the client does not provide one. MUST NOT abort the handshake if the client does not provide one.
2.1. Alternative Server Opt-In 2.1. Alternative Server Opt-In
It is possible that the server might become confused about whether It is possible that the server might become confused about whether
requests' URLs have a "http" or "https" scheme, for various reasons; requests URLs have a "http" or "https" scheme, for various reasons;
see Section 4.4. To ensure that the alternative service has opted see Section 4.4. To ensure that the alternative service has opted
into serving "http" URLs over TLS, clients are required to perform into serving "http" URLs over TLS, clients are required to perform
additional checks before directing "http" requests to it. additional checks before directing "http" requests to it.
Clients MUST NOT send "http" requests over a secured connection, Clients MUST NOT send "http" requests over a secured connection,
unless the chosen alternative service presents a certificate that is unless the chosen alternative service presents a certificate that is
valid for the origin as defined in [RFC2818]. Using an authenticated valid for the origin as defined in [RFC2818]. Using an authenticated
alternative service establishes "reasonable assurances" for the alternative service establishes “reasonable assurances” for the
purposes of [RFC7838]. In addition to authenticating the server, the purposes of [RFC7838]. In addition to authenticating the server, the
client MUST have obtained a valid http-opportunistic response for an client MUST have obtained a valid http-opportunistic response for an
origin (as per Section 2.3) using the authenticated connection. An origin (as per Section 2.3) using the authenticated connection. An
exception to the latter restriction is made for requests for the exception to the latter restriction is made for requests for the
"http-opportunistic" well-known URI. “http-opportunistic” well-known URI.
For example, assuming the following request is made over a TLS For example, assuming the following request is made over a TLS
connection that is successfully authenticated for those origins, the connection that is successfully authenticated for those origins, the
following request/response pair would allow requests for the origins following request/response pair would allow requests for the origins
"http://www.example.com" or "http://example.com" to be sent using a “http://www.example.com” or “http://example.com” to be sent using a
secured connection: secured connection:
HEADERS HEADERS
+ END_STREAM + END_STREAM
+ END_HEADERS + END_HEADERS
:method = GET :method = GET
:scheme = http :scheme = http
:authority = example.com :authority = example.com
:path = /.well-known/http-opportunistic :path = /.well-known/http-opportunistic
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+ END_STREAM + END_STREAM
[ "http://www.example.com", "http://example.com" ] [ "http://www.example.com", "http://example.com" ]
Though this document describes multiple origins, this is only for Though this document describes multiple origins, this is only for
operational convenience. Only a request made to an origin (over an operational convenience. Only a request made to an origin (over an
authenticated connection) can be used to acquire this resource for authenticated connection) can be used to acquire this resource for
that origin. Thus in the example, the request to that origin. Thus in the example, the request to
"http://example.com" cannot be assumed to also provide an http- "http://example.com" cannot be assumed to also provide an http-
opportunistic response for "http://www.example.com". opportunistic response for "http://www.example.com".
2.2. Interaction with "https" URIs 2.2. Interaction with “https” URIs
Clients MUST NOT send "http" requests and "https" requests on the Clients MUST NOT send "http" requests and "https" requests on the
same connection. Similarly, clients MUST NOT send "http" requests same connection. Similarly, clients MUST NOT send "http" requests
for multiple origins on the same connection. for multiple origins on the same connection.
2.3. 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 requested the well-known URI from the origin over o The client has requested the well-known URI from the origin over
an authenticated connection and a 200 (OK) response was provided, an authenticated connection and a 200 (OK) response was provided,
and and
o That response is fresh [RFC7234] (potentially through revalidation o That response is fresh [RFC7234] (potentially through revalidation
[RFC7232]), and [RFC7232]), and
o That response has the media type "application/json", and o That response has the media type “application/json”, and
o That response's payload, when parsed as JSON [RFC7159], contains o That responses payload, when parsed as JSON [RFC7159], contains
an array as the root, and an array as the root, and
o The array contains a string that is a case-insensitive character- o The array contains a string that is a case-insensitive character-
for-character match for the origin in question, serialised into for-character match for the origin in question, serialised into
Unicode as per Section 6.1 of [RFC6454]. Unicode as per Section 6.1 of [RFC6454].
A client MAY treat an "http-opportunistic" resource as invalid if A client MAY treat an “http-opportunistic” resource as invalid if
values it contains are not strings. values it contains are not strings.
This document does not define semantics for "http-opportunistic" This document does not define semantics for “http-opportunistic”
resources on an "https" origin, nor does it define semantics if the resources on an "https" origin, nor does it define semantics if the
resource includes "https" origins. resource includes "https" origins.
Allowing clients to cache the http-opportunistic resource means that Allowing clients to cache the http-opportunistic resource means that
all alternative services need to be able to respond to requests for all alternative services need to be able to respond to requests for
"http" resources. A client is permitted to use an alternative "http" resources. A client is permitted to use an alternative
service without acquiring the http-opportunistic resource from that service without acquiring the http-opportunistic resource from that
service. service.
A client MUST NOT use any cached copies of an http-opportunistic A client MUST NOT use any cached copies of an http-opportunistic
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o Related Information: o Related Information:
4. Security Considerations 4. Security Considerations
4.1. Security Indicators 4.1. Security Indicators
User Agents MUST NOT provide any special security indicators when an User Agents MUST NOT provide any special security indicators 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”).
4.2. Downgrade Attacks 4.2. Downgrade Attacks
A downgrade attack against the negotiation for TLS is possible. A downgrade attack against the negotiation for TLS is possible.
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.
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