Internet DRAFT - draft-miller-http-unauth-tls
draft-miller-http-unauth-tls
Network Working Group M. Miller
Internet-Draft Cisco Systems, Inc.
Intended status: Informational January 23, 2014
Expires: July 27, 2014
Applying Unauthenticated Transport Layer Security (TLS) to Hypertext
Transport Protocol (HTTP) Connections
draft-miller-http-unauth-tls-00
Abstract
With the pervasiveness of passive monitoring and ubiquity of
unencrypted Hypertext Transport Protocol (HTTP), it is desirable to
mitigate passive monitoring without causing an undue burden on HTTP
user agents and servers. This document describes the rationale and
process for using Transport Layer Security (TLS) in an
unauthenticated manner for exchanging HTTP messages. The application
of unauthenticated TLS - particularly when Perfect Forward Secrecy
(PFS) algorithms are used - change monitoring from being a passive
attack into an active attack.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 27, 2014.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. How it Works . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 3
2.2. Upgrade Failure . . . . . . . . . . . . . . . . . . . . . 3
2.3. Caching Upgrade Results . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Normative References . . . . . . . . . . . . . . . . . . 4
5.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The exchange of information through the use of Hypertext Transport
Protocol (HTTP) [RFC2616] is widespread, with the vast majority of
such traffic exchanged in the clear. As described in
[I-D.farrell-perpass-attack], passive monitoring is seen as an attack
on the privacy of users and organizations. The ubiquity of
unencrypted HTTP coupled with the pervasiveness of passive monitoring
means that the vast majority of HTTP traffic can be (and often is)
captured without the knowledge or consent of the primary parties -
namely the HTTP user agent and HTTP server - and with negligible
effort on the part of the passive monitor.
Therefore, it is desirable to apply apply encryption to the HTTP
exchange in the form of Transport Level Security (TLS) [RFC5246].
Traditionally, TLS has only been seen as useful if at least the
server is authenticated in the handshake, and that authentication is
done almost exclusively using PKIX certificates. However, using TLS
in an unauthenticated manner can mitigate passive monitoring attacks
by requiring the attacker to act as a man-in-the-middle, thereby
increasing the effort passive monitoring requires to be effective.
Forgoing TLS authentication eliminates the burden of obtaining
properly issued PKIX certificates, reducing the effort it takes to
deploy an encrypted HTTP server.
1.1. Terminology
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In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
[RFC2119].
This document reuses HTTP terminology from [RFC2616], [RFC2817], and
[RFC2818]. It reuses PKIX terminology from [RFC5280] and [RFC6125].
2. How it Works
When given a "http:" URI, the user agent attempts to establish a TLS
connection to the indicated origin. The exact processes used to
upgrade the connection to TLS is out of scope for this document; it
could use the Upgrade process documented in [RFC2817], or attempt to
connect to the server on the IANA-registered port for HTTP over TLS
(HTTPS) if the requested origin uses the IANA-registered port for
HTTP. During the TLS establishment, the user agent and server ignore
any certificate verification errors it might encounter with regards
to naming (e.g., self-signed certificate, or none of the certificate
identifiers not match the input URL).
Once established, the user agent and server then exchange HTTP
messages as if the connection were unencrypted. The use of HTTP
basic authentication is still NOT RECOMMENDED, and user agents MUST
NOT indicate in any way that the HTTP connection is protected (e.g.,
display a "locked" or "protected" indicator with the HTTP resource).
2.1. Forward Secrecy
The benefits of unauthenticated TLS are only realized if it is less
costly for an attacker to actively interject itself into the TLS
session than to passively collect all traffic and later compromise
the TLS handshakes. Forward secrecy prevents a passive monitor from
decrypting the TLS session if it has compromised the server's private
key. Software MUST use algorithms that provide perfect forward
secrecy (e.g., TLS_DHE, TLS_ECDHE, or TLS_DH_anon) when relying on
unauthenticated TLS.
2.2. Upgrade Failure
If the TLS connection could not be established, user agents need to
determine whether to continue based on their own policies. For
instance, a user agent might (among other possibilities):
1. prompt the user that communications with the server can be
monitored and asking whether the user wishes to proceed anyway;
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2. abandon the connection altogether, informing the user that
privacy protection could not be applied to the connection; or
3. silently continue without any encryption. Note this can
effectively lead to downgrade attacks.
2.3. Caching Upgrade Results
A user agent SHOULD cache the success or failure to establish a TLS
connection with a given origin. How much information about a
successful (or failed) attempt at establishing a TLS connection is
implementation and deployment specific, but needs to at least
indicate if unauthenticated TLS was used.
This cached information can then used for subsequent connections. If
a previous upgrade was successful, the user agent can decide to fail
if a subsequent TLS establishment fails. If a previous upgrade used
a specific certificate chain, the user agent can fail if a different
chain is presented.
3. Security Considerations
This entire document discusses security.
4. IANA Considerations
This document has no actions for IANA.
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
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within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
5.2. Informative References
[I-D.farrell-perpass-attack]
Farrell, S. and H. Tschofenig, "Pervasive Monitoring is an
Attack", draft-farrell-perpass-attack-03 (work in
progress), December 2013.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within HTTP/
1.1", RFC 2817, May 2000.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
Author's Address
Matthew Miller
Cisco Systems, Inc.
Email: mamille2@cisco.com
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