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Versions: 00                                                            
Network Working Group                                           R. Sayre
Internet-Draft                                       Mozilla Corporation
Intended status: Informational                          January 15, 2007
Expires: July 19, 2007

                     Security Requirements for HTTP

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

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Internet-Draft       Security Requirements for HTTP         January 2007


   Recent IESG practice dictates that IETF protocols must specify
   mandatory to implement security mechanisms, so that all conformant
   implementations share a common baseline.  This document examines all
   widely deployed HTTP security technologies, and analyzes the trade-
   offs of each.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  4
   3.  Existing HTTP Security Mechanisms  . . . . . . . . . . . . . .  5
     3.1.  Forms And Cookies  . . . . . . . . . . . . . . . . . . . .  5
     3.2.  HTTP Access Authentication . . . . . . . . . . . . . . . .  6
       3.2.1.  Basic Authentication . . . . . . . . . . . . . . . . .  6
       3.2.2.  Digest Authentication  . . . . . . . . . . . . . . . .  6
       3.2.3.  Other Schemes  . . . . . . . . . . . . . . . . . . . .  7
     3.3.  Centrally-Issued Tickets . . . . . . . . . . . . . . . . .  7
     3.4.  Web Services . . . . . . . . . . . . . . . . . . . . . . .  7
     3.5.  Transport Layer Security . . . . . . . . . . . . . . . . .  8
   4.  Revisions To HTTP  . . . . . . . . . . . . . . . . . . . . . .  9
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.  Normative References . . . . . . . . . . . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 13

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1.  Introduction

   Note: this is document is just a laundry list of security
   technologies and tradeoffs for the moment.

   Recent IESG practice dictates that IETF protocols are required to
   specify mandatory to implement security mechanisms.  The IETF
   Standards Process [RFC2026] does not require that protocols specify
   mandatory security mechanisms.  Strong Security Requirements for IETF
   Standard Protocols [RFC3365] requires that all IETF protocols provide
   a mechanism for implementors to provide strong security.  The
   document does not define the term "strong security".  Security
   Mechanisms for the Internet [RFC3631] is not an IETF procedural RFC,
   but it is perhaps most relevant.  Section 2.2 states:

         We have evolved in the IETF the notion of "mandatory to
         implement" mechanisms.  This philosophy evolves from our
         primary desire to ensure interoperability between different
         implementations of a protocol.  If a protocol offers many
         options for how to perform a particular task, but fails to
         provide for at least one that all must implement, it may be
         possible that multiple, non-interoperable implementations may
         result.  This is the consequence of the selection of
         non-overlapping mechanisms being deployed in the different

   This document examines the effects of applying security constraints
   to Web applications, documents the properties that result from each
   method, and will make Best Current Practice recommendations for HTTP
   security in a later document version.

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2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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3.  Existing HTTP Security Mechanisms

   For HTTP, the IETF generally defines "security mechanisms" as some
   combination of access authentication and/or a secure transport.

3.1.  Forms And Cookies

   Almost all HTTP authentication is accomplished through HTML forms,
   with session keys stored in cookies.  For cookies, most
   implementations rely on the Netscape specification.  One update, HTTP
   State Management Mechanism [RFC2109] is relatively widely
   implemented, but most clients don't advertise support for it.  HTTP
   State Management Mechanism was later updated [RFC2965], but the newer
   version is not widely implemented.

   Forms and cookies have number of properties that make them an
   excellent solution for some implementors.  However, many of those
   properties introduce serious security trade-offs.

   HTML forms provide a large degree of control over presentation, an
   imperative for many websites.  However, this increases user reliance
   on the appearance of the interface.  Many users do not understand the
   construction of URIs [RFC3986], or their presentation in common
   clients [todo: citation].  As a result, forms are extremely
   vulnerable to spoofing.

   HTML forms provide acceptable internationalization if used carefully,
   at the cost of being transmitted as normal HTTP content in all cases
   (credentials are not differentiated in the protocol).

   HTML forms provide a facility for sites to indicate a password should
   never be pre-populated. [@more on autocomplete]

   The cookies that result from a successful form submission make it
   unessecary to validate credentials with each HTTP request, an
   excellent property for scalability.  Cookies are susceptible to a
   large variety of XSS (Cross-site scripting) attacks, and measures to
   prevent such attacks will never be as stringent as necessary for
   authentication credentials, because cookies are used for many
   purposes.  Cookies are also susceptible to a wide variety of attacks
   from malicious intermediaries and observers.  The possible attacks
   depend on the contents of the cookie data.  There is no standard
   format for most of the data.

   HTML forms and cookies provide flexible ways of ending a session from
   the client.

   HTML forms require an HTML rendering engine, which many protocols

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   have no use for.

3.2.  HTTP Access Authentication

   HTTP 1.1 provides a simple authentication framework, and HTTP
   Authentication: Basic and Digest Access Authentication [RFC2617]
   defines two OPTIONAL mechanisms.  Both of these mechanisms are
   extremely rarely used in comparison to forms and cookies, but some
   degree of support for one or both is available in many
   implementations.  Neither scheme provides presentation control,
   logout capabilities, or interoperable internationalization.

3.2.1.  Basic Authentication

   Basic Authentication transmits usernames and passwords in the clear.
   It is very easy to implement, but not at all secure unless used over
   a secure transport.

   Basic has very poor scalability properties, because credentials must
   be revalidated with every request, and secure transports negate many
   of HTTP's caching mechanisms.  Some implementations use cookies in
   combination with Basic credentials, but there is no standard method
   of doing so.

   Since Basic credentials are clear text, they are reusable by any
   party.  This makes them compatible with any authentication database,
   at the cost of making the user vulnerable to mismanaged or malicious
   servers, even over a secure channel.

   Basic is not interoperable when used with credentials that contain
   characters outside of the Latin-1 range.

3.2.2.  Digest Authentication

   In Digest Authentication, the client transmits the results of hashing
   user credentials with properties of the request and values from the
   server challenge.  Digest is susceptible to man in the middle attacks
   when not used over a secure transport.

   Digest has some properties that are preferable to Basic and Cookies.
   Credentials are not immediately reusable by parties that observe or
   recieve them, and session data can be transmitted along side
   credentials with each request, allowing servers to validate
   credentials only when absolutely necessary.  Authentication data
   session keys are distinct from other protocol traffic.

   Digest includes many modes of operation, but only the simplest modes
   enjoy any degree of interoperability.  For example, most

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   implementations do not implement the mode that provides full message
   integrity.  Additionally, implementation experience has shown that
   the mode is impractical, because it requires servers to analyze the
   full request before determining whether the client knows the shared

   Digest is extremely susceptible to offline dictionary attacks, making
   it practical for attackers to perform a namespace walk consisting of
   a few million passwords [todo: cite].

   Many of the most widely-deployed HTTP/1.1 clients are not compliant
   when GET requests include a query string [Apache_Digest].

   Digest requires that authentication databases be expressly designed
   to accomodate it.  As a result, many authentication databases are
   incompatible, including the most common method of storing passwords
   for use with Forms and Cookies.

   Many Digest capabilities included to prevent replay attacks expose
   the server to Denial of Service attacks.

   Digest is not interoperable when used with credentials that contain
   characters outside of the Latin-1 range.

3.2.3.  Other Schemes

   There are many niche schemes that make use of the HTTP Authentication
   framework, but very few are well documented.  Some are bound to
   transport layer connections.

3.3.  Centrally-Issued Tickets

   Many large Internet services rely on authentication schemes that
   center on clients consulting a single service for a time-limited
   ticket that is validated with undocumented heuristics.  Centralized
   ticket issuing has the advantage that users may employ one set of
   credentials for many services, and clients don't send credentials to
   many servers.  This approach is often no more than a sophisticated
   application of Forms and Cookies.

   All of the schemes in wide use are proprietary, undocumented, and
   non-standard.  There are many standardization efforts in progress, as

3.4.  Web Services

   Many security properties mentioned above have been recast in XML-
   based protocols, using HTTP as a substitute for TCP.  Like the

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   amalgam of HTTP technologies mentioned above, the XML-based protocols
   are defined by an ever-changing combination of standard and vendor-
   produced specifications, some of which may be obsoleted at any time
   [WS-Pagecount], with no documented change control procedures.  These
   protocols usually don't have much in common the Architecture of the
   World Wide Web. It's not clear why term "Web" is used to group them,
   but they are obviously out of scope for HTTP-based application

3.5.  Transport Layer Security


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4.  Revisions To HTTP

   Is is possible that HTTP will be revised in the future.  HTTP 1.1
   [RFC2616] and Use and Interpretation of HTTP Version Numbers
   [RFC2145] define conformance requirements in relation to version
   numbers.  In HTTP 1.1, all authentication mechanisms are OPTIONAL,
   and no single transport substrate is specified.  Any HTTP revision
   that adds a mandatory security mechanism or transport substrate MUST
   increment the HTTP version number appropriately.  All widely used
   schemes are non-standard and/or proprietary.

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5.  Security Considerations

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6.  Normative References

              ASF, "Apache HTTP Server - mod_auth_digest".

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2109]  Kristol, D. and L. Montulli, "HTTP State Management
              Mechanism", RFC 2109, February 1997.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2145]  Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, "Use
              and Interpretation of HTTP Version Numbers", RFC 2145,
              May 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.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC2965]  Kristol, D. and L. Montulli, "HTTP State Management
              Mechanism", RFC 2965, October 2000.

   [RFC3365]  Schiller, J., "Strong Security Requirements for Internet
              Engineering Task Force Standard Protocols", BCP 61,
              RFC 3365, August 2002.

   [RFC3631]  Bellovin, S., Schiller, J., and C. Kaufman, "Security
              Mechanisms for the Internet", RFC 3631, December 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

              Bray, T., "WS-Pagecount", September 2004.

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Author's Address

   Robert Sayre
   Mozilla Corporation

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