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rfc:rfc7072

Internet Engineering Task Force (IETF) N. Borenstein Request for Comments: 7072 Mimecast Category: Standards Track M. Kucherawy ISSN: 2070-1721 November 2013

                    A Reputation Query Protocol

Abstract

 This document defines a mechanism to conduct queries for reputation
 information over the HyperText Transfer Protocol (HTTP) using
 JavaScript Object Notation (JSON) as the payload meta-format.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7072.

Copyright Notice

 Copyright (c) 2013 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
 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.

Borenstein & Kucherawy Standards Track [Page 1] RFC 7072 A Reputation Query Protocol November 2013

Table of Contents

 1. Introduction ....................................................2
 2. Terminology and Definitions .....................................2
    2.1. Key Words ..................................................2
    2.2. Other Definitions ..........................................3
 3. Description .....................................................3
    3.1. Overview ...................................................3
    3.2. URI Template ...............................................3
    3.3. Syntax .....................................................4
    3.4. Response ...................................................6
    3.5. Protocol Support ...........................................6
 4. IANA Considerations .............................................7
 5. Security Considerations .........................................7
 6. References ......................................................8
    6.1. Normative References .......................................8
    6.2. Informative References .....................................8
 Appendix A. Acknowledgements .......................................9

1. Introduction

 This document defines a method to query a reputation data service for
 information about an entity, using the HyperText Transfer Protocol
 (HTTP) as the transport mechanism and JSON as the payload meta-
 format.
 The mechanism is a two-stage query:
 1.  A client retrieves a template from a server that describes the
     construction of a Universal Resource Identifier (URI) that will
     be the actual query;
 2.  The client then uses the constructed URI to request the
     reputation data from the server.

2. Terminology and Definitions

 This section defines terms used in the rest of the document.

2.1. Key Words

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [KEYWORDS].

Borenstein & Kucherawy Standards Track [Page 2] RFC 7072 A Reputation Query Protocol November 2013

2.2. Other Definitions

 Other terms of importance in this document are defined in [RFC7070]
 and [RFC7071].

3. Description

3.1. Overview

 The components to the question being asked are the following:
 o  The subject of the query;
 o  The name of the host, or the IP address, at which the reputation
    service is available;
 o  The name of the reputation application, i.e., the context within
    which the subject is being evaluated;
 o  Optionally, names of the specific reputation assertions or
    attributes that are being requested.
 There is no discovery protocol for finding reputation services.
 These are typically subscription services, negotiated between
 operators through some out-of-band method.
 Assertions are discussed in [RFC7071].
 The name of the application, if given, is expected to be one
 registered with IANA in the "Reputation Applications" registry, which
 is defined in [RFC7071].  A server receiving a query about an
 application it does not recognize or explicitly support (e.g., by
 virtue of private agreements or experimental extensions) MUST return
 a 404 error code.
 A reputation query made via [HTTP] encodes the question being asked
 in an HTTP GET method.  The specific syntax of the query itself is
 specified by retrieving a URI template from the reputation service,
 completing the template, and then issuing the query.

3.2. URI Template

 The template file is retrieved by requesting the [WELL-KNOWN-URI]
 "repute-template" from the host providing reputation service, using
 HTTP.  (The registration for this well-known URI is in Section 4.)
 The server returns the template file in a reply that MUST use the

Borenstein & Kucherawy Standards Track [Page 3] RFC 7072 A Reputation Query Protocol November 2013

 text/plain media type (see [MIME]) and SHOULD include an Expires
 field (see Section 14.21 of [HTTP]) indicating a duration for which
 the template is to be considered valid by clients and not re-queried.
 If an Expires field is present, the client SHOULD NOT send another
 query to the same server prior to the timestamp in the field.  If no
 Expires field is present, the client SHOULD wait at least one day
 before sending another query to the same server (i.e., the client
 assumes a default expiration of one day).
 The template file might contain more than one template.  Such a file
 MUST have each template separated by a carriage return (ASCII 0x0D)
 and newline (ASCII 0x0A) character, as is typical for most text-based
 Internet protocols.
 Each template in the file is expanded using the variables that are
 the parameters to the query.  These parameters are either the subject
 about which reputation information is sought (or details associated
 with it) or other parameters that are established out-of-band with
 the reputation service; they are not established by any automated
 discovery described here.  The client then attempts to query each
 expanded template that uses a URI scheme it is capable of querying,
 in the order presented in the file, until the client finds one to
 which it can establish a usable connection and issue the query.
 For example, given the following template:
 http://{service}/{application}/{subject}/{assertion}
 A query about the use of the domain "example.org" in the "email-id"
 application context to a service run at "example.com", where that
 application declares a required "subject" parameter, requesting the
 "SPAM" reputation assertion, would be formed as follows:
 http://example.com/email-id/example.org/spam

3.3. Syntax

 The syntax for the [URI] of the query is constructed using a template
 as per [URI-TEMPLATE].  (See Section 3.2.)  Clients MUST provide the
 following values in the expansion of the template:
 application:  The name of the application reputation in whose context
    the request is being made.  These names are registered with IANA,
    and conform to the ABNF "token" found in [MIME].

Borenstein & Kucherawy Standards Track [Page 4] RFC 7072 A Reputation Query Protocol November 2013

 service:  The hostname or IP address to which the query is being
    sent.  This MUST be the same as the host to which the template
    query was issued.
 subject:  The subject of the query, extracted from some content to be
    evaluated.  The subject portion of the template conforms to the
    ABNF "value" found in [MIME].
 The following variable can also be provided.  It is not mandatory in
 this model, but a specific application (defined in its own extension
 document) might declare it mandatory in a specific context:
 assertion:  The name of the specific assertion of interest to the
    client.  Assertion names conform to the ABNF "token" found in
    [MIME].  If absent, the client is indicating that it requests all
    available assertion information.
 If a template contains a variable that is not required and the client
 does not have a value to insert, it substitutes the empty string into
 the template in place of that variable.  Service providers crafting
 templates MUST do so such that a client doing an empty variable
 expansion will still produce a syntactically and semantically valid
 and unambiguous URI.  For example, given this template:
   http://{service}/{application}/{subject}/{assertion}/{a}/{b}
 If "{a}" and "{b}" are optional and "{a}" expands to the empty
 string, then the resulting URI will have adjacent backslash ("/",
 ASCII 0x2F) characters and one path component after the assertion.
 If the server interpreting the URI's path component removes or
 ignores adjacent backslash characters (such as is done with the UNIX
 filesystem), the server will be unable to distinguish an empty "{a}"
 from an empty "{b}", and it could serve the wrong response.  Where
 possible, the template needs to be constructed such that expansion of
 optional variables yields an unambiguous result.  For example, an
 unambiguous version of the above would be:
   http://{service}/{application}/{subject}/{assertion}/a={a}/b={b}
 ...or, even better, using URI template set expansions:
   http://{service}/{application}/{subject}/{assertion}{?a,b}
 Every application space has a set of assertions applicable to its own
 context.  [RFC7071] defines a single assertion assumed to exist in
 any application that does not define its own assertion set.

Borenstein & Kucherawy Standards Track [Page 5] RFC 7072 A Reputation Query Protocol November 2013

 Reputation applications can extend the set of optional or required
 query parameters as part of their IANA registration actions.  The set
 enumerated above establishes the base set common to all of them.
 Further, additional required or optional extension query parameters
 might be defined by specific reputation service providers, though
 these are private arrangements between client and server and will not
 be registered with IANA.
 Authentication between reputation client and server is outside the
 scope of this specification.  It could be provided through a variety
 of available transport-based or object-based mechanisms, including a
 later extension of this specification.

3.4. Response

 The response is expected to be contained in a media type designed to
 deliver reputons.  A media type designed for this purpose,
 "application/reputon+json", is defined in [RFC7071].
 If the server generates responses that contain an Expires field (see
 Section 14.21 of [HTTP]), that timestamp MUST align with the
 "expires" field within the response, if any.  Failing to do so can
 result in a state where the response has expired, but the HTTP reply
 has not, and the client would in that case be unable to get a fresh
 answer from the reputation server.

3.5. Protocol Support

 A client has to implement HTTP in order to retrieve the query
 template as described in Section 3.2.  Accordingly, a server can
 assume the client will be able to handle a URI template that produces
 a URI for the query using the "http" URI scheme.  The template could
 yield a query string that uses some other URI scheme, in which case
 the client could try that URI as well if it supports issuing queries
 with that URI scheme.
 A server SHOULD include support for providing service over HTTP, and
 publish templates indicating support for this, as a baseline for
 interoperability with arbitrary clients.

Borenstein & Kucherawy Standards Track [Page 6] RFC 7072 A Reputation Query Protocol November 2013

4. IANA Considerations

 This document registers the "repute-template" well-known URI in the
 "Well-Known URI" registry as defined by [WELL-KNOWN-URI], as follows:
 URI suffix:  repute-template
 Change controller:  IETF
 Specification document(s):  [RFC7072]
 Related information:  none

5. Security Considerations

 This document defines particular uses of existing protocols for a
 specific application.  In particular, the basic protocol used for
 this service to retrieve a URI template from a well-known location is
 basic HTTP, which is not secure without certain extensions.  Security
 issues relevant to use of URI templates are discussed in
 [URI-TEMPLATE], and those relevant to well-known URI definitions and
 retrieval are discussed in [WELL-KNOWN-URI].
 The reputation service itself will use HTTP or other transport
 methods to issue queries and receive replies.  Those protocols have
 registered URI schemes and, as such, presumably have documented
 security considerations.  The protocol described here operates atop
 those URI schemes, and does not itself present new security
 considerations.
 Reputation mechanisms represent an obvious security concern, in terms
 of the validity and use of the reputation information.  These issues
 are beyond the scope of this specification.  General information
 pertaining to using or providing reputation services can be found in
 [CONSIDERATIONS].
 The security considerations applicable to HTTP (see Section 15 of
 [HTTP] apply, since this query mechanism for reputation uses that
 protocol.  If it is desirable to conceal the content of the query and
 its response, use of encryption techniques such as HTTP over TLS
 [HTTPS] can be used.

Borenstein & Kucherawy Standards Track [Page 7] RFC 7072 A Reputation Query Protocol November 2013

6. References

6.1. Normative References

 [HTTP]     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.
 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [MIME]     Freed, N. and N. Borenstein, "Multipurpose Internet Mail
            Extensions (MIME) Part One: Format of Internet Message
            Bodies", RFC 2045, November 1996.
 [RFC7070]  Borenstein, N., Kucherawy, M., and A. Sullivan, "An
            Architecture for Reputation Reporting", RFC 7070, November
            2013.
 [RFC7071]  Borenstein, N. and M. Kucherawy, "A Media Type for
            Reputation Interchange", RFC 7071, November 2013.
 [URI-TEMPLATE]
            Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
            and D. Orchard, "URI Template", RFC 6570, March 2012.
 [URI]      Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
            Resource Identifier (URI): Generic Syntax", STD 66, RFC
            3986, January 2005.
 [WELL-KNOWN-URI]
            Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
            Uniform Resource Identifiers (URIs)", RFC 5785, April
            2010.

6.2. Informative References

 [CONSIDERATIONS]
            Kucherawy, M., "Operational Considerations Regarding
            Reputation Services", Work in Progress, May 2013.
 [HTTPS]    Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

Borenstein & Kucherawy Standards Track [Page 8] RFC 7072 A Reputation Query Protocol November 2013

Appendix A. Acknowledgements

 The authors would like to thank the following for their contributions
 to this work: Simon Hunt, Mark Nottingham, David F. Skoll, and Mykyta
 Yevstifeyev.

Authors' Addresses

 Nathaniel Borenstein
 Mimecast
 203 Crescent St., Suite 303
 Waltham, MA 02453
 USA
 Phone: +1 781 996 5340
 EMail: nsb@guppylake.com
 Murray S. Kucherawy
 270 Upland Drive
 San Francisco, CA 94127
 USA
 EMail: superuser@gmail.com

Borenstein & Kucherawy Standards Track [Page 9]

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