draft-ietf-repute-model-08.txt   draft-ietf-repute-model-09.txt 
REPUTE Working Group N. Borenstein REPUTE Working Group N. Borenstein
Internet-Draft Mimecast Internet-Draft Mimecast
Intended status: Standards Track M. Kucherawy Intended status: Standards Track M. Kucherawy
Expires: February 28, 2014 Expires: March 16, 2014
A. Sullivan, Ed. A. Sullivan, Ed.
Dyn, Inc. Dyn, Inc.
August 27, 2013 September 12, 2013
A Model for Reputation Reporting An Architecture for Reputation Reporting
draft-ietf-repute-model-08 draft-ietf-repute-model-09
Abstract Abstract
This document describes a general architecture for a reputation-based This document describes a general architecture for a reputation-based
service and a model for requesting reputation-related data over the service, allowing one to request reputation-related data over the
Internet, where "reputation" refers to predictions or expectations Internet, where "reputation" refers to predictions or expectations
about an entity or an identifier such as a domain name. The document about an entity or an identifier such as a domain name. The document
roughly follows the recommendations of RFC4101 for describing a roughly follows the recommendations of RFC4101 for describing a
protocol model. protocol model.
Status of this Memo Status of this Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on February 28, 2014. This Internet-Draft will expire on March 16, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. High-Level Architecture . . . . . . . . . . . . . . . . . . . 5 3. Related Documents . . . . . . . . . . . . . . . . . . . . . . 5
4. Terminology and Definitions . . . . . . . . . . . . . . . . . 7 4. High-Level Architecture . . . . . . . . . . . . . . . . . . . 5
4.1. Response Set . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Example of a Reputation Service Being Used . . . . . . . . 6
4.2. Reputon . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Terminology and Definitions . . . . . . . . . . . . . . . . . 8
5. Information Represented in a Response Set . . . . . . . . . . 8 5.1. Application . . . . . . . . . . . . . . . . . . . . . . . 8
6. Information Flow in the Reputation Query Protocol . . . . . . 9 5.2. Response Set . . . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5.3. Assertions and Ratings . . . . . . . . . . . . . . . . . . 8
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 9 5.4. Reputon . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Data In Transit . . . . . . . . . . . . . . . . . . . . . 9 6. Information Represented in a Response Set . . . . . . . . . . 9
8.2. Aggregation . . . . . . . . . . . . . . . . . . . . . . . 9 7. Information Flow in the Reputation Query Protocol . . . . . . 10
8.3. Collection Of Data . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 10
9.1. Biased Reputation Agents . . . . . . . . . . . . . . . . . 10 9.1. Data In Transit . . . . . . . . . . . . . . . . . . . . . 10
9.2. Malformed Messages . . . . . . . . . . . . . . . . . . . . 11 9.2. Aggregation . . . . . . . . . . . . . . . . . . . . . . . 11
9.3. Further Discussion . . . . . . . . . . . . . . . . . . . . 11 9.3. Collection Of Data . . . . . . . . . . . . . . . . . . . . 11
10. Informative References . . . . . . . . . . . . . . . . . . . . 11 9.4. Queries Can Reveal Information . . . . . . . . . . . . . . 11
Appendix A. Public Discussion . . . . . . . . . . . . . . . . . . 12 9.5. Compromised Relationships . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 10. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10.1. Biased Reputation Agents . . . . . . . . . . . . . . . . . 12
10.2. Malformed Messages . . . . . . . . . . . . . . . . . . . . 13
10.3. Further Discussion . . . . . . . . . . . . . . . . . . . . 13
11. Informative References . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Public Discussion . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
Historically, many Internet protocols have operated between Historically, many Internet protocols have operated between
unauthenticated entities. For example, an email message's author unauthenticated entities. For example, an email message's author
field (From) [MAIL] can contain any display name or address and is field (From) [MAIL] can contain any display name or address and is
not verified by the recipient or other agents along the delivery not verified by the recipient or other agents along the delivery
path. Similarly, a sending email server using [SMTP] trusts that the path. Similarly, a sending email server using the Simple Mail
[DNS] has led it to the intended receiving server. Both kinds of Transfer Protocol [SMTP] trusts that the Domain Name System [DNS] has
trust are easily betrayed, opening the operation to subversion of led it to the intended receiving server. Both kinds of trust are
some kind, which leads to spam, phishing, and other attacks. easily betrayed, opening the operation to subversion of some kind,
which makes spam, phishing, and other attacks even easier than they
would othewise be.
In recent years, explicit identity authentication mechanisms have In recent years, explicit identity authentication mechanisms have
begun to see wider deployment. For example, the [DKIM] protocol begun to see wider deployment. For example, the [DKIM] protocol
permits associating a validated identifier to a message. This permits associating a validated identifier to a message. This
association is cryptographically strong, and is an improvement over association is cryptographically strong, and is an improvement over
the prior state of affairs, but it does not distinguish between the prior state of affairs, but it does not distinguish between
identifiers of good actors and bad. Even when it is possible to identifiers of good actors and bad. Even when it is possible to
validate the domain name in an author field (e.g. validate the domain name in an author field (e.g.
"trustworthy.example.com" in "john.doe@trustworthy.example.com") "trustworthy.example.com" in "john.doe@trustworthy.example.com")
there is no basis for knowing whether it is associated with a good there is no basis for knowing whether it is associated with a good
skipping to change at page 3, line 38 skipping to change at page 3, line 40
in the hope that some receivers will confuse identity authentication in the hope that some receivers will confuse identity authentication
with identity assessment. The former merely means that the name is with identity assessment. The former merely means that the name is
being used by its owner or their agent, while the latter makes a being used by its owner or their agent, while the latter makes a
statement about the quality of the owner. statement about the quality of the owner.
With the advent of these authentication protocols, it is possible to With the advent of these authentication protocols, it is possible to
statisfy the requirement for a mechanism by which mutually trusted statisfy the requirement for a mechanism by which mutually trusted
parties can exchange assessment information about other actors. For parties can exchange assessment information about other actors. For
these purposes, we may usefully define "reputation" as "the these purposes, we may usefully define "reputation" as "the
estimation in which an identifiable actor is held, especially by the estimation in which an identifiable actor is held, especially by the
community or the Internet public generally". We may call an community or the Internet public generally". (This is based on the
aggregation of individual assessments "reputation input." definition of "reputation" from the 2013 Random House dictionary.)
We may call an aggregation of individual assessments "reputation
input."
While the need for reputation services has been perhaps especially While the need for reputation services has been perhaps especially
clear in the email world, where abuses are commonplace, other clear in the email world, where abuses are commonplace, other
Internet services are coming under attack and may have a similar Internet services are coming under attack and may have a similar
need. For instance, a reputation mechanism could be useful in rating need. For instance, a reputation mechanism could be useful in rating
the security of web sites, the quality of service of an Internet the security of web sites, the quality of service of an Internet
Service Provider (ISP), or an Application Service Provider (ASP). Service Provider (ISP), or an Application Service Provider (ASP).
More generally, there are many different opportunities for use of More generally, there are many different opportunities for use of
reputation services, such as customer satisfaction at e-commerce reputation services, such as customer satisfaction at e-commerce
sites, and even things unrelated to Internet protocols, such as sites, and even things unrelated to Internet protocols, such as
plumbers, hotels, or books. Just as human beings traditionally rely plumbers, hotels, or books. Just as human beings traditionally rely
on the recommendations of trusted parties in the physical world, so on the recommendations of trusted parties in the physical world, so
too they can be expected to make use of such reputation services in a too they can be expected to make use of such reputation services in a
variety of applications on the Internet. variety of applications on the Internet.
A full trust architecture encompasses a range of actors and A full trust architecture encompasses a range of actors and
activities, to enable an end-to-end service for creating, exchanging, activities, to enable an end-to-end service for creating, exchanging,
and consuming trust-related information. One component of that is a and consuming trust-related information. One component of that is a
query mechanism, to permit retrieval of a reputation. Not all such query mechanism, to permit retrieval of a reputation. Not all such
reputation services will need to convey the same information. Some reputation services will need to convey the same information. Some
need only produce a basic rating, while others need to provide need only to produce a basic rating, while others need to provide
underlying detail. This is akin to the difference between check underlying detail. This is akin to the difference between check
approval versus a credit report. approval versus a credit report.
An overall reckoning of goodness versus badness can be defined An overall reckoning of goodness versus badness can be defined
generically, but specific applications are likely to want to describe generically, but specific applications are likely to want to describe
reputations for multiple attributes: an e-commerce site might be reputations for multiple attributes: an e-commerce site might be
rated on price, speed of delivery, customer service, etc., and might rated on price, speed of delivery, customer service, etc., and might
receive very different ratings on each. Therefore, the model defines receive very different ratings on each. Therefore, the architecture
a generic query mechanism and basic format for reputation retrieval, defines a generic query mechanism and basic format for reputation
but allows extensions for each application. retrieval, but allows extensions for each application.
Omitted from this model is the means by which a reputation-reporting Omitted from this architecture is the means by which a reputation-
agent goes about collecting such data and the method for creating an reporting agent goes about collecting such data and the method for
evaluation. The mechanism defined here merely enables asking a creating an evaluation. The mechanism defined here merely enables
question and getting an answer; the remainder of an overall service asking a question and getting an answer; the remainder of an overall
provided by such a reputation agent is specific to the implementation service provided by such a reputation agent is specific to the
of that service and is out of scope here. implementation of that service and is out of scope here.
2. Overview 2. Overview
The basic premise of this reputation system involves a client that is The basic premise of this reputation system involves a client that is
seeking to evaluate content based on an identifier associated with seeking to evaluate content based on an identifier associated with
the content, and a reputation service provider that collects, the content, and a reputation service provider that collects,
aggregates, and makes available for consumption, scores based on the aggregates, and makes available for consumption, scores based on the
collected data. Typically client and service operators enter into collected data. Typically client and service operators enter into
some kind of agreement during which some parameters are exchanged some kind of agreement during which some parameters are exchanged,
such as the location at which the reputation service can be reached, such as: the location at which the reputation service can be reached,
the nature of the reputation data being offered, possibly some client the nature of the reputation data being offered, possibly some client
authentication details, and the like. authentication details, and the like.
Upon receipt of some content the client operator wishes to evaluate Upon receipt of some content the client operator wishes to evaluate
(an Internet message, for example), the client extracts from the (an Internet message, for example), the client extracts from the
content one or more identifiers of interest to be evaluated. content one or more identifiers of interest to be evaluated.
Examples of this include the domain name found in the From: field of Examples of this include the domain name found in the From: field of
a message, or the domain name extracted from a valid DomainKeys a message, or the domain name extracted from a valid DomainKeys
Identified Mail (DKIM) signature. Identified Mail (DKIM) signature.
Next, the goal is to ask the reputation service provider what the Next, the goal is to ask the reputation service provider what the
reputation of the extracted identifier is. The query will contain reputation of the extracted identifier is. The query will contain
the identifier to be evaluated and possibly some context-specific the identifier to be evaluated and possibly some context-specific
information (such as to establish the context of the query, e.g., an information (such as to establish the context of the query, e.g., an
email message) or client-specific information. The client typically email message) or client-specific information. The client typically
folds the data in the response into whatever local evaluation logic folds the data in the response into whatever local evaluation logic
it applies to decide what disposition the content deserves. it applies to decide what disposition the content deserves.
3. High-Level Architecture 3. Related Documents
This document presents a high-level view of the reputation
architecture.
For the purposes of sending and receiving reputation information,
[I-D.REPUTE-MEDIA-TYPE] defines a media type for containing responses
to reputation queries, and a serialization format for these data
(with examples). It also creates the registry for specific
reputation contexts and the parameters related to them.
[I-D.REPUTE-QUERY-HTTP] describes how to construct and issue
reputation queries and replies in the context of this architecture
using the HyperText Transport Protocol (HTTP) as the query protocol.
Finally, [I-D.REPUTE-EMAIL-IDENTIFIERS] defines (and registers) a
first, common, reputation application, namely the evaluation of
portions of an email message as subjects for reputation queries and
replies.
4. High-Level Architecture
This document outlines the reputation query and response mechanism.
It provides the following definitions:
o Vocabulary for the current work and work of this type;
o The types and content of queries that can be supported;
o The extensible range of response information that can be provided;
o A query/response protocol;
o Query/response transport conventions.
It provides an extremely simple query/response model that can be
carried over a variety of transports, including the Domain Name
System. (Although not typically thought of as a 'transport', the DNS
provides generic capabilities and can be thought of as a mechanism
for transporting queries and responses that have nothing to do with
Internet addresses, such as is done with a DNS BlockList [DNSBL].)
Each specification for Repute transport is independent of any other
specification.
The precise syntaxes of both the query and response are application-
specific. An application within this architecture defines the
parameters available to queries of that type, and also defines the
data returned in response to any query.
4.1. Example of a Reputation Service Being Used
A reputation mechanism functions as a component of an overall A reputation mechanism functions as a component of an overall
service. A current example is that of an email system that uses service. A current example is that of an email system that uses
DomainKeys Identified Mail (DKIM; see [DKIM]) to affix a stable DomainKeys Identified Mail (DKIM; see [DKIM]) to affix a stable
identifier to a message and then uses that as a basis for evaluation: identifier to a message and then uses that as a basis for evaluation:
+-------------+ +------------+ +-------------+ +------------+
| Author | | Recipient | | Sender | | Recipient |
+-------------+ +------------+ +-------------+ +------------+
| ^ | ^
V | V |
+-------------+ +------------+ +-------------+ +------------+
| MSA | | MDA | | MSA | | MDA |
+-------------+ +------------+ +-------------+ +------------+
| ^ | ^
| | | |
| +------------+ | +------------+
| | Handling | | | Handling |
| | Filter | | | Filter |
| +------------+ | +------------+
| ^ | ^
| | | |
| +------------+ +------------+ | +------------+ +------------+
| | Reputation |<=====>| Identifier | | | Reputation |<=====>| Identifier |
| | Service | | Assessor | | | Service | | Assessor |
| +------------+ +------------+ | +------------+ +------------+
| ^ | ^
V | V |
+----------------------------------------------------------+ +------------+ Responsible Identifier +------------+
| +------------+ Responsible Identifier +------------+ | | Identifier |. . . . . . . . . . . . . .>| Identifier |
| | Identifier |. . . . . . . . . . . . . .>| Identifier | | | Signer | (DKIM) | Verifier |
| | Signer | | Verifier | | +------------+ +------------+
| +------------+ DKIM Service +------------+ |
+----------------------------------------------------------+
| ^ | ^
V | V |
+-------------+ /~~~~~~~~~~\ +------+-----+ +-------------+ /~~~~~~~~~~\ +------+-----+
| MTA |----->( other MTAs )------>| MTA | | MTA |----->( other MTAs )------>| MTA |
+-------------+ \~~~~~~~~~~/ +------------+ +-------------+ \~~~~~~~~~~/ +------------+
Figure 1: Actors in a Trust Sequence Using DKIM Figure 1: Actors in a Trust Sequence Using DKIM
(See [EMAIL-ARCH] for a general description of the Internet messaging (See [EMAIL-ARCH] for a general description of the Internet messaging
architecture.) In this figure, the solid lines indicate the flow of architecture.) In this figure, the solid lines indicate the flow of
a message; the dotted line indicates transfer of validated a message; the dotted line indicates transfer of validated
identifiers within the message content; and the double line shows the identifiers within the message content; and the double line shows the
query and response of the reputation information. query and response of the reputation information.
Here, the DKIM Service provides one or more stable identifiers that Here, the DKIM Service provides one or more stable identifiers that
is the basis for the reputation query. On receipt of a message from is the basis for the reputation query. On receipt of a message from
skipping to change at page 6, line 16 skipping to change at page 7, line 49
(See [EMAIL-ARCH] for a general description of the Internet messaging (See [EMAIL-ARCH] for a general description of the Internet messaging
architecture.) In this figure, the solid lines indicate the flow of architecture.) In this figure, the solid lines indicate the flow of
a message; the dotted line indicates transfer of validated a message; the dotted line indicates transfer of validated
identifiers within the message content; and the double line shows the identifiers within the message content; and the double line shows the
query and response of the reputation information. query and response of the reputation information.
Here, the DKIM Service provides one or more stable identifiers that Here, the DKIM Service provides one or more stable identifiers that
is the basis for the reputation query. On receipt of a message from is the basis for the reputation query. On receipt of a message from
an MTA, the DKIM Service provides a (possibly empty) set of validated an MTA, the DKIM Service provides a (possibly empty) set of validated
identifiers -- domain names, in this case -- which are the subjects identifiers -- domain names, in this case -- which are the subjects
of reputation queries made by the Identity Assessor. The Identity of reputation queries made by the Identity Assessor. The Identifier
Assessor queries a Reputation Service to determine the reputation of Assessor queries a Reputation Service to determine the reputation of
the provided identifiers, and delivers the identifiers and their the provided identifiers, and delivers the identifiers and their
reputations to the Handling Filter. The Handling Filter makes a reputations to the Handling Filter. The Handling Filter makes a
decision about whether and how to deliver the message to the decision about whether and how to deliver the message to the
recipient based on these and other inputs about the message, possibly recipient based on these and other inputs about the message, possibly
including evaluation mechansisms in addition to DKIM. including evaluation mechanisms in addition to DKIM.
This document outlines the reputation query and response mechanism.
It provides the following definitions:
o Vocabulary for the current work and work of this type;
o The types and content of queries that can be supported;
o The extensible range of response information that can be provided;
o A query/response protocol;
o Query/response transport conventions.
It provides an extremely simple query/response model that can be
carried over a variety of transports, including the Domain Name
System. (Although not typically thought of as a 'transport', the DNS
provides generic capabilities and can be thought of as a mechanism
for transporting queries and responses that have nothing to do with
Internet addresses, such as is one with a DNS BlockList [DNSBL].)
Each specification for Repute transport is independent of any other
specification. A diagram of the basic query service is found in
Figure 2.
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . + 5. Terminology and Definitions
. Reputation Service .
. +------------+ .
. | Reputation | .
. | Database | .
. +------------+ .
. | .
. V .
. +-----------+ Query +----------+ .
. | |. . . . . . . . . . . . . .>| | .
. | Client | | Server | .
. | |< . . . . . . . . . . . . . | | .
. +-----+-----+ Response +----------+ .
. ^ ^ .
+ . . . | . . . . . . . . . . . . . . . . . . . | . . . . +
V |
+-----------+ +-----------+ |
| Transport |<-------------->| Transport |<---+
+-----------+ DNS +-----------+
TCP
UDP
...
Figure 2: Basic Reputation Query Service This section defines terms used in the rest of the document.
The precise syntaxes of both the query and response are application- 5.1. Application
specific. An application of the model defines the parameters
available to queries of that type, and also defines the data returned
in response to any query.
4. Terminology and Definitions An "Application" is a specific context in which reputation queries
are made. Some obvious popular examples include restaurants, movies,
or providers of various services.
This section defines terms used in the rest of the document. Applications have different sets of attributes of interest, and so
the subjects of queries and the resulting responses will vary, in
order to describe the reputations of entities in their respective
contexts. For example, the Application "movies" would have a
different set of properties of interest and associated ratings (see
below) from "restaurants", so it's necessary for them to be formally
enumerated.
4.1. Response Set 5.2. Response Set
A "Response Set" comprises those data that are returned in response A "Response Set" is a representation for data that are returned in
to a reputation query about a particular entity. The types of data response to a reputation query about a particular entity within the
are specific to an application; the data returned in the evaluation context of an Application. The content of the Response Set is
of email senders would be different than the reputation data returned specific to the application; though all applications have a few key
about a movie or a baseball player. fields in common, some of the reputation data returned in the
evaluation of email senders would be different than that returned
about a movie, restaurant, or baseball player.
Response Sets have symbolic names, and these have to be registered Response Sets have symbolic names, and these have to be registered
with IANA, in the Reputation Applications Registry, to prevent name with IANA, in the Reputation Applications Registry, to prevent name
collisions. IANA registries are created in a separate document. collisions. (IANA registries are created in a separate document.)
Each definition of a Response Set also needs to define its registry Each definition of a Response Set also needs to specify its registry
entry. entry, which will include a document that details the content of a
Response Set within that Application.
4.1.1. Assertions and Ratings 5.3. Assertions and Ratings
One of the key properties of a Response Set is called an Assertion. One of the key properties of a Response Set is called an Assertion.
Assertions are claims made about the subject of a reputation query. Assertions are claims made about the subject of a reputation query.
For example, one might assert that a particular restaurant serves For example, one might assert that a particular restaurant serves
good food. In the context of this model, the assertion would be good food. In the context of this architecture, the assertion would
"serves good food". be "serves good food".
Assertions are coupled with a numeric value called a Rating, which is Assertions are coupled with a numeric value called a Rating, which is
an indication of how much the party generating the Response Set an indication of how much the party generating the Response Set
agrees with the assertion being made. For example, with the above agrees with the assertion being made. Ratings are typically
Assertion, a rating of 1.0 indicates strong agreement, while a rating expressed as a floating point value between 0.0 and 1.0 inclusive,
of 0.0 indicates no support for the assertion. with the former indicating no support for the assertion and the
latter indicating total agreement with the assertion.
4.2. Reputon The documents that define applications will also specify the type of
scale in use when generating ratings, to which all reputation service
providers for that application space must adhere. This will allow a
client to change which reputation service provider is being queried
without having to learn through some out-of-band method what the new
provider's ratings mean. For example, a registration might state
that ratings are linear, which would mean a score of "x" is twice as
strong as a value of "x/2". It also allows easier aggregation of
ratings collected from multiple reputation service providers.
5.4. Reputon
A "reputon" is an object that comprises the basic response to a A "reputon" is an object that comprises the basic response to a
reputation query. It contains the response set relevant to the reputation query. It contains the response set relevant to the
subject of the query. Its specific encoding is left to documents subject of the query in a serialized form. Its specific encoding is
that implement this model. left to documents that implement this architecture.
5. Information Represented in a Response Set 6. Information Represented in a Response Set
The basic information to be represented in the protocol is fairly The basic information to be represented in the protocol is fairly
simple, and includes the following: simple, and includes at least the following data:
o the identity of the entity providing the reputation information; o the identity of the entity providing the reputation information;
o the identity of the entity being rated; o the identity of the entity being rated;
o the application context for the query (e.g., email address o the application context for the query (e.g., email address
evaluation); evaluation);
o the overall rating score for that entity; o the overall rating score for that entity;
skipping to change at page 9, line 12 skipping to change at page 10, line 14
also includes the name of the application for which the reputation also includes the name of the application for which the reputation
data is being expressed. data is being expressed.
Each application requires its own specification of the Response Set. Each application requires its own specification of the Response Set.
For example, a specification might be needed for a reputation For example, a specification might be needed for a reputation
Response Set for an "email-sending-domain"; the Response Set might Response Set for an "email-sending-domain"; the Response Set might
include information on how often spam was received from that domain. include information on how often spam was received from that domain.
Additional documents define a [MIME] type for reputation data, and Additional documents define a [MIME] type for reputation data, and
protocols for exchanging such data. protocols for exchanging such data.
6. Information Flow in the Reputation Query Protocol 7. Information Flow in the Reputation Query Protocol
The basic Response Set could be wrapped into a new MIME media type The basic Response Set could be wrapped into a new MIME media type
[MIME] or a DNS RR, and transported accordingly. It also could be [MIME] or a DNS RR, and transported accordingly. It also could be
the integral payload of a purpose-built protocol. For a basic the integral payload of a purpose-built protocol. For a basic
request/response scenario, one entity (the Client) will ask a second request/response scenario, one entity (the client) will ask a second
entity (the Server) for reputation data about a third entity (the entity (the server) for reputation data about a third entity (the
Target), and the second entity will respond with that data. subject), and the second entity will respond with those data.
An application might benefit from an extremely lightweight mechanism, An application might benefit from an extremely lightweight mechanism,
supporting constrained queries and responses, while others might need supporting constrained queries and responses, while others might need
to support larger and more complex responses. to support larger and more complex responses.
7. IANA Considerations 8. IANA Considerations
This document presents no actions for IANA. This document presents no actions for IANA.
[RFC Editor: Please remove this section prior to publication.] [RFC Editor: Please remove this section prior to publication.]
8. Privacy Considerations 9. Privacy Considerations
8.1. Data In Transit 9.1. Data In Transit
Some kinds of reputation data are sensitive, and should not be shared Some reputation exchanges can be sensitive, and should not be shared
publicly. For cases that have such sensitivity, it is imperative to publicly. A client making use of this framework is explicitly
protect the information from unauthorized access and viewing. The revealing that it is interested in particular subjects, and the
model described here neither suggests nor precludes any particular server is revealing what its information sources have reported about
transport mechanism for the data. However, for the purpose of those subjects (in the aggregate). In the email context, for
illustration, a reputation service that operates over HTTP might example, a client is revealing from whom it receives email, and the
employ any of its well-known mechanisms to solve these problems, server is revealing what it (based on its aggregated data) believes
which include OpenPGP [OPENPGP], Transport Layer Security [TLS], and to be true about those subjects.
S/MIME [SMIME].
8.2. Aggregation These can be sensitive things that need to be secured, particularly
when a client is talking to a server outside of its own
administrative domain. Furthermore, certain types of reputation
information are typically perceived as more sensitive than others;
movie ratings, for example, are much less damaging if leaked than a
person's credit rating.
For interchanges that are sensitive to such exposures, it is
imperative to protect the information from unauthorized access and
viewing, and possibly add the capability to do object-level integrity
and origin verification. Not all transport options can be adequately
secured in these ways (e.g., DNS queries and responses are entirely
insecure), and so it might be necessary to change to a transport
method that does have such capabilities or extensions.
The architecture described here neither suggests nor precludes any
particular transport mechanism for the data. However, for the
purpose of illustration, a reputation service that operates over HTTP
might employ any of several well-known mechanisms to solve these
problems, which include OpenPGP [OPENPGP], HTTP over TLS [HTTP-TLS],
and S/MIME [SMIME].
9.2. Aggregation
The data that are collected as input to a reputation calculation are The data that are collected as input to a reputation calculation are
in essence a statement by one party about the actions or output of in essence a statement by one party about the actions or output of
another. What one party says about another is often meant to be kept another. What one party says about another is often meant to be kept
in confidence. Accordingly, steps often need to be taken to secure in confidence. Accordingly, steps often need to be taken to secure
the submission of these input data to a reputation service provider. the submission of these input data to a reputation service provider.
Moreover, although the aggregated reputation is the product provided Moreover, although the aggregated reputation is the product provided
by this service, its inadvertent exposure can have undesirable by this service, its inadvertent exposure can have undesirable
effects. Just as the collection of data about a subject needs due effects. Just as the collection of data about a subject needs due
consideration to privacy and security, so too does the output and consideration to privacy and security, so too does the output and
storage of whatever aggregation the service provider applies. storage of whatever aggregation the service provider applies.
8.3. Collection Of Data 9.3. Collection Of Data
The basic notion of collection and storage of reputation data is The basic notion of collection and storage of reputation data is
obviously a privacy issue in that the opinions of one party about obviously a privacy issue in that the opinions of one party about
another are likely to be sensitive. Inadvertent or unauthorized another are likely to be sensitive. Inadvertent or unauthorized
exposure of those data can lead to personal or commercial damage. exposure of those data can lead to personal or commercial damage.
9. Security Considerations 9.4. Queries Can Reveal Information
This document introduces an overall protocol model, but no When a client asks a service provider about a particular subject, the
service provider can infer the existence of that subject and begin
observing which clients ask about it. This can be an unanticipated
leak of private information.
9.5. Compromised Relationships
Reputation services that limit queries to authorized clients can
cause private information, such as the reputations themselves or the
data used to compute them, to be revealed if the client credentials
are compromised. It is critical to safeguard not only the
interchange of reputation information, and the information once it
has been delivered to the client, but the ability to issue requests
for information as well.
An important consideration here is that compromised credentials are
mainly an exposure of some third party (whose reputation is
improperly revealed), rather than the client or the server.
10. Security Considerations
This document introduces an overall protocol architecture, but no
implementation details. As such, the security considerations implementation details. As such, the security considerations
presented here are very high-level. The detailed analyses of the presented here are very high-level. The detailed analyses of the
various specific components of the protocol can be found the various specific components of the protocol can be found the
documents that instantiate this model. documents that instantiate this architecture.
9.1. Biased Reputation Agents 10.1. Biased Reputation Agents
As with [VBR], an agent seeking to make use of a reputation reporting As with [VBR], an agent seeking to make use of a reputation reporting
service is placing some trust that the service presents an unbiased service is placing some trust that the service presents an unbiased
"opinion" of the object about which reputation is being returned. "opinion" of the object about which reputation is being returned.
The result of trusting the data is, presumably, to guide action taken The result of trusting the data is, presumably, to guide action taken
by the reputation client. It follows, then, that bias in the by the reputation client. It follows, then, that bias in the
reputation service can adversely affect the client. Clients reputation service can adversely affect the client. Clients
therefore need to be aware of this possibility and the effect it therefore need to be aware of this possibility and the effect it
might have. For example, a biased system returning a reputation might have. For example, a biased system returning a reputation
about a DNS domain found in email messages could result in the about a DNS domain found in email messages could result in the
skipping to change at page 11, line 9 skipping to change at page 13, line 7
the scope of the present document. the scope of the present document.
Similarly, a client placing trust in the results returned by such a Similarly, a client placing trust in the results returned by such a
service might suffer if the service itself is compromised, returning service might suffer if the service itself is compromised, returning
biased results under the control of an attacker without the knowledge biased results under the control of an attacker without the knowledge
of the agency providing the reputation service. This might result of the agency providing the reputation service. This might result
from an attack on the data being returned at the source, or from a from an attack on the data being returned at the source, or from a
man-in-the-middle attack. Protocols, therefore, need to be designed man-in-the-middle attack. Protocols, therefore, need to be designed
so as to be as resilient against such attacks as possible. so as to be as resilient against such attacks as possible.
9.2. Malformed Messages 10.2. Malformed Messages
Both clients and servers of reputation systems need to be resistant Both clients and servers of reputation systems need to be resistant
to attacks that involve malformed messages, deliberate or otherwise. to attacks that involve malformed messages, deliberate or otherwise.
Malformations can be used to confound clients and servers alike in Malformations can be used to confound clients and servers alike in
terms of identifying the party or parties responsible for the content terms of identifying the party or parties responsible for the content
under evaluation. This can result in delivery of undesirable or even under evaluation. This can result in delivery of undesirable or even
dangerous content. dangerous content.
9.3. Further Discussion 10.3. Further Discussion
Numerous other topics related to use and management of reputation Involving a third party (in this case, a reputation service provider)
that can influence the handling of incoming content involves ceding
some amount of control to that third party. Numerous other topics
related to the management, operation, and safe use of reputation
systems can be found in [I-D.REPUTE-CONSIDERATIONS]. systems can be found in [I-D.REPUTE-CONSIDERATIONS].
10. Informative References 11. Informative References
[DKIM] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., [DKIM] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", RFC 6376, "DomainKeys Identified Mail (DKIM) Signatures", RFC 6376,
September 2011. September 2011.
[DNS] Mockapetris, P., "Domain names - implementation and [DNS] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
[DNSBL] Levine, J., "DNS Blacklists and Whitelists", RFC 5782, [DNSBL] Levine, J., "DNS Blacklists and Whitelists", RFC 5782,
February 2010. February 2010.
[EMAIL-ARCH] [EMAIL-ARCH]
Crocker, D., "Internet Mail Architecture", RFC 5598, Crocker, D., "Internet Mail Architecture", RFC 5598,
July 2009. July 2009.
[HTTP-TLS]
Rescorla, E., "HTTP over TLS", RFC 2818, May 2000.
[I-D.REPUTE-CONSIDERATIONS] [I-D.REPUTE-CONSIDERATIONS]
Kucherawy, M., "Operational Considerations Regarding Kucherawy, M., "Operational Considerations Regarding
Reputation Services", draft-ietf-repute-considerations Reputation Services", draft-ietf-repute-considerations
(work in progress), November 2012. (work in progress), November 2012.
[I-D.REPUTE-EMAIL-IDENTIFIERS]
Borenstein, N. and M. Kucherawy, "A Reputation Vocabulary
for Email Identifiers",
draft-ietf-repute-email-identifiers (work in progress),
November 2012.
[I-D.REPUTE-MEDIA-TYPE]
Borenstein, N. and M. Kucherawy, "A Media Type for
Reputation Interchange", draft-ietf-repute-media-type
(work in progress), November 2012.
[I-D.REPUTE-QUERY-HTTP]
Borenstein, N. and M. Kucherawy, "Reputation Data
Interchange using HTTP and XML",
draft-ietf-repute-query-http (work in progress),
November 2012.
[MAIL] Resnick, P., "Internet Message Format", RFC 5322, [MAIL] Resnick, P., "Internet Message Format", RFC 5322,
October 2008. October 2008.
[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996. Bodies", RFC 2045, November 1996.
[OPENPGP] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R. [OPENPGP] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
Thayer, "OpenPGP Message Format", RFC 4880, November 2007. Thayer, "OpenPGP Message Format", RFC 4880, November 2007.
[SMIME] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet [SMIME] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2: Message Mail Extensions (S/MIME) Version 3.2: Message
Specification", RFC 5751, January 2010. Specification", RFC 5751, January 2010.
[SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, [SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008. October 2008.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[VBR] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By [VBR] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By
Reference", RFC 5518, April 2009. Reference", RFC 5518, April 2009.
Appendix A. Public Discussion Appendix A. Public Discussion
Public discussion of this suite of documents takes place on the Public discussion of this suite of documents takes place on the
domainrep@ietf.org mailing list. See domainrep@ietf.org mailing list. See
https://www.ietf.org/mailman/listinfo/domainrep. https://www.ietf.org/mailman/listinfo/domainrep.
Authors' Addresses Authors' Addresses
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