REPUTE M. Kucherawy Internet-Draft November 8, 2012 Intended status: Informational Expires: May 12, 2013 Operational Considerations Regarding Reputation Services draft-ietf-repute-considerations-00 Abstract The use of reputation systems is has become a common tool in many applications that seek to apply collected intelligence about traffic sources. Often this is done because it is common or even expected operator practice. It is therefore important to be aware of a number of considerations for both operators and consumers of the data. This document includes a collection of the best advice available regarding providers and consumers of reputation data, based on experience to date. Much of this is based on experience with email reputation systems, but the concepts are generally applicable. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on May 12, 2013. Copyright Notice Copyright (c) 2012 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 Kucherawy Expires May 12, 2013 [Page 1] Internet-Draft Reputation Operations November 2012 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Reputation Clients . . . . . . . . . . . . . . . . . . . . . . 4 5. Reputation Service Providers . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 8. Informative References . . . . . . . . . . . . . . . . . . . . 7 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 7 Kucherawy Expires May 12, 2013 [Page 2] Internet-Draft Reputation Operations November 2012 1. Introduction Reputation services involve collecting feedback from the community about sources of Internet traffic and aggregating that feedback into a rating of some kind. Common examples include feedback about traffic associated with specific email addresses, URIs or parts of URIs, IP addresses, etc. The specific collection, analysis, and rating methods vary from one service to the next and one problem domain to the next, but several operational concepts appear to be common to all of these. The promise of the protection that reputation services offers can be enticing, and many users and operators alike typically engage those services merely because it is expected of them. A critical notion, however, is that doing so explicitly involves a third party in the flow of data those parties receive. This is often taken for granted, with potentially disastrous results. This document highlights this and other considerations in providing and consuming reputation data services. 2. Background The community has historically focused on identifying sources that misbehave, i.e., that earn negative reputations. The purpose here is to identify and filter traffic from bad actors. This grew out of operational need. As the Internet grew, so did the occurence of problematic traffic, especially in email. The pragmatics of email (i.e., the fact that the total IP address space is more constrained than the total email address space) drove the focus on using IP addresses as the focus of reputation, in addition to the fact that IP addresses have a degree of validation (via the TCP/IP infrastructure) where email addresses have had none. A specific example of a reputation service in common use in the email space is the DNS blacklist [DNSBL]. This is a method of querying a database as to whether a source of incoming [SMTP] email traffic should be allowed to relay email, based on previous observations and feedback. The method uses the IP address of the source as the basis for a query to the database using the Domain Name System [DNS] as the interface. [DNSBL] includes several points in its Security Considerations document that are repeated and further developed here. However, regardless of the identifier used as the identifier for a reputation, bad actors can evade detection or the effects of their observed behavior by changing identifiers (e.g., move to a new IP address, register a new domain name, use a sub-domain). This makes the problem space effectively boundless, especially as IPv6 rolls Kucherawy Expires May 12, 2013 [Page 3] Internet-Draft Reputation Operations November 2012 out. 3. Evolution More modern thinking is evolving toward the identification of good actors rather than bad actors, and giving them preferential treatment. This drastically reduces the problem space: There are vastly more IP addresses and email addresses used by bad actors to generate problematic traffic than are used by good actors to generate desirable traffic. Moreover, good actors tend to be represented by stable names and addresses, allowing users to rely on these to identify and give preferential treatment to their traffic. Good actors have no need to hop around to different addresses, and already work to keep their traffic clean. This notion has only been tried to date using manually edited whitelists, but has shown promising results on that scale. 4. Reputation Clients understand that you are granting a third party the ability to affect your incoming traffic, for better or worse this is the point, of course, when everything works properly some cases have occurred where a reputation service provider (RSP) shut down operation, and to encourage consumers to stop querying, it began reporting a maximal negative reputation about all subjects, causing rejection of all incoming traffic during the incident period reputation providers will be the subject of attacks when it's understood that sucess doing so will allow malicious content to evade detection and filtering; clients need to be aware of possible interruptions in service availability or quality understand that some actors will try to game the service, which means that a reputation service is inherently fragile; for operational clients, this should prompt balanced and comparative, rather than unilateral, use of the service try to learn the following things about your RSP, to understand your exposure potential: o their basis for listing or not listing particular subjects Kucherawy Expires May 12, 2013 [Page 4] Internet-Draft Reputation Operations November 2012 o if an RSP is paid by its listees, what are the rate and criteria for rejection? o how the provider collects data about subjects o how many data points are input to the reported reputation o is reputation based on a reliable identifier? o how it etablishes reliability and authenticity of those data o how data validity is maintained (e.g., on-going monitoring of the reported data and sources) o how actively data validity is tracked (e.g., how changes are detected) o how disputed reputations are handled o how data expire o is older information more or less influential than newer? o is the reported reputation a scalar, a Boolean value, a collection of values, or something else? o when transitioning among RSPs, determine the differences between them among these above points; that is, does a particular score from one mean the same thing from the other? ensure the capability of local overrides for cases where the client expects to disagree with the reported reputation be able limit the impact of a negative reputation on content acceptance; for example, rather than rejecting content outright when a negative reputation is returned, simply subject it to additional local analyis have a sensible default to apply when the RSP is not available consider tailoring operation to prefer or emphasize content whose sources have positive reputations; recall that negative reputations are easy to shed, and the universe of things that will earn and maintain positive reputations is relatively small consider querying and cross-referencing multiple RSPs; this helps to detect which are reliable, and offsets the effect of anomalous replies Kucherawy Expires May 12, 2013 [Page 5] Internet-Draft Reputation Operations November 2012 5. Reputation Service Providers make the answers to the questions in Section 4 available on demand to consumers base reputations on accurate identifiers, i.e., something difficult to forge it is important to have a transparent remediation process for disputes of computed reputations provide the ability to request details in the returned result about how the result was reached, allowing the client to decide if the result should be applied, such as: o the result itself o the number of data points used to compute the result o the age range of the data o source diversity of the input data o currency of the result (i.e., when it was computed) o basis of the result (i.e., which identifier was used) harden systems and algorithms as much as practicable against gaming or data poisoning; larger source diversities are harder to overcome with poisoned input, but are expensive to build systems based on positive reputations are promising since positive reputations, if made difficult to earm put a large cost on bad actors 6. Security Considerations Several points are raised above that can be described as threats to the delivery of valid user data. This document highlights and discusses those issues, but introduces no new security issues. 7. IANA Considerations This memo contains no actions for IANA. [RFC Editor: Please remove this section prior to publication.] Kucherawy Expires May 12, 2013 [Page 6] Internet-Draft Reputation Operations November 2012 8. Informative References [DNS] Mockapetris, P., "Domain Names -- Concepts and Facilities", RFC 1034, November 1987. [DNSBL] Levine, J., "DNS Blacklists and Whitelists", RFC 5782, February 2010. [SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, October 2008. Appendix A. Acknowledgements The author wishes to acknowledge the following for their review and constructive criticism of this proposal: (names) Author's Address Murray S. Kucherawy EMail: superuser@gmail.com Kucherawy Expires May 12, 2013 [Page 7]