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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational RFC: RFC 5598 (ref. 'EMAIL-ARCH') ** Obsolete normative reference: RFC 4408 (ref. 'SPF') (Obsoleted by RFC 7208) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 REPUTE Working Group N. Borenstein 3 Internet-Draft Mimecast 4 Intended status: Standards Track M. Kucherawy 5 Expires: March 16, 2014 September 12, 2013 7 A Reputation Response Set for Email Identifiers 8 draft-ietf-repute-email-identifiers-10 10 Abstract 12 This document defines a response set for describing assertions a 13 reputation service provider can make about email identifers, for use 14 in generating reputons. 16 Status of this Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at http://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on March 16, 2014. 33 Copyright Notice 35 Copyright (c) 2013 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (http://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 2. Terminology and Definitions . . . . . . . . . . . . . . . . . . 3 52 2.1. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 2.2. Email Definitions . . . . . . . . . . . . . . . . . . . . . 3 54 2.3. Other Definitions . . . . . . . . . . . . . . . . . . . . . 3 55 3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 3.1. Assertions . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3.2. Response Set Extensions . . . . . . . . . . . . . . . . . . 4 58 3.3. Identifiers . . . . . . . . . . . . . . . . . . . . . . . . 5 59 3.4. Query Extensions . . . . . . . . . . . . . . . . . . . . . 6 60 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 61 4.1. Registration of 'email-id' Reputation Application . . . . . 6 62 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 63 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 64 6.1. Normative References . . . . . . . . . . . . . . . . . . . 7 65 6.2. Informative References . . . . . . . . . . . . . . . . . . 8 66 Appendix A. Positive vs. Negative Assertions . . . . . . . . . . . 8 67 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 8 68 Appendix C. Public Discussion . . . . . . . . . . . . . . . . . . 8 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 71 1. Introduction 73 This document specifies a response set for describing reputation of 74 an email identifier. A "response set" in this context is defined in 75 [I-D.REPUTE-MODEL] and is used to describe assertions a reputation 76 service provider can make about email identifiers as well as meta- 77 data that can be included in such a reply beyond the base set 78 specified there. 80 An atomic reputation response is called a "reputon", defined in 81 [I-D.REPUTE-MEDIA-TYPE]. That document also defines a media type to 82 contain a reputon for transport, and also creates a registry for 83 reputation applications and the interesting parameters of each. 85 2. Terminology and Definitions 87 This section defines terms used in the rest of the document. 89 2.1. Key Words 91 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 92 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 93 document are to be interpreted as described in [KEYWORDS]. 95 2.2. Email Definitions 97 Commonly used definitions describing entities in the email 98 architecture are defined and discussed in [EMAIL-ARCH]. 100 2.3. Other Definitions 102 Other terms of importance in this document are defined in 103 [I-D.REPUTE-MODEL], the base document for the reputation services 104 work. 106 3. Discussion 108 The expression of reputation about an email identifier requires 109 extensions of the base set defined in [I-D.REPUTE-MODEL]. This 110 document defines and registers some common assertions about an entity 111 found in a piece of [MAIL]. 113 3.1. Assertions 115 The "email-id" reputation application recognizes the following 116 assertions: 118 abusive: The subject identifier is associated with sending or 119 handling email of a personally abusive, threatening, or otherwise 120 harassing nature. 122 fraud: The subject identifier is associated with sending or handling 123 of fraudulent email, such as "phishing" (some good discussion on 124 this topic can be found in [IODEF-PHISHING]) 126 invalid-recipients: The subject identifier is associated with 127 delivery attempts to nonexistent recipients 129 malware: The subject identifier is associated with the sending or 130 handling of malware via email 132 spam: The subject identifier is associated with sending or handling 133 of unwanted bulk email 135 For all assertions, the "rating" scale is linear: A value of 0.0 136 means there is no data to support the assertion, a value of 1.0 means 137 all accumulated data support the assertion, and the intervening 138 values have a linear relationship (i.e., a score of "x" is twice as 139 strong of an assertion as a value of "x/2"). 141 3.2. Response Set Extensions 143 The "email-id" reputation application recognizes the following 144 OPTIONAL extensions to the basic response set defined in 145 [I-D.REPUTE-MEDIA-TYPE]: 147 email-id-identity: A token indicating the source of the identifier; 148 that is, where the subject identifier was found in the message. 149 This MUST be one of: 151 dkim: The signing domain, i.e. the value of the "d=" tag, found 152 on a valid [DKIM] signature in the message 154 ipv4: The IPv4 address of the client 156 ipv6: The IPv6 address of the client 158 rfc5321.helo: The RFC5321.Helo value used by the (see [SMTP]) 159 client 161 rfc5321.mailfrom: The RFC5321.MailFrom value of the envelope of 162 the message (see [SMTP]) 164 rfc5322.from: The RFC5322.From field of the message (see [MAIL]) 166 spf: The domain name portion of the identifier (RFC5321.MailFrom 167 or RFC5321.Helo) verified by [SPF] 169 sources: A token relating a count of the number of sources of data 170 that contributed to the reported reputation. This is in contrast 171 to the "sample-size" parameter, which indicates the total number 172 of reports across all reporting sources. 174 A reply that does not contain the "identity" or "sources" extensions 175 is making a non-specific statement about how the reputation returned 176 was developed. A client can use or ignore such a reply at its 177 discretion. 179 3.3. Identifiers 181 In evaluating an email message on the basis of reputation, there can 182 be more than one identifier in the message needing to be validated. 183 For example, a message may have different email addresses in the 184 RFC5321.MailFrom parameter and the RFC5322.From header field. The 185 RFC5321.Helo identifier will obviously be different. Consequently, 186 the software evaluating the email message may need to query for the 187 reputation of more than one identifier. 189 The purpose of including the identity in the reply is to expose to 190 the client the context in which the identifier was extracted from the 191 message under evaluation. In particular, several of the items listed 192 are extracted verbatim from the message and have not been subjected 193 to any kind of validation, while a domain name present in a valid 194 DKIM signature has some more reliable semantics associated with it. 195 Computing or using reputation information about unauthenticated 196 identifiers has substantially reduced value, but can sometimes be 197 useful when combined. For example, a reply that indicates a message 198 contained one of these low-value identifiers with a high "spam" 199 rating might not be worthy of notice, but a reply indicating a 200 message contained several of them could be grounds for suspicion. 202 A client interested in checking these weaker identifiers would issue 203 a query about each of them using the same assertion (e.g., "spam"), 204 and then collate the results to determine which ones and how many of 205 them came back with ratings indicating content of concern, and take 206 action accordingly. For stronger identifiers, decisions can 207 typically be made based on a few or even just one of them. 209 3.4. Query Extensions 211 A query within this application can include the OPTIONAL query 212 parameter "identity" to indicate which specific identity is of 213 interest to the query. Legal values are the same as those listed in 214 Section 3.2. 216 4. IANA Considerations 218 This memo presents one action for IANA, namely the registration of 219 the reputation application "email-id". 221 4.1. Registration of 'email-id' Reputation Application 223 This section registers the "email-id" reputation application, as per 224 the IANA Considerations section of [I-D.REPUTE-MEDIA-TYPE]. The 225 registration parameters are as folows: 227 o Application name: email-id 229 o Short description: Evaluates DNS domain names or IP addresses 230 found in email identifiers 232 o Defining document: [this document] 234 o Status: current 236 o Subject: A string appropriate to the identifier of interest (see 237 Section 3.2 of this document) 239 o Application-specific query parameters: 241 identity: (current) as defined in Section 3.4 of this document 243 o Application-specific assertions: 245 abusive: (current) as defined in Section 3.1 of this document 247 fraud: (current) as defined in Section 3.1 of this document 249 invalid-recipients: (current) as defined in Section 3.1 of this 250 document 252 malware: (current) as defined in Section 3.1 of this document 253 spam: (current) as defined in Section 3.1 of this document 255 o Application-specific response set extensions: 257 identity: (current) as defined in Section 3.2 of this document 259 5. Security Considerations 261 This document is primarily an IANA action and doesn't describe any 262 protocols or protocol elements that might introduce new security 263 concerns. 265 Security considerations relevant to email and email authentication 266 can be found in most of the documents listed in the References 267 sections below. Information specific to use of reputation services 268 can be found in [I-D.REPUTE-CONSIDERATIONS]. 270 6. References 272 6.1. Normative References 274 [DKIM] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., 275 "DomainKeys Identified Mail (DKIM) Signatures", RFC 6376, 276 September 2011. 278 [EMAIL-ARCH] 279 Crocker, D., "Internet Mail Architecture", RFC 5598, 280 July 2009. 282 [I-D.REPUTE-MEDIA-TYPE] 283 Borenstein, N. and M. Kucherawy, "A Media Type for 284 Reputation Interchange", draft-ietf-repute-media-type 285 (work in progress), November 2012. 287 [I-D.REPUTE-MODEL] 288 Borenstein, N. and M. Kucherawy, "A Model for Reputation 289 Reporting", draft-ietf-repute-model (work in progress), 290 November 2012. 292 [KEYWORDS] 293 Bradner, S., "Key words for use in RFCs to Indicate 294 Requirement Levels", BCP 14, RFC 2119, March 1997. 296 [SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 297 October 2008. 299 [SPF] Wong, M. and W. Schlitt, "Sender Policy Framework (SPF) 300 for Authorizing Use of Domains in E-Mail, Version 1", 301 RFC 4408, April 2006. 303 6.2. Informative References 305 [I-D.REPUTE-CONSIDERATIONS] 306 Kucherawy, M., "Operational Considerations Regarding 307 Reputation Services", draft-ietf-repute-considerations 308 (work in progress), November 2012. 310 [IODEF-PHISHING] 311 Cain, P. and D. Jevans, "Extensions to the IODEF-Document 312 Class for Reporting Phishing", RFC 5901, July 2010. 314 [MAIL] Resnick, P., Ed., "Internet Message Format", RFC 5322, 315 October 2008. 317 Appendix A. Positive vs. Negative Assertions 319 [I-D.REPUTE-CONSIDERATIONS] some current theories about reputation, 320 namely that it is possibly more impactful to develop positive 321 reputations and focus on giving preferential treatment to content or 322 sources that earn those. However, the assertions defined in this 323 document are all clearly negative in nature. 325 In effect, this document is recording current use of reputation and 326 of this framework in particular. It is expected that, in the future, 327 the application being registered here will be augmented, and other 328 applications registered, that focus more on positive assertions 329 rather than negative ones. 331 Appendix B. Acknowledgments 333 The authors wish to acknowledge the contributions of the following to 334 this specification: Scott Hollenbeck, Scott Kitterman, Peter Koch, 335 John Levine, Danny McPherson, S. Moonesamy, Doug Otis, and David F. 336 Skoll. 338 Appendix C. Public Discussion 340 Public discussion of this suite of memos takes place on the 341 domainrep@ietf.org mailing list. See 342 https://www.ietf.org/mailman/listinfo/domainrep. 344 Authors' Addresses 346 Nathaniel Borenstein 347 Mimecast 348 203 Crescent St., Suite 303 349 Waltham, MA 02453 350 USA 352 Phone: +1 781 996 5340 353 Email: nsb@guppylake.com 355 Murray S. Kucherawy 356 270 Upland Drive 357 San Francisco, CA 94127 358 USA 360 Email: superuser@gmail.com