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Falk 3 Internet-Draft Return Path 4 Intended status: Informational March 4, 2011 5 Expires: September 5, 2011 7 Redaction of Potentially Sensitive Data from Mail Abuse Reports 8 draft-jdfalk-marf-redaction-00 10 Abstract 12 Email messages often contain information which might be considered 13 private or sensitive, per either regulation or social norms. When 14 such a message becomes the subject of a report intended to be shared 15 with other entities, the report generator may wish to redact or elide 16 the sensitive portions of the message. This memo suggests one method 17 for doing so effectively. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on September 5, 2011. 36 Copyright Notice 38 Copyright (c) 2011 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Recommended Practice . . . . . . . . . . . . . . . . . . . . . 3 55 3. Security and Privacy Considerations . . . . . . . . . . . . . . 4 56 4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 1. Introduction 61 [ARF] defines a message format for sending reports of abuse in the 62 messaging infrastructure, with an eye toward automating both the 63 generating and consumption of those reports. 65 For privacy considerations it might be the policy of a report 66 generator to redact, or obscure, portions of the report that might 67 identify an end user that caused the report to be generated. 68 Precisely how this is done is unspecified in [ARF] as it will 69 generally be a matter of local policy. That specification does 70 admonish generators against being too over-zealous with this 71 practice, as obscuring too much data makes the report inactionable. 73 Previous redaction practices, such as replacing local-parts of 74 addresses with a uniform string like "xxxxxxxx", often frustrated any 75 kind of prioritizing or grouping of reports. 77 Generally, it is assumed that the recipient fields of a message, when 78 copied into a report, are to be obscured to protect the identify of 79 an end user that submitted a complaint about a message. However, it 80 is also presumed that other data will be left intact, data that could 81 be correlated against logs to determine the source of the message 82 that drew a complaint. 84 2. Recommended Practice 86 To enable correlation of reports that might refer to a common but 87 anonymous source, the following redaction practice is recommended: 89 1. Select an arbitrary string that will be used by an Administrative 90 Domain (ADMD) that generates reports. This string will not be 91 changed except according to a key rotation policy or similar. 92 Call this the "redaction key". 93 2. Identify string(s) (such as local-parts of email addresses) in a 94 message that need to be redacted. Call this the "private data". 95 3. Construct a new string that is a copy of the redaction key with 96 the private data concatenated to it. 97 4. Compute a digest of that string with any hashing/digest algorithm 98 such as SHA1. 99 5. Encode that hash with the base64 algorithm as defined in [MIME]. 100 6. Replace the private data with the encoded hash when generating 101 the report. 103 This has the effect of obscuring the data in an irreversible way but 104 still allows the report recipient to observe that numerous reports 105 are about one particular end user. Such detection enables the 106 receiver to prioritize its reactions based on problems that appear to 107 be focused on specific end users that may be under attack. 109 3. Security and Privacy Considerations 111 Security issues with respect to these reports are found in [ARF]. 113 While the method of redaction described in this document may somewhat 114 reduce the likelihood of some types of private data from leaking 115 between Administrative Domains, it is extremely unlikely that report 116 generation software could ever be created to recognize all of the 117 different ways that private information may be expressed through 118 human written language. If further protections are required, 119 implementors may wish to consider establishing legal contracts or 120 other non-technology-based agreements between the relevant entities. 122 4. References 124 [ARF] Shafranovich, Y., Levine, J., and M. Kucherawy, "An 125 Extensible Format for Email Feedback Reports", RFC 5965, 126 August 2010. 128 [MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 129 Extensions (MIME) Part One: Format of Internet Message 130 Bodies", RFC 2045, November 1996. 132 Author's Address 134 J.D. Falk 135 Return Path 136 100 Mathilda Place, Suite 100 137 Sunnyvale, CA 94086 138 US 140 Email: ietf@cybernothing.org 141 URI: http://www.returnpath.net/