MARF Working Group J. Falk, Ed. Internet-Draft Return Path Intended status: Informational April 6, 2011 Expires: October 8, 2011 Redaction of Potentially Sensitive Data from Mail Abuse Reports draft-ietf-marf-redaction-00 Abstract Email messages often contain information which might be considered private or sensitive, per either regulation or social norms. When such a message becomes the subject of a report intended to be shared with other entities, the report generator may wish to redact or elide the sensitive portions of the message. This memo suggests one method for doing so effectively. 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/. 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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 Falk Expires October 8, 2011 [Page 1] Internet-Draft Redaction April 2011 described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Recommended Practice . . . . . . . . . . . . . . . . . . . . . 3 3. Security and Privacy Considerations . . . . . . . . . . . . . . 4 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5 Falk Expires October 8, 2011 [Page 2] Internet-Draft Redaction April 2011 1. Introduction [ARF] defines a message format for sending reports of abuse in the messaging infrastructure, with an eye toward automating both the generating and consumption of those reports. For privacy considerations it might be the policy of a report generator to redact, or obscure, portions of the report that might identify an end user that caused the report to be generated. Precisely how this is done is unspecified in [ARF] as it will generally be a matter of local policy. That specification does admonish generators against being too over-zealous with this practice, as obscuring too much data makes the report non-actionable. Previous redaction practices, such as replacing local-parts of addresses with a uniform string like "xxxxxxxx", often frustrates any kind of prioritizing or grouping of reports. Generally, it is assumed that the recipient-identifying fields of a message, when copied into a report, are to be obscured to protect the identity of then end user who submitted the complaint about the message. However, it is also presumed that other data will be left intact, and that data could theoretically be correlated against log files or other resources to determine the intended recipient of the message. 2. Recommended Practice To enable correlation of reports that might refer to a common but anonymous source, the following redaction practice is recommended (but not required): 1. Select an arbitrary string that will be used by an Administrative Domain (ADMD) that generates reports. This string will not be changed except according to a key rotation policy or similar. Call this the "redaction key". 2. Identify string(s) (such as local-parts of email addresses) in a message that need to be redacted. Call this the "private data". 3. Construct a new string that is a copy of the redaction key with the private data concatenated to it. 4. Compute a digest of that string with any hashing/digest algorithm such as SHA1. 5. Encode that hash with the base64 algorithm as defined in [MIME]. 6. Replace the private data with the encoded hash when generating the report. This has the effect of obscuring the data in an irreversible way but Falk Expires October 8, 2011 [Page 3] Internet-Draft Redaction April 2011 still allows the report recipient to observe that numerous reports are about one particular end user. Such detection enables the receiver to prioritize its reactions based on problems that appear to be focused on specific end users that may be under attack. 3. Security and Privacy Considerations Security issues with respect to these reports are found in [ARF]. While the method of redaction described in this document may somewhat reduce the likelihood of some types of private data from leaking between Administrative Domains, it is extremely unlikely that report generation software could ever be created to recognize all of the different ways that private information may be expressed through human written language. If further protections are required, implementors may wish to consider establishing legal contracts or other non-technology-based agreements between the relevant entities. 4. Acknowledgements Much of the text in this document was initially moved from [DKIM-REPORTING], by Murray Kucherawy and Hilda Fontana with contributions from Monica Chew, Tim Draegen, Michael Adkins, and myself. 5. IANA Considerations This memo includes no request to IANA. 6. References [ARF] Shafranovich, Y., Levine, J., and M. Kucherawy, "An Extensible Format for Email Feedback Reports", RFC 5965, August 2010. [DKIM-REPORTING] Kucherawy, M. and H. Fontana, "Authentication Failure Reporting using the Abuse Report Format", I-D draft-ietf-marf-dkim-reporting, January 2011, . [MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. Falk Expires October 8, 2011 [Page 4] Internet-Draft Redaction April 2011 Author's Address J.D. Falk (editor) Return Path 100 Mathilda Place, Suite 100 Sunnyvale, CA 94086 US Email: ietf@cybernothing.org URI: http://www.returnpath.net/ Falk Expires October 8, 2011 [Page 5]