The -08 version is a significant improvement that aligns the draft's recommendations on mechanisms for redaction and anonymization with the situation-dependent levels of security that are appropriate for those purposes.
idnits 2.12.13 didn't find anything. The -08 version is ready for publication as a Standards Track RFC. Thanks, --David > -----Original Message----- > From: Black, David > Sent: Thursday, January 19, 2012 7:10 PM > To: [email protected]; Murray S. Kucherawy; [email protected]; > [email protected] > Cc: [email protected]; [email protected]; Black, David > Subject: Gen-ART review of draft-ietf-marf-redaction-05 > > Based on discussion with the authors, the -05 version of this draft resolves > the > issues raised in the Gen-ART review of the -04 version. An important element > of > the approach taken to issue [1] has been to explain why the security > requirements > for redaction are significantly weaker than the strength of the secure hashes > that are suggested by the draft. > > Thanks, > --David > > > -----Original Message----- > > From: Black, David > > Sent: Tuesday, January 10, 2012 9:44 PM > > To: [email protected]; Murray S. Kucherawy; [email protected]; > > [email protected] > > Cc: Black, David; [email protected]; [email protected] > > Subject: Gen-ART review of draft-ietf-marf-redaction-04 > > > > I am the assigned Gen-ART reviewer for this draft. For background on > > Gen-ART, please > > see the FAQ at <http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>. > > > > Please resolve these comments along with any other Last Call comments you > > may receive. > > > > Document: draft-ietf-marf-redaction-04 > > Reviewer: David L. Black > > Review Date: January 10, 2012 > > IETF LC End Date: January 18, 2011 > > IESG Telechat Date: January 19, 2011 > > > > Summary: This draft is on the right track but has open issues, described in > > the review. > > > > This draft specifies a method for redacting information from email abuse > > reports > > (e.g., hiding the local part [user] of an email address), while still > > allowing > > correlation of the redacted information across related abuse reports from > > the same > > source. The draft is short, clear, and well written. > > > > There are two open issues: > > > > [1] The first open issue is the absence of security guidance to ensure that > > this > > redaction technique effectively hides the redacted information. The > > redaction > > technique is to concatenate a secret string (called the "redaction key") to > > the > > information to be redacted, apply "any hashing/digest algorithm", convert > > the output > > to base64 and use that base64 string to replace the redacted information. > > > > There are two important ways in which this technique could fail to > > effectively hide > > the redacted information: > > - The secret string may inject insufficient entropy. > > - The hashing/digest algorithm may be weak. > > > > To take an extreme example, if the secret string ("redaction key") consists > > of a > > single ASCII character, and a short email local part is being redacted, > > then the > > output is highly vulnerable to dictionary and brute force attacks because > > only 6 bits > > of entropy are added (the result may look secure, but it's not). Beyond > > this extreme > > example, this is a potentially real concern - e.g., applying the rule of > > thumb that > > ASCII text contains 4-5 bits of entropy per character, the example in > > Appendix A > > uses a "redaction key" of "potatoes" that injects at most 40 bits of > > entropy - > > is that sufficient for email redaction purposes? > > > > To take a silly example, if a CRC is used as the hash with that sort of > > short input, > > the result is not particularly difficult to invert. > > > > I suggest a couple of changes: > > 1) Change "any hashing/digest algorithm" to require use of a secure hash, > > and > > explain what is meant by "secure hash" in the security considerations > > section. > > 2) Require a minimum length of the "redaction key" string, and strongly > > suggest > > (SHOULD) that it be randomly generated (e.g., by running sufficient > > output > > of an entropy-rich random number generator through a base64 converter). > > > > For the latter change, figure out the amount of entropy that should be used > > for redaction - the recommended string length will be larger because > > printable > > ASCII is not entropy-dense (at best it's good for 6 bits of entropy in each > > 8-bit character, and human-written text such as this message has > > significantly > > less). > > > > From a pure security perspective, use of HMAC with specified secure hashes > > (SHA2-family) and an approach of hashing the "redaction key" down to a > > binary > > key for HMAC would be a stronger approach. I suggest that authors consider > > approach, but there may be practical usage concerns that suggest not > > adopting it. > > > > [2] The second open issue is absence of security considerations for the > > redaction > > key. The security considerations section needs to caution that the > > redaction key > > is a secret key that must be managed and protected as a secret key. > > Disclosure > > of a redaction key removes the redaction from all reports that used that > > key. > > As part of this, guidance should be provided on when and how to change the > > redaction key in order to limit the effects of loss of secrecy for a single > > redaction key. > > > > Editorial Nit: I believe that "anonymization" is a better description of > > what > > this draft is doing (as opposed to "redaction"), particularly as the result > > is > > intended to be correlatable via string match across reports from the same > > source. > > > > idnits 2.12.13 didn't find any nits. > > > > Thanks, > > --David > > ---------------------------------------------------- > > David L. Black, Distinguished Engineer > > EMC Corporation, 176 South St., Hopkinton, MA 01748 > > +1 (508) 293-7953 FAX: +1 (508) 293-7786 > > [email protected] Mobile: +1 (978) 394-7754 > > ---------------------------------------------------- _______________________________________________ marf mailing list [email protected] https://www.ietf.org/mailman/listinfo/marf
