Subject: Re: [ippm] Alissa Cooper's No Objection on draft-ietf-ippm-6man-pdm-option-09: (with COMMENT)

From: Nalini J Elkins <[email-masked]>
Date: Mon, 22 May 2017 15:26:46 +0000 (UTC)

Alissa,
Please let me know if you are OK with the proposed change.

>Alissa Cooper has entered the following ballot position for
>draft-ietf-ippm-6man-pdm-option-09: No Objection

>Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
>for more information about IESG DISCUSS and COMMENT positions.

>The document, along with other ballot positions, can be found here:
>https://datatracker.ietf.org/doc/draft-ietf-ippm-6man-pdm-option/

>----------------------------------------------------------------------
>COMMENT:
>----------------------------------------------------------------------

>The analysis in Sec 4.2 seems to be missing some considerations. In cases
>where the packet payload is encrypted and the attacker does not have
>access to the keys, the attacker does not in fact have access to the
>entire packet, in which case PDM provides more information than a packet
>without PDM. Also in those cases, it seems like including PDM information
>would generally make a packet stream more susceptible to traffic analysis
>insofar as the timing and sequence information may provide additional
>indicators about the type of application in use, not just the speed of
>the end host.

Are you OK if I do the following:

OLD------ Since PDM passes in the clear, a concern arises as to whether the data can be used to fingerprint the system or somehow obtain information about the contents of the payload.  
 Let us discuss fingerprinting of the end host first. It is possible that seeing the pattern of deltas or the absolute values could give some information as to the speed of the end host - that is, if it is a very fast system or an older, slow device.   This may be useful to the attacker.  However, if the attacker has access to PDM, the attacker also has access to the entire packet and could make such a deduction based merely on the time frames elapsed between packets WITHOUT PDM.  
 As far as deducing the content of the payload, it appears to us that PDM is quite unhelpful in this regard.

New------
Since PDM passes in the clear, a concern arises as to whether the
data can be used to fingerprint the system or somehow obtaininformation about the contents of the payload.  
Let us discuss fingerprinting of the end host first. It is possiblethat seeing the pattern of deltas or the absolute values could givesome information as to the speed of the end host - that is, if it isa very fast system or an older, slow device.   This may be useful tothe attacker.  However, if the attacker has access to PDM, theattacker also has access to the entire packet and could make such adeduction based merely on the time frames elapsed between packetsWITHOUT PDM.  
As far as deducing the content of the payload, it is conceivablethat an attacker could attempt to deduce the type of application inuse by noting the server time and payload length.   Having said that,some encryption algorithms attempt to obfuscate the packet lengthto avoid just such vulnerabilities.  In the future, encryption algorithmsmay wish to obfuscate the server time as well.