Re: [secdir] Secdir review of draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-05

[Varun Singh <[e-mail]>]

Hi,

Thanks for the comments, comments inline.

On Jun 24, 2013, at 4:37 PM, Sam Hartman wrote:

> 
> 
> Please treat these comments as normal last-call comments.
> 
> I've been asigned as a security directorate reviewer for this draft.
> 
> This draft specifies a mechanism to indicate which packets were
> discarded in a RTP stream.  for the most part, this doesn't seem to have
> any security implications, and the text is clear.  I do have one
> concern.
> 
> Has the WG analyzed implications of providing feedback to an attacker on
> what specific SRTP packets are discarded?  In the past we've run into
> trouble with security systems that were too verbose in error reporting.
> As an example, in certain public-key crypto constructions knowing
> whether a packet produced a decoding error vs a signature error after
> decryption can provide an attacker generating forged packets valuable
> information to attack the system.
> 

In the draft, discarded packets are defined as: packets that were received but
dropped from the jitter buffer because they were either too early (for buffering) 
or too late (for playout). 

Since the timestamp field in the RTP header is not encrypted, 
the endpoint can discard the packet before decrypting or authenticating it.
Forged packets that are discarded are not reported by this metric block.


> It's quite possible that SRTP doesn't have problems in this regard.  I
> just want to confirm that the analysis has been done. 

Cheers,
Varun