[AVT] Comments on draft-perkins-avt-srtp-vbr-audio

[Ingemar Johansson S <[e-mail]>]

Hi

I have now re-read both the draft as well as the paper and my impression is that the draft is good to have as an informational to inform people about a possible issue, therefore I support it.

Today it may be quite far fetched to imagine that much useful information can be extracted this way (I even have problems to get our automated speech recognition exchange understand me...). 
However, anyone who has read a spy novel by Tom Clancy or John le Carré realize that eavesdropping is more or less picking fragments of information from many different sources (including trash-bins). This in combination with Moores law says that implementors should be aware of this issue.

Section 4: My personal feeling is that the recommendations are too far, the idea is that an eavesdropper can extract information from the length of the talk spurts. This to me sounds like a much more difficult task than the VBR case (which is difficult already that). A hangover of e.g 1s is very likely to give 100% activity time for speakers of a particular south-european nationality :-)

Section 5: A variation to the padding is to randomly pad a fraction of the packets up to a large size (less or equal to the largest packet size from the codec) than , this, I believe should confuse the eavesdropper algorithm considerably. It is possible that the same can be applied to VAD case in section 4 as well.

/Ingemar 

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INGEMAR JOHANSSON  M.Sc. 
Senior Research Engineer 

Ericsson AB
Multimedia Technologies
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