RE: draft-tiesel-quic-unreliable-streams-01 - comments

[Roni Even <[e-mail]>]

Hi Ingemar,
It is not CCM the attacker just does heuristics to understand that this is not media but report (RTCP or ACK frames) and drops it, BTW: audio packets may also be small.
This is an example. The claim is that you can use heuristics to drop “selected” frames even though you do not know what is in the packet.
Roni



From: Ingemar Johansson S [mailto:[e-mail]]
Sent: יום ג 07 נובמבר 2017 09:41
To: Philipp S. Tiesel; Roni Even
Cc: QUIC WG
Subject: RE: draft-tiesel-quic-unreliable-streams-01 - comments

Hi Philip and Roni

I assume that by reception reports is meant the RTCP CCM messages such as TMMBR or ?

So.. unless I misunderstood it completely.
I am not at all convinced that media rate/congestion control in QUIC should rely on TMMBR.
SCReAM for instance, specified in the RMCAT WG for instance does not depend on TMMBR as it is ACK clocked, the media transmission is reduced to a very low rate if the ACKs are discarded by an attacker.

I would say that it is more straightforward to use a multipurpose congestion control in QUIC, this is perhaps based on BBR, but SCReAM style is not excluded. In any case this means that it is not possible to prevent rate adaptation.

/Ingemar


From: Philipp S. Tiesel [mailto:[e-mail]]
Sent: den 6 november 2017 10:15
To: Roni Even <[e-mail]<mailto:[e-mail]>>
Cc: QUIC WG <[e-mail]<mailto:[e-mail]>>
Subject: Re: draft-tiesel-quic-unreliable-streams-01 - comments



On 5. Nov 2017, at 08:32, Roni Even <[e-mail]<mailto:[e-mail]>> wrote:
From: Philipp S. Tiesel [mailto:[e-mail]]
On 1. Nov 2017, at 14:03, Roni Even <[e-mail]<mailto:[e-mail]>> wrote:
In the security section “ An active, on path attacker can drop selected
frames “ . What does it mean selected frames, the whole payload is
encrypted.
This is a little complicated:
- Assume having “stream-as-a-message” streams with two different kins of
messages sized A,B
- Assume each message fits into one packet, but two messages will not fit
- Assume one doesn't want to split packets to fill packets to MTU due to
latency constrains  => If an attacker know the inside protocol, the attacker
can distinguish from the packet length wether it is an A or B kind message

To avoid this, one has to pad all packets… I should clarify this.
[Roni Even] I understand this case but what does selected frames mean, I assume that the attacker does not know what is in each stream in order to select a specific one, so why will he just drop one and not the other or why not both?

Assuming the attacker _knows the protocol_, the attacker would also know the sizes of all kinds of messages and may use this knowledge to recover protocol state or selectively drop messages.

For a protocol like HTTP, the attack vector is rather small.
If one uses this against video conferencing applications, an attacker could prevent rate adaption  by dropping reception reports (larger than a pure QUIC ACK, smaller than a video frame).
If one uses this on IoT control stuff, an attacker might be able to learn a lot about the system state by observing sizes and timings.

This is nothing we can fix within QUIC without massive scarifies, but application developers must keep in mind.


AVE!
  Philipp S. Tiesel / phils…
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