Re: Structuring the BKK spin bit discussion

[Roland Zink <[e-mail]>]

Am 31.10.2018 um 19:04 schrieb Christian Huitema:
> On 10/31/2018 10:16 AM, Brian Trammell (IETF) wrote:
>
>> In the case that...
>>
>> - ...an end-to-end connection actually terminates at a location different than the apparent location in the endpoint IP address, because the endpoint IP address is a VPN tunnel endpoint
>> - ...the "hidden" endpoint is very far (> ~3000-5000km) from the apparent location
>> - ...that VPN tunnel exists solely to make the end-to-end association appear to originate from at or near the VPN tunnel endpoint (e.g., anti-geofencing)
> The actual scenario relates to UDP/QUIC proxies, and how they would
> compare to TCP/TLS proxies.
>
> Today, I can build a TCP/TLS proxy that accepts connections at port 443,
> examines the (possibly encrypted) SNI in the client Hello, establishes a
> TCP connection to the hidden destination, and relays TLS packets between
> the 2 connections. TCP is hop by hop, TLS is end to end, examining TCP
> sequence numbers and ACKs does not reveal the hidden leg of the service.
>
> Suppose that I build a QUIC proxy that accepts UDP packets at port 4433,
> and then does pretty much the same job as load balancer: look for the
> (possibly encrypted) SNI inside the client hello for initial packets;
> look for the destination connection ID in other packets; forward the UDP
> packets to the hidden server based on that, and vice versa in the other
> direction. This is sort of equivalent to the TCP/TLS proxy scenario: UDP
> is hop by hop; QUIC and TLS is end to end. The QUIC messages are
> encrypted and don't reveal much, but the spin bit will reveal the
> end-to-end RTT.

I guess this shows that some privacy is lost with the spin bit enabled. 
When writing a proxy you may put some more effort and provide a TOR like 
proxy where the outer QUIC connection is only to the proxy and a inner 
QUIC connection is end to end.

Roland

> Of course, examining the content and timing of packets might in both
> cases reveal the end-to-end RTT, but layering makes a difference. The
> application may be able to implement end-to-end measures to counter the
> analysis of end-to-end traffic, but the application cannot easily
> influence the spin bit.
>
> -- Christian Huitema
>
>
>