[tor-relays] clarification on what Utah State University exit relays store ("360 gigs of log files")

grarpamp grarpamp at gmail.com
Thu Aug 13 11:39:05 UTC 2015

On Thu, Aug 13, 2015 at 3:40 AM, Mike Perry <mikeperry at torproject.org> wrote:
>> But consider looking at average flow lifetimes on the internet. There may
>> be case for going longer, bundling or turfing across a range of ports to falsely
>> trigger a record / bloat, packet switching and so forth.
> This interests me, but we need more details to determine what this looks
> like in practice.

NANOG list could link specific papers regarding nature of the internet.
The various flow exporters have sensible default timeouts tend cover
that ok for purposes intended.

> I suspect that this is one case where the switch to one guard may have
> helped us.

In that various activities such as ssh, browsing, youtube, whatever
are confined to being multiplexed in one stream, that makes sense.

> However, Tor still closes the TCP connection after just one
> hour of inactivity. What if we kept it open longer?

The exporting host has open flow count limited by memory (RAM).
A longer flow might be forced to span two or more records.
The "flags" field of some tools and versions may not mark
a SYN seen in records 2+, the rest of tuple would stay same.
Active timeout gives periodic data on longer flows, typically
retaining start time but implementations can vary on state.

Here's an early IOS 12 default...
  Active flows timeout in 30 minutes (1~60)
  Inactive flows timeout in 15 seconds (10~600)

Also consider what is wished to hide, big iso download,
little http clicks, start time of some characteristic session
rippling across or appearing at edges, active data pumping attack.
And what custom flowish things and flow settings an adversary
might be doing to observe those. Traditional netflow seems
useful as idea base to form a better heuristic analysis system.

> Or what if the first
> hop was an encrypted UDP-based PT, where it was not clear if the session
> was torn down or closed?

In old netflow, UDP, where src/dst ip and port tuple is same,
just times out into a record. Some new exotic DPI might form
session context flow record based on application inside, crypto
would stop the cleartext portion of DPI.

Some flow tools don't reassemble so the frag game might slide
by them in an arms race.

> in this case I am worried it may end up silencing the people I'd really
> like to hear from. I want real data from the field, here.

There's no censor here. Other operators in the field can and should speak up
on topic (and feel free to bash any my errors or lack of paper / code
/ data posting).

> You can say that, but then why isn't this being done in the real world?
> The Snowden leaks seem to indicate exploitation is the weapon of choice.

The Snowden leaks and Bamford also indicate NSA-UTAH, gigawatts, massive
international cable tapping, CARNIVORE, NARUS, X-WHATEVER, etc.
Exploitation could use a few offices full of hackers and some good peering
points and hosts, not that huge $billions level of infrastructure and outside
your borders expenditure. Though blackbagging to stand up an IP in the
target net via an active tap could be useful, the driver to localize
due to cost.

> I suspect other factors are at work that prevent dragnet correlation
> from being reliable, in addition to the economics of exploits today
> (which may be subject to change). These factors are worth investigating
> in detail, and ideally before the exploit cost profiles change.

Yes, bigdata still has to conform to at least some kind of cost
benefit analysis and substantiation too. Where is the line on that
these days... 2^40, 2^56, 2^80...?

> As such, I still look forward to hearing from someone who has worked at
> an ISP/University/etc where this is actually practiced. What is in
> *those* logs?

The questions were of a general "intro to netflow" nature, thus
the links, they and other resource describe all the data fields,
formation of records, timeouts, aggregation, IPFIX extensibility, etc.
Others and I on these lists know what "360 gigs" of netflow looks like.
*What* specific info are you looking for beyond that?
Applicability to exploit? Should people print out flows from a degenerate
client and exit use case and line them up?

More tools and tech...
nfdump, silk

More generally, netflow is not the only passive analysis tool or idea
out there. So focusing on it may be narrow, though it is popular tool.

> Specifically: Can we get someone (hell, anyone really) from Utah to
> weigh in on this one? ;)

Well, I'll speculate that by now they've lawyered up and silenced their
OP such that it's unlikely that we'll hear from them (short of coderman
firing a broadside FOIA at them ;) (We're speculating it's 360 gigs of

> Otherwise, the rest is just paranoid speculation, and bordering on
> trolled-up misinformation. :/


Everybody's now asking questions what is possible, my job is done ;)

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