[Cryptography] Threat analysis - "Meeting Snowden in Princeton" by Ross Anderson
ianG
iang at iang.org
Sat May 2 13:51:45 EDT 2015
Because he's written such a comprehensive and timely threat summary over
the intelligence community as a threat actor, here is Ross Anderson's
post in full, for our record:
https://www.lightbluetouchpaper.org/2015/05/02/meeting-snowden-in-princeton/
Meeting Snowden in Princeton
2015-05-02 Cryptology, Internet censorship, Legal issues, Open-source
security, Politics, Privacy technology, Protocols, Security economics,
Security engineering, Security psychology, Usability Ross Anderson
I’m at Princeton where Ed Snowden is due to speak by live video link in
a few minutes, and have a discussion with Bart Gellmann.
Yesterday he spent four hours with a group of cryptographers from
industry and academia, of which I was privileged to be one. The topic
was the possible and likely countermeasures, both legal and technical,
against state surveillance. Ed attended as the “Snobot”, a telepresence
robot that let him speak to us, listen and move round the room, from a
studio in Moscow. As well as over a dozen cryptographers there was at
least one lawyer and at least one journalist familiar with the leaked
documents. Yesterday’s meeting was under the Chatham House rule, so I
may not say who said what; any new disclosures may have been made by
Snowden, or by one of the journalists, or by one of the cryptographers
who has assisted journalists with the material. Although most of what
was discussed has probably appeared already in one place or another, as
a matter of prudence I’m publishing these notes on the blog while I’m
enjoying US first-amendment rights, and will sanitise them from my
laptop before coming back through UK customs.
The problem of state surveillance is a global one rather than an NSA
issue, and has been growing for years, along with public awareness of
it. But we learned a lot from the leaks; for example, wiretaps on the
communications between data centres were something nobody thought of;
and it might do no harm to think a bit more about the backhaul in CDNs.
(A website that runs TLS to a CDN and then bareback to the main server
is actually worse than nothing, as we lose the ability to shame them.)
Of course the agencies will go for the low-hanging fruit. Second, we
also got some reassurance; for example, TLS works, unless the agencies
have managed to steal or coerce the private keys, or hack the end
systems. (This is a complex discussion given CDNs, problems with the CA
ecology and bugs like Heartbleed.) And it’s a matter of record that Ed
trusted his life to Tor, because he saw from the other side that it worked.
Third, the leaks give us a clear view of an intelligence analyst’s
workflow. She will mainly look in Xkeyscore which is the Google of 5eyes
comint; it’s a federated system hoovering up masses of stuff not just
from 5eyes own assets but from other countries where the NSA cooperates
or pays for access. Data are “ingested” into a vast rolling buffer; an
analyst can run a federated search, using a selector (such as an IP
address) or fingerprint (something that can be matched against the
traffic). There are other such systems: “Dancing oasis” is the middle
eastern version. Some xkeyscore assets are actually compromised
third-party systems; there are multiple cases of rooted SMS servers that
are queried in place and the results exfiltrated. Others involve vast
infrastructure, like Tempora. If data in Xkeyscore are marked as of
interest, they’s moved to Pinwale to be memorialised for 5+ years. This
is one function of the MDRs (massive data repositories, now more
tactfully renamed mission data repositories) like Utah. At present
storage is behind ingestion. Xkeyscore buffer times just depend on
volumes and what storage they managed to install, plus what they manage
to filter out.
As for crypto capabilities, a lot of stuff is decrypted automatically on
ingest (e.g. using a “stolen cert”, presumably a private key obtained
through hacking). Else the analyst sends the ciphertext to CES and they
either decrypt it or say they can’t. There’s no evidence of a “wow”
cryptanalysis; it was key theft, or an implant, or a predicted RNG or
supply-chain interference. Cryptanalysis has been seen of RC4, but not
of elliptic curve crypto, and there’s no sign of exploits against other
commonly used algorithms. Of course, the vendors of some products have
been coopted, notably skype. Homegrown crypto is routinely problematic,
but properly implemented crypto keeps the agency out; gpg ciphertexts
with RSA 1024 were returned as fails.
With IKE the NSA were interested in getting the original handshakes,
harvesting them all systematically worldwide. These are databased and
indexed. The quantum type attacks were common against non-crypto
traffic; it’s easy to spam a poisoned link. However there is no evidence
at all of active attacks on cryptographic protocols, or of any
break-and-poison attack on crypto links. It is however possible that the
hacking crew can use your cryptography to go after your end system
rather than the content, if for example your crypto software has a
buffer overflow.
What else might we learn from the disclosures when designing and
implementing crypto? Well, read the disclosures and use your brain. Why
did GCHQ bother stealing all the SIM card keys for Iceland from Gemalto,
unless they have access to the local GSM radio links? Just look at the
roof panels on US or UK embassies, that look like concrete but are
actually transparent to RF. So when designing a protocol ask yourself
whether a local listener is a serious consideration.
In addition to the Gemalto case, Belgacom is another case of hacking X
to get at Y. The kind of attack here is now completely routine: you look
for the HR spreadsheet in corporate email traffic, use this to identify
the sysadmins, then chain your way in. Companies need to have some clue
if they’re to stop attacks like this succeeding almost trivially. By
routinely hacking companies of interest, the agencies are
comprehensively undermining the security of critical infrastructure, and
claim it’s a “nobody but us” capability. however that’s not going to
last; other countries will catch up.
Would opportunistic encryption help, such as using unauthenticated
Diffie-Hellman everwhere? Quite probably; but governments might then
simply compel the big service forms to make the seeds predictable. At
present, key theft is probably more common than key compulsion in US
operations (though other countries may be different). If the US
government ever does use compelled certs, it’s more likely to be the FBI
than the NSA, because of the latter’s focus on foreign targets. The FBI
will occasionally buy hacked servers to run in place as honeypots, but
Stuxnet and Flame used stolen certs. Bear in mind that anyone outside
the USA has zero rights under US law.
Is it sensible to use medium-security systems such as Skype to hide
traffic, even though they will give law enforcement access? For example,
an NGO contacting people in one of the Stans might not want to
incriminate them by using cryptography. The problem with this is that
systems like Skype will give access not just to the FBI but to all sorts
of really unsavoury police forces.
FBI operations can be opaque because of the care they take with parallel
construction; the Lavabit case was maybe an example. It could have been
easy to steal the key, but then how would the intercepted content have
been used in court? In practice, there are tons of convictions made on
the basis of cargo manifests, travel plans, calendars and other such
plaintext data about which a suitable story can be told. The FBI
considers it to be good practice to just grab all traffic data and
memorialise it forever.
The NSA is even more cautious than the FBI, and won’t use top exploits
against clueful targets unless it really matters. Intelligence services
are at least aware of the risk of losing a capability, unlike vanilla
law enforcement, who once they have a tool will use it against
absolutely everybody.
Using network intrusion detection against bad actors is very much like
the attack / defence evolution seen in the anti-virus business. A system
called Tutelage uses Xkeyscore infrastructure and matches network
traffic against signatures, just like AV, but it has the same
weaknesses. Script kiddies are easily identifiable from their script
signatures via Xkeyscore, but the real bad actors know how to change
network signatures, just as modern malware uses packers to become highly
polymorphic.
Cooperation with companies on network intrusion detection is tied up
with liability games. DDoS attacks from Iran spooked US banks, which
invited the government in to snoop on their networks, but above all
wanted liability protection.
Usability is critical. Lots of good crypto never got widely adopted as
it was too hard to use; think of PGP. On the other hand, Tails is
horrifically vulnerable to traditional endpoint attacks, but you can
give it as a package to journalists to use so they won’t make so many
mistakes. The source has to think “How can I protect myself?” which
makes it really hard, especially for a source without a crypto and
security background. You just can’t trust random journalists to be
clueful about everything from scripting to airgaps. Come to think of it,
a naive source shouldn’t trust their life to securedrop; he should use
gpg before he sends stuff to it but he won’t figure out that it’s a good
idea to suppress key IDs. Engineers who design stuff for whistleblowers
and journalists must be really thoughtful and careful if they want to
ensure their users won’t die when they screw up. The goal should be that
no single error should be fatal, and so long as their failures aren’t
compounded the users will stay alive. Bear in mind that
non-roman-language countries use numeric passwords, and often just 8
digits. And being a target can really change the way you operate. For
example, password managers are great, but not for someone like Ed, as
they put too many of the eggs in one basket. If you’re a target, create
a memory castle, or a token that can be destroyed on short notice. If
you’re a target like Ed, you have to compartmentalise.
On the policy front, one of the eye-openers was the scale of
intelligence sharing – it’s not just 5 eyes, but 15 or 35 or even 65
once you count all the countries sharing stuff with the NSA. So how does
governance work? Quite simply, the NSA doesn’t care about policy. Their
OGC has 100 lawyers whose job is to “enable the mission”; to figure out
loopholes or new interpretations of the law that let stuff get done. How
do you restrain this? Could you use courts in other countries, that have
stronger human-rights law? The precedents are not encouraging. New
Zealand’s GCSB was sharing intel with Bangladesh agencies while the NZ
government was investigating them for human-rights abuses. Ramstein in
Germany is involved in all the drone killings, as fibre is needed to
keep latency down low enough for remote vehicle pilots. The problem is
that the intelligence agencies figure out ways to shield the authorities
from culpability, and this should not happen.
Jurisdiction is a big soft spot. When will CDNs get tapped on the
shoulder by local law enforcement in dodgy countries? Can you lock stuff
out of particular jurisdictions, so your stuff doesn’t end up in Egypt
just for load-balancing reasons? Can the NSA force data to be rehomed in
a friendly jurisdiction, e.g. by a light DoS? Then they “request” stuff
from a partner rather than “collecting” it.
The spooks’ lawyers play games saying for example that they dumped
content, but if you know IP address and file size you often have it; and
IP address is a good enough pseudonym for most intel / LE use. They deny
that they outsource to do legal arbitrage (e.g. NSA spies on Brits and
GCHQ returns the favour by spying on Americans). Are they telling the
truth? In theory there will be an MOU between NSA and the partner agency
stipulating respect for each others’ laws, but there can be caveats,
such as a classified version which says “this is not a binding legal
document”. The sad fact is that law and legislators are losing the
capability to hold people in the intelligence world to account, and also
losing the appetite for it.
The deepest problem is that the system architecture that has evolved in
recent years holds masses of information on many people with no
intelligence value, but with vast potential for political abuse.
Traditional law enforcement worked on individualised suspicion;
end-system compromise is better than mass search. Ed is on the record as
leaving to the journalists all decisions about what targeted attacks to
talk about, as many of them are against real bad people, and as a matter
of principle we don’t want to stop targeted attacks.
Interference with crypto in academia and industry is longstanding.
People who intern with a clearance get a “lifetime obligation” when they
go through indoctrination (yes, that’s what it’s called), and this
includes pre-publication review of anything relevant they write. The
prepublication review board (PRB) at the CIA is notoriously unresponsive
and you have to litigate to write a book. There are also specific
programmes to recruit cryptographers, with a view to having friendly
insiders in companies that might use or deploy crypto.
The export control mechanisms are also used as an early warning
mechanism, to tip off the agency that kit X will be shipped to country Y
on date Z. Then the technicians can insert an implant without anyone at
the exporting company knowing a thing. This is usually much better than
getting stuff Trojanned by the vendor.
Western governments are foolish to think they can develop NOBUS (no-one
but us) technology and press the stop button when things go wrong, as
this might not be true for ever. Stuxnet was highly targeted and
carefully delivered but it ended up in Indonesia too. Developing
countries talk of our first-mover advantage in carbon industrialisation,
and push back when we ask them to burn less coal. They will make the
same security arguments as our governments and use the same techniques,
but without the same standards of care. Bear in mind, on the equities
issue, that attack is way way easier than defence. So is cyber-war
plausible? Politically no, but at the expert level it might eventually
be so. Eventually something scary will happen, and then infrastructure
companies will care more, but it’s doubtful that anyone will do a
sufficiently coordinated attack on enough diverse plant through
different firewalls and so on to pose a major threat to life.
How can we push back on the poisoning of the crypto/security community?
We have to accept that some people are pro-NSA while others are
pro-humanity. Some researchers do responsible disclosure while others
devise zero-days and sell them to the NSA or Vupen. We can push back a
bit by blocking papers from conferences or otherwise denying academic
credit where researchers prefer cash or patriotism to responsible
disclosure, but that only goes so far. People who can pay for a new
kitchen with their first exploit sale can get very patriotic; NSA
contractors have a higher standard of living than academics. It’s best
to develop a culture where people with and without clearances agree that
crypto must be open and robust. The FREAK attack was based on export
crypto of the 1990s.
We must also strengthen post-national norms in academia, while in the
software world we need transparency, not just in the sense of open
source but of business relationships too. Open source makes it harder
for security companies to sell different versions of the product to
people we like and people we hate. And the NSA may have thought dual-EC
was OK because they were so close to RSA; a sceptical purchaser should
have observed how many government speakers help them out at the RSA
conference!
Secret laws are pure poison; government lawyers claim authority and act
on it, and we don’t know about it. Transparency about what governments
can and can’t do is vital.
On the technical front, we can’t replace the existing infrastructure, so
it won’t be possible in the short term to give people mobile phones that
can’t be tracked. However it is possible to layer new communications
systems on top of what already exists, as with the new generation of
messaging apps that support end-to-end crypto with no key escrow. As for
whether such systems take off on a large enough scale to make a
difference, ultimately it will all be about incentives.
(by Ross Anderson)
More information about the cryptography
mailing list