fourth post
How to Remain Secure Against the NSA
Now that we have enough details about how the NSA eavesdrops on the
Internet, including recent disclosures of the NSA's deliberate weakening
of cryptographic systems, we can finally start to figure out how to
protect ourselves.
For the past two weeks, I have been working with the Guardian on NSA
stories, and have read hundreds of top-secret NSA documents provided by
whistleblower Edward Snowden. I wasn't part of today's story -- it was
in process well before I showed up -- but everything I read confirms
what the Guardian is reporting.
At this point, I feel I can provide some advice for keeping secure
against such an adversary.
The primary way the NSA eavesdrops on Internet communications is in the
network. That's where their capabilities best scale. They have invested
in enormous programs to automatically collect and analyze network
traffic. Anything that requires them to attack individual endpoint
computers is significantly more costly and risky for them, and they will
do those things carefully and sparingly.
Leveraging its secret agreements with telecommunications companies --
all the US and UK ones, and many other "partners" around the world --
the NSA gets access to the communications trunks that move Internet
traffic. In cases where it doesn't have that sort of friendly access, it
does its best to surreptitiously monitor communications channels:
tapping undersea cables, intercepting satellite communications, and so on.
That's an enormous amount of data, and the NSA has equivalently enormous
capabilities to quickly sift through it all, looking for interesting
traffic. "Interesting" can be defined in many ways: by the source, the
destination, the content, the individuals involved, and so on. This data
is funneled into the vast NSA system for future analysis.
The NSA collects much more metadata about Internet traffic: who is
talking to whom, when, how much, and by what mode of communication.
Metadata is a lot easier to store and analyze than content. It can be
extremely personal to the individual, and is enormously valuable
intelligence.
The Systems Intelligence Directorate is in charge of data collection,
and the resources it devotes to this is staggering. I read status report
after status report about these programs, discussing capabilities,
operational details, planned upgrades, and so on. Each individual
problem -- recovering electronic signals from fiber, keeping up with the
terabyte streams as they go by, filtering out the interesting stuff --
has its own group dedicated to solving it. Its reach is global.
The NSA also attacks network devices directly: routers, switches,
firewalls, etc. Most of these devices have surveillance capabilities
already built in; the trick is to surreptitiously turn them on. This is
an especially fruitful avenue of attack; routers are updated less
frequently, tend not to have security software installed on them, and
are generally ignored as a vulnerability.
The NSA also devotes considerable resources to attacking endpoint
computers. This kind of thing is done by its TAO -- Tailored Access
Operations -- group. TAO has a menu of exploits it can serve up against
your computer -- whether you're running Windows, Mac OS, Linux, iOS, or
something else -- and a variety of tricks to get them onto your
computer. Your anti-virus software won't detect them, and you'd have
trouble finding them even if you knew where to look. These are hacker
tools designed by hackers with an essentially unlimited budget. What I
took away from reading the Snowden documents was that if the NSA wants
in to your computer, it's in. Period.
The NSA deals with any encrypted data it encounters more by subverting
the underlying cryptography than by leveraging any secret mathematical
breakthroughs. First, there's a lot of bad cryptography out there. If it
finds an Internet connection protected by MS-CHAP, for example, that's
easy to break and recover the key. It exploits poorly chosen user
passwords, using the same dictionary attacks hackers use in the
unclassified world.
As was revealed today, the NSA also works with security product vendors
to ensure that commercial encryption products are broken in secret ways
that only it knows about. We know this has happened historically:
CryptoAG and Lotus Notes are the most public examples, and there is
evidence of a back door in Windows. A few people have told me some
recent stories about their experiences, and I plan to write about them
soon. Basically, the NSA asks companies to subtly change their products
in undetectable ways: making the random number generator less random,
leaking the key somehow, adding a common exponent to a public-key
exchange protocol, and so on. If the back door is discovered, it's
explained away as a mistake. And as we now know, the NSA has enjoyed
enormous success from this program.
TAO also hacks into computers to recover long-term keys. So if you're
running a VPN that uses a complex shared secret to protect your data and
the NSA decides it cares, it might try to steal that secret. This kind
of thing is only done against high-value targets.
How do you communicate securely against such an adversary? Snowden said
it in an online Q&A soon after he made his first document public:
"Encryption works. Properly implemented strong crypto systems are one of
the few things that you can rely on."
I believe this is true, despite today's revelations and tantalizing
hints of "groundbreaking cryptanalytic capabilities" made by James
Clapper, the director of national intelligence in another top-secret
document. Those capabilities involve deliberately weakening the
cryptography.
Snowden's follow-on sentence is equally important: "Unfortunately,
endpoint security is so terrifically weak that NSA can frequently find
ways around it."
Endpoint means the software you're using, the computer you're using it
on, and the local network you're using it in. If the NSA can modify the
encryption algorithm or drop a Trojan on your computer, all the
cryptography in the world doesn't matter at all. If you want to remain
secure against the NSA, you need to do your best to ensure that the
encryption can operate unimpeded.
With all this in mind, I have five pieces of advice:
1) Hide in the network. Implement hidden services. Use Tor to anonymize
yourself. Yes, the NSA targets Tor users, but it's work for them. The
less obvious you are, the safer you are.
2) Encrypt your communications. Use TLS. Use IPsec. Again, while it's
true that the NSA targets encrypted connections -- and it may have
explicit exploits against these protocols -- you're much better
protected than if you communicate in the clear.
3) Assume that while your computer can be compromised, it would take
work and risk on the part of the NSA -- so it probably isn't. If you
have something really important, use an air gap. Since I started working
with the Snowden documents, I bought a new computer that has never been
connected to the Internet. If I want to transfer a file, I encrypt the
file on the secure computer and walk it over to my Internet computer,
using a USB stick. To decrypt something, I reverse the process. This
might not be bulletproof, but it's pretty good.
4) Be suspicious of commercial encryption software, especially from
large vendors. My guess is that most encryption products from large US
companies have NSA-friendly back doors, and many foreign ones probably
do as well. It's prudent to assume that foreign products also have
foreign-installed backdoors. Closed-source software is easier for the
NSA to backdoor than open-source software. Systems relying on master
secrets are vulnerable to the NSA, through either legal or more
clandestine means.
5) Try to use public-domain encryption that has to be compatible with
other implementations. For example, it's harder for the NSA to backdoor
TLS than BitLocker, because any vendor's TLS has to be compatible with
every other vendor's TLS, while BitLocker only has to be compatible with
itself, giving the NSA a lot more freedom to make changes. And because
BitLocker is proprietary, it's far less likely those changes will be
discovered. Prefer symmetric cryptography over public-key cryptography.
Prefer conventional discrete-log-based systems over elliptic-curve
systems; the latter have constants that the NSA influences when they can.
Since I started working with Snowden's documents, I have been using GPG,
Silent Circle, Tails, OTR, TrueCrypt, BleachBit, and a few other things
I'm not going to write about. There's an undocumented encryption feature
in my Password Safe program from the command line; I've been using that
as well.
I understand that most of this is impossible for the typical Internet
user. Even I don't use all these tools for most everything I am working
on. And I'm still primarily on Windows, unfortunately. Linux would be safer.
The NSA has turned the fabric of the Internet into a vast surveillance
platform, but they are not magical. They're limited by the same economic
realities as the rest of us, and our best defense is to make
surveillance of us as expensive as possible.
Trust the math. Encryption is your friend. Use it well, and do your best
to ensure that nothing can compromise it. That's how you can remain
secure even in the face of the NSA.
This essay originally appeared in the "Guardian."
http://www.theguardian.com/world/2013/sep/05/nsa-how-to-remain-secure-surveillanceNSA links:
http://www.theguardian.com/world/2013/sep/05/nsa-gchq-encryption-codes-securityhttp://online.wsj.com/article/SB10001424127887324108204579022874091732470.htmlhttp://www.theguardian.com/business/2013/aug/02/telecoms-bt-vodafone-cables-gchqhttp://www.washingtonpost.com/business/technology/agreements-with-private-companies-protect-us-access-to-cables-data-for-surveillance/2013/07/06/aa5d017a-df77-11e2-b2d4-ea6d8f477a01_story.htmlhttp://www.theguardian.com/world/2013/jul/31/nsa-top-secret-program-online-datahttp://www.theguardian.com/world/2013/jun/27/nsa-data-mining-authorised-obamahttp://www.wired.com/threatlevel/2013/09/nsa-router-hacking/http://www.foreignpolicy.com/articles/2013/06/10/inside_the_nsa_s_ultra_secret_china_hacking_grouphttp://www.informationweek.com/security/government/want-nsa-attention-use-encrypted-communi/240157089 or
http://tinyurl.com/kdxaytfOther NSA backdoors:
http://www.schneier.com/blog/archives/2008/01/nsa_backdoors_i.htmlhttp://www.heise.de/tp/artikel/2/2898/1.htmlhttp://www.heise.de/tp/artikel/5/5263/1.htmlSnowden's interview:
http://www.theguardian.com/world/2013/jun/17/edward-snowden-nsa-files-whistleblowerClapper's comments:
http://www.wired.com/threatlevel/2013/08/black-budget/Surveillance built in to the routers:
https://www.rfc-editor.org/rfc/rfc3924.txtMy tools:
http://www.gnupg.org/https://silentcircle.com/https://tails.boum.org/http://www.cypherpunks.ca/otr/http://www.truecrypt.org/http://bleachbit.sourceforge.net/https://www.schneier.com/passsafe.html