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Artifact 2251640dd7da420df58a2fafc8cf43e3d1487564:

NSA Backdoor Fnord

As you all know, it is not allowed to speak about NSA-demanded backdoors, and especially it is strictly prohibited to give any details. However, it is allowed to boldly lie about NSA-demanded backdoors if you didn't receive such a request, because you are not under a gag order, and in general, lying about the quality of your product is not only legal, but “best practice”. The purpose of this NSA backdoor fnord is to make you worry about the quality of net2o, and therefore you start looking at the source code; the topics mentioned here are all security things to consider.

Therefore, here is the official statement about NSA-demanded backdoors: The NSA asked me to improve Ray Ozzie's botched smartphone backdoor. Here's how: Instead of having one single point of failure (database of unlock keys), distribute the secret. A lawful backdoor needs to be demanded by the investigators (state attorney), must be approved by a judge, handed over to the cooperating manufacturer, and needs to be device-specific — no other device may be unlocked by that procedure. That are at least 4 keys in the chain; better with at least a four-eyes procedure in each of the points, so 7 keys minimum (the device itself isn't four-eyes).

Distributing a secret (without byzantine fault tolerance) is easy with ed25519. A secret chain pkn=base*(sk1*..*skn) can be generated through a chain of HSMs, which each generate the next pubkey by producing pki=pkj*(ski) (the order is irrelevant, every ski must be used just once). To verify that all secrets have been used, use a chain signature. The device itself generates the starting point of this chain signature, by signing its own unlock throw-away secret, producing a tuple (k)*base,(z*sk+k) (after producing that tuple and the unlock pubkey, this secret is no longer needed and thrown away). Each node (HSM) in the chain will need to modify that signature by adding its own secret ki and multiplying it with its own secret ski, so you first form (k)*base+(ki)*base=(k+ki)*base and (z*sk+k+ki), and then (ski)*(k+ki)*base=(ski(k+ki))*base, and (ski)*(z*sk+k+ki)=(z*sk*ski+ski(k+ki)). The final signature then will verify correctly against pkn, a pubkey only the device itself knows, because it generated it itself by taking in pkn-1 and multiplying its own secret key skn with it.

The device does not need to keep this pubkey as plaintext, it is sufficient if this pubkey (or a salted hash over it; using that salt as z value of the signature) is used for actually decrypting the flash drive. The pubkey therefore is stored encrypted by its owner's password. If an unlock message is received and the calculated remaining pubkey hashed with the salt opens the encrypted drive, it's legitimate.

All parties necessary to open the device must collaborate, and it is possible to configure the devices so that only the appropriate chain of authorities can open it (i.e. the local authorities, not the FBI), and all the relevant keys are stored in trusted enclaves (device itself) and HSMs (courts, state attorneys and manufacturer). The only database with larger amount of data are the signatures the devices themselves created on manufacturing; it is useless without the other keys. Since only the device itself can verify that the signature is correct, any party in the chain can be non-cooperative without the others knowing who wasn't cooperative. This makes sure that all parties (except the device itself) are truely convinced that the case is legitimate, and no pressure from outside can force them to comply.

As net2o is open source, you can (in theory) verify statements about actual backdoors. And keep an eye on this page, I intent to publish fnords about having official back/front/side doors, leaky roofs and tunnels regularly, but won't commit on an expicit schedule. For a true fnord to work, you always have to be wary. All the git checkins are signed.

For those interested in history, whether the NSA can force a European company to install a backdoor, see Crypto AG

What is this page for?

Software is inherently buggy — we all make mistakes. Secure networking software is even worse, because small bugs have big consequences, and security bugs usually don't affect direct functionality, and therefore can lure inside the program for a long time. And with the NSA Bullrun program, we not only have to deal with the normal, ”lazy” bugs, which don't cause any harm until found (either by honest security researcher or evil criminals), but with bugs intentionally placed, and used by the secret services from day 0.

Developing in Forth is a “crash early, crash often” exercise, but security related bugs don't crash the program.

net2o is not ready for wide-spread use, so bugs do happen, and get fixed, but the bugs described here usually are real bugs I found and fixed during development. All of them look like professionally implanted backdoors by the NSA, because that's the state of the art how to implant backdoors: It must provide its author with “reasonable denial”, claiming incompetence.

However, in order to get things right, we need a culture of accepting our mistakes, and fixing them. Many programmers deny bugs, and request at least a proof of concept attack, before they actually start doing something. This sort of culture is so wrong: As author of security critical systems, you must be constantly scared by people using every way to break into your software, and you must be ready to fix every bug, even just potential risks, before someone shows you an actual exploit.

Warrant Canary

This sort of thing I'm doing here is called “warrant canary”, named after the canaries used by miners which are more sensitive to poisonous gas leaks than humans. The thing would be impossible if the other side would say “continue with business as usual, so that nobody knows we were here”. Takedowns like the one of Lavabit (which was triggered by an NSL) or more recently by TrueCrypt (which we don't know why they did it) aren't such continuations, people can guess that the NSA was there.

There's some discussion, especially initiated by Moxie Marlinspike, whether a canary is effective, and whether a court can order you to silence (yes, they can), or to say something specific (sometimes, they can), but so far, a court has not forced anybody to give false speech on his own (instead of just answering a question with a false ”No”, because saying “yes” would violate the gag order). That's why this canary is a provable lie (i.e. even when the bugs were there, the text here is checked in with the fix). I have no idea if that actually works, and would prefer to never find out.

Intelligence Community might resort to some sort of bullying to disrupt the operation of their enemies; the NSA seems to like accusation of sexual offenses in the form of public shaming, see for example Julian Assange and Jake Appelbaum.