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Comment by tzs | Hacker News Reader

> The problem is, how do you build a back door that can only be used by people with valid (and just) warrants?

That's an interesting technical problem. A lot of people dismiss it as impossible out of hand, but they are underestimating what you can do with modern cryptography.

You make it a distributed back door that requires several independent third parties to cooperate to use it.

You choose the third parties so that no particular warrant seeker will be able to get enough power or influence over enough of the third parties to force them to enable the back door unless they think the use is valid and just. (You can actually design it so that the warrant seeker does not know who the third parties are).

Some aspects of this may be too complicated to be practical, but it is not impossible.

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No, having worked on crypto I feel confident saying that the smart people, especially those who do understand crypto, know, and state, that it cannot be done.

All solution fundamentally boil down to someone has the keys required to decrypt all your content. This is ignoring the other technical costs (now your service has to record all ephemeral keys as well).

It doesn’t matter /who/ has that decryption key, the requirement is that access to the key is guarded only by policy.

You also resort to “with a warrant” but a NSL is effectively a warrant, and I’m fairly sure the DPRC has “warrants”. Who gets to request those keys? The position of the us government is that they have the right to access data from people in other countries, so can they provide a warrant to access that data? Can Germany ask for the data for someone in the US? What if someone travelled through another country - can that country now access those keys?

Note these all questions regarding /legitimate/ access, I’m completely ignoring police officers looking up people they stopped and stealing nudes, of people stealing the information and using that information to steal money, stalking, etc

I am sick and tired of people who say “modern cryptography is amazing, so it must be able to fulfill my unicorn dreams”. Either stop claiming nonsense or provide a prove that it is possible by designing a system that does what you say must be possible.

Briefly, use a secret sharing protocol to distribute the device key to 500 lawyers around the world from countries other than the country the device holder resides in, with 400 key shares needed to reconstruct the device key. A requester can get the device key if he can convince 400 of the 500 lawyers that his request is legitimate according to whatever the criteria was that the lawyers agreed to when they agreed to become key share holders.

Which layers? Do those lawyers have the competence to handle securing such a key? What happens when those keys are compromised? What is a legal order that would be valid? The US already has warrant exclusions for “emergencies”, how careful will these lawyers be when they’re getting thousands of requests a day? What happens when they get an NSL?

What happens when you’re investigating a criminal act sponsored by one of the governments you supposedly trust? What if they compel the lawyers in their countries to not provide the keys?

I generally dislike “what if” but given the problem space you do actually need to explain how your system works, and how it resolves these problems.

Remember there are plenty of countries with terrible human rights records, but they also still have regular crimes happen.

Your argument fell apart when you said "secret". What do you do to prevent widespread abuse when the secret gets out?

I'm sure that's a reference to Shamir's Secret Sharing Scheme,[0] which is hardly a secret.

0) http://point-at-infinity.org/ssss/

per-device key.

Who holds the per device key? If someone holds all the per device keys (or parts of the per device key) you've painted a bulls eye on their face. In all honesty, I cannot trust the US government with secrets like this because I don't see us being willing to secure it at the same level that we secure our nukes. And dear lord even that level of security likely won't be enough to fend off internal and external threats.

Lawyers? Gross. You didn't address what you do when the key is leaked, and then worse you propose to give decision power to scummy people. Not to mention that some of your worldwide lawyers will be sharia "lawyers" and such.

Then when people point out the problems, you don't answer. You make a lot of assertions that are flat out wrong.

What law would those lawyers apply and who would select them?

> It doesn’t matter /who/ has that decryption key

Of course it matters. Apple already has nearly total power to modify their devices, and are clearly acting with caution. American courts are not going to give a warrant so an officer can steal nudes. There is no a priori reason that your phone should require a greater kind of warrant than your home or your bank account, and wanting zero access at all only makes sense if you think law enforcement has negative utility.

Personally I'd do something more like this: Print one code on the inside of each device, so as to make access strictly harder than physical access, store one code internally as per your other mission-critical keys, distribute one key each to choice governments, inside a physical module so as to prevent clumsy storage and reduce the chance of cloning (since singly-owned keys can just be revoked if stolen), perhaps with some protocol so multiple members are needed to agree, if you are particularly paranoid. That way you can only get access if Apple wills (either given a warrant or otherwise coerced), the court wills (either a genuine case or simply corrupt), and you had physical access to the device. Apple could not then backdate court keys, so can only be coerced by China into providing access for future phones exactly as they are already in the position to do, though of course OS updates means they already effectively have a backdoor.

Except of course to you need the device passcode to install an update. So no Apple can’t just force an update.

But... why? I am not a criminal and no one but me should ever be able to access my device.

Because murderers, kidnappers, and murdered victims also use phones. The article includes commentary from an Indiana State Police task force which claims to have used information from warrants on phones to protect children in some manner.

So? Murderers and kidnappers will benefit from being able to access their victims phone - after all the phone was already weakened to support such access.

Also: murderers and kidnappers don’t have to use broken cryptography. So again the only people who are harmed are people who aren’t criminals.

Also the statement from the Indiana police is extremely vague, and doesn’t make any details available about what they were doing.

Knowing how our government works they would just get tired of leaving each other voicemails and put their private keys on a network share or something.

>several independent third parties to cooperate

Your foolishly conceived system does have any way to ensure that the several parties are not corrupt or evil. You would need to solve that problem first. Assuming it is solved does not work.

In the meantime, devices need to be designed to protect the human rights of users.

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