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Comment by maaku | Hacker News Reader

And where is the private key stored? On Google or Microsoft's server? What then would be the point? (I assume you'll answer that it'll be done client-side, but JavaScript cryptography is a whole mess of fail. But that's a separate issue.)

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And if it is stored client-side, what happens when the user inevitably loses their key? You and I might have backups in multiple places, and on an encrypted USB stick in a bank vault, but my dad doesn't, and the next time he spills wine on his laptop, there goes literally all of his e-mail.

It's stored client-side, and as a back up on the central server, with a passphrase that is the users responsibility.

>> with a passphrase that is the users responsibility.

And there's the rub. "What do you mean, I can't ever see my data again? Why can't you reset my password?"

We know that true security means only the user has the key. But users don't all want that responsibility.

Key escrow services?

See: Clipper.

I'm familiar. There's a big difference between "optional key escrow with a service I have chosen to trust" and "mandatory key escrow" though. Most importantly with regard to the ease of mass surveillance.

Why not simply make the cryptographically secure service opt-in?

This is the real reason why cryptography hasn't caught on. It's opt-in by nature - No matter how hard you try, you can't send someone an encrypted message if they don't have a public key for you to use.

Actually, yes you can. Check out identity-based encryption and Voltage Security. It's currently in use by Wells Fargo, ADP, and other large enterprise customers.

The catch there is that IBE requires a centralized, trusted key-issuing service where you need to enroll to receive your message. If that's compromised, then game over.

...which is another way of saying they shifted the problem without actually solving it.

You do not need a single key-issuing service for IBE:

http://www.argreenhouse.com/society/wcan06/wcan06s4p3.pdf

Of course, you would need to be judicious about which group of key issuers you are willing to trust, but this method will at least reduce the risk. The other nice thing about this is that even if some key issuing service is compromised, the sender can force the receiver to switch services (compare to the TLS model, where dropping a CA is basically a coordination game problem).

PGP, Inc., now Symantec, has been selling a product that does exactly this for years.

Issue the user two smartcards, one for daily use, one that can be used to create a new daily use smartcard. Tell the user to keep the backup smartcard in a safe place.

Yes, someone will inevitably lose both. You just need to ensure that that is a rare event, and that there are alternative systems in place (i.e. that losing access to one system does not prevent people from living their lives).

> And where is the private key stored?

Securely in the Browser, and not directly accessible by js, just like a TMP chip or a smartcard. Could that be a solution?

Potentially, yes. But now we're back to technology/software which doesn't yet exist. If you create it I would use it, though.

Doesn't most computers have TMP chips, which are perfectly capable of storing and generating private keys so the browser doesn't have acccess to them.

Inside the TPM would be a great place to store the private key, simply because it cannot be extracted.

Of course, that introduces a new problem: securely backing up the private key.

Client-side, with a passphrase. A backup could be stored on the server or in your dropbox or wherever you'd like. It would be important, as part of the onboarding process, to communicate the need to keep the key safe and what happens to your old emails should you lose it.

As for using js for public key encryption, I've implemented it for a client and didn't have much trouble. There are libraries that workaround the usual problems. What have you seen out there that would cause a problem?

If you're doing public key crypto on the client side in javascript, then the client side JS must necessarily have access to the private key (unless you have a TPM _and_ browser hooks to use it). This means that suddenly the private key is vulnerable to any XSS attacker that can inject itself into the same origin as your javascript crypto code.

Fair point. XSS likely wouldn't be a problem in the case of a desktop email client. But in the case of a Gmail or Outlook.com frontend, I can see how you would be concerned about something in the js served up by Google or MS capturing the private key and sending it to the server.

That said, couldn't this be mitigated by having a strong passphrase on the private key? How hard is the wrapper to attack?

Also, couldn't security researchers easily monitor the packets on this process and sound the alarm should they find that the js served up by Google or Microsoft suddenly starts sending private keys to the server?

AFAIK a strong key passphrase would be effective at protecting the private key while it's at rest (stolen laptop / hard drive). However as soon as the private key is pulled into memory for a signing or encryption operation the passphrase doesn't matter as the raw key is needed at that point.

As for your second question, there are techniques that perform static and dynamic analysis on javascript to try and detect illegal flows or taint propagation (without having to resort to monitoring the outbound network traffic). See [1] and [2] if you're interested in that topic.

[1] http://static.usenix.org/event/sec10/tech/full_papers/Bandha... [2] http://publik.tuwien.ac.at/files/pub-inf_5310.pdf

Also, this isn't a hypothetical attack. Basically the same setup is used for client-side bitcoin wallets, and there have been reports of thefts (stolen keys).

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