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There has been some talk about the Lavabit's case. New info was published today, but not important.

I'd like to know how Lavabit worked. First I thought they just did something with OpenPGP. Then I realized that maybe it was not the case since the US goverment requested some kind of universal private key for all users. What the hell is that? I read that Lavabit was forced to ensure some kind of backdoor, but I don't get how did it work. If their customers just encrypted the content with their own public/private keys, nobody would be able to access the content. Or is it just the encryption of header info (like sender's and recipient's e-mail address) that Lavabit ensured?

Thanks.

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Lavabit indeed had a master private key, and it was used to encrypt the username and password as it was sent to Lavabit's servers. No matter what Lavabit did from that point on to secure the data, the NSA had collected the SSL session data and saved them for later use. With the private keys, they could decrypt the passwords that were sent over the Internet.

The only thing Lavabit did differently was advertise itself as a secure email service. If you're wondering how you can prevent your own service from being vulnerable. Implement forward secrecy, which is the process of adding two layers of SSL, one on the outside for authentication using a permanent key pair which has been verified by a CA, and the other with a disposable key pair which must be destroyed after use and only stored in RAM. Since this is only temporary, the key can not be retrieved. This is only effective for keeping past data secure. Forward secrecy on Wikipedia

Well, the NSA only collects metadata, so you won't have to worry about it...

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PGP only works when both users are using PGP and already exchanged each others public keys over a trustworthy channel. When you want to send an email to someone you never had contact with you can not do that.

Also, there is no good way for a web-based service to store the users keys on their own computer. There are features like cookies and localstorage to store data on the client, but neither of these guarantee persistence by the specifications. That means the risk to lose ones private keys would be quite high with a client-sided solution.

By the way: You can use PGP over a public email service which doesn't support it officially. You can use any medium which transfers text to exchange PGP-encrypted messages. It just means that you need to do the en- and decryption manually.

What Lavabit was doing was to encrypt the users data with a keypair derived from the users password - the same password which is used to log into the service. By cracking the SSL/TLS connection between client and server it would have been possible to obtain that password, log into the users account and read their email. Also, it was never impossible for Lavabit to obtain any discriminaing information about its users. They complied with search warrants in the past when it was about child pornography and when it targeted specific users.

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  • OK, if I never had contact with someone I can just send an empty e-mail to him with my signature and he will have my public key and we can start communicating totally securely. And about Lavabit, I read that they made big deal out of Snowden's case because it was associated with all users. That said, the service does not look so top-secure to me, as it's presented, because it actually had universal information/backdoor to all of communication? Or is this backdoor thing just associated with the header information? That I'd understand. Nov 14 '13 at 10:18
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    @JakubŽitný No, when you send an email with your public key to someone, that person will have the public key of someone who claims to be you but could also be an imposter or a man-in-the-middle who modified your email. They have no way to verify your identity before they reply.
    – Philipp
    Nov 14 '13 at 10:19
  • On the other hand, if the header security would be the only thing for NSA to decrypt, I don't know why would they made such a big deal out of it.. Am I clear what doesn't seem right to me? Nov 14 '13 at 10:20
  • Ok, yes .. ok, that's still not important.. the thing about PGP I said.. It's that they still can use PGP under Lavabit's security.. So.. that way NSA won't get anything.. right? Snowden should know that. Nov 14 '13 at 10:22
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    @JakubŽitný Meta-information can be just as incriminating as actual information. Especially because it's much easier to analyze it automatically.
    – Philipp
    Nov 14 '13 at 10:24

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