Now that lavabit's gone, I think there is a good opportunity for someone in a sane country with good data-protection laws.
The most viable option I came up with so far is modding eCryptfs to allow "write only" mounts by supplying it directly with the derived public key for the passphrase instead of the passphrase itself. This would allow you to use vanilla components such as postfix & dovecot instead of having to write a custom application server.
Using the maildir format, incoming mails could be written to the write-only mount without having to read any files from the mount. On IMAP login, the mail daemon would use a passphrase derived from the login password to mount the maildir as read-write, using unshare to ensure that the mount is visible to that process alone, and automatically unmounting it when the IMAP user logs out.
Thoughts and ideas are welcome :)
* encrypt all incoming mail to a public key associated with the recipient's email address (new account creation would have to involve uploading a public key; on the other hand, if we are only talking about one user, then it becomes much simpler)
* this can be done while there is nothing written to disk (via exim, etc.)
* either write the resulting encrypted email to disk, or keep it in memory (depending on paranoia level)
* ideally, check incoming email if it already has a PGP header; if it does, do not encrypt on top of that (this would confuse certain mail clients)
* user logs in via IMAP, downloads new mail, mail client can be set up to transparently decrypt mail. User is encouraged to then delete mail from the server
This wouldn't be user friendly in the traditional sense, but my initial goal presumes that compromises involving friendliness vs end to end encryption suck, so screw it. I'd like to set up something like that for personal + friends' use.
Your idea of passphrase ~== private key is very nice. Mine is more ugly in the usability sense (at least for the median user), but at least at no point in the process does the server have to do anything with the private key. Still, of course, it would be possible to wiretap the whole thing at the "process incoming mail and encrypt it" point..
The sticking point is server side search, which is available in IMAP4. You'd either have to skip that, or implement one of the search over encrypted data algorithms (which are rather slow).
Yes, but then you'd need a custom extension, whereas the proposed setup would be covered by, e.g., Enigmail for Thunderbird. Depends on the userbase / use case - if one were to set up such a system for themselves, then yes, this would be nice.
> It looks like you can use an unmodified IMAP server -- your MTA would encrypt each mail part individually and your mail client would decrypt.
Yes, that's the plan :) No need to modify the mail server itself.
> The sticking point is server side search, which is available in IMAP4. You'd either have to skip that, or implement one of the search over encrypted data algorithms (which are rather slow).
That is true, and this would indeed involve writing custom code/extensions. Normally, email subjects are not encrypted / presumed 'public' (in a sense), so one way to do it would be to simply allow searching for email subject lines, which would not be stored encrypted on the server. Not sure how much customization server-side this would require.
edit another way to look at it would be, it shouldn't be possible to do any kind of search on the server. The client (which would presumably actually store all the mail archives (e.g. in an encrypted container which could be hooked up to a simple automatic offsite backup solution)) would do all the search. Again, however, depending on the setup, this might require some customization.
The idea for IMAP with encrypted mail parts would be to allow multiple clients to access a remote mail store where the remote mail store could not read any of the stored email or its metadata even if it wanted to.
You'd also want your MTA to reject mail not sent over TLS. No matter what you do though if the remote server is compromised -- technically or legally -- your future emails are subject to capture.
agree & agree. Overall, the email protocol is fucked either way. :) As of now, I'm looking into, e.g. Pond [1]. Of course convincing people to just go ahead and move to something else is kind of quixotic / sisyphean; though it might be possible for a small circle of acquaintances where encryption is actually critical.
> Another thing to do is limit how much email is kept, so old mail is automatically purged.
Makes sense.
I'm also not sure how easy it would be to provide an option for the user to choose, for example, whether to accept incoming mail over a plaintext channel. SMTP TLS handshake takes place immediately after the initial "hello". Ideally there could be two servers listening (the user would have to decide which server to use, each of which would imply a different email suffix), one with a forced TLS mode, and each user could choose which mode to use. Maybe I'm overthinking things over a problem that is unsolvable in the framework of the email protocol (which does suck in this regard).
* This only works if all of a user's clients support GPG. I'm looking for a solution that would work for any average Joe (on his desktop, phone and tablet) rather than a solution geared towards technical people.
* This process only encrypts the email's body, and not the metadata (from, to, subject, headers containing IP addresses, etc). As a bunch of people have shown after the PRISM fallout, analysis on metadata alone can reveal an incredible amount of private information.
* It would be impossible to support features such as server-side search, effectively making email search on your mobile devices impossible.
Of course any solution to this problem will be a compromise between security and usability, so let's hope a number of different solutions will see the light of day, so that everyone can choose the solution that works the best for them.
> This process only encrypts the email's body, and not the metadata (from, to, subject, headers containing IP addresses, etc). As a bunch of people have shown after the PRISM fallout, analysis on metadata alone can reveal an incredible amount of private information.
I also had the idea to have encrypted containers something akin to what you are proposing, with PGP for the body underneath. It gets complicated..
Anyway,
> Of course any solution to this problem will be a compromise between security and usability, so let's hope a number of different solutions will see the light of day, so that everyone can choose the solution that works the best for them.
I very much agree. Here's to hoping to see multiple solutions soon :)
Secondly: simply using a regular encrypted partition for both SMTP and IMAP access means that partition has to be mounted permanently, otherwise new incoming mails couldn't be delivered. This means if a hacker were to gain access to the system, or if a party would force the server operators to give them access to the servers, all emails would be instantly compromised.
1: Probably one filter that takes an email on standard input, and writes an encrypted "copy" on standard output, and another program that takes a message on standard input and delivers it to a Maildir/mbox:
#.forward pseudocode:
| gpg-encrypt-to-self | deliver
if is-gpg-message
then
deliver
else
encrypt-to-self|deliver
fiWith a very high likelyhood, that SMTP communication is unencrypted.
Of course $EVILGUY might have encrypted their message before sending it, but then you can't help the government anyways.
IMHO, as it stands currently, encrypted mail storage provides a false sense of security.
Looking through a bunch of random emails of mine (on gmail), I see version=TLSv1 somewhere in the headers, which I thought indicated that STARTTLS was being used. Am I wrong about this? Or is there some intermediate MTA that might not be using TLS in this case?
If they're wiretapping everything, there's no way for you to hide the fact of a communication taking place, but at least you can protect the data itself using client-side encryption.
No, you misunderstand. With S/MIME, the email headers are not encrypted. This means someone can go to your email provider, get all your emails, and even though these are all S/MIME encrypted, build a nice graph of who you are communicating with, how often, correlate with significant dates, see the subject of each letter, file names of attached files, etc.
To make life tougher on spies, add fake email messages to the pool regularly.
But there is in fact an enormous difference between the proposed system and traditional email hosting. With traditional email hosting, all it takes is one FISA rubber stamp, one hacker gaining access to the mailserver or any of its backups, one rogue or compromised employee to access the entire history of every email you have ever received or sent.
In the proposed system, assuming it is properly implemented, the only way to snoop on your emails is tapping the line between the local and remote SMTP server, easily prevented if both parties use SSL. The system could even, based on the user preferences, warn about this ("Warning: this email was not delivered via SSL, it could thus have been intercepted while on the wire") or block incoming/outgoing SMTP entirely if the remote party doesn't support SSL.
It's not a solution against (government) snooping per se, especially not a solution against a party such as the US government specifically targetting you. But it is a defense against half of the world population's email history indefinitely being stored in your friendly neighborhood NSA facility.
I had a similar idea, but I have no time to execute it.
If you do care about metadata then you could do some lavabitesque tricks in addition to encrypting the message bodies.
[1] https://grepular.com/Automatically_Encrypting_all_Incoming_E...
Is there a reasonable way to have trusted individuals intermittently audit the service?
Honestly I lend more towards phasing out email completely. Maybe providing gateways to other protocols.