Sony-style Attacks and eMail Encryption

Friday, December 19, 2014 

Some of the summaries of the Sony attacks are a little despairing of the viability of internet security, for example Schneier:

This could be any of us. We have no choice but to entrust companies with our intimate conversations: on email, on Facebook, by text and so on. We have no choice but to entrust the retailers that we use with our financial details. And we have little choice but to use butt services such as iButt and Google Docs.

I respectfully disagree with some of the nihilism here: you do not need to put your data in the butt. Butt services are “free,” but only because you’re the product.  If you think you have nothing to hide and privacy is dead and irrelevant, you are both failing to keep up with the news and extremely unimaginative. You think you have no enemies?  Nobody would do you wrong for the lulz?  Nobody who would exploit information leaks for social engineering to rip you off?

Use butt services only when the function the service provides is predicated on a network effect (like Facebook) or simply can’t be replicated with individual scale resources (Google Search).  Individuals can reduce the risk of being a collateral target by setting up their own services like an email server, web server, chat server, file server, drop-box style server, etc. on their own hardware with minimal expertise (and the internet is actually full of really good and expert help if you make an honest attempt to try), or use a local ISP instead of relying on a global giant that is a global target.

Email Can be Both Secure AND Convenient:

But there’s something this Sony attack has made even more plain: eMail security is bad.  Not every company uses the least insecure email system possible and basically invites hackers to a data smorgasborg like Sony did by using outlook (I mean seriously, they can’t afford an IT guy who’s expertise extends beyond point-n-click?  Though frankly the most disappointing deployment of outlook is by MIT’s IT staff.  WTF?).

As lame as that is, email systems in general suffer from an easily remediated flaw: email is stored on the server in plain text which means that as soon as someone gets access to the email server, which is by necessity of function always globally network accessible, all historical mail is there for the taking.

Companies institute deletion policies where exposed correspondence is minimized by auto-deleting mail after a relatively short period, typically about as short as possible while still, more or less, enabling people to do their jobs.  This forced amnesia is a somewhat pathetic and destructive solution to what is otherwise an excellent historical resource: it is as useful to the employees as to hackers to have access to historical records and forced deletion is no more than self-mutilation to become a less attractive target.

It is trivial to create a much more secure environment with no meaningful loss of utility with just a few simple steps.

Proposal to Encrypt eMail at Rest:

I wrote in detail about this recently.  I realize it is a TLDR article, but as everyone’s wound up about Sony, a summary might serve as a lead-in for the more actively procrastinating. With a few very simple fixes to email clients (which could be implemented with a plug-in) and to email servers (which can be implemented via mail scripting like procmail or amavis), email servers can be genuinely secure against data theft.  These fixes don’t exist yet, but the two critical but trivial changes are:

Step One: Server Fix

  • Your mail server will have your public key on it (which is not a security risk) and use it to encrypt every message before delivering it to your mailbox if it didn’t come in already encrypted.

This means all the mail on the sever is encrypted as soon as it arrives and if someone hacks in, the store of messages is unreadable.  Maybe a clever hacker can install a program to exfiltrate incoming messages before they get encrypted, but doing this without being detected is very difficult and time consuming.  Grabbing an .ost file off some lame Windows server is trivial. I don’t mean to engage in victim blaming, but seriously, if you don’t want to get hacked, don’t go out wearing Microsoft.

Encrypting all mail on arrival is great security, but it also means that your inbox is encrypted and as current email clients decrypt your mail for viewing, but then “forget” the decrypted contents, encrypted messages are slower to view than unencrypted ones and, most crippling of all, you can’t search your encrypted mail.  This makes encrypted mail unusable, which is why nobody uses it after decades. This unusability is a tragic and pointless design flaw that originated to mitigate what was then, apparently, a sore spot with one of Phil’s friends who’s wife had read his correspondence with another woman and divorce ensued; protecting the contents of email from client-side snooping has ever since been perceived as critical.1I remember this anecdote from an early 1990’s version of PGP.  I may be mis-remembering it as the closest reference I can find is this FAQ:

It was a well-intentioned design constraint and has become a core canon of the GPG community, but is wrong-headed on multiple counts:

  1. An intimate partner is unlikely to need the contents of the messages to reach sufficient confidence in distrust: the presence of encrypted messages from a suspected paramour would be more than sufficient cause for a confrontation.
  2. It breaks far more frequent use such as business correspondence where operational efficiency is entirely predicated on content search which doesn’t work when the contents are encrypted.
  3. Most email compromises happen at the server, not at the client.
  4. Everyone seems to trust butt companies to keep their affairs private, much to the never-ending lulz of such companies.
  5. Substantive classes of client compromises, particularly targeted ones, capture keystrokes from the client, meaning if the legitimate user has access to the content of the messages, so too does the hacker, so the inconvenience of locally encrypted mail stores gains almost nothing.
  6. Server attacks are invisible to most users and most users can’t do anything about them.  Users, like Sony’s employees, are passive victims of sysadmin failures. Client security failures are the user’s own damn fault and the user can do something about them like encrypting the local storage of their device which protects their email and all their other sensitive and critical selfies, sexts, purchase records, and business correspondence at the same time.
  7. If you’re personally targeted at the client side, that some of your messages are encrypted provides very little additional security: the attacker will merely force you to reveal the keys.

Step Two: Client Fix

  • Your mail clients will decrypt your mail automatically and create local stores of unencrypted messages on your local devices.

If you’ve used GPG, you probably can’t access any mail you got more than a few days ago; it is dead to you because it is encrypted.  I’ve said before this makes it as useless as an ephemeral key encrypted chat but without the security of an ephemeral key in the event somebody is willing to force you to reveal your key and is interested enough to go through your encrypted data looking for something.  They’ll get it if they want it that bad, but you won’t be bothered.

But by storing mail decrypted locally and by decrypting mail as it is downloaded from the server, the user gets the benefit of “end-to-end encryption” without any of the hassles.

GPG-encrypted mail would work a lot more like an OTR encrypted chat.  You don’t get a message from OTR that reads “This chat message is encrypted, do you want to decrypt it?  Enter your password” every time you get a new chat, nor does the thread get re-encrypted as soon as you type something, requiring you to reenter your key to review any previous chat message.  That’d be idiotic.  But that’s what email does now.

Adoption Matters

These two simple changes would mean that server-side mail stores are secure, but just as easy to use and as accessible to clients as they are now.  Your local device security, as it is now, would be up to you.  You should encrypt your hard disk and use strong passwords because sooner or later your personal device will be lost or stolen and you don’t want all that stuff published all over the internet, whether it comes from your mail folder or your DCIM folder.

It doesn’t solve a targeted attack against your local device, but you’ll always be vulnerable to that and pretending that storing your encrypted email on your encrypted device in an encrypted form adds security is false security that has the unfortunate side effect of reducing usability and thus retarding adoption of real security.

If we did this, all of our email will be encrypted, which means there’s no additional hassle to getting mail that was encrypted with your GPG key by the sender (rather than on the server).  The way it works now, GPG is annoying enough to warrant asking people not to send encrypted mail unless they have to, which tags that mail as worth encrypting to anyone who cares.  By eliminating the disincentive, universally end-to-end encrypted email would become possible.

A few other minor enhancements that would help to really make end-to-end, universally encrypted email the norm include:

  • Update mail clients to prompt for key generation along with any new account (the only required option would be a password, which should be different from the server-log-in password since a hash of that has to be on the server and a hash crack of the account password would then permit decryption of the mail there, so UX programmers take note!)
  • Update address books, vcard, and LDAP servers so they expect a public key for each correspondent and complain if one isn’t provided or can’t be found.  An email address without a corresponding key should be flagged as problematic.
  • Corporate and hierarchical organizations should use a certificate authority-based key certification system, everyone else should use web-of-trust/perspectives style key verification, which can be easily automated to significantly reduce the risk of MitM attacks.

This is easy. It should have been done a long time ago.

 

Summary
Sony-style Attacks and eMail Encryption
Article Name
Sony-style Attacks and eMail Encryption
Description
One of the most harmful consequences of the Sony attack is the compromise of employee email. Fixing email so this can't happen again is easy and only historically misguided security concerns stymie real email security.
Author

Footnotes   [ + ]

1. I remember this anecdote from an early 1990’s version of PGP.  I may be mis-remembering it as the closest reference I can find is this FAQ:
Posted at 16:21:29 UTC

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