On e-mail encryption

You know what pisses me off? Bad arguments. As a philosophy major, I read lots fo bad arguments. As a "philosophy hobbyist," I still do. And nothing makes me madder than those arguments that are so hideously wrong you don't even know where to begin explaining the problem.

I ran into one of those at work today.  Because of HIPAA and other such laws, we're looking into encryption products (laptop drives, database, e-mail, etc.), and I was stupid enough to volunteer for the assignment. Of course, it proably doesn't matter, because the whole effort is doomed from the start. There is absolutely zero buy-in from our IT staff on the idea of deploying encryption products. The only person who is even remotely pleased with the idea is the boss, and I'm the only one of the staff who isn't dead-set against it. The network administrator is particularly against the idea, and without his support, it just isn't going to happen.

Anyway, the particular comment that pissed me off was concerning anti-virus filtering in our mail system. Basically, one of our network people was concerned that we might get encrypted viruses, and because they're encrypted, the anti-virus filters wouldn't be able to catch them. As support, this person cited a virus report from earlier this week about a "new" virus that works by enclosing the executable in a password-protected ZIP archive with the password in the message body. This "encryption" stops the virus filter from catching it, but if we just blocked all encrypted files, we wouldn't have to worry about it.

Now, to me, this entire argument sounds like complete bull. Of course, I'm not an expert on e-mail, network security, or encryption, so I could be wrong. If that's the case, somebody please correct me.  But the more I think about it, the more I feel like this is one of those arguments that's just barely true enough that you can make it with a straight face, and yet still have it be completely misleading.

First, I certainly never suggested that we allow any old encrypted file through the mail filters. Just because a file is encrypted doesn't automatically make it trustworthy. An attacker could certainly find a freeware symetric encryption utility from FooBaz Questionable Software, LLC, use it to encrypt a virus, and send it to everyone in the world along with the decryption key and instructions on how to get the naked pictures of Pamela Anderson out of the encrypted file. That would just be a variation on the password-protected ZIP file trick.

My choice would be to use a standard public-key system, like PGP or GnuPG. If you stick to allowing just encrypted messages in that format, then the "virus problem" goes away.  After all, the whole point of public-key cryptosystems is that the recipient of the encrypted file already has the decryption key before the file is even encrypted. Hell, the recipient is the one who generates both of the keys. To send public-key encrypted mass-mail, you'd have to encrypt the malicious attachment separately for each recipient. And since many recipients won't have a key pair, or the attacker won't the recipient's public key, the target audience is dramatically cut at the outset.

Plus you can have accountability in public-key cryptosystems.  After all, that's what digital signatures are for - so you can know who sent a message. If you're really paranoid, you could only accept encrypted attachments from messages signed by someone you trust.

Of course, nothing about public-key cryptography can prevent a someone with your public key from intentionally sending you a virus. And that's where the "just true enough" part comes in. Yes, an encrypted virus sent by a malicious attacker trusted by user won't be detected by the mail filters. Is this a problem? Well, if you have to do business with people you can't trust, then I guess so. But if you don't publish your public keys and don't do business with 13 year old script-kiddies, I don't see it as a big concern.  Besides, this is negated by the other anti-encryption argument this person has been pushing: that the data we're dealing with isn't really important enough to bother with.

So let me get this straight: we can't do e-mail encryption because we're swapping unimportant data with untrustworthy people. My question is: then why are we even bothering? We ought to just lock the doors and start browsing the want ads!

Sigh.... I'm done blowing off steam now. Time to start working on my CV.

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