Long live PGP

The other day I ran into two rants against PGP, What's the matter with PGP?, which still is relatively reasonable, and then the raving PGP Problem by people running a security consulting shop called Latacora. It's this second diatribe that made me write this post, because the amount of badmouthing of PGP done there, on the blog of a company promising to teach startups “security“ on top, is not only unwarranted, it's also actively damaging to meaningful encryption.

Let me start with what I think are the fundamental fallacies of the Latacora folks is: They seem to think that identity, and hence key management, is something that others can do for you, and that thinking about crypto is “bad user experience“. In contrast, I'd argue that crypto you don't notice isn't crypto at all (but instead somewhere on the obfuscation spectrum), and that identity management done by others is equivalent to them encrypting for you.

You see, if you're encrypting something, you're encrypting it for someone. In public key encryption, this “someone“ has two aspects: a real-world entity (your friend, a bank, whatever), and a public key. Any crypto system that does not make this separation transparent and asks you the question of how well you think the two things match (and whether you care), is fundamentally broken. That's because that question plainly has to be answered. If it's not you who answers it, it's someone else. And hence that someone else is free to change the mapping from key to real-world entity, and hence they determine which real-world entity gets to read what you've encrypted.

This, by the way, is how https is regularly subverted by businesses, anti-virus software, and occasionally state actors, who simply make your browser trust their word on who is what. At that moment, they can inspect everything your browser exchanges with the rest of the world, be it in “anti-virus portals” or bluntly in surveillance systems. This is also why very few users of “encrypted” messengers would even notice if the operating company snooped on them.

The big advantage of PGP is what the Latacora people call „obnoxious UX“. Yes, you have to make up your mind on keys, yes, you have to explicitly manage them: but that is what you need to understand if you want meaningful encryption, and plastering abstractions on top of that only gives extra levels people have to understand – and that can break. No: if you want to do encryption, you'll have to understand key management, and PGP makes that as explicit and transparent as any crypto system I've ever seen. That's a feature, not a bug.

Actually, this one thing is far more important than regular key rotation (as an aside: I'm not aware of anyone ever having broken a PGP secret key because too much material has been encrypted using it; it's certainly not a major reason for failing encryption) or the latest cryptographic primitives (even 1024 bit RSA keys still require serious investment to break, 20 years after they've been state of the art).

More genrally, the scenarios requiring frequent key rotation mostly imagine a targeted attack from a state actor, following you into hotel rooms to steal your secret key and install key loggers to skim your passphrase (or similar). Frankly: it's an illusion to believe a muggle (or even normal wizards doing their daily work) could withstand such a determined and comptentent state actor for a long time.

But that's not necessary. It's already great progress if Google, the (normal) police, and the people at your employer's computation centre can't read the content of your mails unless they really try hard. Actually, most “adversaries” are not terribly determined and/or terribly competent. You hence don't need a perfect cryptosystem. It just needs to withstand the most basic of man-in-the-middle attacks (which fends off the not terribly competent adversaries), and it needs to require at least a bit of individual effort to break each person's crypto (which fends off the not terribly determined ones). Any system with centralised identity management fails at least on the side of the individual effort – get the central entity to collude, or break it, and you have it all. And given the central entity at least legally sits somewhere if it's commercial, at least for the state of residence it fails the withstand-most-basic criterion as well: The average state has no trouble obtaining court orders as soon as it moans “terrorism”.

PGP, on the other hand, does a fairly good job on both counts once people have grokked it, at least a much better one than anything SSL-based I've ever seen. People can understand the basic operations of PGP if they want, something that is much harder with SSL and X.509. The problem is that few people want to understand that. But in that case, any kind of crypto is doomed. Hence, the problem isn't PGP, it is, as so often, education. Working on that is effort well spent, as once people have understood PGP to the level of confidently using it, they have a much better chance of being able to competently use other, less explicit crypto systems.

Having said that: sure, PGP and its UIs could be improved. But you can't get around PGP's long-term keys for e-mail, and whatever alternative you'd come up with, you'll still need keyrings and reasonable UIs to mark up the trust in there. And, in particular, you'll still need open standards so you don't have to take a single company's word for what it does.

That's basically where I think Latacora's arguments are harmful. But since most of the claims in the article are fairly outrageous, I can't resist commenting them, too:

  • “Absurd Complexity“ – that's not a terribly credible charge given the page comes over HTTPS, which in many ways is a lot more complex than OpenPGP, in particular because it contains the nightmare that is X.509. But really: Much as I am all for reducing complexity, I'm even more for maintaining backward compatibility. Being able to read encrypted mails I got in the 1990ies matters to me, and anything flexible enough to at least support modern crypto and deal with archive data will have to have a certain amount of complexity. Start something new, and in 10 years it'll look the same. Or worse. Only it won't be able to read archival data, and it'll have repeated the history of early bugs software simply has, in particular when you have to worry about side channel attacks.
  • “Swiss Army Knife“ – that would be more convincing if they said how exactly PGP signatures are “mediocre“ or the encryption is a “pretty bad job“. I accept the argument they make a bit down that people may want to have forward secrecy in IM and it's easy to have there, so going for PGP alternatives may be a good idea there. But then I can't remember the last time I used PGP over XMPP, so these alternatives have existed for a long time, without any need to kill PGP.
  • “Mired in Backwards Compatibility“ – well, as said above, backwards compatiblity is great if your systems live a long time. And OpenPGP is doing a reasonable job to have both backwards compatiblity and evolvability. That rolling out new features isn't instantaneous, in particular for a volunteer effort that PGP is, is useless criticism: Build another distributed, open, volunteer effort, and it'll go the same way. Oh, and just incidentally: HTTPS is from the nineties, too, and the X.509 standard was published in 1988.
  • ”Obnoxious UX“, “Long-Term Secrets“, “Incoherent Identity“ – these are the core of Latacora's fallacies; see above.
  • “Broken Authentication“ – I can't say I've thought through the problem they're pointing to here; if it is as bad as they claim, there's no reason not to fix it within OpenPGP rather than invent something entirely new.
  • “Leaks Metadata“ – sure. As long as there's SMTP, there's no way around having quite a bit of cleartext: intermediate mail servers will have an idea who's mailing whom (though of course there's still Mixmaster). Having e-mail, or at least something that doesn't require me to be always online, is so important that the metadata leaks are an almost negligible price to pay, at least compared to the fine-grained activity profile you leak when you leave your phone online all the time, or the loss of control when you (or people you trust) can't run the necessary infrastructure components (as in: a mail server) any more.
  • ”No Forward Secrecy“ – fair enough, but again that's hard to have in store-and-forward e-mail, in particular when you'd like to have mailing lists and the like. Of course, it's true that »[a]gainst serious adversaries and without forward secrecy, breaches are a question of “when”, not “if”.« But on the other hand, most serious adversaries lose interest in the cleartext hours, weeks, or at worst a few years after the communication, or at least stop being terribly serious. So, for these intents and purposes holding up a couple of years is plenty good.
  • “Clumsy Keys“ – yeah, thinking about a good way to migrate to ED25519 keys (and ways to make such migrations easier with OpenPGP in the future) would be nice. But in my experience nobody types in even the short ED25519 keys, and if they don't, it really doesn't matter if the key is 80 or 4000 bytes. People will compare 32 byte fingerprints anyway (if you're lucky).
  • “Negotiation“ – well, at some point their criticism of legacy becomes a bit boring. And again, of course HTTPS negotiates as well, as will anything that survives longer than a single marketing campaign; that may not matter much to consultants of startup companies, but it matters to almost everyone else.
  • “Janky Code“ – I've not audited GnuPG, but others have. I'm convinced it's not pretty everywhere, but I'd still trust it a lot more than anything that just turns up on github, even if it were written in Rust. Thank you, Werner Koch. Really. And blaiming efail on gnupg simply is inappropriate. The problem there was HTML in mails. That, indeed, needs to die.

Given their criticisms, it's not surprising what the Latacora folks think the solutions are: Essentially: “Trust your friendly commercial entity to manage your crypto for you. And forget about open standards like e-mail, because they give people far to much freedom. Such as forwarding your mails.”

I'm sorry, but these “solutions“ are ridiculous. I consider it a lot more important that I have the freedom to do with what other people have encrypted for me than fixing any of the issues Latacora has with PGP (ignoring the fact that any attempt to control what people do with cleartext is a non-starter anyway).

Even if the state of the PGP world were a lot worse than it actually is: Killing an open standard and forcing people into proprietary, centralised platforms certainly is a large step back over where we are. Stopping the badmouthing of PGP and contributing effort to educate the public about what encryption is and does: That's what it takes to finally make meaningful encryption available to the muggle masses.

Kategorie: edv