February 23, 2017

Archives for December 2008

Government Shouldn't "Help" Citizens Pick Tough Questions for Obama

A couple of weeks ago, Julian Sanchez at Ars Technica, Ben Smith at Politico and others noted a disturbing pattern on the incoming Obama administration’s Change.gov website: polite but pointed user-submitted questions about the Blagojevich scandal and other potentially uncomfortable topics were being flagged as “inappropriate” by other visitors to the site.

In less than a week, more than a million votes-for-particular-questions were cast. The transition team closed submissions and posted answers to the five most popular questions. The usefulness and interest of these answers was sharply limited: They reiterated some of the key talking points and platform language of Obama’s campaign without providing any new information. The transition site is now hosting a second round of this process.

It shouldn’t surprise us that there are, among the Presdient-elect’s many supporters, some who would rather protect their man from inconvenient questions. And for all the enthusiastic talk about wide-open debate, a crowdsourced system that lets anyone flag an item as inappropriate can give these few a perverse kind of veto over the discussion.

If the site’s operators recognize this kind of deliberative narrowing as a problem, there are ways to deal with it. One could require a consensus judgement of “inappropriateness” by a cross-section of Change.gov users that is large enough, or is diverse with respect to geography, time of visit, amount of past involvement in the site, or any number of other criteria before taking a question out of circulation. Questions that have been preliminarily flagged as inappropriate could enter a secondary moderation queue where their appropriateness can be debated, leading to a considered “up or down” vote on whether a given question belongs in the mix. The Obama transition team could even crowdsource this problem itself, looking for lay input (or input from experts at places like Digg) about how to make sure that reasonable-but-pointed questions stay in, while off topic, off color, or otherwise unacceptable ones remain out.

But what are the incentives of the new administration’s online team? They might well find it convenient, as Julian writes, to “crowdsource a dodge” to inconvenient questions–if the users of Change.gov adopt an expansive view of “inappropriateness,” the Obama team will likely benefit slightly from soft, supportive questions in the near term, though it will run the risk of allowing substantive problems, or citizen concerns, to fester over the longer term. And that tradeoff could hold much more appeal for the median administration staffer than it does for the median American.

In other words, having the administration’s own tech people manage the moderation of questions directed at the President may be like having the fox guard the henhouse. I agree that even this is much more open than recent past administrations, but I think the more interesting question here is what would be ideal.

I suspect this key plank of the new administration’s plans will never be able to be fully realized within government. The President needs to answer questions that a nonzero number of his most enthusiastic supporters are willing to characterize as “inappropriate.” And for that to happen, the online moderation needs to take place outside of .gov. A collective move toward one of the .org alternatives, for this key activity of sifting questions, would be a great first step. That way, the goal of finding tough but honest questions can plausibly sit paramount.

Researchers Show How to Forge Site Certificates

Today at the Chaos Computing Congress, a group of researchers (Alex Sotirov, Marc Stevens, Jake Appelbaum, Arjen Lenstra, Benne de Weger, and David Molnar) announced that they have found a way to forge website certificates that will be accepted as valid by most browsers. This means that they can successfully impersonate any website, even for secure connections.

Let me unpack that for non-experts.

One of the cornerstones of web security is the use of secure connections. When your browser makes a secure connection to (say) Amazon and gets a page to display, the browser displays in its address bar a URL like “https://www.amazon.com”. The “https” indicates that the secure (https) protocol was used, and the browser also displays a happy blue lock or key icon to tell you the connection was secured.

The browser cooperates with Amazon’s web server to secure the connection via a two-step process. First, the two computers negotiate a shared secret key that they can use to communicate privately, using crypto tricks that I won’t describe here. Second, your browser authenticates Amazon’s web server, that is, it assures itself that the party on the other end of the connection is the genuine Amazon.com server.

Amazon has a digital certificate that it sends to your browser, as part of proving its identity. The certificate is issued by a party called a certification authority or CA. Your browser comes pre-programmed with a list of CAs its trusts; you can change the list but hardly anyone does. If your browser makes an encrypted connection to “amazon.com”, and the party on the other end of the connection owns a certificate for the name “amazon.com”, and that certificate was issued by a CA that your browser trusts, then your browser will conclude that it has a secure connection to amazon.com.

Now we can understand what the researchers accomplished: they showed how to forge a certificate corresponding to any address on the Web. For example, they can forge a certificate that allows themselves, or you, or me, or anybody, to impersonate amazon.com, or freedom-to-tinker.com, or maybe even fbi.gov. That is supposed to be impossible, for obvious reasons.

The forged certificates will say they were issued by a CA called “Equifax Secure Global eBusiness”, which is trusted by the major browsers. The forged certificates will be perfectly valid; but they will have been made by forgers, not by the Equifax CA.

To do this, the researchers exploited a cryptographic weakness in one of the digital signature methods, “MD5 with RSA”, supported by the Equifax CA. The first step in this digital signature method is to compute the hash (strictly speaking, the cryptographic hash) of the certificate contents.

The hash is a short (128-bit) code that is supposed to be a kind of unique digest of the certificate contents. To be secure, the hash method has to have several properties, one of which is that it should be infeasible to find a collision, that is, to find two values A and B which have the same hash.

It was already known how to find collisions in MD5, but the researchers improved the existing collision-finding methods, so that they can now find two values R and F that have the same hash, where R is a “real” certificate that the CA will be willing to sign, and F is a forged certificate. This is deadly, because it means that a digital signature on R will also be a valid signature on F — so the attacker can ask the CA to sign the real certificate R, then copy the resulting signature onto F — putting a valid CA signature onto a certificate that the CA would never voluntarily sign.

To demonstrate this, the researchers created a forged certificate signed by the Equifax CA. For safety, they made the forged certificate expire in the past and point to a harmless site. But it’s clear from their description that they can forge a certificate for any site they want.

Whose fault is this? Partly it’s a consequence of problems with the MD5 hash method. It’s been known for a few years that MD5 is in the process of melting down, so prudent designers have been moving away from MD5, replacing it with newer, better hash methods. Similarly, prudent CAs should not be signing certificates that use MD5-based signature methods; instead they should insist on signature methods involving stronger hashes. The Equifax CA did not follow this precaution.

The problem can be fixed, for now, by having CAs refuse to create new MD5-based signatures. But this is a sobering reminder that the certification process that underlies web site authentication — a mechanism we all rely upon daily — is far from bulletproof.

Internet voting-a-go-go

Yes, we know that there’s no such thing as a perfect voting system, but the Estonians are doing their best to get as far away from perfection as possible. According to the latest news reports, Estonia is working up a system to vote from mobile phones. This follows on their earlier web-based Internet voting. What on earth are they thinking?

Let’s review some basics. The Estonian Internet voting scheme builds on the Estonian national ID card, which is a smartcard. You get the appropriate PCMCIA adapter and you can stick it into your laptop. Then, through some kind of browser plug-in, it can authenticate you to the voting server. No card, no voter impersonation. The Estonian system “avoids” the problem of voter bribery / coercion by allowing the voter to cast as many votes as they want, but only the last one actually counts. As I understand it, a voter may also arrive, on election day, at some sort of official polling place and substitute a paper ballot for their prior electronic ballot.

The threats to this were and are obvious. What if some kind of malware/virus/worm contraption infects your web browser and/or host operating system, waits for you to connect to the election server, and then quietly substitutes its own choices for yours? You would never know that the attack occurred and thus would never think to do anything about it. High tech. Very effective. And, of course, somebody can still watch over your shoulder while you vote. At that point, they just need to keep you from voting again. They could accomplish this by simply having you vote at the last minute, under supervision, or they could “borrow” your ID card until it’s too late to vote again. Low tech. Still effective.

But wait, there’s more! The central database must necessarily have your vote recorded alongside your name in order to allow subsequent votes to invalidate earlier votes. That means they’ve almost certainly got the technical means to deanonymize your vote. Do you trust your government to have a database that says exactly for whom you voted? Even if the vote contents are somehow encrypted, the government has all the necessary key material to decrypt it. (And, an aforementioned compromised host platform could be leaking this data, regardless.)

Okay, what about voting by cellular telephone? A modern cell phone is really no different from a modern web browser. An iPhone is running more-or-less the same OS X and Safari browser that’s featured on Apple’s Mac products. Even non-smart-phones tend to have an environment that’s powerful and general-purpose. There’s every reason to believe that these platforms are every bit as vulnerable to software attacks as we see with Windows systems. Just because hackers aren’t necessarily targeting these systems doesn’t mean they couldn’t. Ultimately, that means that the vulnerabilities of the phone system are exactly the same as the web system. No better. No worse.

Of course, crypto can be done in a much more sophisticated fashion. One Internet voting system, Helios, is quite sophisticated in this fashion, doing end-to-end crypto in JavaScript in your browser. With its auditability, Helios gives you the chance to challenge the entire client/server process to prove that it maintained your vote’s integrity. There’s nothing, however, in Helios to prevent an evil browser from leaking how you voted, thus compromising your anonymity. An evil election server could possibly be prevented from compromising your anonymity, depending on how the decryption keys are managed, but all the above privacy concerns still apply.

Yes, of course, Internet and cell-phone voting have lots of appeal. Vote from anywhere! At any time! If Estonia did more sophisticated cryptography, they could at least have a hope at getting some integrity guarantees (which they appear to be lacking, at present). Estonians have absolutely no privacy guarantees and thus insufficient protection from bribery and coercion. And we haven’t even scratched the surface of denial-of-service attacks. In 2007, Estonia suffered a large, coordinated denial-or-service attack, allegedly at the hands of Russian attackers. I’m reasonably confident that they’re every bit as vulnerable to such attacks today, and cell-phone voting would be no less difficult for resourceful attackers to disrupt.

In short, if you care about voter privacy, to defeat bribery and coercion, then you want voters to vote in a traditional polling place. If you care about denial of service, then you want these polling places to be operable even if the power goes out. If you don’t care about any of that, then consider the alternative. Publish in the newspaper a list of every voter and how they voted, for all the world to see, and give those voters a week to submit any corrections they might desire. If you were absolutely trying to maximize election integrity, nothing would beat it. Of course, if you feel that publishing such data in the newspaper could cause people to be too scared to vote their true preferences, then maybe you should pay more attention to voter privacy.

(More on this from Eric Rescorla’s Educated Guesswork.)