June 25, 2017

Archives for March 2008

Comcast and BitTorrent: Why You Can't Negotiate with a Protocol

The big tech policy news yesterday was Comcast’s announcement that it will stop impeding BitTorrent traffic, but instead will respond to network congestion by slowing traffic from the highest-volume users, regardless of what those users are doing. Comcast also announced a deal with BitTorrent, aimed at developing more effective ways of channeling peer-to-peer traffic through networks.

It may seem natural to respond to a network issue involving BitTorrent by making a deal with BitTorrent – and much of the reporting and commentary has taken that line – but there is something odd about the BitTorrent deal, which only becomes clear when we unpack the difference between the BitTorrent protocol and the BitTorrent company. The BitTorrent protocol is a set of technical rules used by desktop software programs to coordinate the peer-to-peer distribution of files. The company BitTorrent Inc. is just one maker of software that uses the protocol – indeed, it’s a relatively minor player in that market. Most people who use the BitTorrent protocol don’t use software from BitTorrent Inc.

What this means is that changes in BitTorrent Inc’s products won’t have much effect on Comcast’s network. What Comcast needs, if it wants to change conditions in its network, is to change the BitTorrent protocol.

The problem is that you can’t negotiate with a protocol, for the same reason that you can’t negotiate with (say) the English language. You can use the language to negotiate with someone, but you can’t have a negotiation where the other party is the language. You can negotiate with the Queen of England, or English Department at Princeton, or the people who publish the most popular dictionary. But the language itself just isn’t the kind of entity that can make an agreement or have an intention.

This property of protocols – that you can’t get a meeting with them, convince them to change their behavior, or make a deal with them – seems especially challenging to some Washington policymakers. If, as they do, you live in a world driven by meetings and deal-making, a world where problem-solving means convincing someone to change something, then it’s natural to think that every protocol, and every piece of technology, must be owned and managed by some entity.

Engineers sometimes make a similar mistake in thinking about technology markets. We like to think that technologies are designed by engineers, but often it’s more accurate to say that some technology was designed by a market. And where the market is in charge, there is nobody to call when the technology needs to be changed.

Will Comcast and BitTorrent Inc. succeed in improving the BitTorrent protocol? Maybe. But it won’t be enough simply to have a better protocol. They’ll also have to convince the population of BitTorrent users to switch.

UPDATE (April 2): A reader points out that BitTorrent Inc bought uTorrent, one of the popular client programs implementing the BitTorrent protocol. This means that BitTorrent Inc has more leverage to force adoption of new protocol versions than I had thought. Still, I stand by the basic point of the post, that BitTorrent Inc doesn’t have unilateral power to change the protocol.

California review of the ES&S AutoMARK and M100

California’s Secretary of State has been busy. It appears that ES&S (manufacturers of the Ink-a-Vote voting system, used in Los Angeles, as well as the iVotronic systems that made news in Sarasota, Florida in 2006) submitted its latest and greatest “Unity 3.0.1.1” system for California certification. ES&S systems were also considered by Ohio’s study last year, which found a variety of security problems.

California already analyzed the Ink-a-Vote. This time, ES&S submitted their AutoMARK ballot marking device, which has generated some prior fame for being more accessible than other electronic voting solutions, as well has having generated some prior infamy for having gone through various hardware changes without being resubmitted for certification. ES&S also submitted its M100 precinct-based tabulation systems, which would work in conjunction with the AutoMARK devices. (Most voters would vote with pen on a bubble sheet. The AutoMARK presents a fancy computer interface but really does nothing more than mark the bubble sheet on behalf of the voter.) ES&S apparently did not submit its iVotronic systems.

The results? Certification denied.

Let’s start with the letter from the Secretary to the vendor and work our way down.

ES&S failed to submit “California Use Procedures” to address issues that they were notified about back in December as part of their conditional certification of an earlier version of the system. This can only be interpreted as vendor incompetence. Here’s a choice quote:

ES&S submitted what it stated were its revised, completed California Use Procedures on March 4th. Staff spent several days reviewing the document, which is several hundred pages in length. Staff found revisions expressly called for in the testing reports, but found that none of the changes promised two months earlier in Mr. Groh’ s letter of January 11, 2008, were included.

The accessibility report is very well done and should be required reading for anybody wanting to understand accessibility issues from a broad perspective. They found:

  • Physical access has some limitations.
  • There are some personal safety hazards.
  • Voters with severe manual dexterity impairments may not be able to independently remove the ballot from the AutoMARK and cast it.
  • The keypad controls present challenges for some voters.
  • It takes more time to vote with the audio interface.
  • The audio ballot navigation can be confusing.
  • Write-in difficulties frustrated some voters.
  • The voting accuracy was limited by write-in failures.
  • Many of the spoken instructions and prompts are inadequate.
  • The system lacks support for good public hygiene.
  • There were some reliability concerns.
  • The vendor’s pollworker training and materials need improvement.

Yet still, they note that “We are not aware of any public device that has more flexibility in accommodating the wide range of physical and dexterity abilities that voters may have. The key, as always, is whether pollworkers and voters will be able to identify and implement the optimal input system without better guidance or expert support. In fact, it may be that the more flexible a system is, the more difficult it is for novices to navigate through the necessary choices for configuring the access options in order to arrive at the best solution.” One of their most striking findings was how long it took test subjects to use the system. Audio-only voters needed an average of almost 18 minutes to use the machine on a simplified ballot (minimum 10 minutes; maximum 35 minutes). Write-in votes were exceptionally difficult. And, again, this is arguably one of the best voting systems available, at least from an accessibility perspective.

Okay, you were all waiting to learn more about the security problems. Let’s go. The “red team” exercise was performed by the Freeman Craft McGregor Group. It’s a bit skimpy and superficial. Nonetheless, they say:

  • You can swap out the PCMCIA memory cards in the precinct-based ballot tabulator (model M100), while in the precinct. This attack would be unlikely to be detected.
  • There’s no cryptography of any kind protecting the data written to the PCMCIA cards. If an attacker can learn the file format (which isn’t very hard to do), and can get physical access to the card while in transit or storage, then the attacker can trivially substitute alternative vote records.
  • The back-end “Election Reporting Manager” has a feature to add or remove votes from the vote totals. This would be visible in the audit logs, if anybody bothered to look at them, but these sorts of logs aren’t typically produced to the public. (Hart InterCivic has a very similar “Adjust Vote Totals” feature with similar vulnerabilities.)
  • The high speed central ballot tabulator (the M650) writes its results to a Zip disk, again with no cryptography or anything else to protect the data in transit.
  • The database in which audit records are kept has a password that can be “cracked” (we’re not told how). Once you’re into the database, you can create new accounts, delete old audit records, and otherwise cause arbitrary mayhem.
  • Generally speaking, a few minutes of physical access is all you need to compromise any of the back-end tools.
  • All of the physical key locks could be picked in “five seconds to one minute.” The wire and paper-sticker tamper-evidence seals could also be easily bypassed.

And then there’s the source code analysis, prepared by atsec (who normally make a living doing Common Criteria analyses). Again, the public report is less detailed than it can and should be (and we have no idea how much more is in the private report). Where should we begin?

The developer did not provide detailed build instructions that would explain how the system is constructed from the source code. Among the missing aspects were details about versions of compilers, build environment and preconditions, and ordering requirements.

This was one of our big annoyances when working on California’s original top-to-bottom review last summer. It’s fantastically helpful to be able to compile the program. You need to do that if you want to run various automated tools that might check for bugs. Likewise, there’s no substitute for being able to add debugging print statements and use other debugging techniques when you want to really understand how something works. Vendors should be required to provide not just source code but everything necessary to produce a working build of the software.

The M100 ballot counter is designed to load and dynamically execute binary files that are stored on the PCMCIA card containing the election definition (A.12) in cleartext without effective integrity protection (A.1).

Or, in other words, election officials must never, ever believe the results they get from electronic vote tabulation without doing a suitable random sample of the paper ballots, by hand, to make sure that the paper ballots are consistent with the electronic tallies. (Similarly fundamental vulnerabilities exist with other vendors’ precinct-based optical scanners.)

The M100 design documentation contains a specification of the data structure layout for information stored on the PCMCIA card. The reviewer compared the actual structures as defined in the source code to the documentation, and none of the actual structures matched the specification. Each one showed significant differences to or omissions from the specification.

I require the students in my sophomore-level software engineering class to keep their specs in synchrony with their code as their code evolves. If college sophomores can do it, you’d think professional programmers could do it as well.

The user’s guide for the Election Reporting Manager describes how a password is constructed from publicly-available data. This password cannot be changed, and anyone reading the documentation can use this information to deduce the password. This is not an effective authentication mechanism.

While this report doesn’t get into the ES&S iVotronic, the iVotronic version 8 systems had three character passwords, fixed from the factory. (They apparently fixed this in the version 9 software which is now already a few years old.) You’d think they would have gone around and fixed this issue elsewhere in their software, since it’s so fundamental.

A.4 “EDM iVotronic Password Scramble Key and Algorithm”: A hardcoded key is used to obfuscate passwords before storing them in a database. The scrambling algorithm is very weak and reversible, allowing an attacker with access to the scrambled password to retrieve the actual password. The iVotronic is supported by the Unity software but is not being used for California elections.

Well, okay, maybe they didn’t fix the iVotronic passwords, then, either. Other passwords throughout the system are similarly hard-coded and/or poorly stored. And, given that, you can trivially tamper with any and all of the audit logs in the system that might otherwise contain records of what damage you might have done.

In the area of cryptography and key management, multiple potential and actual vulnerabilities were identified, including inappropriate use of symmetric cryptography for authenticity checking (A.9) and several different very weak homebrewed ciphers (A.4, A.7, A.8, A.11). In addition, the code and comments indicated that a checksum algorithm that is suitable only for detecting accidental corruption is used inappropriately with the claimed intent of detecting malicious tampering (A.1).

We’ve seen similar ill-conceived mechanisms used by other vendors, so it’s similarly unsurprising to see it here. The number one lesson these vendors should take home is thou shalt not implement thine own cryptography, particularly when the stuff they’re doing is all pretty standard and could be pulled from places like the OpenSSL library support code. And even then, you have to know what you’re doing. As Aggelos Kiayias once quipped, don’t use cryptography; use a cryptographer.

The developers generally assume that input data will be supplied in the correct expected format. Many modules that process input data do not perform data validation such as range checks for input numbers or checking validity of internal cross references in interlinked data, leading to potentially exploitable vulnerabilities when those assumptions turn out to be incorrect.

They’re talking about buffer overflow vulnerabilities. This is one of the core techniques that an attacker might use to gain leverage. If an attacker compromises one solitary memory card on its way back to Election Central, then corrupt data on that might be able to attack the tabulation system, and thus effect the outcome of the entire election. This report doesn’t contain enough information for us to conclude whether ES&S’s Unity systems are vulnerable in this fashion, but these are exactly the kinds of poor development practices that enable viral attacks.

Finally, a few summary bullets jumped out at me:

  • The system design does not consistently use privilege separation, leading to large amounts of code being potentially security-critical due to having privileges to modify data.
  • Unhelpful or misleading comments in the code.
  • Subjectively, large amount of source code compared to the functionality implemented.

Okay, let’s get this straight. The code is bloated, the comments are garbage, and the system is broadly not engineered to restrict privileges. Put that all together, and you’re guaranteed a buggy, error-prone, security vulnerable program that must be incredibly painful to maintain and extend. This is the kind of issue that leads smart companies to start over from scratch (while simultaneously supporting the old version until the new version gets up to speed). Is ES&S or any other voting system vendor doing a from-scratch implementation in order to get it right? They’ll never get there any other way.

[Sidebar: I live in Texas. Texas’s Secretary of State, like California’s, is responsible for certifying voting equipment for use in the state. If you visit their web page and scroll to the bottom, you’ll see links for each of the vendors. There are three vendors who are presently certified to sell election equipment here: Hart InterCivic, ES&S and Premier (née Diebold). Nothing yet published on the Texas site post-dates the California or Ohio studies, but Texas’s examiners recently considered a new submission from Hart InterCivic. It will be very interesting to see whether they take any of the staggering security flaws in Hart’s system into consideration. If they do, it would be a big chance for Texas to catch up to the rest of the country. Incidentally, I have offered my services to be on Texas’s board of election examiners on several occasions. Thus far, they haven’t responded. The offer remains open.]

The Security Mindset and "Harmless Failures"

Bruce Schneier has an interesting new essay about how security people see the world. Here’s a sample:

Uncle Milton Industries has been selling ant farms to children since 1956. Some years ago, I remember opening one up with a friend. There were no actual ants included in the box. Instead, there was a card that you filled in with your address, and the company would mail you some ants. My friend expressed surprise that you could get ants sent to you in the mail.

I replied: “What’s really interesting is that these people will send a tube of live ants to anyone you tell them to.”

Security requires a particular mindset. Security professionals – at least the good ones – see the world differently. They can’t walk into a store without noticing how they might shoplift. They can’t use a computer without wondering about the security vulnerabilities. They can’t vote without trying to figure out how to vote twice. They just can’t help it.

This kind of thinking is not natural for most people. It’s not natural for engineers. Good engineering involves thinking about how things can be made to work; the security mindset involves thinking about how things can be made to fail. It involves thinking like an attacker, an adversary or a criminal. You don’t have to exploit the vulnerabilities you find, but if you don’t see the world that way, you’ll never notice most security problems.

I’ve often speculated about how much of this is innate, and how much is teachable. In general, I think it’s a particular way of looking at the world, and that it’s far easier to teach someone domain expertise – cryptography or software security or safecracking or document forgery – than it is to teach someone a security mindset.

The ant farm story illustrates another aspect of the security mindset. Your first reaction to the might have been, “So what? What’s so harmful about sending a package of ordinary ants to an unsuspecting person?” Even Bruce Schneier, who has the security mindset in spades, doesn’t point to any terrible consequence of misdirecting the tube of ants. (You might worry about the ants’ welfare, but in that case ant farms are already problematic.) If you have the security mindset, you’ll probably find the possibility of ant misdirection to be irritating; you’ll feel that something should have been done about it; and you’ll probably file it away in your mental attic, in case it becomes relevant later.

This interest in “harmless failures” – cases where an adversary can cause an anomalous but not directly harmful outcome – is another hallmark of the security mindset. Not all “harmless failures” lead to big trouble, but it’s surprising how often a clever adversary can pile up a stack of seemingly harmless failures into a dangerous tower of trouble. Harmless failures are bad hygiene. We try to stamp them out when we can.

To see why, consider the donotreply.com email story that hit the press recently. When companies send out commercial email (e.g., an airline notifying a passenger of a flight delay) and they don’t want the recipient to reply to the email, they often put in a bogus From address like A clever guy registered the domain donotreply.com, thereby receiving all email addressed to donotreply.com. This included “bounce” replies to misaddressed emails, some of which contained copies of the original email, with information such as bank account statements, site information about military bases in Iraq, and so on. Misdirected ants might not be too dangerous, but misdirected email can cause no end of trouble.

The people who put donotreply.com email addresses into their outgoing email must have known that they didn’t control the donotreply.com domain, so they must have thought of any reply messages directed there as harmless failures. Having gotten that far, there are two ways to avoid trouble. The first way is to think carefully about the traffic that might go to donotreply.com, and realize that some of it is actually dangerous. The second way is to think, “This looks like a harmless failure, but we should avoid it anyway. No good can come of this.” The first way protects you if you’re clever; the second way always protects you.

Which illustrates yet another part of the security mindset: Don’t rely too much on your own cleverness, because somebody out there is surely more clever and more motivated than you are.