SSL and internet security news

Monthly Archive: December 2016

How Signal Is Evading Censorship

Signal, the encrypted messaging app I prefer, is being blocked in both Egypt and the UAE. Recently, the Signal team developed a workaround: domain fronting.

Signal’s new anti-censorship feature uses a trick called “domain fronting,” Marlinspike explains. A country like Egypt, with only a few small internet service providers tightly controlled by the government, can block any direct request to a service on its blacklist. But clever services can circumvent that censorship by hiding their traffic inside of encrypted connections to a major internet service, like the content delivery networks (CDNs) that host content closer to users to speed up their online experience — or in Signal’s case, Google’s App Engine platform, designed to host apps on Google’s servers.

“Now when people in Egypt or the United Arab Emirates send a Signal message, it’ll look identical to something like a Google search,” Marlinspike says. “The idea is that using Signal will look like using Google; if you want to block Signal you’ll have to block Google.”

The trick works because Google’s App Engine allows developers to redirect traffic from to their own domain. Google’s use of TLS encryption means that contents of the traffic, including that redirect request, are hidden, and the internet service provider can see only that someone has connected to That essentially turns Google into a proxy for Signal, bouncing its traffic and fooling the censors.

This isn’t a new trick (Tor uses it too, for example), but it does work.

Powered by WPeMatico

Security Risks of TSA PreCheck

Former TSA Administrator Kip Hawley wrote an op-ed pointing out the security vulnerabilities in the TSA’s PreCheck program:

The first vulnerability in the system is its enrollment process, which seeks to verify an applicant’s identity. We know verification is a challenge: A 2011 Government Accountability Office report on TSA’s system for checking airport workers’ identities concluded that it was “not designed to provide reasonable assurance that only qualified applicants” got approved. It’s not a stretch to believe a reasonably competent terrorist could construct an identity that would pass PreCheck’s front end.

The other step in PreCheck’s “intelligence-driven, risk-based security strategy” is absurd on its face: The absence of negative information about a person doesn’t mean he or she is trustworthy. News reports are filled with stories of people who seemed to be perfectly normal right up to the moment they committed a heinous act. There is no screening algorithm and no database check that can accurately predict human behavior — especially on the scale of millions. It is axiomatic that terrorist organizations recruit operatives who have clean backgrounds and interview well.

None of this is news.

Back in 2004, I wrote:

Imagine you’re a terrorist plotter with half a dozen potential terrorists at your disposal. They all apply for a card, and three get one. Guess which are going on the mission? And they’ll buy round-trip tickets with credit cards and have a “normal” amount of luggage with them.

What the Trusted Traveler program does is create two different access paths into the airport: high security and low security. The intent is that only good guys will take the low-security path, and the bad guys will be forced to take the high-security path, but it rarely works out that way. You have to assume that the bad guys will find a way to take the low-security path.

The Trusted Traveler program is based on the dangerous myth that terrorists match a particular profile and that we can somehow pick terrorists out of a crowd if we only can identify everyone. That’s simply not true. Most of the 9/11 terrorists were unknown and not on any watch list. Timothy McVeigh was an upstanding US citizen before he blew up the Oklahoma City Federal Building. Palestinian suicide bombers in Israel are normal, nondescript people. Intelligence reports indicate that Al Qaeda is recruiting non-Arab terrorists for US operations.

I wrote much the same thing in 2007:

Background checks are based on the dangerous myth that we can somehow pick terrorists out of a crowd if we could identify everyone. Unfortunately, there isn’t any terrorist profile that prescreening can uncover. Timothy McVeigh could probably have gotten one of these cards. So could have Eric Rudolph, the pipe bomber at the 1996 Olympic Games in Atlanta. There isn’t even a good list of known terrorists to check people against; the government list used by the airlines has been the butt of jokes for years.

And have we forgotten how prevalent identity theft is these days? If you think having a criminal impersonating you to your bank is bad, wait until they start impersonating you to the Transportation Security Administration.

The truth is that whenever you create two paths through security — a high-security path and a low-security path — you have to assume that the bad guys will find a way to exploit the low-security path. It may be counterintuitive, but we are all safer if the people chosen for more thorough screening are truly random and not based on an error-filled database or a cursory background check.

In a companion blog post, Hawley has more details about why the program doesn’t work:

In the sense that PreCheck bars people who were identified by intelligence or law enforcement agencies as possible terrorists, then it was intelligence-driven. But using that standard for PreCheck is ridiculous since those people already get extra screening or are on the No-Fly list. The movie Patriots Day, out now, reminds us of the tragic and preventable Boston Marathon bombing. The FBI sent agents to talk to the Tsarnaev brothers and investigate them as possible terror suspects. And cleared them. Even they did not meet the “intelligence-driven” definition used in PreCheck.

The other problem with “intelligence-driven” in the PreCheck context is that intelligence actually tells us the opposite; specifically that terrorists pick clean operatives. If TSA uses current intelligence to evaluate risk, it would not be out enrolling everybody they can into pre-9/11 security for everybody not flagged by the security services.

Hawley and I may agree on the problem, but we have completely opposite solutions. The op-ed was too short to include details, but they’re in a companion blog post. Basically, he wants to screen PreCheck passengers more:

In the interests of space, I left out details of what I would suggest as short-and medium-term solutions. Here are a few ideas:

  • Immediately scrub the PreCheck enrollees for false identities. That can probably be accomplished best and most quickly by getting permission from members, and then using, commercial data. If the results show that PreCheck has already been penetrated, the program should be suspended.

  • Deploy K-9 teams at PreCheck lanes.

  • Use Behaviorally trained officers to interact with and check the credentials of PreCheck passengers.

  • Use Explosives Trace Detection cotton swabs on PreCheck passengers at a much higher rate. Same with removing shoes.

  • Turn on the body scanners and keep them fully utilized.

  • Allow liquids to stay in the carry-on since TSA scanners can detect threat liquids.

  • Work with the airlines to keep the PreCheck experience positive.

  • Work with airports to place PreCheck lanes away from regular checkpoints so as not to diminish lane capacity for non-PreCheck passengers. Rental Car check-in areas could be one alternative. Also, downtown check-in and screening (with secure transport to the airport) is a possibility.

These solutions completely ignore the data from the real-world experiment PreCheck has been. Hawley writes that PreCheck tells us that “terrorists pick clean operatives.” That’s exactly wrong. PreCheck tells us that, basically, there are no terrorists. If 1) it’s an easier way through airport security that terrorists will invariably use, and 2) there have been no instances of terrorists using it in the 10+ years it and its predecessors have been in operation, then the inescapable conclusion is that the threat is minimal. Instead of screening PreCheck passengers more, we should screen everybody else less. This is me in 2012: “I think the PreCheck level of airport screening is what everyone should get, and that the no-fly list and the photo ID check add nothing to security.”

I agree with Hawley that we need to overhaul airport security. Me in 2010: “Airport security is the last line of defense, and it’s not a very good one.” We need to recognize that the actual risk is much lower than we fear, and ratchet airport security down accordingly. And then we need to continue to invest in investigation and intelligence: security measures that work regardless of the tactic or target.

Powered by WPeMatico

Encryption Working Group Annual Report from the US House of Representatives

The Encryption Working Group of the House Judiciary Committee and the House Energy and Commerce Committee has released its annual report.

Observation #1: Any measure that weakens encryption works against the national interest.

Observation #2: Encryption technology is a global technology that is widely and increasingly available around the world.

Observation #3: The variety of stakeholders, technologies, and other factors create different and divergent challenges with respect to encryption and the “going dark” phenomenon, and therefore there is no one-size-fits-all solution to the encryption challenge.

Observation #4: Congress should foster cooperation between the law enforcement community and technology companies.

Powered by WPeMatico