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Evaluating the GCHQ Exceptional Access Proposal

The so-called Crypto Wars have been going on for 25 years now. Basically, the FBI — and some of their peer agencies in the UK, Australia, and elsewhere — argue that the pervasive use of civilian encryption is hampering their ability to solve crimes and that they need the tech companies to make their systems susceptible to government eavesdropping. Sometimes their complaint is about communications systems, like voice or messaging apps. Sometimes it’s about end-user devices. On the other side of this debate is pretty much all technologists working in computer security and cryptography, who argue that adding eavesdropping features fundamentally makes those systems less secure.

A recent entry in this debate is a proposal by Ian Levy and Crispin Robinson, both from the UK’s GCHQ (the British signals-intelligence agency — basically, its NSA). It’s actually a positive contribution to the discourse around backdoors; most of the time government officials broadly demand that the tech companies figure out a way to meet their requirements, without providing any details. Levy and Robinson write:

In a world of encrypted services, a potential solution could be to go back a few decades. It’s relatively easy for a service provider to silently add a law enforcement participant to a group chat or call. The service provider usually controls the identity system and so really decides who’s who and which devices are involved — they’re usually involved in introducing the parties to a chat or call. You end up with everything still being end-to-end encrypted, but there’s an extra ‘end’ on this particular communication. This sort of solution seems to be no more intrusive than the virtual crocodile clips that our democratically elected representatives and judiciary authorise today in traditional voice intercept solutions and certainly doesn’t give any government power they shouldn’t have.

On the surface, this isn’t a big ask. It doesn’t affect the encryption that protects the communications. It only affects the authentication that assures people of whom they are talking to. But it’s no less dangerous a backdoor than any others that have been proposed: It exploits a security vulnerability rather than fixing it, and it opens all users of the system to exploitation of that same vulnerability by others.

In a blog post, cryptographer Matthew Green summarized the technical problems with this GCHQ proposal. Basically, making this backdoor work requires not only changing the cloud computers that oversee communications, but it also means changing the client program on everyone’s phone and computer. And that change makes all of those systems less secure. Levy and Robinson make a big deal of the fact that their backdoor would only be targeted against specific individuals and their communications, but it’s still a general backdoor that could be used against anybody.

The basic problem is that a backdoor is a technical capability — a vulnerability — that is available to anyone who knows about it and has access to it. Surrounding that vulnerability is a procedural system that tries to limit access to that capability. Computers, especially internet-connected computers, are inherently hackable, limiting the effectiveness of any procedures. The best defense is to not have the vulnerability at all.

That old physical eavesdropping system Levy and Robinson allude to also exploits a security vulnerability. Because telephone conversations were unencrypted as they passed through the physical wires of the phone system, the police were able to go to a switch in a phone company facility or a junction box on the street and manually attach alligator clips to a specific pair and listen in to what that phone transmitted and received. It was a vulnerability that anyone could exploit — not just the police — but was mitigated by the fact that the phone company was a monolithic monopoly, and physical access to the wires was either difficult (inside a phone company building) or obvious (on the street at a junction box).

The functional equivalent of physical eavesdropping for modern computer phone switches is a requirement of a 1994 U.S. law called CALEA — and similar laws in other countries. By law, telephone companies must engineer phone switches that the government can eavesdrop, mirroring that old physical system with computers. It is not the same thing, though. It doesn’t have those same physical limitations that make it more secure. It can be administered remotely. And it’s implemented by a computer, which makes it vulnerable to the same hacking that every other computer is vulnerable to.

This isn’t a theoretical problem; these systems have been subverted. The most public incident dates from 2004 in Greece. Vodafone Greece had phone switches with the eavesdropping feature mandated by CALEA. It was turned off by default in the Greek phone system, but the NSA managed to surreptitiously turn it on and use it to eavesdrop on the Greek prime minister and over 100 other high-ranking dignitaries.

There’s nothing distinct about a phone switch that makes it any different from other modern encrypted voice or chat systems; any remotely administered backdoor system will be just as vulnerable. Imagine a chat program added this GCHQ backdoor. It would have to add a feature that added additional parties to a chat from somewhere in the system — and not by the people at the endpoints. It would have to suppress any messages alerting users to another party being added to that chat. Since some chat programs, like iMessage and Signal, automatically send such messages, it would force those systems to lie to their users. Other systems would simply never implement the “tell me who is in this chat conversation” feature¬≠which amounts to the same thing.

And once that’s in place, every government will try to hack it for its own purposes¬≠ — just as the NSA hacked Vodafone Greece. Again, this is nothing new. In 2010, China successfully hacked the back-door mechanism Google put in place to meet law-enforcement requests. In 2015, someone — we don’t know who — hacked an NSA backdoor in a random-number generator used to create encryption keys, changing the parameters so they could also eavesdrop on the communications. There are certainly other stories that haven’t been made public.

Simply adding the feature erodes public trust. If you were a dissident in a totalitarian country trying to communicate securely, would you want to use a voice or messaging system that is known to have this sort of backdoor? Who would you bet on, especially when the cost of losing the bet might be imprisonment or worse: the company that runs the system, or your country’s government intelligence agency? If you were a senior government official, or the head of a large multinational corporation, or the security manager or a critical technician at a power plant, would you want to use this system?

Of course not.

Two years ago, there was a rumor of a WhatsApp backdoor. The details are complicated, and calling it a backdoor or a vulnerability is largely inaccurate — but the resultant confusion caused some people to abandon the encrypted messaging service.

Trust is fragile, and transparency is essential to trust. And while Levy and Robinson state that “any exceptional access solution should not fundamentally change the trust relationship between a service provider and its users,” this proposal does exactly that. Communications companies could no longer be honest about what their systems were doing, and we would have no reason to trust them if they tried.

In the end, all of these exceptional access mechanisms, whether they exploit existing vulnerabilities that should be closed or force vendors to open new ones, reduce the security of the underlying system. They reduce our reliance on security technologies we know how to do well — cryptography — to computer security technologies we are much less good at. Even worse, they replace technical security measures with organizational procedures. Whether it’s a database of master keys that could decrypt an iPhone or a communications switch that orchestrates who is securely chatting with whom, it is vulnerable to attack. And it will be attacked.

The foregoing discussion is a specific example of a broader discussion that we need to have, and it’s about the attack/defense balance. Which should we prioritize? Should we design our systems to be open to attack, in which case they can be exploited by law enforcement — and others? Or should we design our systems to be as secure as possible, which means they will be better protected from hackers, criminals, foreign governments and — unavoidably — law enforcement as well?

This discussion is larger than the FBI’s ability to solve crimes or the NSA’s ability to spy. We know that foreign intelligence services are targeting the communications of our elected officials, our power infrastructure, and our voting systems. Do we really want some foreign country penetrating our lawful-access backdoor in the same way the NSA penetrated Greece’s?

I have long maintained that we need to adopt a defense-dominant strategy: We should prioritize our need for security over our need for surveillance. This is especially true in the new world of physically capable computers. Yes, it will mean that law enforcement will have a harder time eavesdropping on communications and unlocking computing devices. But law enforcement has other forensic techniques to collect surveillance data in our highly networked world. We’d be much better off increasing law enforcement’s technical ability to investigate crimes in the modern digital world than we would be to weaken security for everyone. The ability to surreptitiously add ghost users to a conversation is a vulnerability, and it’s one that we would be better served by closing than exploiting.

This essay originally appeared on Lawfare.com.

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Security Vulnerability in ESS ExpressVote Touchscreen Voting Computer

Of course the ESS ExpressVote voting computer will have lots of security vulnerabilities. It’s a computer, and computers have lots of vulnerabilities. This particular vulnerability is particularly interesting because it’s the result of a security mistake in the design process. Someone didn’t think the security through, and the result is a voter-verifiable paper audit trail that doesn’t provide the security it promises.

Here are the details:

Now there’s an even worse option than “DRE with paper trail”; I call it “press this button if it’s OK for the machine to cheat” option. The country’s biggest vendor of voting machines, ES&S, has a line of voting machines called ExpressVote. Some of these are optical scanners (which are fine), and others are “combination” machines, basically a ballot-marking device and an optical scanner all rolled into one.

This video shows a demonstration of ExpressVote all-in-one touchscreens purchased by Johnson County, Kansas. The voter brings a blank ballot to the machine, inserts it into a slot, chooses candidates. Then the machine prints those choices onto the blank ballot and spits it out for the voter to inspect. If the voter is satisfied, she inserts it back into the slot, where it is counted (and dropped into a sealed ballot box for possible recount or audit).

So far this seems OK, except that the process is a bit cumbersome and not completely intuitive (watch the video for yourself). It still suffers from the problems I describe above: voter may not carefully review all the choices, especially in down-ballot races; counties need to buy a lot more voting machines, because voters occupy the machine for a long time (in contrast to op-scan ballots, where they occupy a cheap cardboard privacy screen).

But here’s the amazingly bad feature: “The version that we have has an option for both ways,” [Johnson County Election Commissioner Ronnie] Metsker said. “We instruct the voters to print their ballots so that they can review their paper ballots, but they’re not required to do so. If they want to press the button ‘cast ballot,’ it will cast the ballot, but if they do so they are doing so with full knowledge that they will not see their ballot card, it will instead be cast, scanned, tabulated and dropped in the secure ballot container at the backside of the machine.” [TYT Investigates, article by Jennifer Cohn, September 6, 2018]

Now it’s easy for a hacked machine to cheat undetectably! All the fraudulent vote-counting program has to do is wait until the voter chooses between “cast ballot without inspecting” and “inspect ballot before casting.” If the latter, then don’t cheat on this ballot. If the former, then change votes how it likes, and print those fraudulent votes on the paper ballot, knowing that the voter has already given up the right to look at it.

A voter-verifiable paper audit trail does not require every voter to verify the paper ballot. But it does require that every voter be able to verify the paper ballot. I am continuously amazed by how bad electronic voting machines are. Yes, they’re computers. But they also seem to be designed by people who don’t understand computer (or any) security.

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Hacking Police Bodycams

Suprising no one, the security of police bodycams is terrible.

Mitchell even realized that because he can remotely access device storage on models like the Fire Cam OnCall, an attacker could potentially plant malware on some of the cameras. Then, when the camera connects to a PC for syncing, it could deliver all sorts of malicious code: a Windows exploit that could ultimately allow an attacker to gain remote access to the police network, ransomware to spread across the network and lock everything down, a worm that infiltrates the department’s evidence servers and deletes everything, or even cryptojacking software to mine cryptocurrency using police computing resources. Even a body camera with no Wi-Fi connection, like the CeeSc, can be compromised if a hacker gets physical access. “You know not to trust thumb drives, but these things have the same ability,” Mitchell says.

BoingBoing post.

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1Password’s Travel Mode

The 1Password password manager has just introduced “travel mode,” which allows you to delete your stored passwords when you’re in other countries or crossing borders:

Your vaults aren’t just hidden; they’re completely removed from your devices as long as Travel Mode is on. That includes every item and all your encryption keys. There are no traces left for anyone to find. So even if you’re asked to unlock 1Password by someone at the border, there’s no way for them to tell that Travel Mode is even enabled.

In 1Password Teams, Travel Mode is even cooler. If you’re a team administrator, you have total control over which secrets your employees can travel with. You can turn Travel Mode on and off for your team members, so you can ensure that company information stays safe at all times.

The way this works is important. If the scary border police demand that you unlock your 1Password vault, those passwords/keys are not there for the border police to find.

The only flaw — and this is minor — is that the system requires you to lie. When the scary border police ask you “do you have any other passwords?” or “have you enabled travel mode,” you can’t tell them the truth. In the US, lying to a federal office is a felony.

I previously described a system that doesn’t require you to lie. It’s more complicated to implement, though.

This is a great feature, and I’m happy to see it implemented.

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Computer Alarm that Triggers When Lid Is Opened

Do Not Disturb” is a Macintosh app that send an alert when the lid is opened. The idea is to detect computer tampering.

Wire article:

Do Not Disturb goes a step further than just the push notification. Using the Do Not Disturb iOS app, a notified user can send themselves a picture snapped with the laptop’s webcam to catch the perpetrator in the act, or they can shut down the computer remotely. The app can also be configured to take more custom actions like sending an email, recording screen activity, and keeping logs of commands executed on the machine.

Can someone please make one of these for Windows?

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Adding Backdoors at the Chip Level

Interesting research into undetectably adding backdoors into computer chips during manufacture: “Stealthy dopant-level hardware Trojans: extended version,” also available here:

Abstract: In recent years, hardware Trojans have drawn the attention of governments and industry as well as the scientific community. One of the main concerns is that integrated circuits, e.g., for military or critical-infrastructure applications, could be maliciously manipulated during the manufacturing process, which often takes place abroad. However, since there have been no reported hardware Trojans in practice yet, little is known about how such a Trojan would look like and how difficult it would be in practice to implement one. In this paper we propose an extremely stealthy approach for implementing hardware Trojans below the gate level, and we evaluate their impact on the security of the target device. Instead of adding additional circuitry to the target design, we insert our hardware Trojans by changing the dopant polarity of existing transistors. Since the modified circuit appears legitimate on all wiring layers (including all metal and polysilicon), our family of Trojans is resistant to most detection techniques, including fine-grain optical inspection and checking against “golden chips”. We demonstrate the effectiveness of our approach by inserting Trojans into two designs — a digital post-processing derived from Intel’s cryptographically secure RNG design used in the Ivy Bridge processors and a side-channel resistant SBox implementation¬≠ — and by exploring their detectability and their effects on security.

The moral is that this kind of technique is very difficult to detect.

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