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" featurewhich 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 islargelyinaccurate -- 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.
Good essay on the inherent vulnerabilities in the cell phone standards and the market barriers to fixing them.
So far, industry and policymakers have largely dragged their feet when it comes to blocking cell-site simulators and SS7 attacks. Senator Ron Wyden, one of the few lawmakers vocal about this issue, sent a letter in August encouraging the Department of Justice to "be forthright with federal courts about the disruptive nature of cell-site simulators." No response has ever been published.
The lack of action could be because it is a big task -- there are hundreds of companies and international bodies involved in the cellular network. The other reason could be that intelligence and law enforcement agencies have a vested interest in exploiting these same vulnerabilities. But law enforcement has other effective tools that are unavailable to criminals and spies. For example, the police can work directly with phone companies, serving warrants and Title III wiretap orders. In the end, eliminating these vulnerabilities is just as valuable for law enforcement as it is for everyone else.
As it stands, there is no government agency that has the power, funding and mission to fix the problems. Large companies such as AT&T, Verizon, Google and Apple have not been public about their efforts, if any exist.
Abstract: Payment card fraud results in billions of dollars in losses annually. Adversaries increasingly acquire card data using skimmers, which are attached to legitimate payment devices including point of sale terminals, gas pumps, and ATMs. Detecting such devices can be difficult, and while many experts offer advice in doing so, there exists no large-scale characterization of skimmer technology to support such defenses. In this paper, we perform the first such study based on skimmers recovered by the NYPD's Financial Crimes Task Force over a 16 month period. After systematizing these devices, we develop the Skim Reaper, a detector which takes advantage of the physical properties and constraints necessary for many skimmers to steal card data. Our analysis shows the Skim Reaper effectively detects 100% of devices supplied by the NYPD. In so doing, we provide the first robust and portable mechanism for detecting card skimmers.
Earlier this month, I wrote about a statement by the Five Eyes countries about encryption and back doors. (Short summary: they like them.) One of the weird things about the statement is that it was clearly written from a law-enforcement perspective, though we normally think of the Five Eyes as a consortium of intelligence agencies.
Susan Landau examines the details of the statement, explains what's going on, and why the statement is a lot less than what it might seem.
Some of us -- myself included -- have proposed lawful government hacking as an alternative to backdoors. A new report from the Center of Internet and Society looks at the security risks of allowing government hacking. They include:
Disincentive for vulnerability disclosure
Cultivation of a market for surveillance tools
Attackers co-opt hacking tools over which governments have lost control
Attackers learn of vulnerabilities through government use of malware
Government incentives to push for less-secure software and standards
Government malware affects innocent users.
These risks are real, but I think they're much less than mandating backdoors for everyone. From the report's conclusion:
Government hacking is often lauded as a solution to the "going dark" problem. It is too dangerous to mandate encryption backdoors, but targeted hacking of endpoints could ensure investigators access to same or similar necessary data with less risk. Vulnerabilities will never affect everyone, contingent as they are on software, network configuration, and patch management. Backdoors, however, mean everybody is vulnerable and a security failure fails catastrophically. In addition, backdoors are often secret, while eventually, vulnerabilities will typically be disclosed and patched.
The key to minimizing the risks is to ensure that law enforcement (or whoever) report all vulnerabilities discovered through the normal process, and use them for lawful hacking during the period between reporting and patching. Yes, that's a big ask, but the alternatives are worse.
According to a new CSIS report, "going dark" is not the most pressing problem facing law enforcement in the age of digital data:
Over the past year, we conducted a series of interviews with federal, state, and local law enforcement officials, attorneys, service providers, and civil society groups. We also commissioned a survey of law enforcement officers from across the country to better understand the full range of difficulties they are facing in accessing and using digital evidence in their cases. Survey results indicate that accessing data from service providers -- much of which is not encrypted -- is the biggest problem that law enforcement currently faces in leveraging digital evidence.
This is a problem that has not received adequate attention or resources to date. An array of federal and state training centers, crime labs, and other efforts have arisen to help fill the gaps, but they are able to fill only a fraction of the need. And there is no central entity responsible for monitoring these efforts, taking stock of the demand, and providing the assistance needed. The key federal entity with an explicit mission to assist state and local law enforcement with their digital evidence needs -- the National Domestic Communications Assistance Center (NDCAC)has a budget of $11.4 million, spread among several different programs designed to distribute knowledge about service providers' policies and products, develop and share technical tools, and train law enforcement on new services and technologies, among other initiatives.
In addition to bemoaning the lack of guidance and help from tech companies -- a quarter of survey respondents said their top issue was convincing companies to hand over suspects' data -- law enforcement officials also reported receiving barely any digital evidence training. Local police said they'd received only 10 hours of training in the past 12 months; state police received 13 and federal officials received 16. A plurality of respondents said they only received annual training. Only 16 percent said their organizations scheduled training sessions at least twice per year.
This is a point that Susan Landau has repeatedly made, and also one I make in my new book. The FBI needs technical expertise, not backdoors.
The New York Times is reporting about a company called Securus Technologies that gives police the ability to track cell phone locations without a warrant:
The service can find the whereabouts of almost any cellphone in the country within seconds. It does this by going through a system typically used by marketers and other companies to get location data from major cellphone carriers, including AT&T, Sprint, T-Mobile and Verizon, documents show.
Last month, Wired published a long article about Ray Ozzie and his supposed new scheme for adding a backdoor in encrypted devices. It's a weird article. It paints Ozzie's proposal as something that "attains the impossible" and "satisfies both law enforcement and privacy purists," when (1) it's barely a proposal, and (2) it's essentially the same key escrow scheme we've been hearing about for decades.
Basically, each device has a unique public/private key pair and a secure processor. The public key goes into the processor and the device, and is used to encrypt whatever user key encrypts the data. The private key is stored in a secure database, available to law enforcement on demand. The only other trick is that for law enforcement to use that key, they have to put the device in some sort of irreversible recovery mode, which means it can never be used again. That's basically it.
I have no idea why anyone is talking as if this were anything new. Severalcryptographershavealreadyexplained why this key escrow scheme is no better than any other key escrow scheme. The short answer is (1) we won't be able to secure that database of backdoor keys, (2) we don't know how to build the secure coprocessor the scheme requires, and (3) it solves none of the policy problems around the whole system. This is the typical mistake non-cryptographers make when they approach this problem: they think that the hard part is the cryptography to create the backdoor. That's actually the easy part. The hard part is ensuring that it's only used by the good guys, and there's nothing in Ozzie's proposal that addresses any of that.
I worry that this kind of thing is damaging in the long run. There should be some rule that any backdoor or key escrow proposal be a fully specified proposal, not just some cryptography and hand-waving notions about how it will be used in practice. And before it is analyzed and debated, it should have to satisfy some sort of basic security analysis. Otherwise, we'll be swatting pseudo-proposals like this one, while those on the other side of this debate become increasingly convinced that it's possible to design one of these things securely.
Already people are using the National Academies report on backdoors for law enforcement as evidence that engineers are developing workable and secure backdoors. Writing in Lawfare, Alan Z. Rozenshtein claims that the report -- and a related New York Timesstory -- "undermine the argument that secure third-party access systems are so implausible that it's not even worth trying to develop them." Susan Landau effectively corrects this misconception, but the damage is done.
Here's the thing: it's not hard to design and build a backdoor. What's hard is building the systems -- both technical and procedural -- around them. Here's Rob Graham:
He's only solving the part we already know how to solve. He's deliberately ignoring the stuff we don't know how to solve. We know how to make backdoors, we just don't know how to secure them.
A bunch of us cryptographers have already explained why we don't think this sort of thing will work in the foreseeable future. We write:
Exceptional access would force Internet system developers to reverse "forward secrecy" design practices that seek to minimize the impact on user privacy when systems are breached. The complexity of today's Internet environment, with millions of apps and globally connected services, means that new law enforcement requirements are likely to introduce unanticipated, hard to detect security flaws. Beyond these and other technical vulnerabilities, the prospect of globally deployed exceptional access systems raises difficult problems about how such an environment would be governed and how to ensure that such systems would respect human rights and the rule of law.
The reason so few of us are willing to bet on massive-scale key escrow systems is that we've thought about it and we don't think it will work. We've looked at the threat model, the usage model, and the quality of hardware and software that exists today. Our informed opinion is that there's no detection system for key theft, there's no renewability system, HSMs are terrifically vulnerable (and the companies largely staffed with ex-intelligence employees), and insiders can be suborned. We're not going to put the data of a few billion people on the line an environment where we believe with high probability that the system will fail.