Entries Tagged "encryption"

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WhatsApp Security Vulnerability

Back in March, Rolf Weber wrote about a potential vulnerability in the WhatsApp protocol that would allow Facebook to defeat perfect forward secrecy by forcibly change users’ keys, allowing it—or more likely, the government—to eavesdrop on encrypted messages.

It seems that this vulnerability is real:

WhatsApp has the ability to force the generation of new encryption keys for offline users, unbeknown to the sender and recipient of the messages, and to make the sender re-encrypt messages with new keys and send them again for any messages that have not been marked as delivered.

The recipient is not made aware of this change in encryption, while the sender is only notified if they have opted-in to encryption warnings in settings, and only after the messages have been re-sent. This re-encryption and rebroadcasting effectively allows WhatsApp to intercept and read users’ messages.

The security loophole was discovered by Tobias Boelter, a cryptography and security researcher at the University of California, Berkeley. He told the Guardian: “If WhatsApp is asked by a government agency to disclose its messaging records, it can effectively grant access due to the change in keys.”

The vulnerability is not inherent to the Signal protocol. Open Whisper Systems’ messaging app, Signal, the app used and recommended by whistleblower Edward Snowden, does not suffer from the same vulnerability. If a recipient changes the security key while offline, for instance, a sent message will fail to be delivered and the sender will be notified of the change in security keys without automatically resending the message.

WhatsApp’s implementation automatically resends an undelivered message with a new key without warning the user in advance or giving them the ability to prevent it.

Note that it’s an attack against current and future messages, and not something that would allow the government to reach into the past. In that way, it is no more troubling than the government hacking your mobile phone and reading your WhatsApp conversations that way.

An unnamed “WhatsApp spokesperson” said that they implemented the encryption this way for usability:

In WhatsApp’s implementation of the Signal protocol, we have a “Show Security Notifications” setting (option under Settings > Account > Security) that notifies you when a contact’s security code has changed. We know the most common reasons this happens are because someone has switched phones or reinstalled WhatsApp. This is because in many parts of the world, people frequently change devices and Sim cards. In these situations, we want to make sure people’s messages are delivered, not lost in transit.

He’s technically correct. This is not a backdoor. This really isn’t even a flaw. It’s a design decision that put usability ahead of security in this particular instance. Moxie Marlinspike, creator of Signal and the code base underlying WhatsApp’s encryption, said as much:

Under normal circumstances, when communicating with a contact who has recently changed devices or reinstalled WhatsApp, it might be possible to send a message before the sending client discovers that the receiving client has new keys. The recipient’s device immediately responds, and asks the sender to reencrypt the message with the recipient’s new identity key pair. The sender displays the “safety number has changed” notification, reencrypts the message, and delivers it.

The WhatsApp clients have been carefully designed so that they will not re-encrypt messages that have already been delivered. Once the sending client displays a “double check mark,” it can no longer be asked to re-send that message. This prevents anyone who compromises the server from being able to selectively target previously delivered messages for re-encryption.

The fact that WhatsApp handles key changes is not a “backdoor,” it is how cryptography works. Any attempt to intercept messages in transmit by the server is detectable by the sender, just like with Signal, PGP, or any other end-to-end encrypted communication system.

The only question it might be reasonable to ask is whether these safety number change notifications should be “blocking” or “non-blocking.” In other words, when a contact’s key changes, should WhatsApp require the user to manually verify the new key before continuing, or should WhatsApp display an advisory notification and continue without blocking the user.

Given the size and scope of WhatsApp’s user base, we feel that their choice to display a non-blocking notification is appropriate. It provides transparent and cryptographically guaranteed confidence in the privacy of a user’s communication, along with a simple user experience. The choice to make these notifications “blocking” would in some ways make things worse. That would leak information to the server about who has enabled safety number change notifications and who hasn’t, effectively telling the server who it could MITM transparently and who it couldn’t; something that WhatsApp considered very carefully.

How serious this is depends on your threat model. If you are worried about the US government—or any other government that can pressure Facebook—snooping on your messages, then this is a small vulnerability. If not, then it’s nothing to worry about.

Slashdot thread. Hacker News thread. BoingBoing post. More here.

EDITED TO ADD (1/24): Zeynep Tufekci takes the Guardian to task for their reporting on this vulnerability. (Note: I signed on to her letter.)

EDITED TO ADD (2/13): The vulnerability explained by the person who discovered it.

This is a good explanation of the security/usability trade-off that’s at issue here.

Posted on January 17, 2017 at 6:09 AM • View Comments

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 Google.com 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 Google.com. 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.

Posted on December 28, 2016 at 6:20 AM • View Comments

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.

Posted on December 21, 2016 at 9:25 AM • View Comments

Google Releases Crypto Test Suite

Google has released Project Wycheproof—a test suite designed to test cryptographic libraries against a series of known attacks. From a blog post:

In cryptography, subtle mistakes can have catastrophic consequences, and mistakes in open source cryptographic software libraries repeat too often and remain undiscovered for too long. Good implementation guidelines, however, are hard to come by: understanding how to implement cryptography securely requires digesting decades’ worth of academic literature. We recognize that software engineers fix and prevent bugs with unit testing, and we found that many cryptographic issues can be resolved by the same means

The tool has already found over 40 security bugs in cryptographic libraries, which are (all? mostly?) currently being fixed.

News article. Slashdot thread.

Posted on December 20, 2016 at 6:12 AM • View Comments

Giving Up on PGP

Filippo Valsorda wrote an excellent essay on why he’s giving up on PGP. I have long believed PGP to be more trouble than it is worth. It’s hard to use correctly, and easy to get wrong. More generally, e-mail is inherently difficult to secure because of all the different things we ask of it and use it for.

Valsorda has a different complaint, that its long-term secrets are an unnecessary source of risk:

But the real issues, I realized, are more subtle. I never felt confident in the security of my long-term keys. The more time passed, the more I would feel uneasy about any specific key. Yubikeys would get exposed to hotel rooms. Offline keys would sit in a far away drawer or safe. Vulnerabilities would be announced. USB devices would get plugged in.

A long-term key is as secure as the minimum common denominator of your security practices over its lifetime. It’s the weak link.

Worse, long-term key patterns, like collecting signatures and printing fingerprints on business cards, discourage practices that would otherwise be obvious hygiene: rotating keys often, having different keys for different devices, compartmentalization. Such practices actually encourage expanding the attack surface by making backups of the key.

Both he and I favor encrypted messaging, either Signal or OTR.

EDITED TO ADD (1/13): More PGP criticism.

Posted on December 16, 2016 at 5:36 AM • View Comments

My Priorities for the Next Four Years

Like many, I was surprised and shocked by the election of Donald Trump as president. I believe his ideas, temperament, and inexperience represent a grave threat to our country and world. Suddenly, all the things I had planned to work on seemed trivial in comparison. Although Internet security and privacy are not the most important policy areas at risk, I believe he—and, more importantly, his cabinet, administration, and Congress—will have devastating effects in that area, both in the US and around the world.

The election was so close that I’ve come to see the result as a bad roll of the dice. A few minor tweaks here and there—a more enthusiastic Sanders endorsement, one fewer of Comey’s announcements, slightly less Russian involvement—and the country would be preparing for a Clinton presidency and discussing a very different social narrative. That alternative narrative would stress business as usual, and continue to obscure the deep social problems in our society. Those problems won’t go away on their own, and in this alternative future they would continue to fester under the surface, getting steadily worse. This election exposed those problems for everyone to see.

I spent the last month both coming to terms with this reality, and thinking about the future. Here is my new agenda for the next four years:

One, fight the fights. There will be more government surveillance and more corporate surveillance. I expect legislative and judicial battles along several lines: a renewed call from the FBI for backdoors into encryption, more leeway for government hacking without a warrant, no controls on corporate surveillance, and more secret government demands for that corporate data. I expect other countries to follow our lead. (The UK is already more extreme than us.) And if there’s a major terrorist attack under Trump’s watch, it’ll be open season on our liberties. We may lose a lot of these battles, but we need to lose as few as possible and as little of our existing liberties as possible.

Two, prepare for those fights. Much of the next four years will be reactive, but we can prepare somewhat. The more we can convince corporate America to delete their saved archives of surveillance data and to store only what they need for as long as they need it, the safer we’ll all be. We need to convince Internet giants like Google and Facebook to change their business models away from surveillance capitalism. It’s a hard sell, but maybe we can nibble around the edges. Similarly, we need to keep pushing the truism that privacy and security are not antagonistic, but rather are essential for each other.

Three, lay the groundwork for a better future. No matter how bad the next four years get, I don’t believe that a Trump administration will permanently end privacy, freedom, and liberty in the US. I don’t believe that it portends a radical change in our democracy. (Or if it does, we have bigger problems than a free and secure Internet.) It’s true that some of Trump’s institutional changes might take decades to undo. Even so, I am confident—optimistic even—that the US will eventually come around; and when that time comes, we need good ideas in place for people to come around to. This means proposals for non-surveillance-based Internet business models, research into effective law enforcement that preserves privacy, intelligent limits on how corporations can collect and exploit our data, and so on.

And four, continue to solve the actual problems. The serious security issues around cybercrime, cyber-espionage, cyberwar, the Internet of Things, algorithmic decision making, foreign interference in our elections, and so on aren’t going to disappear for four years while we’re busy fighting the excesses of Trump. We need to continue to work towards a more secure digital future. And to the extent that cybersecurity for our military networks and critical infrastructure allies with cybersecurity for everyone, we’ll probably have an ally in Trump.

Those are my four areas. Under a Clinton administration, my list would have looked much the same. Trump’s election just means the threats will be much greater, and the battles a lot harder to win. It’s more than I can possibly do on my own, and I am therefore substantially increasing my annual philanthropy to support organizations like EPIC, EFF, ACLU, and Access Now in continuing their work in these areas.

My agenda is necessarily focused entirely on my particular areas of concern. The risks of a Trump presidency are far more pernicious, but this is where I have expertise and influence.

Right now, we have a defeated majority. Many are scared, and many are motivated—and few of those are applying their motivation constructively. We need to harness that fear and energy to start fixing our society now, instead of waiting four or even eight years, at which point the problems would be worse and the solutions more extreme. I am choosing to proceed as if this were cowpox, not smallpox: fighting the more benign disease today will be much easier than subjecting ourselves to its more virulent form in the future. It’s going to be hard keeping the intensity up for the next four years, but we need to get to work. Let’s use Trump’s victory as the wake-up call and opportunity that it is.

Posted on December 15, 2016 at 3:50 AM •

Let's Encrypt Is Making Web Encryption Easier

That’s the conclusion of a research paper:

Once [costs and complexity] are eliminated, it enables big hosting providers to issue and deploy certificates for their customers in bulk, thus quickly and automatically enable encryption across a large number of domains. For example, we have shown that currently, 47% of LE certified domains are hosted at three large hosting companies (Automattic/wordpress.com, Shopify, and OVH).

Paper: “No domain left behind: is Let’s Encrypt democratizing encryption?”

Abstract: The 2013 National Security Agency revelations of pervasive monitoring have lead to an “encryption rush” across the computer and Internet industry. To push back against massive surveillance and protect users privacy, vendors, hosting and cloud providers have widely deployed encryption on their hardware, communication links, and applications. As a consequence, the most of web traffic nowadays is encrypted. However, there is still a significant part of Internet traffic that is not encrypted. It has been argued that both costs and complexity associated with obtaining and deploying X.509 certificates are major barriers for widespread encryption, since these certificates are required to established encrypted connections. To address these issues, the Electronic Frontier Foundation, Mozilla Foundation, and the University of Michigan have set up Let’s Encrypt (LE), a certificate authority that provides both free X.509 certificates and software that automates the deployment of these certificates. In this paper, we investigate if LE has been successful in democratizing encryption: we analyze certificate issuance in the first year of LE and show from various perspectives that LE adoption has an upward trend and it is in fact being successful in covering the lower-cost end of the hosting market.

Reddit thread.

Posted on December 14, 2016 at 6:46 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.