Tag Archives: iPhone

Faking an iPhone Reboot

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2022/01/faking-an-iphone-reboot.html

Researchers have figured how how to intercept and fake an iPhone reboot:

We’ll dissect the iOS system and show how it’s possible to alter a shutdown event, tricking a user that got infected into thinking that the phone has been powered off, but in fact, it’s still running. The “NoReboot” approach simulates a real shutdown. The user cannot feel a difference between a real shutdown and a “fake shutdown.” There is no user-interface or any button feedback until the user turns the phone back “on.”

It’s a complicated hack, but it works.

Uses are obvious:

Historically, when malware infects an iOS device, it can be removed simply by restarting the device, which clears the malware from memory.

However, this technique hooks the shutdown and reboot routines to prevent them from ever happening, allowing malware to achieve persistence as the device is never actually turned off.

I see this as another manifestation of the security problems that stem from all controls becoming software controls. Back when the physical buttons actually did things — like turn the power, the Wi-Fi, or the camera on and off — you could actually know that something was on or off. Now that software controls those functions, you can never be sure.

Testing Faraday Cages

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2021/12/testing-faraday-cages.html

Matt Blaze tested a variety of Faraday cages for phones, both commercial and homemade.

The bottom line:

A quick and likely reliable “go/no go test” can be done with an Apple AirTag and an iPhone: drop the AirTag in the bag under test, and see if the phone can locate it and activate its alarm (beware of caching in the FindMy app when doing this).

This test won’t tell you the exact attenuation level, of course, but it will tell you if the attenuation is sufficient for most practical purposes. It can also detect whether an otherwise good bag has been damaged and compromised.

At least in the frequency ranges I tested, two commercial Faraday pouches (the EDEC OffGrid and Mission Darkness Window pouches) yielded excellent performance sufficient to provide assurance of signal isolation under most real-world circumstances. None of the makeshift solutions consistently did nearly as well, although aluminum foil can, under ideal circumstances (that are difficult to replicate) sometimes provide comparable levels of attenuation.

Zero-Click iPhone Exploits

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2021/09/zero-click-iphone-exploits.html

Citizen Lab is reporting on two zero-click iMessage exploits, in spyware sold by the cyberweapons arms manufacturer NSO Group to the Bahraini government.

These are particularly scary exploits, since they don’t require to victim to do anything, like click on a link or open a file. The victim receives a text message, and then they are hacked.

More on this here.

Apple’s NeuralHash Algorithm Has Been Reverse-Engineered

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2021/08/apples-neuralhash-algorithm-has-been-reverse-engineered.html

Apple’s NeuralHash algorithm — the one it’s using for client-side scanning on the iPhone — has been reverse-engineered.

Turns out it was already in iOS 14.3, and someone noticed:

Early tests show that it can tolerate image resizing and compression, but not cropping or rotations.

We also have the first collision: two images that hash to the same value.

The next step is to generate innocuous images that NeuralHash classifies as prohibited content.

This was a bad idea from the start, and Apple never seemed to consider the adversarial context of the system as a whole, and not just the cryptography.

New iMessage Security Features

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2021/01/new-imessage-security-features.html

Apple has added added security features to mitigate the risk of zero-click iMessage attacks.

Apple did not document the changes but Groß said he fiddled around with the newest iOS 14 and found that Apple shipped a “significant refactoring of iMessage processing” that severely cripples the usual ways exploits are chained together for zero-click attacks.

Groß notes that memory corruption based zero-click exploits typically require exploitation of multiple vulnerabilities to create exploit chains. In most observed attacks, these could include a memory corruption vulnerability, reachable without user interaction and ideally without triggering any user notifications; a way to break ASLR remotely; a way to turn the vulnerability into remote code execution;; and a way to break out of any sandbox, typically by exploiting a separate vulnerability in another operating system component (e.g. a userspace service or the kernel).

Impressive iPhone Exploit

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2020/12/impressive-iphone-exploit.html

This is a scarily impressive vulnerability:

Earlier this year, Apple patched one of the most breathtaking iPhone vulnerabilities ever: a memory corruption bug in the iOS kernel that gave attackers remote access to the entire device­ — over Wi-Fi, with no user interaction required at all. Oh, and exploits were wormable­ — meaning radio-proximity exploits could spread from one nearby device to another, once again, with no user interaction needed.

[…]

Beer’s attack worked by exploiting a buffer overflow bug in a driver for AWDL, an Apple-proprietary mesh networking protocol that makes things like Airdrop work. Because drivers reside in the kernel — ­one of the most privileged parts of any operating system­ — the AWDL flaw had the potential for serious hacks. And because AWDL parses Wi-Fi packets, exploits can be transmitted over the air, with no indication that anything is amiss.

[…]

Beer developed several different exploits. The most advanced one installs an implant that has full access to the user’s personal data, including emails, photos, messages, and passwords and crypto keys stored in the keychain. The attack uses a laptop, a Raspberry Pi, and some off-the-shelf Wi-Fi adapters. It takes about two minutes to install the prototype implant, but Beer said that with more work a better written exploit could deliver it in a “handful of seconds.” Exploits work only on devices that are within Wi-Fi range of the attacker.

There is no evidence that this vulnerability was ever used in the wild.

EDITED TO ADD: Slashdot thread.

New Bluetooth Vulnerability

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2020/09/new-bluetooth-vulnerability.html

There’s a new unpatched Bluetooth vulnerability:

The issue is with a protocol called Cross-Transport Key Derivation (or CTKD, for short). When, say, an iPhone is getting ready to pair up with Bluetooth-powered device, CTKD’s role is to set up two separate authentication keys for that phone: one for a “Bluetooth Low Energy” device, and one for a device using what’s known as the “Basic Rate/Enhanced Data Rate” standard. Different devices require different amounts of data — and battery power — from a phone. Being able to toggle between the standards needed for Bluetooth devices that take a ton of data (like a Chromecast), and those that require a bit less (like a smartwatch) is more efficient. Incidentally, it might also be less secure.

According to the researchers, if a phone supports both of those standards but doesn’t require some sort of authentication or permission on the user’s end, a hackery sort who’s within Bluetooth range can use its CTKD connection to derive its own competing key. With that connection, according to the researchers, this sort of erzatz authentication can also allow bad actors to weaken the encryption that these keys use in the first place — which can open its owner up to more attacks further down the road, or perform “man in the middle” style attacks that snoop on unprotected data being sent by the phone’s apps and services.

Another article:

Patches are not immediately available at the time of writing. The only way to protect against BLURtooth attacks is to control the environment in which Bluetooth devices are paired, in order to prevent man-in-the-middle attacks, or pairings with rogue devices carried out via social engineering (tricking the human operator).

However, patches are expected to be available at one point. When they’ll be, they’ll most likely be integrated as firmware or operating system updates for Bluetooth capable devices.

The timeline for these updates is, for the moment, unclear, as device vendors and OS makers usually work on different timelines, and some may not prioritize security patches as others. The number of vulnerable devices is also unclear and hard to quantify.

Many Bluetooth devices can’t be patched.

Final note: this seems to be another example of simultaneous discovery:

According to the Bluetooth SIG, the BLURtooth attack was discovered independently by two groups of academics from the École Polytechnique Fédérale de Lausanne (EPFL) and Purdue University.

New iPhone Zero-Day Discovered

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2020/04/new_iphone_zero.html

Last year, ZecOps discovered two iPhone zero-day exploits. They will be patched in the next iOS release:

Avraham declined to disclose many details about who the targets were, and did not say whether they lost any data as a result of the attacks, but said “we were a bit surprised about who was targeted.” He said some of the targets were an executive from a telephone carrier in Japan, a “VIP” from Germany, managed security service providers from Saudi Arabia and Israel, people who work for a Fortune 500 company in North America, and an executive from a Swiss company.

[…]

On the other hand, this is not as polished a hack as others, as it relies on sending an oversized email, which may get blocked by certain email providers. Moreover, Avraham said it only works on the default Apple Mail app, and not on Gmail or Outlook, for example.

Hacking Voice Assistants with Ultrasonic Waves

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2020/03/hacking_voice_a_1.html

I previously wrote about hacking voice assistants with lasers. Turns you can do much the same thing with ultrasonic waves:

Voice assistants — the demo targeted Siri, Google Assistant, and Bixby — are designed to respond when they detect the owner’s voice after noticing a trigger phrase such as ‘Ok, Google’.

Ultimately, commands are just sound waves, which other researchers have already shown can be emulated using ultrasonic waves which humans can’t hear, providing an attacker has a line of sight on the device and the distance is short.

What SurfingAttack adds to this is the ability to send the ultrasonic commands through a solid glass or wood table on which the smartphone was sitting using a circular piezoelectric disc connected to its underside.

Although the distance was only 43cm (17 inches), hiding the disc under a surface represents a more plausible, easier-to-conceal attack method than previous techniques.

Research paper. Demonstration video.

New Unpatchable iPhone Exploit Allows Jailbreaking

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2019/10/new_unpatchable.html

A new iOS exploit allows jailbreaking of pretty much all version of the iPhone. This is a huge deal for Apple, but at least it doesn’t allow someone to remotely hack people’s phones.

Some details:

I wanted to learn how Checkm8 will shape the iPhone experience­ — particularly as it relates to security­ — so I spoke at length with axi0mX on Friday. Thomas Reed, director of Mac offerings at security firm Malwarebytes, joined me. The takeaways from the long-ranging interview are:

  • Checkm8 requires physical access to the phone. It can’t be remotely executed, even if combined with other exploits.
  • The exploit allows only tethered jailbreaks, meaning it lacks persistence. The exploit must be run each time an iDevice boots.

  • Checkm8 doesn’t bypass the protections offered by the Secure Enclave and Touch ID.

  • All of the above means people will be able to use Checkm8 to install malware only under very limited circumstances. The above also means that Checkm8 is unlikely to make it easier for people who find, steal or confiscate a vulnerable iPhone, but don’t have the unlock PIN, to access the data stored on it.

  • Checkm8 is going to benefit researchers, hobbyists, and hackers by providing a way not seen in almost a decade to access the lowest levels of iDevices.

Also:

“The main people who are likely to benefit from this are security researchers, who are using their own phone in controlled conditions. This process allows them to gain more control over the phone and so improves visibility into research on iOS or other apps on the phone,” Wood says. “For normal users, this is unlikely to have any effect, there are too many extra hurdles currently in place that they would have to get over to do anything significant.”

If a regular person with no prior knowledge of jailbreaking wanted to use this exploit to jailbreak their iPhone, they would find it extremely difficult, simply because Checkm8 just gives you access to the exploit, but not a jailbreak in itself. It’s also a ‘tethered exploit’, meaning that the jailbreak can only be triggered when connected to a computer via USB and will become untethered once the device restarts.

Massive iPhone Hack Targets Uyghurs

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2019/09/massive_iphone_.html

China is being blamed for a massive surveillance operation that targeted Uyghur Muslims. This story broke in waves, the first wave being about the iPhone.

Earlier this year, Google’s Project Zero found a series of websites that have been using zero-day vulnerabilities to indiscriminately install malware on iPhones that would visit the site. (The vulnerabilities were patched in iOS 12.1.4, released on February 7.)

Earlier this year Google’s Threat Analysis Group (TAG) discovered a small collection of hacked websites. The hacked sites were being used in indiscriminate watering hole attacks against their visitors, using iPhone 0-day.

There was no target discrimination; simply visiting the hacked site was enough for the exploit server to attack your device, and if it was successful, install a monitoring implant. We estimate that these sites receive thousands of visitors per week.

TAG was able to collect five separate, complete and unique iPhone exploit chains, covering almost every version from iOS 10 through to the latest version of iOS 12. This indicated a group making a sustained effort to hack the users of iPhones in certain communities over a period of at least two years.

Four more news stories.

This upends pretty much everything we know about iPhone hacking. We believed that it was hard. We believed that effective zero-day exploits cost $2M or $3M, and were used sparingly by governments only against high-value targets. We believed that if an exploit was used too frequently, it would be quickly discovered and patched.

None of that is true here. This operation used fourteen zero-days exploits. It used them indiscriminately. And it remained undetected for two years. (I waited before posting this because I wanted to see if someone would rebut this story, or explain it somehow.)

Google’s announcement left out of details, like the URLs of the sites delivering the malware. That omission meant that we had no idea who was behind the attack, although the speculation was that it was a nation-state.

Subsequent reporting added that malware against Android phones and the Windows operating system were also delivered by those websites. And then that the websites were targeted at Uyghurs. Which leads us all to blame China.

So now this is a story of a large, expensive, indiscriminate, Chinese-run surveillance operation against an ethnic minority in their country. And the politics will overshadow the tech. But the tech is still really impressive.

EDITED TO ADD: New data on the value of smartphone exploits:

According to the company, starting today, a zero-click (no user interaction) exploit chain for Android can get hackers and security researchers up to $2.5 million in rewards. A similar exploit chain impacting iOS is worth only $2 million.

EDITED TO ADD (9/6): Apple disputes some of the claims Google made about the extent of the vulnerabilities and the attack.

EDITED TO ADD (9/7): More on Apple’s pushbacks.

Cellebrite Claims It Can Unlock Any iPhone

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2019/06/cellebrite_clai.html

The digital forensics company Cellebrite now claims it can unlock any iPhone.

I dithered before blogging this, not wanting to give the company more publicity. But I decided that everyone who wants to know already knows, and that Apple already knows. It’s all of us that need to know.

iPhone Apps Surreptitiously Communicated with Unknown Servers

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2019/06/iphone_apps_sur.html

Long news article (alternate source) on iPhone privacy, specifically the enormous amount of data your apps are collecting without your knowledge. A lot of this happens in the middle of the night, when you’re probably not otherwise using your phone:

IPhone apps I discovered tracking me by passing information to third parties ­ just while I was asleep ­ include Microsoft OneDrive, Intuit’s Mint, Nike, Spotify, The Washington Post and IBM’s the Weather Channel. One app, the crime-alert service Citizen, shared personally identifiable information in violation of its published privacy policy.

And your iPhone doesn’t only feed data trackers while you sleep. In a single week, I encountered over 5,400 trackers, mostly in apps, not including the incessant Yelp traffic.

How Apple’s "Find My" Feature Works

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2019/06/how_apples_find.html

Matthew Green intelligently speculates about how Apple’s new “Find My” feature works.

If you haven’t already been inspired by the description above, let me phrase the question you ought to be asking: how is this system going to avoid being a massive privacy nightmare?

Let me count the concerns:

  • If your device is constantly emitting a BLE signal that uniquely identifies it, the whole world is going to have (yet another) way to track you. Marketers already use WiFi and Bluetooth MAC addresses to do this: Find My could create yet another tracking channel.
  • It also exposes the phones who are doing the tracking. These people are now going to be sending their current location to Apple (which they may or may not already be doing). Now they’ll also be potentially sharing this information with strangers who “lose” their devices. That could go badly.

  • Scammers might also run active attacks in which they fake the location of your device. While this seems unlikely, people will always surprise you.

The good news is that Apple claims that their system actually does provide strong privacy, and that it accomplishes this using clever cryptography. But as is typical, they’ve declined to give out the details how they’re going to do it. Andy Greenberg talked me through an incomplete technical description that Apple provided to Wired, so that provides many hints. Unfortunately, what Apple provided still leaves huge gaps. It’s into those gaps that I’m going to fill in my best guess for what Apple is actually doing.

iOS Shortcut for Recording the Police

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2019/06/ios_shortcut_fo.html

Hey Siri; I’m getting pulled over” can be a shortcut:

Once the shortcut is installed and configured, you just have to say, for example, “Hey Siri, I’m getting pulled over.” Then the program pauses music you may be playing, turns down the brightness on the iPhone, and turns on “do not disturb” mode.

It also sends a quick text to a predetermined contact to tell them you’ve been pulled over, and it starts recording using the iPhone’s front-facing camera. Once you’ve stopped recording, it can text or email the video to a different predetermined contact and save it to Dropbox.

Fingerprinting iPhones

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2019/05/fingerprinting_7.html

This clever attack allows someone to uniquely identify a phone when you visit a website, based on data from the accelerometer, gyroscope, and magnetometer sensors.

We have developed a new type of fingerprinting attack, the calibration fingerprinting attack. Our attack uses data gathered from the accelerometer, gyroscope and magnetometer sensors found in smartphones to construct a globally unique fingerprint. Overall, our attack has the following advantages:

  • The attack can be launched by any website you visit or any app you use on a vulnerable device without requiring any explicit confirmation or consent from you.
  • The attack takes less than one second to generate a fingerprint.
  • The attack can generate a globally unique fingerprint for iOS devices.
  • The calibration fingerprint never changes, even after a factory reset.
  • The attack provides an effective means to track you as you browse across the web and move between apps on your phone.

* Following our disclosure, Apple has patched this vulnerability in iOS 12.2.

Research paper.

iPhone FaceTime Vulnerability

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2019/01/iphone_facetime.html

This is kind of a crazy iPhone vulnerability: it’s possible to call someone on FaceTime and listen on their microphone — and see from their camera — before they accept the call.

This is definitely an embarrassment, and Apple was right to disable Group FaceTime until it’s fixed. But it’s hard to imagine how an adversary can operationalize this in any useful way.

New York governor Andrew M. Cuomo wrote: “The FaceTime bug is an egregious breach of privacy that puts New Yorkers at risk.” Kinda, I guess.

EDITED TO ADD (1/30): This bug/vulnerability was first discovered by a 14-year-old, whose mother tried to alert Apple with no success.

iOS 12.1 Vulnerability

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2018/11/ios_121_vulnera.html

This is really just to point out that computer security is really hard:

Almost as soon as Apple released iOS 12.1 on Tuesday, a Spanish security researcher discovered a bug that exploits group Facetime calls to give anyone access to an iPhone users’ contact information with no need for a passcode.

[…]

A bad actor would need physical access to the phone that they are targeting and has a few options for viewing the victim’s contact information. They would need to either call the phone from another iPhone or have the phone call itself. Once the call connects they would need to:

  • Select the Facetime icon
  • Select “Add Person”
  • Select the plus icon
  • Scroll through the contacts and use 3D touch on a name to view all contact information that’s stored.

Making the phone call itself without entering a passcode can be accomplished by either telling Siri the phone number or, if they don’t know the number, they can say “call my phone.” We tested this with both the owners’ voice and a strangers voice, in both cases, Siri initiated the call.

Defeating the iPhone Restricted Mode

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2018/07/defeating_the_i.html

Recently, Apple introduced restricted mode to protect iPhones from attacks by companies like Cellebrite and Greyshift, which allow attackers to recover information from a phone without the password or fingerprint. Elcomsoft just announced that it can easily bypass it.

There is an important lesson in this: security is hard. Apple Computer has one of the best security teams on the planet. This feature was not tossed out in a day; it was designed and implemented with a lot of thought and care. If this team could make a mistake like this, imagine how bad a security feature is when implemented by a team without this kind of expertise.

This is the reason actual cryptographers and security engineers are very skeptical when a random company announces that their product is “secure.” We know that they don’t have the requisite security expertise to design and implement security properly. We know they didn’t take the time and care. We know that their engineers think they understand security, and designed to a level that they couldn’t break.

Getting security right is hard for the best teams on the world. It’s impossible for average teams.

Russian Censorship of Telegram

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2018/06/russian_censors.html

Internet censors have a new strategy in their bid to block applications and websites: pressuring the large cloud providers that host them. These providers have concerns that are much broader than the targets of censorship efforts, so they have the choice of either standing up to the censors or capitulating in order to maximize their business. Today’s Internet largely reflects the dominance of a handful of companies behind the cloud services, search engines and mobile platforms that underpin the technology landscape. This new centralization radically tips the balance between those who want to censor parts of the Internet and those trying to evade censorship. When the profitable answer is for a software giant to acquiesce to censors’ demands, how long can Internet freedom last?

The recent battle between the Russian government and the Telegram messaging app illustrates one way this might play out. Russia has been trying to block Telegram since April, when a Moscow court banned it after the company refused to give Russian authorities access to user messages. Telegram, which is widely used in Russia, works on both iPhone and Android, and there are Windows and Mac desktop versions available. The app offers optional end-to-end encryption, meaning that all messages are encrypted on the sender’s phone and decrypted on the receiver’s phone; no part of the network can eavesdrop on the messages.

Since then, Telegram has been playing cat-and-mouse with the Russian telecom regulator Roskomnadzor by varying the IP address the app uses to communicate. Because Telegram isn’t a fixed website, it doesn’t need a fixed IP address. Telegram bought tens of thousands of IP addresses and has been quickly rotating through them, staying a step ahead of censors. Cleverly, this tactic is invisible to users. The app never sees the change, or the entire list of IP addresses, and the censor has no clear way to block them all.

A week after the court ban, Roskomnadzor countered with an unprecedented move of its own: blocking 19 million IP addresses, many on Amazon Web Services and Google Cloud. The collateral damage was widespread: The action inadvertently broke many other web services that use those platforms, and Roskomnadzor scaled back after it became clear that its action had affected services critical for Russian business. Even so, the censor is still blocking millions of IP addresses.

More recently, Russia has been pressuring Apple not to offer the Telegram app in its iPhone App Store. As of this writing, Apple has not complied, and the company has allowed Telegram to download a critical software update to iPhone users (after what the app’s founder called a delay last month). Roskomnadzor could further pressure Apple, though, including by threatening to turn off its entire iPhone app business in Russia.

Telegram might seem a weird app for Russia to focus on. Those of us who work in security don’t recommend the program, primarily because of the nature of its cryptographic protocols. In general, proprietary cryptography has numerous fatal security flaws. We generally recommend Signal for secure SMS messaging, or, if having that program on your computer is somehow incriminating, WhatsApp. (More than 1.5 billion people worldwide use WhatsApp.) What Telegram has going for it is that it works really well on lousy networks. That’s why it is so popular in places like Iran and Afghanistan. (Iran is also trying to ban the app.)

What the Russian government doesn’t like about Telegram is its anonymous broadcast feature­ — channel capability and chats — ­which makes it an effective platform for political debate and citizen journalism. The Russians might not like that Telegram is encrypted, but odds are good that they can simply break the encryption. Telegram’s role in facilitating uncontrolled journalism is the real issue.

Iran attempts to block Telegram have been more successful than Russia’s, less because Iran’s censorship technology is more sophisticated but because Telegram is not willing to go as far to defend Iranian users. The reasons are not rooted in business decisions. Simply put, Telegram is a Russian product and the designers are more motivated to poke Russia in the eye. Pavel Durov, Telegram’s founder, has pledged millions of dollars to help fight Russian censorship.

For the moment, Russia has lost. But this battle is far from over. Russia could easily come back with more targeted pressure on Google, Amazon and Apple. A year earlier, Zello used the same trick Telegram is using to evade Russian censors. Then, Roskomnadzor threatened to block all of Amazon Web Services and Google Cloud; and in that instance, both companies forced Zello to stop its IP-hopping censorship-evasion tactic.

Russia could also further develop its censorship infrastructure. If its capabilities were as finely honed as China’s, it would be able to more effectively block Telegram from operating. Right now, Russia can block only specific IP addresses, which is too coarse a tool for this issue. Telegram’s voice capabilities in Russia are significantly degraded, however, probably because high-capacity IP addresses are easier to block.

Whatever its current frustrations, Russia might well win in the long term. By demonstrating its willingness to suffer the temporary collateral damage of blocking major cloud providers, it prompted cloud providers to block another and more effective anti-censorship tactic, or at least accelerated the process. In April, Google and Amazon banned­ — and technically blocked­ — the practice of “domain fronting,” a trick anti-censorship tools use to get around Internet censors by pretending to be other kinds of traffic. Developers would use popular websites as a proxy, routing traffic to their own servers through another website­ — in this case Google.com­ — to fool censors into believing the traffic was intended for Google.com. The anonymous web-browsing tool Tor has used domain fronting since 2014. Signal, since 2016. Eliminating the capability is a boon to censors worldwide.

Tech giants have gotten embroiled in censorship battles for years. Sometimes they fight and sometimes they fold, but until now there have always been options. What this particular fight highlights is that Internet freedom is increasingly in the hands of the world’s largest Internet companies. And while freedom may have its advocates — ­the American Civil Liberties Union has tweeted its support for those companies, and some 12,000 people in Moscow protested against the Telegram ban­ — actions such as disallowing domain fronting illustrate that getting the big tech companies to sacrifice their near-term commercial interests will be an uphill battle. Apple has already removed anti-censorship apps from its Chinese app store.

In 1993, John Gilmore famously said that “The Internet interprets censorship as damage and routes around it.” That was technically true when he said it but only because the routing structure of the Internet was so distributed. As centralization increases, the Internet loses that robustness, and censorship by governments and companies becomes easier.

This essay previously appeared on Lawfare.com.