French software engineer and technical writer Alexis Lours has published a detailed analysis of the new lock mode added to iOS 16 in the third beta. There’s good news and bad news: it will protect your iPhone against some of the world’s most sophisticated cyberattacks (such as Pegasus). But it will also significantly slow down performance when browsing the web.
What is iOS 16 Lockdown Mode?
Before discussing the Lours tests, it is worth explaining what the lock mode is and what it is used for. This is not, we would like to emphasize, a feature intended for the average user. This is an ultra-private mode for people who fear cyberattacks “from private companies developing state-sponsored mercenary spyware.” Here is Apple’s explanation:
“Lockdown mode is an extreme optional protection that should only be used if you personally believe you are the target of a highly sophisticated cyberattack. Most people are never targeted by attacks of this nature.
In other words, you probably won’t use this mode unless you’re a Saudi journalist critical of the monarchy or a Russian expat baiting the oligarchs. However, it’s still worth looking at how it works, which can provide some insight into Apple’s approach to privacy and the performance costs of extreme privacy protections.
What is lock mode for?
“When iPhone is in Lockdown Mode,” Apple explains, “it won’t work as usual. Apps, websites, and features will be severely restricted for security reasons, and some experiences will be completely unavailable.
It is important. Lockdown mode doesn’t wave a magic wand or magically protect an iPhone from cyberattacks; rather, it’s a trade-off that disables many iPhone features to make attacking the device more difficult.
Following testing, Lours offers this list of features that have been disabled, in most cases “to reduce possible user tracking”.
- WebAssembly
- MP3 playback
- MathML
- Gamepad API
- Web-sound API
- WebGL
- JPEG2000
- Speech recognition API
- MediaDevices.getUserMedia()
- RTCDataChannel
- PDF Viewer
- SVG fonts
A non-engineer will likely find much of this list confusing. What real differences will they notice in actual iPhone use? In short, parts of the web won’t work, performance will be affected, and hackers will see multiple avenues of attack cut off.
How much will lock mode slow down my iPhone?
Knowing that lockdown mode disables just-in-time (JIT) JavaScript compilation (along with other “complex web technologies” that Apple doesn’t name), Ours suspected that it would cause a significant performance hit when browsing the web, and therefore tested before and after activating Containment Mode using three benchmarks:
- Octane, which measures “the performance of a JavaScript engine”
- Speedometer 2.0, which measures “the responsiveness of web applications”
- MotionMark 1.2, which measures “a browser’s ability to animate complex scenes at a target frame rate”
Using lockdown mode resulted in performance drops of 95%, 65%, and 20% in the three respective tests. It’s a bit of a variation, but suggests that the mode will definitely have a performance impact should only be used by the most at-risk users.
iOS 16 is currently in beta testing and could still change significantly before its fall launch. We’ll look forward to seeing if Apple can find a way to reduce this performance hit, but it’s likely that extreme protections just require extreme compromises.