Alexis Lours, a software engineer and tech writer from France, has published a detailed analysis of the new Lockdown Mode added to iOS 16 in the third beta.
There’s good news and bad news. It will protect your iPhone from some of the most sophisticated cyberattacks in the world (such as Pegasus). But it will also massively slow down performance when browsing the web.
What is iOS 16’s Lockdown Mode?
Before we get into Lours’ testing, it’s worth explaining what Lockdown Mode is, and what it’s for. This is not, we’d like to stress, a feature intended for the average user. It’s an ultra-high-privacy mode for individuals who fear cyberattacks “from private companies developing state-sponsored mercenary spyware.” Here’s Apple’s explanation:
“Lockdown Mode is an extreme, optional protection that should only be used if you believe you may be personally targeted by a highly sophisticated cyberattack. Most people are never targeted by attacks of this nature.”
(For a slightly more detailed guide to the purpose of Lockdown Mode, read Apple’s press release.)
In other words, you probably won’t be using this mode unless you’re a monarchy-critical Saudi journalist or oligarch-baiting Russian ex-pat. However, it’s still interesting to look at the way it works, which can give an insight into Apple’s approach to privacy, and the performance costs of extreme privacy protections.
What does Lockdown Mode do?
“When iPhone is in Lockdown Mode,” Apple explains, “it will not function as it typically does. Apps, websites, and features will be strictly limited for security, and some experiences will be completely unavailable.”
This is important. Lockdown Mode doesn’t wave a magic wand and magically protect an iPhone from cyberattacks; rather, it is a compromise that disables many of the iPhone’s features in order to make attacking the device more difficult.
Following testing, Lours offers this list of features that have been disabled, in most cases “as a way to reduce possible user tracking.”
- WebAssembly
- MP3 Playback
- MathML
- Gamepad API
- Web Audio API
- WebGL
- JPEG 2000
- Speech Recognition API
- MediaDevices.getUserMedia()
- RTCDataChannel
- PDF Viewer
- SVG Fonts
A non-engineer is likely to find much of that list baffling. What actual differences will they notice in real-world iPhone use?
How much will Lockdown Mode slow down my iPhone?
Knowing the Lockdown Mode disables just-in-time (JIT) JavaScript compilation (as well as other “complex web technologies” that Apple doesn’t name), Ours suspected that it would result in a major drop in performance when browsing the web, and therefore tested before and after activating Lockdown Mode using three benchmarks:
- Octane, which measures “a JavaScript engine’s performance”
- Speedometer 2.0, which measures “the responsiveness of web applications”
- MotionMark 1.2, which measures “a browser’s capability 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. Which is a fair bit of variation, but suggests that the mode should only be used by the most at-risk users.
iOS 16 is currently in the beta phase of testing, and may yet change significantly before it’s launched in the fall. We will wait with interest to see if Apple can find a way to reduce this performance drop, but it’s likely that extreme protections simply require extreme compromises.
