Two-tier encryption: Apple, the UK and the backdoor nobody is allowed to confirm

This morning I came across an article on Macanorak that opens with a very simple example, one I’ve been turning over in my head for a while now.

Alice and Bill live in the UK. They have the same iPhone, they use iCloud, and they pay Apple exactly the same. Alice has Advanced Data Protection (ADP) turned on, so most of her iCloud data is end-to-end encrypted. Bill doesn’t have it, and he can’t turn it on.

The only difference between them is that Alice enabled it before February 2025. Bill was too late.

I’ve just written three articles in a row about the EU Kids Act and age verification, where everything ended up resting on a cryptographic piece that still doesn’t work properly. This case is the other side of the coin: cryptography that works perfectly, and a government that is bothered by it.

Some context: encrypted is not the same as end-to-end encrypted

To follow this mess you need a clear picture of a distinction that often gets blurred.

All of iCloud is encrypted. But in the standard configuration, Apple holds the keys for most categories: it can decrypt your data if needed, and a court can compel it to hand that data over. Only a few sensitive categories (Keychain, Health data, Messages in iCloud…) are end-to-end encrypted by default.

With ADP turned on, that list grows:

The last column is what matters. With ADP, Apple does not have the keys to that data. It’s not that it won’t give them to you: it simply doesn’t have them. And that is exactly what collides with what the British government asked for.

What happened, in order

The story goes back a long way. In 2016, after the San Bernardino attack, the FBI tried to force Apple to build a version of iOS that would bypass the protections on the attacker’s iPhone. Tim Cook refused publicly and called that software “the equivalent of cancer”: a master key that, once built, would work on any iPhone. The FBI eventually got in with help from a third party and dropped the case.

Almost ten years later, the UK stepped in:

The gag deserves a moment. Anyone who receives a TCN is legally barred from acknowledging it. So for nearly two years we’ve had a dispute everyone knows about and that neither side can officially talk about. One of the lawyers for Liberty and Privacy International compared it in court to the emperor’s new clothes, and I think that’s a fair description.

Apple’s third way

The dilemma Apple was handed was essentially this:

flowchart TD
    A["TCN · keep the capability to access ADP-protected data"] --> B{"What does Apple do?"}
    B -->|Comply| C["Build an access mechanism · a backdoor by another name"]
    B -->|Refuse| D["Break a UK legal order"]
    B -->|Third way| E["Withdraw ADP for new UK users"]
    E --> F["Apple holds the keys again · can respond to court orders"]

It chose the third. If you don’t offer end-to-end encryption, you hold the keys again, you can respond to court orders as always, and you don’t have to build any new mechanism.

Here’s where it gets interesting. Apple couldn’t switch ADP off for people who already had it, because it deliberately designed it that way. According to its own security documentation, its servers can’t change that setting or roll it back: only the user’s trusted devices can.

That’s where the two tiers come from. Alice is still protected because the system is well built. Bill isn’t because he was too late, or because he bought his iPhone in time but never knew ADP had to be turned on by hand. Either way, there’s nothing left for Bill to do.

It’s a beautiful irony, in the worst sense. Alice still being protected proves what Apple had been saying for ten years: if the system is well designed, not even the manufacturer can get in. Which is precisely what the government didn’t want to hear.

Why there’s no such thing as a master key

The author of the article tries to be fair to the British government, and so do I. The underlying argument is reasonable: serious criminals use encryption, and police need to be able to access data when a judge authorises it. A TCN isn’t a blank cheque either: it needs approval from a Judicial Commissioner and doesn’t grant access to anything on its own.

The problem is technical, not a matter of good intentions. End-to-end encryption doesn’t work like a safe where the manufacturer keeps a spare key for when a court order arrives. There is no spare key. The only way to get one is to change the system so that someone other than your devices can get in.

And a mechanism that lets the authorised party in can also be discovered and exploited by someone who isn’t authorised. You don’t have to be paranoid for this: you only need to have seen a few security incidents. Tim Cook put it better in 2016 than I could: “If you put a back door in, then that back door is for everybody. For good guys and bad guys.”

And this isn’t just about Apple. If this precedent sticks, the same can be asked of WhatsApp, Signal, password managers, banks… any service that relies on real end-to-end encryption. Meredith Whittaker, president of Signal, said years ago that they would rather leave the UK than weaken their encryption.

What I take away

First, something practical. Outside the UK, ADP is still available. It’s in Settings → [your name] → iCloud → Advanced Data Protection. Before turning it on you need to set up a recovery contact or a recovery key, and that matters: if you lose access to both, Apple won’t be able to help you recover that data, because it really doesn’t have the keys. That’s the price of nobody else being able to get in, and I think it’s a reasonable one.

What has happened in the UK leaves a pretty clear lesson: the windows for turning on privacy can close. Bill didn’t do anything wrong. He just didn’t turn it on in time, and now it’s no longer up to him.

Second, I agree with the original article’s conclusion. It’s easy to blame Apple for leaving British users without encryption, but it was handed an impossible choice and picked the least bad option. The unfairness of having two classes of customers wasn’t created by Apple: it was created by a secret order asking for something a well-designed system cannot give.

And what worries me most about the whole case isn’t the technical side but the secrecy. An order nobody can confirm, about a dispute everybody knows about, argued in a tribunal behind closed doors. The debate over whether we want end-to-end encryption is legitimate and worth having, but it has to happen in public, not through the back door.

Source: Two-Tier Encryption in the UK, on Macanorak, which covers the timeline in detail and links to all the primary sources.