They wouldn't have to ban it, they could just alter the protocol to make it impossible. iMessage is designed to only work on devices manufactured by a single company. All of those devices have secure cryptographic elements built into them. It's not a stretch to think Apple could lock down iMessage under the guise of security.
The only way I could see this happening is if they have all of the public keys of the secure cryptographic elements in a database of all Apple devices ever created. Because otherwise, it would just be trivial to emulate a "secure cryptographic element" if it's just a public/private key.
They aren't running a client by Apple. A glance at other posts seems they are using Apple code, but that would just be a matter of reverse engineering if the code required the secure enclave.
I can't think of a way that a server would be able to prove a device is Apple or not if you were to replicate the protocol completely. Only if there was some established public/private key would this be possible. And then the private key on the device would be in a secure enclave that you could feed it data to sign to prove the device is an authorized device.
I wouldn't be surprised if they in fact do have a list of serial numbers for all the mac, ios, tvos devices they have ever sold, linked with some corresponding device-unique public key data?
I don't know how the secure enclave works in detail but if there is a private key inside it that it uses for attestation / signing, presumably it could also have a certificate signed by an internal Apple provisioning CA infrastructure which Apple can verify on their end.
Importantly, this matters even for those older devices that were created without secure enclaves. iMessage still used this PKI architecture back before every new mac/iphone/ipad had a SE.
Of course they have all of the public keys of the secure cryptographic elements of all Apple devices (that run iMessage) ever created. Why wouldn't they?
They are already a gatekeeper with core services that are required to be interoperable. Even if iMessage specifically hasn't yet been declared a core service, Apple is in the crosshairs and behavior like banning competitors will be harmful to their legal position at a very sensitive time for them.
Your link—hell, even the URL slug and headline—make it clear that this is something Google is claiming to the EU, not something the EU itself is claiming.
Yes, it's possible that the EU will rule that iMessage needs to fall under these rules, too, but citing a major competitor (who's even more under the gun for the same stuff themselves) making the argument that Apple should be restricted is, shall we say, not super persuasive on its own.
>who's even more under the gun for the same stuff themselves
Are they, though? Google allows alternative app stores on Android, they already implement an interoperable, open standard in their primary texting app (RCS), they allow alternative browsers on the Play store itself, and they don't block interoperability with other platforms the way Apple does.
That's not to say they're not under the gun, but what they're under the gun for is different, like bribing Epic and others to not move to their own app store or make a self-updating app downloadable from their website.
They're both monopolistic asshole companies, don't get me wrong, but they're using fairly different strategies.
> they already implement an interoperable, open standard in their primary texting app (RCS)
Yes, but Apple has announced they will do the same thing. That is not the same thing as interop with the actual iMessage protocol. Similarly, Google Messages does not allow interop with its encryption and newly announced sticker/effects, which remain proprietary to the Google Messages app.
You're right, my statement was factually incorrect. The correct statement is "Apple is currently fighting an effort to require iMessage to be interoperable".
The argument stands. It would be a bad idea for Apple to ban competition from iMessage, even with an attempt at plausible deniability, while they are fighting European regulators about interoperability on multiple fronts.
