That definition is insufficient to capture a secure system. It's not enough for a system to do this. You have to actually know / be able to prove it's doing this.
It's worth repeating this because tech firms have made the definition so confused, but encryption was developed to let you use a trusted device to communicate over an untrusted medium (radio). If your trust in the communications medium is the same as your level of trust in the device, which for so-called "E2E" messengers it is, then the whole system doesn't make any sense.
What Meta/Signal sell is kind of a smokescreen because they control both the clients and the medium and the key directory too, so nothing is really limited. They can update the logic at any moment to disable the encryption for you, the person you're talking to, or everyone, and nobody would ever know. They can also update the client to upload your private key if you're being specifically targeted, or use a weak RNG or suppress a key rotation notification or any one of a million other things. In fact, they might have already done that without anyone noticing. I pointed out in other posts that they already undermined one of the most basic properties of a modern cryptographic system (that the adversary can't tell if you're sending the same message twice) and they did so for typical government-type reasons of controlling rumors and misinformation, as they see it.
For E2E messengers to work conceptually they'd need to allow arbitrary third party clients, so you could choose to trust that client and then use the WhatsApp/Signal networks even though you don't trust them. Or at the very least, they'd need a very sophisticated and transparent auditing programme. They won't do either of those things.
It's worth repeating this because tech firms have made the definition so confused, but encryption was developed to let you use a trusted device to communicate over an untrusted medium (radio). If your trust in the communications medium is the same as your level of trust in the device, which for so-called "E2E" messengers it is, then the whole system doesn't make any sense.
What Meta/Signal sell is kind of a smokescreen because they control both the clients and the medium and the key directory too, so nothing is really limited. They can update the logic at any moment to disable the encryption for you, the person you're talking to, or everyone, and nobody would ever know. They can also update the client to upload your private key if you're being specifically targeted, or use a weak RNG or suppress a key rotation notification or any one of a million other things. In fact, they might have already done that without anyone noticing. I pointed out in other posts that they already undermined one of the most basic properties of a modern cryptographic system (that the adversary can't tell if you're sending the same message twice) and they did so for typical government-type reasons of controlling rumors and misinformation, as they see it.
For E2E messengers to work conceptually they'd need to allow arbitrary third party clients, so you could choose to trust that client and then use the WhatsApp/Signal networks even though you don't trust them. Or at the very least, they'd need a very sophisticated and transparent auditing programme. They won't do either of those things.