When a weakness is introduced into that defense, even if it's a secret key held only by trusted governments and only (they promise) to be used in emergencies, that key is a method of attack that anyone, anywhere can use against everyone. The only defense is that the secret key remain secret, and there are an endless number of ways it could be comprimised, ranging from human error, phishing, or plain old brute forcing. A single key for all Whatsapp conversations is a valuable enough prize for criminals all over the world to invest serious money in custom hardware to crack it.
Currently, encryption schemes like Whatsapp's rely on generation of new keys for every message, making the value of attacking any one message limited. Without this defense, Whatsapp will be cracked, sooner or later. And once someone publicly reveals that key, every single message sent before that point becomes compromised. Maybe even publicly exposed. Would you be okay with that? Exposing your private message history to the internet because governments wanted to snoop?
If there is a key which decrypts everything, then there is a risk it can be stolen or guessed and used to decrypt anyone's messages. This risk does not exist in current, properly designed systems.
Any government which wishes to add a backdoor to an E2E encrypted messaging system must understand that they will be HEAVILY undermining the security and privacy rights for all users of the service which has the backdoor.
Whatsapp decided to go for E2E encryption for commercial and marketing purposes following all those privacy scandals.
They did not have to. They could have gone with P2P encryption, i.e. that their databases could have stored messages in cleartext. That way authorities would not have needed to ask for any backdoor. As already mentioned, this is how cellular operators work (that's obviously something governments wanted).
I think we might see legislation brought in in the future in order to force this.
Okay. Let's just get rid of E2E entirely and let Facebook mine not only our metadata but also the content of our messages. Nice plan.
> let Facebook mine not only our metadata...
Don't use Facebook, then.
Yes, but if you make it too easy, oversight fails or is worked around with legalese, and the powers are abused at scale.
> Bugging a phone really means illegal/covert operations these days
My view here is that it should be difficult - the security services should only be able to intercept someone's communications with a legally obtained warrant to do so (the oversight you mentioned); then powers are far more likely to only be used where the is a credible threat.
That's a very bold claim.
Lawful wiretapping exists because it is accepted (and reasonable) that privacy should stop in specific circumstances, e.g. a criminal investigation.
As I wrote before seeing this in black or white is naive. Wiretapping is useful for society. The key is to have proper oversight.
By the way, to lawfully wiretap a phone the authorities only need the phone number: The operator will then duplicate all traffic transparently and on the fly. Bugging a phone really means illegal/covert operations these days...