So excuse what may be my profound ignorance, but aren't there 2 unencrypted points in every communication that they could intercept? Very roughly, I assume eve

So excuse what may be my profound ignorance, but aren't there 2 unencrypted points in every communication that they could intercept? Very roughly, I assume every Whatsapp message follows something along the lines of: 1. Unencrypted input 2. Encryption 3. Encrypted transmission 4. Decryption 5. Unencrypted stream to display handler Technically - what's to stop them from compelling Apple and Google into putting a software keyboard logger inbetween 1 & 2 and another output logger between 4 & 5? Edit: I'm not saying this backdoor would be secure btw. Of course it wouldn't. But that seems to me a separate issue than "breaking encryption"