Notable aspects --
Looks like they're taking it seriously:
"Are End-To-End security bugs eligible for Google’s Vulnerability Rewards Program?
Yes, we have specifically expanded the scope of our Vulnerability Rewards Program to include End-To-End. This means that reports of exploitable security bugs within End-To-End are eligible for a reward."
Should be an interesting trove of JS tricks:
"JavaScript crypto has very real risk of side-channel attacks
Since JavaScript code doesn't control the instructions being executed by the CPU — the JavaScript engine can perform optimizations out of the code’s control — it creates the risk of security-sensitive information leaks.
End-To-End requires user interaction for private operations in normal use, mitigating this risk. Non-user-interaction actions are rate-limited and done in fixed time. End-To-End’s crypto operations are performed in a different process from the web apps it interacts with.
The End-To-End library is as timing-aware it can be and we’ve invested effort to mitigate any exploitable risk."