How we built it


TLS clients offer lists of 16-bit code points (e.g. cipher suites) that servers select from. To remain extensible, servers must ignore unknown values. However, servers may have bugs and reject unknown values. These servers will interoperate with existing clients, so the mistake may spread unnoticed, breaking extensibility for the whole ecosystem. We will reserve some values to advertise at random, to prevent such mistakes before broken servers are widespread.

Status in Chromium

Enabled by default (launch bug) in:

  • Chrome for desktop release 55
  • Opera release 42
  • Opera for Android release 42

Consensus & Standardization

  • No public signals
  • No public signals
  • No public signals
  • No signals


Last updated on 2016-09-19