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 (tracking bug)

Consensus & Standardization

After a feature ships in Chrome, the values listed here are not guaranteed to be up to date.

  • No signal
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Search tags

tls, ssl, grease,

Last updated on 2020-11-09