[ech] custom TLS client hello extensions

Stephen Farrell stephen.farrell at cs.tcd.ie
Thu Mar 2 01:25:07 UTC 2023


One of the outstanding things I need to figure out for
ECH is how (or whether) to handle custom extensions [1]
for client hello messages. So far, I've done basically
nothing about those but at least considering it seems
like a thing that needs doing.

So - does anyone have a pointer to an example of code
that uses such extensions? That'd help me try figure out
how to handle 'em with ECH, if that turns out to be
needed. (Or to at least test that I'm not breaking


[1] https://www.openssl.org/docs/manmaster/man3/SSL_CTX_add_custom_ext.html
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