[ech] custom TLS client hello extensions

Matt Caswell matt at openssl.org
Thu Mar 2 10:34:26 UTC 2023

On 02/03/2023 01:25, Stephen Farrell wrote:
> Hiya,
> 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
> stuff:-)

Well there are some tests of the custom extensions code here:


The "serverinfo" code also uses custom extensions internally, so this 
test is also relevant:


The QUIC transport parameters are also implemented via custom extensions 
- but this uses some internal APIs to do it so I'm not sure how easy it 
would be to isolate this code:



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