Re: wget2 | OpenSSL OCSP: Do not contact OCSP responder if stapled OCSP response is available (#578)

[Ander Juaristi (@juaristi)]

Ander Juaristi commented:


Hi @rockdaboot Thanks for bringing this up. I was totally aware of this and 
even tried to fix it one day, but couldn't.

We currently contact OCSP responders on the certificate callback: 
`X509_STORE_CTX_set_verify_cb`. And the stapled OCSP is of course checked at 
the stapled OCSP callback: `SSL_CTX_set_tlsext_status_cb`. The problem is that 
for most servers the `Certificate` message comes before the `CertificateStatus` 
message (this is the stapled OCSP), and OpenSSL calls the callbacks as it sees 
the messages. Hence, the certificate callback gets called before the stapled 
OCSP callback, and that causes the OCSP requests to be sent.

I have always thought the whole cert chain should be completely validated 
before the handshake finishes (read: before `SSL_do_handshake` returns). So 
ideally, we should contact OCSP at some point after the `Certificate` and 
`CertificateStatus` have been processed (at this point we should also know the 
whole cert chain), but before the handshake is finished. I remember one day I 
was looking at other hooks in OpenSSL that would allow me to inject my code 
somewhere at that point, but unfortunately found none. If what I'm thinking 
can't be reliably done, I guess we should just wait for the handshake to 
complete normally, then check OCSP (if needed), and close the connection if we 
can't verify.

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