If a client offers ECH, but the server rejects it, the client completes
the handshake with ClientHelloOuter in order to authenticate retry keys.
Implement this flow. This is largely allowing the existing handshake to
proceed, but with some changes:
- Certificate verification uses the other name. This CL routes this up to
the built-in verifier and adds SSL_get0_ech_name_override for the
callback.
- We need to disable False Start to pick up server Finished in TLS 1.2.
- Client certificates, notably in TLS 1.3 where they're encrypted,
should only be revealed to the true server. Fortunately, not sending
client certs is always an option, so do that.
Channel ID has a similar issue. I've just omitted the extension in
ClientHelloOuter because it's deprecated and is unlikely to be used
with ECH at this point. ALPS may be worth some pondering but, the way
it's currently used, is not sensitive.
(Possibly we should change the draft to terminate the handshake before
even sending that flight...)
- The session is never offered in ClientHelloOuter, but our internal
book-keeping doesn't quite notice.
I had to replace ech_accept with a tri-state ech_status to correctly
handle an edge case in SSL_get0_ech_name_override: when ECH + 0-RTT +
reverify_on_resume are all enabled, the first certificate verification
is for the 0-RTT session and should be against the true name, yet we
have selected_ech_config && !ech_accept. A tri-state tracks when ECH is
actually rejected. I've maintained this on the server as well, though
the server never actually cares.
Bug: 275
Change-Id: Ie55966ca3dc4ffcc8c381479f0fe9bcacd34d0f8
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/48135
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
The first thing any deployment will want to monitor is whether ECH was
actually used. Also it's useful if the command-line tool can output
this. (The alert is how the client signals it discarded the connection
due to ECH reject.)
This also disables ECH with the handoff mechanism for now. (The
immediate cause being that ech_accept isn't serialized.) We'll probably
need to make some decisions around the ordering here, since ECH affects
where the true ClientHello is available.
Bug: 275
Change-Id: Ie4559733290e653a514fcd94431090bf86bc3172
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/47911
Reviewed-by: Adam Langley <agl@google.com>
We didn't end up deploying this. We also never implemented the final
RFC, so what we do have isn't useful for someone who wishes to deploy
it anyway.
Update-Note: Token binding APIs are removed.
Change-Id: Iecea7c3dcf9d3e2644a3b7afaf61511310b45d5f
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/47584
Reviewed-by: Adam Langley <agl@google.com>
These APIs were used by Chromium to control the carve-out for the TLS
1.3 downgrade signal. As of
https://chromium-review.googlesource.com/c/chromium/src/+/2324170,
Chromium no longer uses them.
Update-Note: SSL_CTX_set_ignore_tls13_downgrade,
SSL_set_ignore_tls13_downgrade, and SSL_is_tls13_downgrade now do
nothing. Calls sites should be removed. (There are some copies of older
Chromium lying around, so I haven't removed the functions yet.) The
enforcement was already on by default, so this CL does not affect
callers that don't use those functions.
Change-Id: I016af8291cd92051472d239c4650602fe2a68f5b
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/44124
Reviewed-by: Adam Langley <agl@google.com>
David Benjamin
Adam Langley