Check the second ClientHello's PSK binder on resumption.

We perform all our negotiation based on the first ClientHello (for
consistency with what |select_certificate_cb| observed), which is in the
transcript, so we can ignore most of the second one.

However, we ought to check the second PSK binder. That covers the client
key share, which we do consume. In particular, we'll want to check if it
we ever send half-RTT data on these connections (we do not currently do
this). It is also a tricky computation, so we enforce the peer handled
it correctly.

Tested that both Chrome and Firefox continue to interop with this check,
when configuring uncommon curve preferences that trigger HRR. (Normally
neither browser sees HRRs against BoringSSL servers.)

Update-Note: This does enforce some client behavior that we hadn't been
    enforcing previously. However, it only figures into TLS 1.3 (not many
    implementations yet), and only clients which hit HelloRetryRequest
    (rare), so this should be low risk.
Change-Id: I42126585ec0685d009542094192e674cbd22520d
Commit-Queue: David Benjamin <>
Reviewed-by: Steven Valdez <>
11 files changed
tree: 7e37a34a4e807a098687a1bf8020a4f57b2990f8
  1. .clang-format
  2. .github/
  3. .gitignore
  7. CMakeLists.txt
  15. codereview.settings
  16. crypto/
  17. decrepit/
  18. fuzz/
  19. go.mod
  20. include/
  21. sources.cmake
  22. ssl/
  23. third_party/
  24. tool/
  25. util/


BoringSSL is a fork of OpenSSL that is designed to meet Google's needs.

Although BoringSSL is an open source project, it is not intended for general use, as OpenSSL is. We don't recommend that third parties depend upon it. Doing so is likely to be frustrating because there are no guarantees of API or ABI stability.

Programs ship their own copies of BoringSSL when they use it and we update everything as needed when deciding to make API changes. This allows us to mostly avoid compromises in the name of compatibility. It works for us, but it may not work for you.

BoringSSL arose because Google used OpenSSL for many years in various ways and, over time, built up a large number of patches that were maintained while tracking upstream OpenSSL. As Google's product portfolio became more complex, more copies of OpenSSL sprung up and the effort involved in maintaining all these patches in multiple places was growing steadily.

Currently BoringSSL is the SSL library in Chrome/Chromium, Android (but it's not part of the NDK) and a number of other apps/programs.

Project links:

There are other files in this directory which might be helpful: