Negotiate ciphers before resumption.

This changes our resumption strategy. Before, we would negotiate ciphers
only on fresh handshakes. On resumption, we would blindly use whatever
was in the session.

Instead, evaluate cipher suite preferences on every handshake.
Resumption requires that the saved cipher suite match the one that would
have been negotiated anyway. If client or server preferences changed
sufficiently, we decline the session.

This is much easier to reason about (we always pick the best cipher
suite), simpler, and avoids getting stuck under old preferences if
tickets are continuously renewed. Notably, although TLS 1.2 ticket
renewal does not work in practice, TLS 1.3 will renew tickets like
there's no tomorrow.

It also means we don't need dedicated code to avoid resuming a cipher
which has since been disabled. (That dedicated code was a little odd
anyway since the mask_k, etc., checks didn't occur. When cert_cb was
skipped on resumption, one could resume without ever configuring a
certificate! So we couldn't know whether to mask off RSA or ECDSA cipher
suites.)

Add tests which assert on this new arrangement.

BUG=116

Change-Id: Id40d851ccd87e06c46c6ec272527fd8ece8abfc6
Reviewed-on: https://boringssl-review.googlesource.com/11847
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
6 files changed
tree: 4b793e5679eb928332f517a278af74a45df3cf0b
  1. .clang-format
  2. .github/
  3. .gitignore
  4. API-CONVENTIONS.md
  5. BUILDING.md
  6. CMakeLists.txt
  7. CONTRIBUTING.md
  8. FUZZING.md
  9. INCORPORATING.md
  10. LICENSE
  11. PORTING.md
  12. README.md
  13. STYLE.md
  14. codereview.settings
  15. crypto/
  16. decrepit/
  17. fuzz/
  18. include/
  19. infra/
  20. ssl/
  21. third_party/
  22. tool/
  23. util/
README.md

BoringSSL

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.

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