This flag is set when an ASN1_STRING is created from a codepath that is
aware it is an "mstring" (CHOICE of multiple string or string-like
types). With setters like X509_set_notBefore, it is very easy to
accidentally lose the flag on some field that normally has it.

The only place the flag is checked is X509_time_adj_ex. X509_time_adj_ex
usually transparently picks UTCTime vs GeneralizedTime, as in the X.509
CHOICE type. But if writing to an existing object AND if the object
lacks the flag, it will lock to whichever type the object was
previously. It is likely any caller hitting this codepath is doing so
unintentionally and has a latent bug that won't trip until 2050.

In fact, one of the ways callers might accidentally lose the
ASN1_STRING_FLAG_MSTRING flag is by using X509_time_adj_ex!
X509_time_adj_ex(NULL) does not use an mstring-aware constructor. This
CL avoids needing such a notion in the first place.

Looking through callers, the one place that wants the old behavior is a
call site within OpenSSL, to set the producedAt field in OCSP. That
field is a GeneralizedTime, rather than a UTCTime/GeneralizedTime
CHOICE. We dropped that code, but I'm making a note of it to remember
when filing upstream.

Update-Note: ASN1_STRING_FLAG_MSTRING is no longer defined and
X509_time_adj_ex now behaves more predictably. Callers that actually
wanted to lock to a specific type should call ASN1_UTCTIME_adj or

Change-Id: Ib9e1c9dbd0c694e1e69f938da3992d1ffc9bd060
Commit-Queue: David Benjamin <>
Reviewed-by: Adam Langley <>
4 files changed
tree: bfa6e142fddf0133279cddf0b3b1a4dbbf2031e9
  1. .github/
  2. crypto/
  3. decrepit/
  4. fuzz/
  5. include/
  6. ssl/
  7. third_party/
  8. tool/
  9. util/
  10. .clang-format
  11. .gitignore
  15. CMakeLists.txt
  16. codereview.settings
  19. go.mod
  20. go.sum
  26. sources.cmake


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: