libcrypto is part of OpenSSL which is famous for not maintaining ABI compatibility across versions and generally you should be using the most recent version of OpenSSL.  Depending what and where you have your copy installed, it's also possible the build picked up the wrong set of include files for that version of libcrypto and libssl.  You may be able to see that in the output of the build of _ssl.so.  Python's top-level setup.py file contains the code that tries to find the include files and lib files for various extension modules; for _ssl.so, see setup.py:810 and beyond.  Apple has deprecated the use of the system-supplied OpenSSL libraries and, in 10.11, the include files for OpenSSL are no longer included in Xcode or the Command Line Tools so you need to use a third-party copy of OpenSSL anyway.  If you aren't using a MacPorts or Homebrew, you can adapt the recipes in the Developer's Guide as necessary.  (Or you could use a pre-built Python 3.5, like that downloadable from python.org or MacPorts or Homebrew).