Older Versions and Platforms

* What does "old" mean here?

Any OpenSSL release before 1.0.2, and any platform that is not in wide use,
and doesn't get full support.  Or something like that.

* Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?

For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier
versions, uniqueIdentifier was incorrectly used for X.509 certificates.
The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier.
Change your code to use the new name when compiling against OpenSSL 0.9.7.