The manpage for RSA_sign() says about the type parameter:
typedenotes the message digest algorithm that was used to generatem. It usually is one ofNID_sha1,NID_ripemd160andNID_md5; see objects(3) for details.
I included the headers as suggested, but my IDE claims there are no variables starting with NID_ and I couldn't find the objects manpage anywhere on the internet.
What am I missing?
Apparently the objects manpage has never been written. Here's the bug report from whoopin' 2007.
As Dan Grossman helpfully pointed out, the objects manpage would document objects.h; including either that, or engine.h as the RSA manpage suggests, fixed the problem.