Unlike the PKey::DSA and PKey::RSA classes, PKey::EC provides a private_key?() rather than private?() method and is thus incompatible with the other OpenSSL classes that rely on them, i.e. it makes impossible to generate a certificate signing request:
Unfortunately it's not done by simply renaming the methods appropriately. It still would fail because OpenSSL::PKey::EC#public_key returns an OpenSSL::PKey::EC::Point instead of another OpenSSL::PKey::EC, and as a consequence, there's no reference to an EVP_PKEY that is needed internally. The whole EC interface needs an overhaul. I'll set up a parent task referencing all the issues that piled up since the release of 1.9.3. The goal would be to make EC follow the general PKey interface, allowing to use them interchangeably wherever a PKey instance is expected.