The RSA e (exponent) and n (modulus) parameters are initially backed by the rsa_e and rsa_n fields. These fields are then used to instantiate the internal privateKey and publicKey objects in generatePrivateKeyIfParams() and generatePublicKeyIfParams(). However, both rsa_e and rsa_n are set to null after use. This means that once either of the private or public keys has been created, the other cannot be. Consequently, the RSA object can only be used for private or public functions, but not for both.

For example:

orig = OpenSSL::PKey::RSA.generate(2048)
copy = OpenSSL::PKey::RSA.new
[:e, :n, :d, :p, :q, :iqmp, :dmp1, :dmq1].each do |param|
  copy.send("#{param}=", orig.send(param))
end

# e and n were set first, copy will now act only as a public key

# public_encrypt will succeed
copy.public_encrypt('Test')

# private_encrypt will fail with an 'OpenSSL::PKey::RSAError: private key needed' exception
copy.private_encrypt('Test')

When the above code is run using the MRI standard library, both the public_encrypt and private_encrypt calls succeed.

This pull request modifies generatePrivateKeyIfParams() and generatePublicKeyIfParams() so that they will obtain the e and n parameters from either privateKey or publicKey if rsa_e and rsa_n have already been consumed.