The EVP_PKEY_new() function allocates an empty EVP_PKEY
structure which is used by OpenSSL to store private keys.
EVP_PKEY_free() frees up the private key key.
NOTES
The EVP_PKEY structure is used by various OpenSSL functions
which require a general private key without reference to any
particular algorithm.
The structure returned by EVP_PKEY_new() is empty. To add a
private key to this empty structure the functions described in
EVP_PKEY_set1_RSA(3) should be used.
RETURN VALUES
EVP_PKEY_new() returns either the newly allocated EVP_PKEY
structure of NULL if an error occurred.