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.
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.
EVP_PKEY_new() returns either the newly allocated EVP_PKEY structure of NULL if an error occurred.
EVP_PKEY_free() does not return a value.