EVP_PKEY_set1_RSA(), EVP_PKEY_set1_DSA(), EVP_PKEY_set1_DH() and EVP_PKEY_set1_EC_KEY() set the key referenced by pkey to key.EVP_PKEY_get1_RSA(), EVP_PKEY_get1_DSA(), EVP_PKEY_get1_DH() and EVP_PKEY_get1_EC_KEY() return the referenced key in pkey or NULL if the key is not of the correct type.
EVP_PKEY_assign_RSA() EVP_PKEY_assign_DSA(), EVP_PKEY_assign_DH() and EVP_PKEY_assign_EC_KEY() also set the referenced key to key however these use the supplied key internally and so key will be freed when the parent pkey is freed.
EVP_PKEY_type() returns the type of key corresponding to the value type. The type of a key can be obtained with EVP_PKEY_type(pkey->type). The return value will be EVP_PKEY_RSA, EVP_PKEY_DSA, EVP_PKEY_DH or EVP_PKEY_EC for the corresponding key types or NID_undef if the key type is unassigned.