int ec_key_gen(unsigned char* pub_key_x, unsigned char* pub_key_y, unsigned char* priv_key);
unsigned long check_key(unsigned char* given_key_x, unsigned char* given_key_y);
unsigned long compute_shared_ECDHE_key(unsigned char* given_key_x, unsigned char* given_key_y, unsigned char* priv_key, unsigned char* shared_key, unsigned char* derived_key);
int generate_sha256_hash(const unsigned char *message, size_t message_len, unsigned char *digest);
int aes_gcm(int enc, unsigned char *key, unsigned char *iv, unsigned char* plaintext, int plaintext_len, unsigned char *ciphertext,  int* op_ciphertext_len, unsigned char* tag);