diff --git a/lib/include/chiaki/ecdh.h b/lib/include/chiaki/ecdh.h
index af9dc36..01e5c93 100644
--- a/lib/include/chiaki/ecdh.h
+++ b/lib/include/chiaki/ecdh.h
@@ -36,6 +36,7 @@ typedef struct chiaki_ecdh_t
 CHIAKI_EXPORT ChiakiErrorCode chiaki_ecdh_init(ChiakiECDH *ecdh);
 CHIAKI_EXPORT void chiaki_ecdh_fini(ChiakiECDH *ecdh);
 CHIAKI_EXPORT ChiakiErrorCode chiaki_ecdh_get_local_pub_key(ChiakiECDH *ecdh, uint8_t *key_out, size_t *key_out_size, uint8_t *handshake_key, uint8_t *sig_out, size_t *sig_out_size);
+CHIAKI_EXPORT ChiakiErrorCode chiaki_ecdh_derive_secret(ChiakiECDH *ecdh, uint8_t *remote_key, size_t remote_key_size, uint8_t *handshake_key, uint8_t *remote_sig, size_t remote_sig_size);
 
 #ifdef __cplusplus
 }
diff --git a/lib/src/ecdh.c b/lib/src/ecdh.c
index 9aca9ea..715dec1 100644
--- a/lib/src/ecdh.c
+++ b/lib/src/ecdh.c
@@ -65,5 +65,46 @@ CHIAKI_EXPORT ChiakiErrorCode chiaki_ecdh_get_local_pub_key(ChiakiECDH *ecdh, ui
 	if(!HMAC(EVP_sha256(), handshake_key, CHIAKI_HANDSHAKE_KEY_SIZE, key_out, *key_out_size, sig_out, (unsigned int *)sig_out_size))
 		return CHIAKI_ERR_UNKNOWN;
 
+	return CHIAKI_ERR_SUCCESS;
+}
+
+CHIAKI_EXPORT ChiakiErrorCode chiaki_ecdh_derive_secret(ChiakiECDH *ecdh, uint8_t *remote_key, size_t remote_key_size, uint8_t *handshake_key, uint8_t *remote_sig, size_t remote_sig_size)
+{
+	EC_POINT *point = EC_POINT_new(ecdh->group);
+	if(!point)
+		return CHIAKI_ERR_UNKNOWN;
+
+	if(!EC_POINT_oct2point(ecdh->group, point, remote_key, remote_key_size, NULL))
+	{
+		EC_POINT_free(point);
+		return CHIAKI_ERR_UNKNOWN;
+	}
+
+	EC_KEY *remote_ec_key = EC_KEY_new();
+	if(!remote_ec_key)
+	{
+		EC_POINT_free(point);
+		return CHIAKI_ERR_UNKNOWN;
+	}
+
+	if(!EC_KEY_set_group(remote_ec_key, ecdh->group))
+	{
+		EC_KEY_free(remote_ec_key);
+		EC_POINT_free(point);
+		return CHIAKI_ERR_UNKNOWN;
+	}
+
+	if(!EC_KEY_set_public_key(remote_ec_key, point))
+	{
+		EC_KEY_free(remote_ec_key);
+		EC_POINT_free(point);
+		return CHIAKI_ERR_UNKNOWN;
+	}
+	EC_POINT_free(point);
+
+	// TODO: do derivation
+
+	EC_KEY_free(remote_ec_key);
+
 	return CHIAKI_ERR_SUCCESS;
 }
\ No newline at end of file
diff --git a/lib/src/nagare.c b/lib/src/nagare.c
index a0b39e2..4e7a037 100644
--- a/lib/src/nagare.c
+++ b/lib/src/nagare.c
@@ -200,6 +200,11 @@ static void nagare_takion_data_expect_bang(ChiakiNagare *nagare, uint8_t *buf, s
 
 	CHIAKI_LOGI(nagare->log, "Nagare bang looks good so far\n");
 
+	chiaki_ecdh_derive_secret(&nagare->session->ecdh,
+			ecdh_pub_key_buf.buf, ecdh_pub_key_buf.size,
+			nagare->session->handshake_key,
+			ecdh_sig_buf.buf, ecdh_sig_buf.size);
+
 error:
 	chiaki_mirai_signal(&nagare->bang_mirai, true);
 }