Breaking change to the kx_kk_3() API

Last DH should be `se`, not `es`.

Fixes #32

hydrogen.h

@@ -219,7 +219,7 @@ int hydro_kx_kk_2(hydro_kx_session_keypair *kp, uint8_t packet2[hydro_kx_KK_PACK
 
 int hydro_kx_kk_3(hydro_kx_state *state, hydro_kx_session_keypair *kp,
                   const uint8_t packet2[hydro_kx_KK_PACKET2BYTES],
-                  const uint8_t peer_static_pk[hydro_kx_PUBLICKEYBYTES]);
+                  const hydro_kx_keypair *static_kp);
 
 /* NOISE_XX */
 

impl/kx.h

@@ -306,7 +306,7 @@ hydro_kx_kk_2(hydro_kx_session_keypair *kp, uint8_t packet2[hydro_kx_KK_PACKET2B
     if (hydro_kx_scalarmult(&state, dh_res, state.eph_kp.sk, peer_eph_pk) != 0) {
         return -1;
     }
-    if (hydro_kx_scalarmult(&state, dh_res, static_kp->sk, peer_eph_pk) != 0) {
+    if (hydro_kx_scalarmult(&state, dh_res, state.eph_kp.sk, peer_static_pk) != 0) {
         return -1;
     }
     hydro_kx_final(&state, kp->rx, kp->tx);
@@ -317,7 +317,7 @@ hydro_kx_kk_2(hydro_kx_session_keypair *kp, uint8_t packet2[hydro_kx_KK_PACKET2B
 int
 hydro_kx_kk_3(hydro_kx_state *state, hydro_kx_session_keypair *kp,
               const uint8_t packet2[hydro_kx_KK_PACKET2BYTES],
-              const uint8_t peer_static_pk[hydro_kx_PUBLICKEYBYTES])
+              const hydro_kx_keypair *static_kp)
 {
     uint8_t        dh_res[hydro_x25519_BYTES];
     const uint8_t *peer_eph_pk = packet2;
@@ -325,7 +325,7 @@ hydro_kx_kk_3(hydro_kx_state *state, hydro_kx_session_keypair *kp,
     if (hydro_kx_scalarmult(state, dh_res, state->eph_kp.sk, peer_eph_pk) != 0) {
         return -1;
     }
-    if (hydro_kx_scalarmult(state, dh_res, state->eph_kp.sk, peer_static_pk) != 0) {
+    if (hydro_kx_scalarmult(state, dh_res, static_kp->sk, peer_eph_pk) != 0) {
         return -1;
     }
     hydro_kx_final(state, kp->tx, kp->rx);

tests/tests.c

@@ -314,7 +314,7 @@ test_kx_kk(void)
 
     hydro_kx_kk_1(&st_client, packet1, server_static_kp.pk, &client_static_kp);
     hydro_kx_kk_2(&kp_server, packet2, packet1, client_static_kp.pk, &server_static_kp);
-    hydro_kx_kk_3(&st_client, &kp_client, packet2, server_static_kp.pk);
+    hydro_kx_kk_3(&st_client, &kp_client, packet2, &client_static_kp);
 
     assert(hydro_equal(kp_client.tx, kp_server.rx, hydro_kx_SESSIONKEYBYTES));
     assert(hydro_equal(kp_client.rx, kp_server.tx, hydro_kx_SESSIONKEYBYTES));