Add packet session key identifiers

tests/protocol_auth.rs

@@ -50,10 +50,33 @@ fn encrypted_packet_round_trips() {
     let decoded = protocol::decode(&packet).unwrap();
     assert_eq!(decoded.header.kind, PacketKind::Input);
     assert_eq!(decoded.header.conn_id, conn_id);
+    assert_eq!(
+        decoded.header.session_key_id,
+        protocol::session_key_id(&key)
+    );
     let plain = protocol::decrypt_body(&decoded, &key, CLIENT_TO_SERVER).unwrap();
     assert_eq!(plain, b"hello");
 }
 
+#[test]
+fn encrypted_packet_rejects_wrong_session_key_id_before_decrypt() {
+    let key = crypto::random_32();
+    let wrong_key = crypto::random_32();
+    let packet = protocol::encode_encrypted(
+        PacketKind::Input,
+        crypto::random_16(),
+        1,
+        0,
+        &key,
+        CLIENT_TO_SERVER,
+        b"hello",
+    )
+    .unwrap();
+    let decoded = protocol::decode(&packet).unwrap();
+    let err = protocol::decrypt_body(&decoded, &wrong_key, CLIENT_TO_SERVER).unwrap_err();
+    assert!(err.to_string().contains("session key id"));
+}
+
 #[test]
 fn attach_ticket_is_sealed_and_verifies_scope() {
     let dir = tempfile::tempdir().unwrap();