Make client public key verification optional

bukkit/src/main/java/com/github/games647/fastlogin/bukkit/BukkitLoginSession.java

@@ -32,6 +32,8 @@ import com.github.games647.fastlogin.core.shared.LoginSession;
 
 import java.util.Optional;
 
+import javax.annotation.Nullable;
+
 /**
  * Represents a client connecting to the server.
  *
@@ -83,6 +85,7 @@ public class BukkitLoginSession extends LoginSession {
         return verifyToken.clone();
     }
 
+    @Nullable
     public ClientPublicKey getClientPublicKey() {
         return clientPublicKey;
     }

bukkit/src/main/java/com/github/games647/fastlogin/bukkit/FastLoginBukkit.java

@@ -117,7 +117,7 @@ public class FastLoginBukkit extends JavaPlugin implements PlatformPlugin<Comman
             if (pluginManager.isPluginEnabled("ProtocolSupport")) {
                 pluginManager.registerEvents(new ProtocolSupportListener(this, core.getAntiBot()), this);
             } else if (pluginManager.isPluginEnabled("ProtocolLib")) {
-                ProtocolLibListener.register(this, core.getAntiBot());
+                ProtocolLibListener.register(this, core.getAntiBot(), core.getConfig().getBoolean("verifyClientKeys"));
 
                 if (isPluginInstalled("floodgate")) {
                     if (getConfig().getBoolean("floodgatePrefixWorkaround")){

bukkit/src/main/java/com/github/games647/fastlogin/bukkit/listener/protocollib/NameCheckTask.java

@@ -27,8 +27,6 @@ package com.github.games647.fastlogin.bukkit.listener.protocollib;
 
 import com.comphenix.protocol.ProtocolLibrary;
 import com.comphenix.protocol.events.PacketEvent;
-import com.comphenix.protocol.wrappers.BukkitConverters;
-import com.comphenix.protocol.wrappers.WrappedProfilePublicKey.WrappedProfileKeyData;
 import com.github.games647.fastlogin.bukkit.BukkitLoginSession;
 import com.github.games647.fastlogin.bukkit.FastLoginBukkit;
 import com.github.games647.fastlogin.bukkit.event.BukkitFastLoginPreLoginEvent;
@@ -38,7 +36,6 @@ import com.github.games647.fastlogin.core.shared.JoinManagement;
 import com.github.games647.fastlogin.core.shared.event.FastLoginPreLoginEvent;
 
 import java.security.PublicKey;
-import java.util.Optional;
 import java.util.Random;
 
 import org.bukkit.command.CommandSender;
@@ -49,6 +46,8 @@ public class NameCheckTask extends JoinManagement<Player, CommandSender, Protoco
 
     private final FastLoginBukkit plugin;
     private final PacketEvent packetEvent;
+
+    private final ClientPublicKey clientKey;
     private final PublicKey serverKey;
 
     private final Random random;
@@ -57,11 +56,12 @@ public class NameCheckTask extends JoinManagement<Player, CommandSender, Protoco
     private final String username;
 
     public NameCheckTask(FastLoginBukkit plugin, Random random, Player player, PacketEvent packetEvent,
-                         String username, PublicKey serverKey) {
+                         String username, ClientPublicKey clientKey, PublicKey serverKey) {
         super(plugin.getCore(), plugin.getCore().getAuthPluginHook(), plugin.getBedrockService());
 
         this.plugin = plugin;
         this.packetEvent = packetEvent;
+        this.clientKey = clientKey;
         this.serverKey = serverKey;
         this.random = random;
         this.player = player;
@@ -71,10 +71,7 @@ public class NameCheckTask extends JoinManagement<Player, CommandSender, Protoco
     @Override
     public void run() {
         try {
-            Optional<WrappedProfileKeyData> clientKey = packetEvent.getPacket()
+            super.onLogin(username, new ProtocolLibLoginSource(player, random, serverKey, clientKey));
-                .getOptionals(BukkitConverters.getWrappedPublicKeyDataConverter()).read(0);
-
-            super.onLogin(username, new ProtocolLibLoginSource(player, random, serverKey, clientKey.orElse(null)));
         } finally {
             ProtocolLibrary.getProtocolManager().getAsynchronousManager().signalPacketTransmission(packetEvent);
         }
@@ -104,8 +101,7 @@ public class NameCheckTask extends JoinManagement<Player, CommandSender, Protoco
         core.getPendingLogin().put(ip + username, new Object());
 
         byte[] verify = source.getVerifyToken();
-        WrappedProfileKeyData key = source.getClientPublicKey();
+        ClientPublicKey clientKey = source.getClientKey();
-        ClientPublicKey clientKey = new ClientPublicKey(key.getExpireTime(), key.getKey(), key.getSignature());
 
         BukkitLoginSession playerSession = new BukkitLoginSession(username, verify, clientKey, registered, profile);
         plugin.putSession(player.getAddress(), playerSession);

bukkit/src/main/java/com/github/games647/fastlogin/bukkit/listener/protocollib/ProtocolLibListener.java

@@ -49,6 +49,7 @@ import java.security.PublicKey;
 import java.security.SecureRandom;
 import java.security.SignatureException;
 import java.time.Instant;
+import java.util.Optional;
 
 import org.bukkit.entity.Player;
 
@@ -66,7 +67,9 @@ public class ProtocolLibListener extends PacketAdapter {
     private final KeyPair keyPair = EncryptionUtil.generateKeyPair();
     private final AntiBotService antiBotService;
 
-    public ProtocolLibListener(FastLoginBukkit plugin, AntiBotService antiBotService) {
+    private final boolean verifyClientKeys;
+
+    public ProtocolLibListener(FastLoginBukkit plugin, AntiBotService antiBotService, boolean verifyClientKeys) {
         //run async in order to not block the server, because we are making api calls to Mojang
         super(params()
                 .plugin(plugin)
@@ -75,14 +78,15 @@ public class ProtocolLibListener extends PacketAdapter {
 
         this.plugin = plugin;
         this.antiBotService = antiBotService;
+        this.verifyClientKeys = verifyClientKeys;
     }
 
-    public static void register(FastLoginBukkit plugin, AntiBotService antiBotService) {
+    public static void register(FastLoginBukkit plugin, AntiBotService antiBotService, boolean verifyClientKeys) {
         // they will be created with a static builder, because otherwise it will throw a NoClassDefFoundError
         // TODO: make synchronous processing, but do web or database requests async
         ProtocolLibrary.getProtocolManager()
                 .getAsynchronousManager()
-                .registerAsyncHandler(new ProtocolLibListener(plugin, antiBotService))
+                .registerAsyncHandler(new ProtocolLibListener(plugin, antiBotService, verifyClientKeys))
                 .start();
     }
 
@@ -141,6 +145,13 @@ public class ProtocolLibListener extends PacketAdapter {
             plugin.getLog().warn("GameProfile {} tried to send encryption response at invalid state", sender.getAddress());
             sender.kickPlayer(plugin.getCore().getMessage("invalid-request"));
         } else {
+            if (session.getClientPublicKey() == null) {
+                // we cannot verify the signature if no public was provided
+                plugin.getLog().error("No public key provided for signed nonce {}", sender);
+                sender.kickPlayer(plugin.getCore().getMessage("invalid-verify-token"));
+                return;
+            }
+
             Either<byte[], ?> either = packetEvent.getPacket().getSpecificModifier(Either.class).read(0);
             Object signatureData = either.right().get();
             long salt = FuzzyReflection.getFieldValue(signatureData, Long.TYPE, true);
@@ -176,9 +187,13 @@ public class ProtocolLibListener extends PacketAdapter {
         }
 
         PacketContainer packet = packetEvent.getPacket();
-        WrappedProfileKeyData profileKey = packet.getOptionals(BukkitConverters.getWrappedPublicKeyDataConverter())
+        var profileKey = packet.getOptionals(BukkitConverters.getWrappedPublicKeyDataConverter())
-            .read(0).orElse(null);
+            .read(0);
-        if (profileKey != null && !verifyPublicKey(profileKey)) {
+
+        var clientKey = profileKey.flatMap(this::verifyPublicKey);
+        if (verifyClientKeys && !clientKey.isPresent()) {
+            // missing or incorrect
+            // expired always not allowed
             player.kickPlayer(plugin.getCore().getMessage("invalid-public-key"));
             plugin.getLog().warn("Invalid public key from player {}", username);
             return;
@@ -187,20 +202,24 @@ public class ProtocolLibListener extends PacketAdapter {
         plugin.getLog().trace("GameProfile {} with {} connecting", sessionKey, username);
 
         packetEvent.getAsyncMarker().incrementProcessingDelay();
-        Runnable nameCheckTask = new NameCheckTask(plugin, random, player, packetEvent, username, keyPair.getPublic());
+        Runnable nameCheckTask = new NameCheckTask(plugin, random, player, packetEvent, username, clientKey.orElse(null), keyPair.getPublic());
         plugin.getScheduler().runAsync(nameCheckTask);
     }
 
-    private boolean verifyPublicKey(WrappedProfileKeyData profileKey) {
+    private Optional<ClientPublicKey> verifyPublicKey(WrappedProfileKeyData profileKey) {
         Instant expires = profileKey.getExpireTime();
         PublicKey key = profileKey.getKey();
         byte[] signature = profileKey.getSignature();
         ClientPublicKey clientKey = new ClientPublicKey(expires, key, signature);
         try {
-            return EncryptionUtil.verifyClientKey(clientKey, Instant.now());
+            if (EncryptionUtil.verifyClientKey(clientKey, Instant.now())) {
+                return Optional.of(clientKey);
+            }
         } catch (SignatureException | InvalidKeyException | NoSuchAlgorithmException ex) {
-            return false;
+            return Optional.empty();
         }
+
+        return Optional.empty();
     }
 
     private String getUsername(PacketContainer packet) {

bukkit/src/main/java/com/github/games647/fastlogin/bukkit/listener/protocollib/ProtocolLibLoginSource.java

@@ -30,7 +30,7 @@ import com.comphenix.protocol.ProtocolManager;
 import com.comphenix.protocol.events.PacketContainer;
 import com.comphenix.protocol.reflect.StructureModifier;
 import com.comphenix.protocol.wrappers.WrappedChatComponent;
-import com.comphenix.protocol.wrappers.WrappedProfilePublicKey.WrappedProfileKeyData;
+import com.github.games647.fastlogin.bukkit.listener.protocollib.packet.ClientPublicKey;
 import com.github.games647.fastlogin.core.shared.LoginSource;
 
 import java.net.InetSocketAddress;
@@ -49,17 +49,17 @@ class ProtocolLibLoginSource implements LoginSource {
 
     private final Random random;
 
-    private final WrappedProfileKeyData clientPublicKey;
+    private final ClientPublicKey clientKey;
     private final PublicKey publicKey;
 
     private final String serverId = "";
     private byte[] verifyToken;
 
-    public ProtocolLibLoginSource(Player player, Random random, PublicKey serverPublicKey, WrappedProfileKeyData clientPublicKey) {
+    public ProtocolLibLoginSource(Player player, Random random, PublicKey serverPublicKey, ClientPublicKey clientKey) {
         this.player = player;
         this.random = random;
         this.publicKey = serverPublicKey;
-        this.clientPublicKey = clientPublicKey;
+        this.clientKey = clientKey;
     }
 
     @Override
@@ -112,8 +112,8 @@ class ProtocolLibLoginSource implements LoginSource {
         return player.getAddress();
     }
 
-    public WrappedProfileKeyData getClientPublicKey() {
+    public ClientPublicKey getClientKey() {
-        return clientPublicKey;
+        return clientKey;
     }
 
     public String getServerId() {

bukkit/src/main/java/com/github/games647/fastlogin/bukkit/listener/protocollib/VerifyResponseTask.java

@@ -263,7 +263,7 @@ public class VerifyResponseTask implements Runnable {
 
             EquivalentConverter<WrappedProfileKeyData> converter = BukkitConverters.getWrappedPublicKeyDataConverter();
             var key = new WrappedProfileKeyData(clientKey.expiry(), clientKey.key(), sharedSecret);
-            startPacket.getOptionals(converter).write(0, Optional.of(key));
+            startPacket.getOptionals(converter).write(0, Optional.ofNullable(key));
         } else {
             //uuid is ignored by the packet definition
             WrappedGameProfile fakeProfile = new WrappedGameProfile(UUID.randomUUID(), username);

core/src/main/resources/config.yml

@@ -272,6 +272,15 @@ autoRegisterFloodgate: false
 # Enabling this might lead to people gaining unauthorized access to other's accounts!
 floodgatePrefixWorkaround: false
 
+# This option resembles the vanilla configuration option 'enforce-secure-profile' in the 'server.properties' file.
+# It verifies if the incoming cryptographic key in the login request from the player is signed by Mojang. This key
+# is necessary for servers where you or other in-game players want to verify that a chat message sent and signed by
+# this player is not modified by any third-party. Modifications by your server would also invalidate the message.
+#
+# This feature is only relevant if you use the plugin in ProtocolLib mode. This also the case if you don't have any
+# proxies in use.
+verifyClientKeys: true
+
 # Database configuration
 # Recommended is the use of MariaDB (a better version of MySQL)