diff --git a/LaunchServer/source/auth/handler/CachedAuthHandler.java b/LaunchServer/source/auth/handler/CachedAuthHandler.java
index 6e40b38..2aa40d3 100644
--- a/LaunchServer/source/auth/handler/CachedAuthHandler.java
+++ b/LaunchServer/source/auth/handler/CachedAuthHandler.java
@@ -25,7 +25,7 @@
 	@Override
 	public final synchronized UUID auth(String username, String accessToken) throws IOException {
 		Entry entry = getEntry(username);
-		if (entry == null || !updateAuth(entry.uuid, username, accessToken)) {
+		if (entry == null || !updateAuth(entry.uuid, entry.username, accessToken)) {
 			return null; // Account doesn't exist
 		}
 
diff --git a/LaunchServer/source/auth/handler/FileAuthHandler.java b/LaunchServer/source/auth/handler/FileAuthHandler.java
index 98fd59f..05e4908 100644
--- a/LaunchServer/source/auth/handler/FileAuthHandler.java
+++ b/LaunchServer/source/auth/handler/FileAuthHandler.java
@@ -27,7 +27,7 @@
 
 public abstract class FileAuthHandler extends AuthHandler {
 	@LauncherAPI public final Path file;
-	@LauncherAPI public final boolean md5UUIDs;
+	@LauncherAPI public final boolean offlineUUIDs;
 
 	// Instance
 	private final SecureRandom random = SecurityHelper.newRandom();
@@ -41,7 +41,9 @@
 	protected FileAuthHandler(BlockConfigEntry block) {
 		super(block);
 		file = IOHelper.toPath(block.getEntryValue("file", StringConfigEntry.class));
-		md5UUIDs = block.getEntryValue("md5UUIDs", BooleanConfigEntry.class);
+		offlineUUIDs = block.getEntryValue("offlineUUIDs", BooleanConfigEntry.class);
+
+		// Read auth handler file
 		if (IOHelper.isFile(file)) {
 			LogHelper.info("Reading auth handler file");
 			try {
@@ -162,12 +164,12 @@
 	protected abstract void writeAuthFile() throws IOException;
 
 	private UUID genUUIDFor(String username) {
-		if (md5UUIDs) {
+		if (offlineUUIDs) {
 			UUID md5UUID = PlayerProfile.md5UUID(username);
 			if (!authsMap.containsKey(md5UUID)) {
 				return md5UUID;
 			}
-			LogHelper.warning("MD5 UUID has been already registered, using random: '%s'", username);
+			LogHelper.warning("Offline UUID collision, using random: '%s'", username);
 		}
 
 		// Pick random UUID
diff --git a/Launcher/source/Launcher.java b/Launcher/source/Launcher.java
index da1b3f8..6738903 100644
--- a/Launcher/source/Launcher.java
+++ b/Launcher/source/Launcher.java
@@ -262,13 +262,15 @@
 		@LauncherAPI public final RSAPublicKey publicKey;
 		@LauncherAPI public final Map<String, byte[]> runtime;
 
+		@LauncherAPI
 		@SuppressWarnings("AssignmentToCollectionOrArrayFieldFromParameter")
 		public Config(String address, int port, RSAPublicKey publicKey, Map<String, byte[]> runtime) {
 			this.address = InetSocketAddress.createUnresolved(address, port);
-			this.publicKey = publicKey;
-			this.runtime = runtime;
+			this.publicKey = Objects.requireNonNull(publicKey, "publicKey");
+			this.runtime = Collections.unmodifiableMap(new HashMap<>(runtime));
 		}
 
+		@LauncherAPI
 		public Config(HInput input) throws IOException, InvalidKeySpecException {
 			String localAddress = input.readASCII(255);
 			address = InetSocketAddress.createUnresolved(
diff --git a/Launcher/source/client/ClientLauncher.java b/Launcher/source/client/ClientLauncher.java
index 562ca51..885cfd4 100644
--- a/Launcher/source/client/ClientLauncher.java
+++ b/Launcher/source/client/ClientLauncher.java
@@ -307,7 +307,7 @@
 
 			// Client params
 			this.pp = pp;
-			this.accessToken = accessToken;
+			this.accessToken = SecurityHelper.verifyToken(accessToken);
 			this.autoEnter = autoEnter;
 			this.fullScreen = fullScreen;
 			this.ram = ram;
diff --git a/Launcher/source/client/PlayerProfile.java b/Launcher/source/client/PlayerProfile.java
index 95e6794..a8d6bd9 100644
--- a/Launcher/source/client/PlayerProfile.java
+++ b/Launcher/source/client/PlayerProfile.java
@@ -1,6 +1,7 @@
 package launcher.client;
 
 import java.io.IOException;
+import java.util.Objects;
 import java.util.UUID;
 
 import launcher.LauncherAPI;
@@ -31,10 +32,10 @@
 
 	@LauncherAPI
 	public PlayerProfile(UUID uuid, String username, String skinURL, String cloakURL) {
-		this.uuid = uuid;
-		this.username = username;
-		this.skinURL = skinURL;
-		this.cloakURL = cloakURL;
+		this.uuid = Objects.requireNonNull(uuid, "uuid");
+		this.username = VerifyHelper.verifyUsername(username);
+		this.skinURL = skinURL == null ? null : IOHelper.verifyURL(skinURL);
+		this.cloakURL = cloakURL == null ? null : IOHelper.verifyURL(cloakURL);
 	}
 
 	@Override
diff --git a/Launcher/source/hasher/DirWatcher.java b/Launcher/source/hasher/DirWatcher.java
index 32ae5a7..d165135 100644
--- a/Launcher/source/hasher/DirWatcher.java
+++ b/Launcher/source/hasher/DirWatcher.java
@@ -13,6 +13,7 @@
 import java.util.Collection;
 import java.util.Deque;
 import java.util.LinkedList;
+import java.util.Objects;
 
 import com.sun.nio.file.ExtendedWatchEventModifier;
 import com.sun.nio.file.SensitivityWatchEventModifier;
@@ -41,8 +42,8 @@
 
 	@LauncherAPI
 	public DirWatcher(Path dir, HashedDir hdir, FileNameMatcher matcher) throws IOException {
-		this.dir = dir;
-		this.hdir = hdir;
+		this.dir = Objects.requireNonNull(dir, "dir");
+		this.hdir = Objects.requireNonNull(hdir, "hdir");
 		this.matcher = matcher;
 		service = dir.getFileSystem().newWatchService();
 
diff --git a/Launcher/source/hasher/HashedFile.java b/Launcher/source/hasher/HashedFile.java
index b4b0256..9f59a84 100644
--- a/Launcher/source/hasher/HashedFile.java
+++ b/Launcher/source/hasher/HashedFile.java
@@ -7,6 +7,7 @@
 import launcher.LauncherAPI;
 import launcher.helper.IOHelper;
 import launcher.helper.SecurityHelper;
+import launcher.helper.VerifyHelper;
 import launcher.serialize.HInput;
 import launcher.serialize.HOutput;
 
@@ -19,7 +20,8 @@
 
 	@LauncherAPI
 	public HashedFile(long size, byte[] digest) {
-		this.size = size;
+		this.size = VerifyHelper.verifyLong(size,
+			VerifyHelper.L_NOT_NEGATIVE, "Illegal size: " + size);
 		this.digest = Arrays.copyOf(digest, digest.length);
 	}
 
diff --git a/Launcher/source/request/auth/AuthRequest.java b/Launcher/source/request/auth/AuthRequest.java
index 3fccd5c..02b3ea2 100644
--- a/Launcher/source/request/auth/AuthRequest.java
+++ b/Launcher/source/request/auth/AuthRequest.java
@@ -8,6 +8,7 @@
 import launcher.client.PlayerProfile;
 import launcher.helper.IOHelper;
 import launcher.helper.SecurityHelper;
+import launcher.helper.VerifyHelper;
 import launcher.request.Request;
 import launcher.serialize.HInput;
 import launcher.serialize.HOutput;
@@ -19,7 +20,7 @@
 	@LauncherAPI
 	public AuthRequest(Launcher.Config config, String login, byte[] encryptedPassword) {
 		super(config);
-		this.login = login;
+		this.login = VerifyHelper.verify(login, VerifyHelper.NOT_EMPTY, "Login can't be empty");
 		this.encryptedPassword = Arrays.copyOf(encryptedPassword, encryptedPassword.length);
 	}
 
diff --git a/Launcher/source/request/update/UpdateRequest.java b/Launcher/source/request/update/UpdateRequest.java
index e99a64a..862a7c4 100644
--- a/Launcher/source/request/update/UpdateRequest.java
+++ b/Launcher/source/request/update/UpdateRequest.java
@@ -11,6 +11,7 @@
 import java.time.Instant;
 import java.util.ArrayDeque;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Queue;
 
 import launcher.Launcher;
@@ -47,7 +48,7 @@
 	public UpdateRequest(Launcher.Config config, String dirName, Path dir, FileNameMatcher matcher) {
 		super(config);
 		this.dirName = IOHelper.verifyFileName(dirName);
-		this.dir = dir;
+		this.dir = Objects.requireNonNull(dir, "dir");
 		this.matcher = matcher;
 	}
 
diff --git a/Launcher/source/request/uuid/ProfileByUUIDRequest.java b/Launcher/source/request/uuid/ProfileByUUIDRequest.java
index acfe04b..c568b3d 100644
--- a/Launcher/source/request/uuid/ProfileByUUIDRequest.java
+++ b/Launcher/source/request/uuid/ProfileByUUIDRequest.java
@@ -1,6 +1,7 @@
 package launcher.request.uuid;
 
 import java.io.IOException;
+import java.util.Objects;
 import java.util.UUID;
 
 import launcher.Launcher;
@@ -16,7 +17,7 @@
 	@LauncherAPI
 	public ProfileByUUIDRequest(Launcher.Config config, UUID uuid) {
 		super(config);
-		this.uuid = uuid;
+		this.uuid = Objects.requireNonNull(uuid, "uuid");
 	}
 
 	@LauncherAPI
diff --git a/Launcher/source/serialize/HInput.java b/Launcher/source/serialize/HInput.java
index 5c5e8db..97c9b96 100644
--- a/Launcher/source/serialize/HInput.java
+++ b/Launcher/source/serialize/HInput.java
@@ -5,6 +5,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.math.BigInteger;
+import java.util.Objects;
 import java.util.UUID;
 
 import launcher.LauncherAPI;
@@ -15,7 +16,7 @@
 
 	@LauncherAPI
 	public HInput(InputStream stream) {
-		this.stream = stream;
+		this.stream = Objects.requireNonNull(stream, "stream");
 	}
 
 	@LauncherAPI
diff --git a/Launcher/source/serialize/HOutput.java b/Launcher/source/serialize/HOutput.java
index 81983bb..225579a 100644
--- a/Launcher/source/serialize/HOutput.java
+++ b/Launcher/source/serialize/HOutput.java
@@ -4,6 +4,7 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.math.BigInteger;
+import java.util.Objects;
 import java.util.UUID;
 
 import launcher.LauncherAPI;
@@ -14,7 +15,7 @@
 
 	@LauncherAPI
 	public HOutput(OutputStream stream) {
-		this.stream = stream;
+		this.stream = Objects.requireNonNull(stream, "stream");
 	}
 
 	@Override