diff --git a/src/main/java/net/szum123321/textile_backup/core/FileTreeHashBuilder.java b/src/main/java/net/szum123321/textile_backup/core/FileTreeHashBuilder.java
new file mode 100644
index 0000000..a6084e6
--- /dev/null
+++ b/src/main/java/net/szum123321/textile_backup/core/FileTreeHashBuilder.java
@@ -0,0 +1,66 @@
+/*
+    A simple backup mod for Fabric
+    Copyright (C) 2022  Szum123321
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+package net.szum123321.textile_backup.core;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.function.Supplier;
+import java.util.zip.Checksum;
+
+public class FileTreeHashBuilder {
+    private final static ThreadLocal<byte[]> buff =
+            ThreadLocal.withInitial(() -> new byte[Long.BYTES]);
+    private final Object lock = new Object();
+    private final Supplier<Checksum> hasherProvider;
+    private long hash = 0, filesProcessed = 0, filesTotalSize = 0;
+
+    public FileTreeHashBuilder(Supplier<Checksum> provider) { hasherProvider = provider; }
+
+    public void update(Path path, long newHash) throws IOException {
+        byte[] raw = buff.get();
+        var hasher = hasherProvider.get();
+
+        long size = Files.size(path);
+
+        hasher.update(ByteBuffer.wrap(raw).putLong(size).array());
+        hasher.update(path.toString().getBytes(StandardCharsets.UTF_8));
+        hasher.update(ByteBuffer.wrap(raw).putLong(hash).array());
+
+        synchronized (lock) {
+            //This way exact order of files processed doesn't matter.
+            this.hash ^= hasher.getValue();
+            filesProcessed++;
+            filesTotalSize += size;
+        }
+    }
+
+    public long getValue() {
+        var hasher = hasherProvider.get();
+        byte[] raw = buff.get();
+
+        hasher.update(ByteBuffer.wrap(raw).putLong(hash).array());
+        hasher.update(ByteBuffer.wrap(raw).putLong(filesProcessed).array());
+        hasher.update(ByteBuffer.wrap(raw).putLong(filesTotalSize).array());
+
+        return hasher.getValue();
+    }
+}
diff --git a/src/main/java/net/szum123321/textile_backup/core/create/FileInputStreamSupplier.java b/src/main/java/net/szum123321/textile_backup/core/create/FileInputStreamSupplier.java
index 465c004..1f9daf8 100644
--- a/src/main/java/net/szum123321/textile_backup/core/create/FileInputStreamSupplier.java
+++ b/src/main/java/net/szum123321/textile_backup/core/create/FileInputStreamSupplier.java
@@ -1,3 +1,21 @@
+/*
+    A simple backup mod for Fabric
+    Copyright (C) 2022  Szum123321
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
 package net.szum123321.textile_backup.core.create;
 
 import net.szum123321.textile_backup.TextileBackup;
@@ -16,7 +34,6 @@ public record FileInputStreamSupplier(Path path, String name, CompressionStatus.
     @Override
     public InputStream getInputStream() throws IOException {
         try {
-            //TODO: put in hasher
             return new HashingInputStream(Files.newInputStream(path), path, null, builder);
         } catch (IOException e) {
             builder.update(path, e);
diff --git a/src/main/java/net/szum123321/textile_backup/core/create/HashingInputStream.java b/src/main/java/net/szum123321/textile_backup/core/create/HashingInputStream.java
index 612b625..0b50904 100644
--- a/src/main/java/net/szum123321/textile_backup/core/create/HashingInputStream.java
+++ b/src/main/java/net/szum123321/textile_backup/core/create/HashingInputStream.java
@@ -1,3 +1,21 @@
+/*
+    A simple backup mod for Fabric
+    Copyright (C) 2022  Szum123321
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
 package net.szum123321.textile_backup.core.create;
 
 import net.szum123321.textile_backup.core.CompressionStatus;
diff --git a/src/main/java/net/szum123321/textile_backup/core/create/InputSupplier.java b/src/main/java/net/szum123321/textile_backup/core/create/InputSupplier.java
index 246df54..e90e8d4 100644
--- a/src/main/java/net/szum123321/textile_backup/core/create/InputSupplier.java
+++ b/src/main/java/net/szum123321/textile_backup/core/create/InputSupplier.java
@@ -1,3 +1,21 @@
+/*
+    A simple backup mod for Fabric
+    Copyright (C) 2022  Szum123321
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
 package net.szum123321.textile_backup.core.create;
 
 import org.apache.commons.compress.parallel.InputStreamSupplier;
@@ -5,10 +23,8 @@ import org.apache.commons.compress.parallel.InputStreamSupplier;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.Path;
-
 public interface InputSupplier extends InputStreamSupplier {
     InputStream getInputStream() throws IOException;
     Path getPath();
-
     String getName();
 }
diff --git a/src/main/java/net/szum123321/textile_backup/core/restore/HashingOutputStream.java b/src/main/java/net/szum123321/textile_backup/core/restore/HashingOutputStream.java
new file mode 100644
index 0000000..6757fa4
--- /dev/null
+++ b/src/main/java/net/szum123321/textile_backup/core/restore/HashingOutputStream.java
@@ -0,0 +1,55 @@
+/*
+    A simple backup mod for Fabric
+    Copyright (C) 2022  Szum123321
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+package net.szum123321.textile_backup.core.restore;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.io.FilterOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.file.Path;
+import java.util.zip.Checksum;
+
+public class HashingOutputStream extends FilterOutputStream {
+    private final Path path;
+    private final Checksum hasher;
+
+    public HashingOutputStream(OutputStream out, Path path, Checksum hasher) {
+        super(out);
+        this.path = path;
+        this.hasher = hasher;
+    }
+
+    @Override
+    public void write(int b) throws IOException {
+        super.write(b);
+        hasher.update(b);
+    }
+
+    @Override
+    public void write(byte[] @NotNull b, int off, int len) throws IOException {
+        super.write(b, off, len);
+        hasher.update(b, off, len);
+    }
+
+    @Override
+    public void close() throws IOException {
+        super.close();
+    }
+}