diff --git a/src/main/java/com/sheepit/client/Md5.java b/src/main/java/com/sheepit/client/Md5.java
new file mode 100644
index 0000000..94d919c
--- /dev/null
+++ b/src/main/java/com/sheepit/client/Md5.java
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2023 Laurent CLOUET
+ * Author Laurent CLOUET <laurent.clouet@nopnop.net>
+ *
+ * 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; version 2
+ * of the License.
+ *
+ * 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, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+package com.sheepit.client;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.security.DigestInputStream;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.HashMap;
+import java.util.Map;
+
+public class Md5 {
+	private static Map<String, String> cache = new HashMap<>();
+	
+	// TODO: check if the file has changed (cache the time of modification)
+	// TODO: to avoid memory increase, check if files are deleted
+	
+	public String get(String path) {
+		if (cache.containsKey(path) == false) {
+			generate(path);
+		}
+		return cache.get(path);
+	}
+	
+	public void generate(String path) {
+		try {
+			MessageDigest md = MessageDigest.getInstance("MD5");
+			InputStream is = Files.newInputStream(Paths.get(path));
+			DigestInputStream dis = new DigestInputStream(is, md);
+			byte[] buffer = new byte[8192];
+			while (dis.read(buffer) > 0)
+				; // process the entire file
+			String data = Utils.convertBinaryToHex(md.digest());
+			dis.close();
+			is.close();
+			cache.put(path, data);
+		}
+		catch (NoSuchAlgorithmException | IOException e) {
+			cache.put(path, "");
+		}
+	}
+}
diff --git a/src/main/java/com/sheepit/client/Utils.java b/src/main/java/com/sheepit/client/Utils.java
index 507cde4..1e6f464 100644
--- a/src/main/java/com/sheepit/client/Utils.java
+++ b/src/main/java/com/sheepit/client/Utils.java
@@ -68,21 +68,8 @@ public class Utils {
 	}
 	
 	public static String md5(String path_of_file_) {
-		try {
-			MessageDigest md = MessageDigest.getInstance("MD5");
-			InputStream is = Files.newInputStream(Paths.get(path_of_file_));
-			DigestInputStream dis = new DigestInputStream(is, md);
-			byte[] buffer = new byte[8192];
-			while (dis.read(buffer) > 0)
-				; // process the entire file
-			String data = convertBinaryToHex(md.digest());
-			dis.close();
-			is.close();
-			return data;
-		}
-		catch (NoSuchAlgorithmException | IOException e) {
-			return "";
-		}
+		Md5 md5 = new Md5();
+		return md5.get(path_of_file_);
 	}
 	
 	public static String convertBinaryToHex(byte[] bytes) {