diff --git a/src/KeyKeeper/PasswordStore/FileFormatUtil.cs b/src/KeyKeeper/PasswordStore/FileFormatUtil.cs
new file mode 100644
index 0000000..c98ccaf
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/FileFormatUtil.cs
@@ -0,0 +1,45 @@
+using System;
+using System.IO;
+using System.Text;
+
+namespace KeyKeeper.PasswordStore;
+
+static class FileFormatUtil
+{
+    public static int WriteVarUint16(Stream str, ulong number)
+    {
+        int size = 0;
+        do {
+            ushort portion = (ushort)(number & 0x7fff);
+            number >>= 15;
+            if (number != 0)
+                portion |= 1 << 15;
+            size += 2;
+            str.WriteByte((byte)(portion & 0xff));
+            str.WriteByte((byte)(portion >> 8));
+        }
+        while (number != 0);
+        return size;
+    }
+
+    public static int WriteU8TaggedString(Stream str, string s)
+    {
+        byte[] b = Encoding.UTF8.GetBytes(s);
+        if (b.Length > 255)
+            throw new ArgumentException("string too long");
+        str.WriteByte((byte)b.Length);
+        str.Write(b);
+        return b.Length + 1;
+    }
+
+    public static int WriteU16TaggedString(Stream str, string s)
+    {
+        byte[] b = Encoding.UTF8.GetBytes(s);
+        if (b.Length > 65535)
+            throw new ArgumentException("string too long");
+        str.WriteByte((byte)(b.Length & 0xff));
+        str.WriteByte((byte)(b.Length >> 8));
+        str.Write(b);
+        return b.Length + 2;
+    }
+}
\ No newline at end of file
diff --git a/src/KeyKeeper/PasswordStore/IPassStoreEntry.cs b/src/KeyKeeper/PasswordStore/IPassStoreEntry.cs
deleted file mode 100644
index dbeea0c..0000000
--- a/src/KeyKeeper/PasswordStore/IPassStoreEntry.cs
+++ /dev/null
@@ -1,10 +0,0 @@
-using System;
-
-namespace KeyKeeper.PasswordStore;
-
-public interface IPassStoreEntry
-{
-    string Name { get; set; }
-    PassStoreEntryType Type { get; set; }
-    DateTime CreationDate { get; }
-}
diff --git a/src/KeyKeeper/PasswordStore/PassStoreEntry.cs b/src/KeyKeeper/PasswordStore/PassStoreEntry.cs
new file mode 100644
index 0000000..ed4513e
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/PassStoreEntry.cs
@@ -0,0 +1,37 @@
+using System;
+using System.IO;
+using KeyKeeper.PasswordStore.Crypto;
+
+namespace KeyKeeper.PasswordStore;
+
+public abstract class PassStoreEntry
+{
+    public Guid Id { get; set; }
+    public DateTime CreationDate { get; protected set; }
+    public DateTime ModificationDate { get; set; }
+    public Guid IconType { get; set; }
+    public string Name { get; set; }
+    public PassStoreEntryType Type { get; set; }
+
+    public void WriteToStream(Stream str)
+    {
+        MemoryStream tmp = new();
+        BinaryWriter wr = new(tmp);
+        wr.Write(Id.ToByteArray());
+        ulong timestamp = (ulong) new DateTimeOffset(CreationDate.ToUniversalTime()).ToUnixTimeSeconds();
+        FileFormatUtil.WriteVarUint16(tmp, timestamp);
+        timestamp = (ulong) new DateTimeOffset(ModificationDate.ToUniversalTime()).ToUnixTimeSeconds();
+        FileFormatUtil.WriteVarUint16(tmp, timestamp);
+        wr.Write(IconType.ToByteArray());
+        FileFormatUtil.WriteU8TaggedString(tmp, Name);
+        wr.Write(InnerSerialize());
+        byte[] serializedEntry = tmp.ToArray();
+        tmp.Dispose();
+
+        wr = new(str);
+        wr.Write7BitEncodedInt(serializedEntry.Length);
+        wr.Write(serializedEntry);
+    }
+
+    protected abstract byte[] InnerSerialize();
+}