diff --git a/libsrc/core/archive.hpp b/libsrc/core/archive.hpp
index af7efc5e..dc381a4a 100644
--- a/libsrc/core/archive.hpp
+++ b/libsrc/core/archive.hpp
@@ -910,6 +910,54 @@ namespace ngcore
     }
   };
 
+  // HashArchive =================================================================
+  // This class enables to easily create hashes for archivable objects by xoring
+  // threw its data
+
+  class NGCORE_API HashArchive : public Archive
+  {
+    size_t hash_value;
+    char* h;
+    int offset;
+  public:
+    HashArchive() : Archive(true)
+      { h = (char*)&hash_value; }
+
+    using Archive::operator&;
+    Archive & operator & (double & d) override { return ApplyHash(d); }
+    Archive & operator & (int & i) override { return ApplyHash(i); }
+    Archive & operator & (short & i) override { return ApplyHash(i); }
+    Archive & operator & (long & i) override { return ApplyHash(i); }
+    Archive & operator & (size_t & i) override { return ApplyHash(i); }
+    Archive & operator & (unsigned char & i) override { return ApplyHash(i); }
+    Archive & operator & (bool & b) override { return ApplyHash(b); }
+    Archive & operator & (std::string & str) override
+    { for(auto c : str) ApplyHash(c);  return *this; }
+    Archive & operator & (char *& str) override
+    { char* s = str; while(*s != '\0') ApplyHash(*(s++)); return *this; }
+
+    // HashArchive can be used in const context
+    template<typename T>
+      Archive & operator& (const T& val) const
+    { return (*this) & const_cast<T&>(val); }
+
+    size_t GetHash() const { return hash_value; }
+
+  private:
+    template<typename T>
+      Archive& ApplyHash(T val)
+    {
+      auto n = sizeof(T);
+      char* pval = (char*)&val;
+      for(int i = 0; i < n; i++)
+        {
+          h[offset++] ^= pval[i];
+          offset %= 8;
+        }
+      return *this;
+    }
+  };
+
 } // namespace ngcore
 
 #endif // NETGEN_CORE_ARCHIVE_HPP
diff --git a/libsrc/core/bitarray.cpp b/libsrc/core/bitarray.cpp
index db9fc114..2523ce5f 100644
--- a/libsrc/core/bitarray.cpp
+++ b/libsrc/core/bitarray.cpp
@@ -83,6 +83,18 @@ namespace ngcore
     return *this;
   }
 
+  bool BitArray :: operator==(const BitArray& other) const
+  {
+    if(size != other.Size())
+      return false;
+    for(auto i : Range(size/CHAR_BIT))
+      if(data[i] != other.data[i])
+        return false;
+    for(auto i : Range(size%CHAR_BIT))
+      if(Test(i + size * (size/CHAR_BIT)) != other.Test(i + size * (size/CHAR_BIT)))
+        return false;
+    return true;
+  }
 
   BitArray & BitArray :: operator= (const BitArray & ba2)
   {
@@ -115,29 +127,39 @@ namespace ngcore
     return cnt;
   }
 
-  Archive & operator & (Archive & archive, BitArray & ba)
+  void BitArray :: DoArchive(Archive& archive)
   {
-    if (archive.Output())
+    if(archive.GetVersion("netgen") >= "v6.2.2007-62")
       {
-        archive << ba.Size();
-        for (size_t i = 0; i < ba.Size(); i++)
-          archive << ba[i];
+        archive.NeedsVersion("netgen", "v6.2.2007-62");
+        auto size = Size();
+        archive & size;
+        if(archive.Input())
+          SetSize(size);
+        archive.Do(data, size/CHAR_BIT+1);
       }
     else
       {
-        size_t size;
-        archive & size;
-        ba.SetSize (size);
-        ba.Clear();
-        for (size_t i = 0; i < size; i++)
+        if (archive.Output())
           {
-            bool b;
-            archive & b;
-            if (b) ba.SetBit(i);
+            throw Exception("should not get here");
+            archive << Size();
+            for (size_t i = 0; i < Size(); i++)
+              archive << (*this)[i];
+          }
+        else
+          {
+            size_t size;
+            archive & size;
+            SetSize (size);
+            Clear();
+            for (size_t i = 0; i < size; i++)
+              {
+                bool b;
+                archive & b;
+                if (b) SetBit(i);
+              }
           }
       }
-    return archive;
   }
-
-
-}
+} // namespace ngcore
diff --git a/libsrc/core/bitarray.hpp b/libsrc/core/bitarray.hpp
index 9c0823cf..4005fc81 100644
--- a/libsrc/core/bitarray.hpp
+++ b/libsrc/core/bitarray.hpp
@@ -131,6 +131,7 @@ public:
     return Test(i);
   }
 
+  NGCORE_API bool operator==(const BitArray& other) const;
 
   /// invert all bits
   NGCORE_API BitArray & Invert ();
@@ -145,6 +146,9 @@ public:
   NGCORE_API BitArray & operator= (const BitArray & ba2);
 
   NGCORE_API size_t NumSet () const;
+
+  NGCORE_API void DoArchive(Archive& archive);
+
 private:
   ///
   unsigned char Mask (size_t i) const
@@ -190,11 +194,8 @@ private:
     return res;
   }
 
-
   NGCORE_API std::ostream & operator<<(std::ostream & s, const BitArray & ba);
 
-  NGCORE_API Archive & operator & (Archive & archive, BitArray & ba);
-
 } // namespace ngcore
 
 #endif // NETGEN_CORE_BITARRAY