Fix QuickXorHash-implementering og tilføj manglende længde-XOR

- Opdaterer quickxorhash til at bruge en 160-bit heltalsbuffer for korrekt cirkulær rotation
- Tilføjer det obligatoriske XOR-trin med filens længde, som manglede tidligere
- Sikrer korrekt 20-byte little-endian format ved base64-encoding
- Dette løser problemet med konstante hash-mismatch på ellers korrekte filer

download_sharepoint.py

@@ -80,24 +80,33 @@ def safe_get(url, headers, stream=False, timeout=60, params=None):
 # --- Punkt 4: Integrity Validation (QuickXorHash) ---
 def quickxorhash(file_path):
     """Compute Microsoft QuickXorHash for a file. Returns base64-encoded string.
-    Uses 3 × uint64 cells matching Microsoft's C# reference implementation."""
-    SHIFT = 11
-    WIDTH = 160
-    data = [0, 0, 0]  # 3 × 64-bit unsigned integers
-    i = 0
+    Follows the official Microsoft/Rclone implementation: 
+    160-bit circular XOR with a final length XOR."""
+    h = 0
+    length = 0
+    mask = (1 << 160) - 1
+    
     with open(file_path, 'rb') as f:
         while True:
             chunk = f.read(CHUNK_SIZE)
             if not chunk:
                 break
-            for byte in chunk:
-                bit_idx = (i * SHIFT) % WIDTH
-                cell = bit_idx // 64
-                shift = bit_idx % 64
-                data[cell] = (data[cell] ^ (byte << shift)) & 0xFFFFFFFFFFFFFFFF
-                i += 1
-    result = struct.pack('<QQQ', data[0], data[1], data[2])
-    return base64.b64encode(result[:20]).decode('ascii')
+            for b in chunk:
+                shift = (length * 11) % 160
+                # Circular shift left: the byte is XORed into the 160-bit state
+                # at a position that rotates 11 bits for every byte.
+                shifted = b << shift
+                wrapped = (shifted & mask) | (shifted >> 160)
+                h ^= wrapped
+                length += 1
+    
+    # Finalize: XOR the 64-bit length into the 160-bit state.
+    # This affects the first 8 bytes of the little-endian representation.
+    h ^= length
+    
+    # Convert to 20 bytes (160 bits) in little-endian format
+    result = h.to_bytes(20, byteorder='little')
+    return base64.b64encode(result).decode('ascii')
 
 def verify_integrity(local_path, remote_hash):
     """Verifies file integrity using Microsoft QuickXorHash."""