diff --git a/src/hashtree.py b/src/hashtree.py
--- a/src/hashtree.py
+++ b/src/hashtree.py
@@ -28,7 +28,7 @@ class HashTree:
 			progress=Progress(leafCount)
 			for i in range(leafCount):
 				data=f.read(HashTree.BLOCK_SIZE)
-				res.insertLeaf(hashlib.sha256(data).digest()[HashTree.HASH_LEN:])
+				res.insertLeaf(hashlib.sha256(data).digest()[-HashTree.HASH_LEN:])
 
 				progress.p(i)
 			progress.done()
@@ -70,7 +70,7 @@ class HashTree:
 	## Updates the node at index and all its ancestors.
 	def updateNode(self,index):
 		while index>=0:
-			self.store[index]=hashlib.sha256(self.store[index*2+1]+self.store[index*2+2]).digest()[HashTree.HASH_LEN:]
+			self.store[index]=hashlib.sha256(self.store[index*2+1]+self.store[index*2+2]).digest()[-HashTree.HASH_LEN:]
 			index=(index-1)//2
 			
 	## Fast construction of the tree over the leaves. O(n).
@@ -78,7 +78,7 @@ class HashTree:
 		print(datetime.now(), "building tree:")
 		progress=Progress(-1, self.leafStart-1)
 		for i in range(self.leafStart-1,-1,-1):
-			self.store[i]=hashlib.sha256(self.store[i*2+1]+self.store[i*2+2]).digest()[HashTree.HASH_LEN:]
+			self.store[i]=hashlib.sha256(self.store[i*2+1]+self.store[i*2+2]).digest()[-HashTree.HASH_LEN:]
 			progress.p(i)
 		progress.done()