diff --git a/src/datafile.py b/src/datafile.py
new file mode 100644
--- /dev/null
+++ b/src/datafile.py
@@ -0,0 +1,29 @@
+from hashtree import HashTree
+
+
+BLOCK_SIZE=HashTree.BLOCK_SIZE
+
+
+class DataFile:
+	def __init__(self,fileHandle):
+		self._lastIndex=0
+		self._f=fileHandle
+
+	@staticmethod
+	def open(filename,mode="rb"):
+		return DataFile(open(filename,mode=mode))
+
+	def writeAt(self,i,blockData):
+		if i!=self._lastIndex+1:
+			self._f.seek(i*BLOCK_SIZE)
+		self._f.write(blockData)
+		self._lastIndex=i
+
+	def readFrom(self,i,byteCount=BLOCK_SIZE):
+		if i!=self._lastIndex+1:
+			self._f.seek(i*BLOCK_SIZE)
+		self._lastIndex=i
+		return self._f.read(byteCount)
+
+	def close(self):
+		self._f.close()