Initial data commit

Task/SHA-256-Merkle-tree/Python/sha-256-merkle-tree.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python
+# compute the root label for a SHA256 Merkle tree built on blocks of a given
+# size (default 1MB) taken from the given file(s)
+import argh
+import hashlib
+import sys
+
+@argh.arg('filename', nargs='?', default=None)
+def main(filename, block_size=1024*1024):
+    if filename:
+        fin = open(filename, 'rb')
+    else:
+        fin = sys.stdin
+
+    stack = []
+    block = fin.read(block_size)
+    while block:
+        # a node is a pair: ( tree-level, hash )
+        node = (0, hashlib.sha256(block).digest())
+        stack.append(node)
+
+        # concatenate adjacent pairs at the same level
+        while len(stack) >= 2 and stack[-2][0] == stack[-1][0]:
+            a = stack[-2]
+            b = stack[-1]
+            l = a[0]
+            stack[-2:] = [(l+1, hashlib.sha256(a[1] + b[1]).digest())]
+
+        block = fin.read(block_size)
+
+    while len(stack) > 1:
+        # at the end we have to concatenate even across levels
+        a = stack[-2]
+        b = stack[-1]
+        al = a[0]
+        bl = b[0]
+        stack[-2:] = [(max(al, bl)+1, hashlib.sha256(a[1] + b[1]).digest())]
+
+    print(stack[0][1].hex())
+
+
+argh.dispatch_command(main)