obelisk

commit 24a277654df91c955e2edc9ec8dc9a20bcf112b4
parent efdd930fa0b7808d663da689d4f0f08824f78c36
Author: parazyd <parazyd@dyne.org>
Date:   Wed,  7 Apr 2021 17:21:41 +0200

Implement merkle tree/branch functions.

Diffstat:
A
electrumobelisk/hashes.py
 | 
37
+++++++++++++++++++++++++++++++++++++
A
electrumobelisk/merkle.py
 | 
57
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

2 files changed, 94 insertions(+), 0 deletions(-)
diff --git a/electrumobelisk/hashes.py b/electrumobelisk/hashes.py
@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+# Copyright (C) 2020-2021 Ivan J. <parazyd@dyne.org>
+#
+# This file is part of obelisk
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License version 3
+# as published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+""" Cryptographic hash functions and helpers """
+import hashlib
+
+_sha256 = hashlib.sha256
+
+
+def sha256(inp):
+    """ Simple wrapper of hashlib sha256. """
+    return _sha256(inp).digest()
+
+
+def double_sha256(inp):
+    """ sha256 of sha256, as used extensively in bitcoin """
+    return sha256(sha256(inp))
+
+
+def hash_to_hex_str(inp):
+    """Convert a big-endian binary hash to displayed hex string.
+    Display form of a binary hash is reversed and converted to hex.
+    """
+    return bytes(reversed(inp)).hex()
diff --git a/electrumobelisk/merkle.py b/electrumobelisk/merkle.py
@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+# Copyright (C) 2020-2021 Ivan J. <parazyd@dyne.org>
+#
+# This file is part of obelisk
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License version 3
+# as published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""Module for calculating merkle branches"""
+from math import ceil, log
+
+from hashes import double_sha256
+
+
+def branch_length(hash_count):
+    """Return the length of a merkle branch given the number of hashes"""
+    return ceil(log(hash_count, 2))
+
+
+def merkle_branch_and_root(hashes, index):
+    """Return a (merkle branch, merkle_root) pair given hashes, and the
+    index of one of those hashes.
+    """
+    hashes = list(hashes)
+    if not isinstance(index, int):
+        raise TypeError("index must be an integer")
+    # This also asserts hashes is not empty
+    if not 0 <= index < len(hashes):
+        raise ValueError("index out of range")
+    length = branch_length(len(hashes))
+
+    branch = []
+    for _ in range(length):
+        if len(hashes) & 1:
+            hashes.append(hashes[-1])
+        branch.append(hashes[index ^ 1])
+        index >>= 1
+        hashes = [
+            double_sha256(hashes[n] + hashes[n + 1])
+            for n in range(0, len(hashes), 2)
+        ]
+    return branch, hashes[0]
+
+
+def merkle_branch(tx_hashes, tx_pos):
+    """Return a merkle branch given hashes and the tx position"""
+    branch, _root = merkle_branch_and_root(tx_hashes, tx_pos)
+    branch = [bytes(reversed(h)).hex() for h in branch]
+    return branch