tmerkle.py - obelisk - Electrum server using libbitcoin as its backend
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tmerkle.py (1976B)
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1 #!/usr/bin/env python3
2 # Copyright (C) 2020-2021 Ivan J. <parazyd@dyne.org>
3 #
4 # This file is part of obelisk
5 #
6 # This program is free software: you can redistribute it and/or modify
7 # it under the terms of the GNU Affero General Public License version 3
8 # as published by the Free Software Foundation.
9 #
10 # This program is distributed in the hope that it will be useful,
11 # but WITHOUT ANY WARRANTY; without even the implied warranty of
12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 # GNU Affero General Public License for more details.
14 #
15 # You should have received a copy of the GNU Affero General Public License
16 # along with this program. If not, see <http://www.gnu.org/licenses/>.
17 """Module for calculating merkle branches"""
18 from math import ceil, log
19
20 from electrumobelisk.util import double_sha256
21
22
23 def branch_length(hash_count):
24 """Return the length of a merkle branch given the number of hashes"""
25 return ceil(log(hash_count, 2))
26
27
28 def merkle_branch_and_root(hashes, index):
29 """Return a (merkle branch, merkle_root) pair given hashes, and the
30 index of one of those hashes.
31 """
32 hashes = list(hashes)
33 if not isinstance(index, int):
34 raise TypeError("index must be an integer")
35 # This also asserts hashes is not empty
36 if not 0 <= index < len(hashes):
37 raise ValueError("index out of range")
38 length = branch_length(len(hashes))
39
40 branch = []
41 for _ in range(length):
42 if len(hashes) & 1:
43 hashes.append(hashes[-1])
44 branch.append(hashes[index ^ 1])
45 index >>= 1
46 hashes = [
47 double_sha256(hashes[n] + hashes[n + 1])
48 for n in range(0, len(hashes), 2)
49 ]
50 return branch, hashes[0]
51
52
53 def merkle_branch(tx_hashes, tx_pos):
54 """Return a merkle branch given hashes and the tx position"""
55 branch, _root = merkle_branch_and_root(tx_hashes, tx_pos)
56 branch = [bytes(reversed(h)).hex() for h in branch]
57 return branch