obelisk

Electrum server using libbitcoin as its backend
git clone https://git.parazyd.org/obelisk
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merkle.py (1976B)


      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