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#!/usr/bin/env python3
# Copyright (c) 2022 The Bitcoin Core developers
# Distributed under the MIT software license, see the accompanying
# file COPYING or http://www.opensource.org/licenses/mit-license.php.
"""Helper routines relevant for compact block filters (BIP158).
"""
from .crypto.siphash import siphash
def bip158_basic_element_hash(script_pub_key, N, block_hash):
""" Calculates the ranged hash of a filter element as defined in BIP158:
'The first step in the filter construction is hashing the variable-sized
raw items in the set to the range [0, F), where F = N * M.'
'The items are first passed through the pseudorandom function SipHash, which takes a
128-bit key k and a variable-sized byte vector and produces a uniformly random 64-bit
output. Implementations of this BIP MUST use the SipHash parameters c = 2 and d = 4.'
'The parameter k MUST be set to the first 16 bytes of the hash (in standard
little-endian representation) of the block for which the filter is constructed. This
ensures the key is deterministic while still varying from block to block.'
"""
M = 784931
block_hash_bytes = bytes.fromhex(block_hash)[::-1]
k0 = int.from_bytes(block_hash_bytes[0:8], 'little')
k1 = int.from_bytes(block_hash_bytes[8:16], 'little')
return (siphash(k0, k1, script_pub_key) * (N * M)) >> 64
def bip158_relevant_scriptpubkeys(node, block_hash):
""" Determines the basic filter relevant scriptPubKeys as defined in BIP158:
'A basic filter MUST contain exactly the following items for each transaction in a block:
- The previous output script (the script being spent) for each input, except for
the coinbase transaction.
- The scriptPubKey of each output, aside from all OP_RETURN output scripts.'
"""
spks = set()
for tx in node.getblock(blockhash=block_hash, verbosity=3)['tx']:
# gather prevout scripts
for i in tx['vin']:
if 'prevout' in i:
spks.add(bytes.fromhex(i['prevout']['scriptPubKey']['hex']))
# gather output scripts
for o in tx['vout']:
if o['scriptPubKey']['type'] != 'nulldata':
spks.add(bytes.fromhex(o['scriptPubKey']['hex']))
return spks
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