1  #!/usr/bin/env python3
 2  # Copyright (c) 2022 The Bitcoin Core developers
 3  # Distributed under the MIT software license, see the accompanying
 4  # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 5  """Helper routines relevant for compact block filters (BIP158).
 6  """
 7  from .crypto.siphash import siphash
 8  
 9  
10  def bip158_basic_element_hash(script_pub_key, N, block_hash):
11      """ Calculates the ranged hash of a filter element as defined in BIP158:
12  
13      'The first step in the filter construction is hashing the variable-sized
14      raw items in the set to the range [0, F), where F = N * M.'
15  
16      'The items are first passed through the pseudorandom function SipHash, which takes a
17      128-bit key k and a variable-sized byte vector and produces a uniformly random 64-bit
18      output. Implementations of this BIP MUST use the SipHash parameters c = 2 and d = 4.'
19  
20      'The parameter k MUST be set to the first 16 bytes of the hash (in standard
21      little-endian representation) of the block for which the filter is constructed. This
22      ensures the key is deterministic while still varying from block to block.'
23      """
24      M = 784931
25      block_hash_bytes = bytes.fromhex(block_hash)[::-1]
26      k0 = int.from_bytes(block_hash_bytes[0:8], 'little')
27      k1 = int.from_bytes(block_hash_bytes[8:16], 'little')
28      return (siphash(k0, k1, script_pub_key) * (N * M)) >> 64
29  
30  
31  def bip158_relevant_scriptpubkeys(node, block_hash):
32      """ Determines the basic filter relevant scriptPubKeys as defined in BIP158:
33  
34      'A basic filter MUST contain exactly the following items for each transaction in a block:
35         - The previous output script (the script being spent) for each input, except for
36           the coinbase transaction.
37         - The scriptPubKey of each output, aside from all OP_RETURN output scripts.'
38      """
39      spks = set()
40      for tx in node.getblock(blockhash=block_hash, verbosity=3)['tx']:
41          # gather prevout scripts
42          for i in tx['vin']:
43              if 'prevout' in i:
44                  spks.add(bytes.fromhex(i['prevout']['scriptPubKey']['hex']))
45          # gather output scripts
46          for o in tx['vout']:
47              if o['scriptPubKey']['type'] != 'nulldata':
48                  spks.add(bytes.fromhex(o['scriptPubKey']['hex']))
49      return spks