# Copyright (c) 2017, 2020 Pieter Wuille
# 2023 The Software Heritage developers
#
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"""Reference implementation for Bech32/Bech32m and segwit addresses."""
from enum import Enum
from typing import List, Optional, Tuple
[docs]
class Encoding(Enum):
"""Enumeration type to list the various supported encodings."""
BECH32 = 1
BECH32M = 2
CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
BECH32M_CONST = 0x2BC830A3
[docs]
def convert_bits(
data: List[int], from_bits: int, to_bits: int, pad: bool = False
) -> List[int]:
assert from_bits <= 8 and to_bits <= 8 and from_bits > 0 and to_bits > 0
acc = 0
bits = 0
ret = []
maxv = (1 << to_bits) - 1
max_acc = (1 << (from_bits + to_bits - 1)) - 1
for value in data:
if value < 0 or (value >> from_bits) > 0:
raise ValueError("Out of range")
acc = ((acc << from_bits) | value) & max_acc
bits += from_bits
while bits >= to_bits:
bits -= to_bits
ret.append((acc >> bits) & maxv)
if pad:
if bits:
ret.append((acc << (to_bits - bits)) & maxv)
elif bits >= from_bits or ((acc << (to_bits - bits)) & maxv):
raise ValueError("Padding is disabled but bits are left unwritten…")
return ret
[docs]
def bech32_polymod(values: List[int]) -> int:
"""Internal function that computes the Bech32 checksum."""
generator = [0x3B6A57B2, 0x26508E6D, 0x1EA119FA, 0x3D4233DD, 0x2A1462B3]
chk = 1
for value in values:
top = chk >> 25
chk = (chk & 0x1FFFFFF) << 5 ^ value
for i in range(5):
chk ^= generator[i] if ((top >> i) & 1) else 0
return chk
[docs]
def bech32_hrp_expand(hrp: str) -> List[int]:
"""Expand the HRP into values for checksum computation."""
return [ord(x) >> 5 for x in hrp] + [0] + [ord(x) & 31 for x in hrp]
[docs]
def bech32_verify_checksum(hrp: str, data: List[int]) -> Optional[Encoding]:
"""Verify a checksum given HRP and converted data characters."""
const = bech32_polymod(bech32_hrp_expand(hrp) + data)
if const == 1:
return Encoding.BECH32
if const == BECH32M_CONST:
return Encoding.BECH32M
return None
[docs]
def bech32_create_checksum(hrp: str, data: List[int], spec: Encoding) -> List[int]:
"""Compute the checksum values given HRP and data."""
values = bech32_hrp_expand(hrp) + data
const = BECH32M_CONST if spec == Encoding.BECH32M else 1
polymod = bech32_polymod(values + [0, 0, 0, 0, 0, 0]) ^ const
return [(polymod >> 5 * (5 - i)) & 31 for i in range(6)]
[docs]
def bech32_encode(hrp: str, data: List[int], spec: Encoding) -> str:
"""Compute a Bech32 string given HRP and data values."""
combined = data + bech32_create_checksum(hrp, data, spec)
return hrp + "1" + "".join([CHARSET[d] for d in combined])
[docs]
def bech32_decode(bech: str) -> Tuple[str, List[int], Encoding]:
"""Validate a Bech32/Bech32m string, and determine HRP and data."""
if any(ord(x) < 33 or ord(x) > 126 for x in bech):
raise ValueError("Non alphanumeric characters")
if bech.lower() != bech and bech.upper() != bech:
raise ValueError("Mixed case is not allowed")
bech = bech.lower()
pos = bech.rfind("1")
if pos < 1 or pos + 7 > len(bech) or len(bech) > 90:
raise ValueError("Unable to find separator")
if not all(x in CHARSET for x in bech[pos + 1 :]):
raise ValueError("Characters outside the Bech32 character set")
hrp = bech[:pos]
data = [CHARSET.find(x) for x in bech[pos + 1 :]]
spec = bech32_verify_checksum(hrp, data)
if spec is None:
raise ValueError("Checksum error")
return (hrp, data[:-6], spec)
