# Copyright (c) 2017 Pieter Wuille
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
"""Reference implementation for Bech32 and segwit addresses."""
from typing import List, Union
CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
[docs]
def bech32_polymod(values: List[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
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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]):
"""Verify a checksum given HRP and converted data characters."""
return bech32_polymod(bech32_hrp_expand(hrp) + data) == 1
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def bech32_create_checksum(hrp: str, data: List[int]):
"""Compute the checksum values given HRP and data."""
values = bech32_hrp_expand(hrp) + data
polymod = bech32_polymod(values + [0, 0, 0, 0, 0, 0]) ^ 1
return [(polymod >> 5 * (5 - i)) & 31 for i in range(6)]
[docs]
def bech32_encode(hrp: str, data: List[int]):
"""Compute a Bech32 string given HRP and data values."""
combined = data + bech32_create_checksum(hrp, data)
return hrp + '1' + ''.join([CHARSET[d] for d in combined])
[docs]
def bech32_decode(bech: str):
"""Validate a Bech32 string, and determine HRP and data."""
if ((any(ord(x) < 33 or ord(x) > 126 for x in bech)) or (bech.lower() != bech and bech.upper() != bech)):
return (None, None)
bech = bech.lower()
pos = bech.rfind('1')
if pos < 1 or pos + 7 > len(bech) or len(bech) > 90:
return (None, None)
if not all(x in CHARSET for x in bech[pos + 1:]):
return (None, None)
hrp = bech[:pos]
data = [CHARSET.find(x) for x in bech[pos + 1:]]
if not bech32_verify_checksum(hrp, data):
return (None, None)
return (hrp, data[:-6])
[docs]
def convertbits(data: Union[List[int], bytes], frombits: int, tobits: int, pad: bool = True) -> Union[List[int], None]:
"""General power-of-2 base conversion."""
acc: int = 0
bits: int = 0
ret: List[int] = []
maxv: int = (1 << tobits) - 1
max_acc = (1 << (frombits + tobits - 1)) - 1
for value in data:
if value < 0 or (value >> frombits):
return None
acc = ((acc << frombits) | value) & max_acc
bits += frombits
while bits >= tobits:
bits -= tobits
ret.append((acc >> bits) & maxv)
if pad:
if bits:
ret.append((acc << (tobits - bits)) & maxv)
elif bits >= frombits or ((acc << (tobits - bits)) & maxv):
return None
return ret
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def decode(hrp: str, addr: str):
"""Decode a segwit address."""
hrpgot, data = bech32_decode(addr)
if hrpgot is None or data is None:
return (None, None)
if hrpgot != hrp:
return (None, None)
decoded = convertbits(data[1:], 5, 8, False)
if decoded is None or len(decoded) < 2 or len(decoded) > 40:
return (None, None)
if data[0] > 16:
return (None, None)
if data[0] == 0 and len(decoded) != 20 and len(decoded) != 32:
return (None, None)
return (data[0], decoded)
[docs]
def encode(hrp: str, witver: int, witprog: List[int]):
"""Encode a segwit address."""
converted = convertbits(witprog, 8, 5)
if converted is None:
return None
ret = bech32_encode(hrp, [witver] + converted)
if decode(hrp, ret) == (None, None):
return None
return ret