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# Copyright (c) 2017, 2020 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/Bech32m and segwit addresses."""
from enum import Enum
class Encoding(Enum):
"""Enumeration type to list the various supported encodings."""
BECH32 = 1
BECH32M = 2
CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
BECH32M_CONST = 0x2bc830a3
def bech32_polymod(values):
"""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
def bech32_hrp_expand(hrp):
"""Expand the HRP into values for checksum computation."""
return [ord(x) >> 5 for x in hrp] + [0] + [ord(x) & 31 for x in hrp]
def bech32_verify_checksum(hrp, data):
"""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
def bech32_create_checksum(hrp, data, spec):
"""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)]
def bech32_encode(hrp, data, spec):
"""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])
def bech32_decode(bech):
"""Validate a Bech32/Bech32m 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, None)
bech = bech.lower()
pos = bech.rfind('1')
# remove the requirement that bech32m be less than 90 chars
if pos < 1 or pos + 7 > len(bech):
return (None, None, None)
if not all(x in CHARSET for x in bech[pos+1:]):
return (None, None, None)
hrp = bech[:pos]
data = [CHARSET.find(x) for x in bech[pos+1:]]
spec = bech32_verify_checksum(hrp, data)
if spec is None:
return (None, None, None)
return (hrp, data[:-6], spec)
def convertbits(data, frombits, tobits, pad=True):
"""General power-of-2 base conversion."""
acc = 0
bits = 0
ret = []
maxv = (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
def decode(hrp, addr):
"""Decode a segwit address."""
hrpgot, data, spec = bech32_decode(addr)
if hrpgot != hrp:
return (None, None)
decoded = convertbits(data[1:], 5, 8, False)
if decoded is None or len(decoded) < 2:
return (None, None)
if data[0] > 16:
return (None, None)
return (data[0], decoded)
def encode(hrp, witver, witprog):
"""Encode a segwit address."""
spec = Encoding.BECH32 if witver == 0 else Encoding.BECH32M
ret = bech32_encode(hrp, [witver] + convertbits(witprog, 8, 5), spec)
if decode(hrp, ret) == (None, None):
return None
return ret
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