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#!/usr/bin/env python3
# Copyright (c) 2017 Pieter Wuille
# Distributed under the MIT software license, see the accompanying
# file COPYING or http://www.opensource.org/licenses/mit-license.php.
"""Reference implementation for Bech32 and segwit addresses."""
CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
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."""
return bech32_polymod(bech32_hrp_expand(hrp) + data) == 1
def bech32_create_checksum(hrp, data):
"""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)]
def bech32_encode(hrp, data):
"""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])
def bech32_decode(bech):
"""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])
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 = bech32_decode(addr)
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)
def encode(hrp, witver, witprog):
"""Encode a segwit address."""
ret = bech32_encode(hrp, [witver] + convertbits(witprog, 8, 5))
if decode(hrp, ret) == (None, None):
return None
return ret
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