bech32_utils.py

from enum import Enum


class Encoding(Enum):
    BECH32 = 1
    BECH32M = 2


CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
BECH32M_CONST = 0x2bc830a3


def bech32_polymod(values):
    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):
    return [ord(x) >> 5 for x in hrp] + [0] + [ord(x) & 31 for x in hrp]


def bech32_verify_checksum(hrp, data):
    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):
    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):
    combined = data + bech32_create_checksum(hrp, data, spec)
    return hrp + '1' + ''.join([CHARSET[d] for d in combined])


def bech32_decode(bech):
    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')
    if pos < 1 or pos + 7 > len(bech) or len(bech) > 90:
        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):
    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):
    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 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
    if data[0] == 0 and spec != Encoding.BECH32 or data[0] != 0 and spec != Encoding.BECH32M:
        return None, None
    return data[0], decoded


def encode(hrp, witver, witprog):
    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