bech32 encoder

bech32_encoder.py

# This is a bech32 encoder
# run with command line arguments
# $ python3 bech32_encoder.py <prefix> <address>
# $ python3 bech32_encoder.py wit 0x000000000000000000000000000000000000dead

import sys
from typing import List, AnyStr
import unicodedata
from enum import Enum


def bytes_to_int(bts: bytes) -> int:
    return int.from_bytes(bts, 'big')


def int_to_bytes(i: int) -> bytes:
    length = max(1, (i.bit_length() + 7) // 8)
    return i.to_bytes(length, 'big')


Bytes = List[int]


class BaseConversionError(Exception):
    pass


def convert_bits(data: Bytes, from_bits: int, to_bits: int, pad=True) -> Bytes:
    """General power-of-2 base conversion."""
    acc = 0
    bits = 0
    ret = []
    max_v = (1 << to_bits) - 1
    max_acc = (1 << (from_bits + to_bits - 1)) - 1
    for value in data:
        if value < 0 or (value >> from_bits):
            raise BaseConversionError
        acc = ((acc << from_bits) | value) & max_acc
        bits += from_bits
        while bits >= to_bits:
            bits -= to_bits
            ret.append((acc >> bits) & max_v)
    if pad:
        if bits:
            ret.append((acc << (to_bits - bits)) & max_v)
    elif bits >= from_bits or ((acc << (to_bits - bits)) & max_v):

        raise BaseConversionError
    return ret


def normalize_string(txt: AnyStr) -> str:
    if isinstance(txt, bytes):
        utxt = txt.decode('utf8')
    elif isinstance(txt, str):
        utxt = txt
    else:
        raise TypeError('String value expected')

    return unicodedata.normalize('NFKD', utxt)


ALPHABET = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
CHARSET = 'qpzry9x8gf2tvdw0s3jn54khce6mua7l'
BASE = len(ALPHABET)


class Bech32Encoding(Enum):
    """Enumeration type to list the various supported encodings."""
    BECH32 = 1
    BECH32M = 2


class Bech32DecodeError(Exception):
    pass


def bech32_poly_mod(values) -> 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


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]


def bech32_verify_checksum(hrp: str, data) -> bool:
    """Verify a checksum given HRP and converted data characters."""
    return bech32_poly_mod(bech32_hrp_expand(hrp) + data) == 1


def bech32_create_checksum(hrp: str, data):
    """Compute the checksum values given HRP and data."""
    values = bech32_hrp_expand(hrp) + data
    polymod = bech32_poly_mod(values + [0, 0, 0, 0, 0, 0]) ^ 1
    return [(polymod >> 5 * (5 - i)) & 31 for i in range(6)]


def bech32_decode_address(bech: str):
    bech, separator = bech.lower(), bech.find('1')
    hrp_ = bech[:separator]
    data = [CHARSET.find(x) for x in bech[separator + 1:]]
    decoded = data[:-6]
    try:
        if any(ord(x) < 33 or ord(x) > 126 for x in bech):
            raise Bech32DecodeError('Character outside US-ASCII [33-126] range')
        if (bech.lower() != bech) and (bech.upper() != bech):
            raise Bech32DecodeError('Mixed upper and lower case')
        if separator == 0:
            raise Bech32DecodeError('Empty human readable part')
        elif separator == -1:
            raise Bech32DecodeError('No separator character')
        elif separator + 7 > len(bech):
            raise Bech32DecodeError('Checksum too short')
        if not all(x in CHARSET for x in bech[separator + 1:]):
            raise Bech32DecodeError('Character not in charset')
        if not bech32_verify_checksum(hrp_, data):
            raise Bech32DecodeError('Invalid checksum')
        if decoded is None or len(decoded) < 2:
            raise Bech32DecodeError('Witness program too short')
    except Bech32DecodeError as error:
        print(error)
    b256 = convert_bits(decoded, from_bits=5, to_bits=8, pad=True)
    return b256


def bech32_encode_address(hrp: str, data: str) -> str:
    hex_bytes = [b for b in bytes.fromhex(data)]
    data = convert_bits(data=hex_bytes, from_bits=8, to_bits=5, pad=False)

    checksum = bech32_create_checksum(hrp=hrp, data=data)

    combined = data + checksum

    return normalize_string(hrp + '1' + ''.join([CHARSET[i] for i in combined]))


if __name__ == '__main__':
    public_key = sys.argv[2]
    prefix = sys.argv[1]
    if public_key.startswith('0x'):
        public_key = public_key[2:]

    address = bech32_encode_address(prefix, public_key)
    print(address)