trezor-firmware/core/src/trezor/crypto/bech32.py

# 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
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# THE SOFTWARE.

"""Reference implementation for Bech32 and segwit addresses."""

if False:
    from typing import Iterable, List, Optional, Tuple, Union, TypeVar

    A = TypeVar("A")
    B = TypeVar("B")
    # usage: OptionalTuple[int, List[int]] is either (None, None) or (someint, somelist)
    # but not (None, somelist)
    OptionalTuple = Union[Tuple[None, None], Tuple[A, B]]

CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"


def bech32_polymod(values: List[int]) -> int:
    """Internal function that computes the Bech32 checksum."""
    generator = [0x3B6A_57B2, 0x2650_8E6D, 0x1EA1_19FA, 0x3D42_33DD, 0x2A14_62B3]
    chk = 1
    for value in values:
        top = chk >> 25
        chk = (chk & 0x1FF_FFFF) << 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: List[int]) -> bool:
    """Verify a checksum given HRP and converted data characters."""
    return bech32_polymod(bech32_hrp_expand(hrp) + data) == 1


def bech32_create_checksum(hrp: str, data: List[int]) -> 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)]


def bech32_encode(hrp: str, data: List[int]) -> str:
    """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: str, max_bech_len: int = 90) -> OptionalTuple[str, List[int]]:
    """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) > max_bech_len:
        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: Iterable[int], frombits: int, tobits: int, pad: bool = True
) -> Optional[List[int]]:
    """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: str, addr: str) -> OptionalTuple[int, List[int]]:
    """Decode a segwit address."""
    hrpgot, data = bech32_decode(addr)
    if data is None or 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: str, witver: int, witprog: Iterable[int]) -> Optional[str]:
    """Encode a segwit address."""
    data = convertbits(witprog, 8, 5)
    if data is None:
        return None
    ret = bech32_encode(hrp, [witver] + data)
    if decode(hrp, ret) == (None, None):
        return None
    return ret