BIP-380 output descriptors checksum

descriptors_checksum.py

import sys

INPUT_CHARSET = "0123456789()[],'/*abcdefgh@:$%{}IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~ijklmnopqrstuvwxyzABCDEFGH`#\"\\ "
CHECKSUM_CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
GENERATOR = [0xf5dee51989, 0xa9fdca3312, 0x1bab10e32d, 0x3706b1677a, 0x644d626ffd]

def descsum_polymod(symbols):
    """Internal function that computes the descriptor checksum."""
    chk = 1
    for value in symbols:
        top = chk >> 35
        chk = (chk & 0x7ffffffff) << 5 ^ value
        for i in range(5):
            chk ^= GENERATOR[i] if ((top >> i) & 1) else 0
    return chk

def descsum_expand(s):
    """Internal function that does the character to symbol expansion"""
    groups = []
    symbols = []
    for c in s:
        if not c in INPUT_CHARSET:
            return None
        v = INPUT_CHARSET.find(c)
        symbols.append(v & 31)
        groups.append(v >> 5)
        if len(groups) == 3:
            symbols.append(groups[0] * 9 + groups[1] * 3 + groups[2])
            groups = []
    if len(groups) == 1:
        symbols.append(groups[0])
    elif len(groups) == 2:
        symbols.append(groups[0] * 3 + groups[1])
    return symbols

def descsum_check(s):
    """Verify that the checksum is correct in a descriptor"""
    if s[-9] != '#':
        return False
    if not all(x in CHECKSUM_CHARSET for x in s[-8:]):
        return False
    symbols = descsum_expand(s[:-9]) + [CHECKSUM_CHARSET.find(x) for x in s[-8:]]
    return descsum_polymod(symbols) == 1


def descsum_create(s):
    """Add a checksum to a descriptor without"""
    symbols = descsum_expand(s) + [0, 0, 0, 0, 0, 0, 0, 0]
    checksum = descsum_polymod(symbols) ^ 1
    return s + '#' + ''.join(CHECKSUM_CHARSET[(checksum >> (5 * (7 - i))) & 31] for i in range(8))

def help():
    print(f"""help:
    {sys.argv[0]} <command> <param>

command:
    create: create checksum
    check:  verify checksum
""")

def main() -> int:
    if len(sys.argv) != 3:
        help()
        sys.exit(1)
    cmd = sys.argv[1]
    param = sys.argv[2]
    if cmd == "create":
        sum = descsum_create(param)
        print(f"sum={sum}")
    elif cmd == "check":
        chk = descsum_check(param)
        print(f"valid={chk}")
    else:
        help()
    return 0

if __name__ == '__main__':
    main()

BIP-380 TestVectors

$ python3 descriptors_checksum.py create "raw(deadbeef)"
sum=raw(deadbeef)#89f8spxm
$ python3 descriptors_checksum.py check "raw(deadbeef)#89f8spxm"
valid=True