convert a smart health card url to JSON

decode_shc.py

# Decode Smart Health Card URL
import argparse
import base64
import json
import zlib
from urllib.parse import urlparse

parser = argparse.ArgumentParser(description='Decode Smart Health Card URL')
parser.add_argument('url', help='URL to decode')


def unzlib(data):
    """inflate a headerless and crcless deflated data
    """
    return zlib.decompress(data, wbits=-15)


def main():
    args = parser.parse_args()
    # get the decimal-encoded part of the url
    decimal = urlparse(args.url).path[1:]
    # decode to JWS string
    data = ''.join(chr(int(''.join(decimal[i:i + 2]), 10) + 45)
                   for i in range(0, len(decimal), 2))
    # decode base64 parts
    parts = [base64.urlsafe_b64decode(s + '===') for s in data.split('.')]
    card = {
        'header': json.loads(parts[0]),
        'payload': json.loads(unzlib(parts[1])),
        'signature': parts[2].hex()
    }
    print(json.dumps(card, indent=2))


if __name__ == "__main__":
    main()