#!/usr/bin/env python3

import sys

def main():
    if len(sys.argv) < 2:
        print("Benutzung: 13 Byte bzw. 26bit Hex ffff0123456789abcdef012345 ".format(sys.argv[0]))
        sys.exit(1)
    byte_array = bytearray.fromhex(sys.argv[1]) #from RADIO HACKER
    if len(byte_array)!=13:
        print(byte_array)
        print("Falsche Länge ! {}".format(byte_array))
        sys.exit(1)
    checksum=0
    for i in range(2,12):
        checksum=checksum^byte_array[i]
    if checksum==byte_array[12]:
        print("Checksumme ok")
    else:
        print(checksum)
        print(f"Falsche Checksumme, sollte sein {checksum:02X} aber ist {byte_array[12]:02X}")
    ide = int.from_bytes(byte_array[2:6], byteorder='big')
    print(f"ide {ide:08X}")
    button=(byte_array[6]>>4)&0x3
    print(f"button {button:01X}")
    counter=byte_array[6]&0xF
    counter=counter<<6
    counter+=byte_array[7]>>2 #the two lsb are the two msb of the secret/crypt
    print(f"counter {counter:03X}")
    secret = int.from_bytes(byte_array[8:12], byteorder='big')
    secret=secret>>2
    secret+=(byte_array[7]&0x3)<<30 #the two bits after the counter are the high bits of the secret/crypt
    print(f"secret {secret:08X}")
    #this is needed for the next CTF
    print("\ndata for htcrack:")
    print(f"UID {ide:08X}")
    #IV is in this case just the counter plus 4bits with the button value
    iv=(counter<<4)+button
    print(f"nRx {iv:08X}")
    print(f"aRx {secret^0xFFFFFFFF:08X}")

if __name__ == "__main__":
    try:
        main()
    except KeyboardInterrupt:
        print("Abbruch durch Benutzer")
    finally:
        print("Bye bye")