In this exercise you have to brute force the key given one plaintext ciphertext pair encrypted with TC01. In the file Specification a short specification of the cipher is given, the file Reference Implementation [python] contains a reference implementation of the cipher written in Python.
The key will be 64 bit of the form: 0x0000 0000 000* ****. Where a * signifies that this part of the key is unknown. In this case this means that the 20 least significant bits are unknown (and the 44 most significant bits are 0).
Note: All in/output to this website is given in hexadecimal notation in python you can easily interpret a hex as an integer by using:
int(0x0123AFF, 16).
And you can output an integer in hexadecimal format by using a string format:
"%016X"%(123456)