In order to spend any bitcoin, you need the private key associated with the address.
It is not trivial to get the private key from the public key, in fact, there is no known way to calculate the private key from the public key. Quantum computing may change this, however, we are still a long way away from a Quantum Computer being able to get the private key from the public key.
It can decode 64 bit range with Kangoroo in a maximum of 5 minutes. In other words, the range and public key are certain, and it is clear in how many minutes it will be resolved. I would be glad if you look at it here.