Actually, you can. There's a huge gulf between things that we know we could compute given enough time, even if that time is impossible to actually be given, and things we know can never be computed given infinite computing power.
Something like the perfect security of either hiding or binding in a commitment protocol can never be broken given computers of infinite capacity and speed because it's mathematically impossible. That is opposed to computational security, which only states that the property can't be broken within any usable time frame. This is often in the order of hundreds of millions of years in practical cryptographic systems. The point is, it can be technically be done.
Breaking RSA can factored just by brute forcing. It might take a lot of time, but actually doing it is not hard for sufficiently small keys. We just increase the key size until it takes a long time.
Something like the perfect security of either hiding or binding in a commitment protocol can never be broken given computers of infinite capacity and speed because it's mathematically impossible. That is opposed to computational security, which only states that the property can't be broken within any usable time frame. This is often in the order of hundreds of millions of years in practical cryptographic systems. The point is, it can be technically be done.
Breaking RSA can factored just by brute forcing. It might take a lot of time, but actually doing it is not hard for sufficiently small keys. We just increase the key size until it takes a long time.