The safest way to get a working registration key is to buy it directly from the official website of Active Uneraser or from authorized resellers. This ensures you get a legitimate key and avoids any potential scams.
Here is the irony: You are trying to recover important, valuable data. To do that, you are considering running untrusted, unsigned executable code from a hacker (the crack) with full administrative privileges on the same drive that contains your lost files.