@internets you are asking a difficult but important question. Older versions of Ransomware were not coded very well. They were easily cracked by security researchers. However, in the past year the quality of the malicious code has significantly improved. That tends to happen when money is on the line. Modern variants of ransomware are very robust and manage asymmetric keys expertly. They are virtually impossible to break on the client side. It is possible if their Command and Control infrastructure is compromised or seized by authorities and the private keys are recovered. This happens, but not often enough.

A number of security organizations are now pooling their resources to create tools for keys which have been recovered. First you need to determine the variant a victim has (not that easy as they may claim to be something different) and then apply the private key in a way to recover files but not harm the system. The good news is, a site is now up to do both. Check out https://www.nomoreransom.org/

Again, they don't have the private keys for every variant, but victims might get lucky. They do have a checker to easily identify the variant. I know some of the researchers behind this site. They are from top security companies in the industry and are serious about addressing the scourge we call Ransomware. - Hope that helps.