i know it is hard to understand the technical part of it which is why i mentioned examples (bitfinex cold storage). here is the address
https://blockchain.info/address/16rCmCmbuWDhPjWTrpQGaU3EPdZF7MTdUk and it contains 137,203 or $1.2 billion. and since it has made lots of transactions you can see its public key in all of those (outgoing) transactions. here is the public key:
02f0bb0774f61a63a610719f73c63f0019c0db62bdfc3682bc55f911538c766674
if it were possible, it would have been stolen already!
RawDog is just trolling here by saying "work a little bit"! it is impossible as of today and in the near future. maybe some day after 100 years with advancement we get enough computing power to find a reverse solution for it and break it but not any sooner. and if we get closer to something like that a simple fork can change bitcoin in a way to prevent it. you still have nothing to worry about, these things don't happen over night.
for example, years ago (2012) SHA1 was considered less secure and everyone slowly moved to other hashings to increase their security until it was no longer used for anything important (2013). finally after years that nobody used it anymore it was broken (last year - 2017) by putting a huge amount of computing power (roughly 110 years of computing from a single GPU for just one of the phases) in it by Google.
