With all broken encryption and hashing algorithms of the past, they are 100% secure... until they're not. It is to the best of our knowledge that the current algorithms are secure, but it is very naive to say that they will remain that way forever. Additionally, quantum computers capable of running Shor's algorithm at large enough scale can definitely break current encryption used in cryptocurrencies, so it's only a matter of time before quantum-resistant algorithms will become the new normal across the board.