>>519184180
they're not based on AES-256
Bitcoin uses a non-nist(non-nsa) elliptic curve cryptography to generate public/private key pairs and verify/sign transactions, these keys are susceptible to quantum algorithms but bitcoin is again further protected so that the public key is only known when you spend funds, public keys are hashed with sha256 and then ripemd160. (when you spend funds from an address, the blockchain verifies that your public key matches the address when hashed with sha256 and ripemd160).
so even if you break public/private key crytopgrahy with quantum computing, you need to break ripemd160 and sha256 too for most bitcoin address to get their funds,
there is no guarantee sha256 and ripemd160 will ever be breakable at-least not for thousands of years, if there is a flaw in their designs then you'll have to break both of them.
if quantum computing attacks become feasible then the network just has to agree to switch to a quantum safe public/private key cryptography
if sha256 or ripemd160 are demonstrated to be broken then they just have to switch to a safer hash function
Atleast in Bitcoin's case you can just upgrade everyone's keys, there will be time, unless its a super human alien thats attacking the network then people will have time to switch over to stronger keys