Mitigating the risks
Bitcoin allows different types of transactions such as escrow and shared ownership. For the purpose of this section, we’re limiting it to simple person-to-person transactions only.
Problem: Exposed public key
You still could protect your public key. There are two type of addresses - ‘pay to public key’ (p2pk) and the hashed public key. The hashed public key is a one-way cryptographic function, the public key is not directly revealed by the address. However, the public key does get revealed once a transaction is sent from that address. This is why you should avoid address reuse as best you can.
Solution - Avoid address reuse
Avoid address reuse as best you can1. If you would like to stay at the Bitcoin network, move your funds to a new address that hasn’t their public keys exposed. Keep in mind though - if Q-Day were to happen, the market is expected to crash and the confidence in Bitcoin and its technology would be lost too.
Is that all?
Actually, it is not that simple. As in the above, we’re assuming that there is no quantum computer that will take advantage of the “window opportunity”. As soon as you make a transaction, your public key will be revealed. So, until your transaction isn’t mined - you are at risk for an attack. The adversary will first derive your private key from the public key and then initiate a competing transaction to their own address. They will try to get priority over the original transaction by offering a higher mining fee - stealing your coins.
It takes 10 minutes for a Bitcoin transaction to be mined, unless there is a network congestion, which has happened frequently in the past.. It could take much longer. So the rule is - as long as there isn’t a quantum comptuer that is faster than the network - your funds are safe.
Currently it is unclear how fast a quantum computer will be in the future. If a quantum computer will be close to the 10 minutes mark (making it faster than the network), Bitcoin would be inherently broken.
Solution 2 - Migrating to a post-quantum secure blockchain
Migrating to a post-quantum secure blockchain, the blockchain would be inherently resistant to quantum attacks. If Q-Day were to happen, this would drive the price up and give confidence to its technology.
The price increase would occur because of the masses losing confidence in quantum unsafe blockchain technology and increased confidence in post-quantum secure blockchains. Post-quantum secure blockchains would serve a real use case, which is protecting the assets from quantum attacks, driving up its value.