DIY Quantum Protection for Bitcoin

[Stuart LaForge]

Ok, so I think I have come up with a simple low technology method of
safeguarding bitcoin against Quantum computing algorithms like Shor's.

First you need to but 2 hardware cold wallets (e.g. Trezor, Ledger,
etc.) Create a seed phrase to generate a public key with one of them and
send your BTC to it.

When you want to spend or transfer bitcoin, you set up (or reset) a seed
phrase on your second wallet. Spend whatever bitcoin you need to and
then transfer the remaining balance to the second wallet. When you
spend/send bitcoin, the public key of the sending wallet gets exposed on
the blockchain in a way that a quantum computer could use it to crack
the private key for the spending wallet, so the idea is to empty that
wallet completely. The public key of the receiving wallet is kept secret
because it does not show up anywhere during the transaction. The only
private key that a quantum computer could derive would be for the empty
wallet that you no longer use.

Then when you want to spend/send money from your second wallet, factory
reset the original wallet and create a new seed phrase for it to
generate a novel public. Spend your bitcoin from the second wallet and
immediately send the remaining balance to the, now reset 1st wallet that
has a brand new seed phrase / public key that has never been exposed on
the blockchain and cannot be used to hack your private key.

Then, when you want to perform another transaction, rinse and repeat.
Always resetting and reseeding the unused wallet to get a fresh public
key before use. With two hardware wallets, you should be able to keep
this up indefinitely. It is a little bit of a hassle, but from what I
understand of the bitcoin protocol, it should keep your bitcoins safe
from quantum computing algorithms with existing technology. Let me know
if you find a weakness in this scheme.

Stuart LaForge

[John Clark]

Keeping the public key unexposed is a well known defense and it does offer a little protection but the trouble is the public key isn't just exposed when you initiate a transaction, it's exposed from the moment the transaction hits the holding area where unconfirmed transactions wait in a decentralized queue before being processed by miners, depending on how busy the network is that could be anywhere from a few minutes to a few hours, and in the quantum world that is a long time; a sufficiently powerful quantum computer could crack your private key faster than block confirmation time. Also, if anybody has ever sent to an address more than once then those coins are already exposed to a future quantum attacker. And when it comes to early bitcoins, like Satoshi's one million bitcoins, the public key is directly in the output script and so the coins are already fully exposed.

John K Clark