Thanks to Murch and Josie for their insights here Tweet link.

Hashing public keys offers a level of security, but it's not enough to protect against quantum attacks. In this article, we’ll explore why this vulnerability exists in Bitcoin's P2PKH (Pay-to-Public-Key-Hash) transactions.

2. How P2PKH Transactions Work

In a typical P2PKH transaction, the public key is hidden until the transaction is spent. This setup only reveals the public key when funds are being moved

3. Vulnerability in the Mempool

Once the public key is revealed, there’s a window of time where a quantum attack becomes possible. After the transaction enters the mempool, an attacker with a quantum computer can target the public key to derive the private key before the transaction is confirmed.

4. Exploiting the Window of Time

During this window, an attacker can compute the private key and create a conflicting transaction spending the same coins. By offering a higher fee, they incentivize miners to include their transaction over the original one.

5. Transaction Hijacking and Selfish Mining

This technique is known as transaction hijacking. Quantum computers could also exploit Bitcoin through selfish mining, using Grover’s algorithm to gain an advantage in hash rate

view all related items

0 sats \ 0 replies \ @TwoLargePizzas 8h

Sure, maybe. But there's still some fundamental assumptions built into this.

First of all, quantum computers are not magic. They can theoretically do things faster than classical computers but they're still bound by physical time constraints.

Using Grover's Algorithm for searching unsorted databases has quadratic speedup compared to classical computers. When applied to breaking SHA-256, Grover's algorithm would theoretically take around 2^128 / 4 ≈ 2^127 steps on a quantum computer.

The exact time it takes for a single step depends on the specific implementation and hardware of the quantum computer. For today's early-stage machines, each operation might take microseconds to milliseconds.

With those speeds, breaking SHA-256 would still take a very long time:

At 1 microsecond per operation: ~300 years
At 1 millisecond (0.001 second) per operation: ~90,000 years

These are rough estimates and don't account for the significant overhead of error correction, control systems, and other aspects needed to make a large-scale quantum computer work reliably.

So yes, while quantum computers can do it significantly faster than classical computers we're still talking about huge numbers.

0 sats \ 0 replies \ @anon 10h

This is wrong. A soft-fork could allow hash-protected coins to be spent in a commit-reveal scheme where the signature was is committed to in secret, then the signature and pubkey revealed later to actually spend the coins.

0 sats \ 0 replies \ @nitter 17h bot

https://xcancel.com/BTCillustrated/status/1855230598153150544

0 sats \ 0 replies \ @Imyourfed 17h

Just awesome Thanks for sharing!

Why Hashing Public Keys Doesn’t Provide Quantum Resistance

2. How P2PKH Transactions Work

3. Vulnerability in the Mempool

4. Exploiting the Window of Time

5. Transaction Hijacking and Selfish Mining