The channels in question are secured using a hash while they remain active. Funding transactions are conducted via P2WSH (Pay-to-Witness-Script-Hash), which ensures that the raw public keys involved in the 2-of-2 multisig setup are concealed on the blockchain for the duration of the channel’s activity. Lightning payments utilize a hash-based mechanism, transmitted through HTLCs (Hashed Time-Lock Contracts). This setup depends on the revelation of a hash preimage rather than the direct exposure of public keys. A quantum adversary observing the blockchain is unable to discern the necessary keys.
The potential attack opportunity is significantly reduced to a force-close event. When a channel is terminated and a commitment transaction is made public on the blockchain, the locking script is revealed for the first time, including the local_delayedpubkey, which is a conventional elliptic-curve public key. By design, the node that initiates this broadcast cannot immediately access its funds, as a CSV (CheckSequenceVerify) timelock, generally lasting for 144 blocks (approximately 24 hours), must elapse first.
In a hypothetical post-quantum environment, an attacker observing the mempool could notice that a commitment transaction has been confirmed, extract the now-visible public key, apply Shor’s algorithm to calculate the private key, and then attempt to access the output before the timelock runs out. HTLC outputs that occur during a force-close can present additional opportunities, with some windows being as brief as 40 blocks, translating to roughly six to seven hours.
This represents a tangible and specific risk. Nonetheless, it is a contest against time, requiring an attacker to solve one of the most complex mathematical challenges within a limited timeframe for each intended theft. This is not a passive, simultaneous drain on all Lightning wallets.