Lightning Network ‘Helplessly Broken’ Against Quantum Computers, Warns Udi Wertheimer Crypto analyst and Taproot developer Udi Wertheimer has stated that the Lightning Network is fundamentally vulnerable in a post-quantum scenario and claimed that its design leaves user funds exposed in ways that cannot be mitigated under current assumptions. According to Wertheimer, the core issue stems from how public and private keys function in cryptocurrency systems. While traditional cryptography relies on the idea that private keys cannot be derived from public keys, he explained that sufficiently advanced quantum computers, which are known as cryptographically relevant quantum computers (CRQCs), could break this assumption by calculating private keys directly from public ones. Lightning’s Weak Spot In most on-chain Bitcoin usage, users can reduce exposure by avoiding address reuse, which helps keep public keys from being exposed unnecessarily. However, Wertheimer argued that this defense does not apply to the Lightning Network, where public keys must be shared as part of its basic operation. Lightning relies on payment channels, which are essentially multi-signature arrangements between two parties. To open and maintain these channels, participants exchange public keys with counterparties. As a result, these keys are not only exposed but also stored by third parties, sometimes without users fully knowing who controls the infrastructure behind their channels. As such, if any entity holding these public keys gains access to a CRQC, or if such data is leaked to an entity that does, then private keys could be derived without user interaction, thereby enabling the theft of funds. Wertheimer further claimed that such an attack would not require the high-speed quantum capabilities often discussed in theoretical scenarios, as there would be no need to intercept transactions in real time. Instead, attackers could work offline using already available public key data. The problem is compounded by the opaque