Hourglass V2 Update

The proposal to implement a rate-limit on Pay-to-PubKey (P2PK) unspent transaction outputs (UTXOs) in the Bitcoin network has sparked considerable debate. Critics argue that such a measure would fundamentally compromise Bitcoin's permissionless nature, which is predicated on the principle that the possession of private keys grants unconditional rights to spend associated funds as the owner sees fit. A key concern raised is that by imposing restrictions on the movement of coins, particularly for those who may be slower to act (referred to as "laggards"), the system inadvertently provides a tactical advantage to potential quantum attackers. These attackers, it is feared, could exploit the window created by the rate-limiting to compromise the security of P2PK UTXOs that remain unspent. The specific structure proposed, known as Hourglass V2, is criticized for its potential to extend this vulnerability over an extended period—up to 32 years—thereby magnifying the risk of attack on these critical cryptographic components of the Bitcoin ecosystem. This critique was shared among members of the Bitcoin Development Mailing List, indicating the depth of technical scrutiny and the high stakes involved in safeguarding the network against emerging threats.