DropKick ⚽️ - A minimal commit/reveal PQ rescue protocol

It operates by embedding a hidden commitment within a blockchain block, which can later be revealed through an SPV-style proof to enable the spending of legacy coins in a new PQ-secure wallet. The core of the protocol features the commitment H(H(w, Q), Q) where Q is a post-quantum public key and w is a witness to a one-way function f. This setup utilizes the blockchain's trustless timestamping to secure early knowledge of a secret witness against quantum threats.

The protocol shows flexibility across various one-way functions and does not necessitate the confiscation of coins. Instead, it can be applied to UTXOs with decidable knowledge asymmetries. DropKick minimizes its impact on the blockchain up to the reveal phase, where the commitment proofs are added, consuming minimal space and computational resources. Unlike similar protocols such as Tadge Dryja’s Lifeboat/Lifejacket, DropKick uses a simpler implementation with potentially less security due to its relaxed commitment ordering requirements. This design eliminates the need for a centralized index database by leveraging merkle trees to embed commitments indirectly through blocks, thus reducing on-chain visibility of commitments and broadening potential use cases. However, this design also requires a longer delay between commit and reveal phases, depending on the value of the UTXO involved. For more details on the proving and verifying steps involved in DropKick, please visit conduition.io/bitcoin/dropkick.

Discussions from the Bitcoin Development Mailing List highlight that DropKick's effectiveness depends heavily on the prior deployment of robust PQC within the Bitcoin network, specifically designed to support such commit/reveal mechanisms. This dependency underscores the necessity of having a foundational PQC system in place for effective implementation at the user level, particularly to manage and rescue coins during crises. On-chain PQC ensures the integrity and security of transactions against potential quantum computing threats, playing a crucial role in securely aggregating commitments and providing secure endpoints for coin transfers in emergencies.

Moreover, discussions raise concerns about potential vulnerabilities to time-dilation attacks where attackers might manipulate block appearance speeds to delay a victim’s reveal transaction, increasing risks during the commit/reveal phase. Additional worries include the possibility of distributed denial-of-service attacks targeted at aggregators, inflation of proof costs by third parties, and risks associated with binding malleability of opening proofs. Despite these challenges, the adaptability and formalization of issues within DropKick present an intriguing advancement in cryptocurrency protocols aimed at enhancing user flexibility and security in a post-quantum world.