DropKick ⚽️ - A minimal commit/reveal PQ rescue protocol

DropKick is a new commit/reveal rescue protocol designed to aid Bitcoin users, referred to as quantum procrastinators, who fail to transfer their assets into Post-Quantum Cryptography (PQC) enabled wallets by the designated Q-Day. The protocol operates by making a hidden commitment on the blockchain, which can later be revealed with an SPV-style proof to facilitate the spending of legacy coins in a new PQ-secure wallet. This system utilizes the blockchain's inherent trustless timestamping capabilities to prove the early knowledge of a secret witness, safeguarding it from potential adversaries like quantum computers.

The technical foundation of DropKick revolves around the commitment H(H(w, Q), Q) embedded within a block, such as an OP_RETURN or a taproot tweak. Q represents a post-quantum public key and w is a witness to a one-way function f. When the time comes, this witness along with a signature from Q can authorize a coin spend. The verifier checks the validity and age of the commitment opening, confirms the calculation s = f(x), and validates the PQ-signature from Q.

Regarding its features, DropKick offers generality across various one-way functions based on knowledge asymmetries, ensuring compatibility without needing to confiscate any coins by applying it specifically to UTXOs with decidable knowledge asymmetries. Its design allows for a minimal impact on the blockchain until the reveal phase, where the commitment opening proofs are added to the blockchain, consuming little space and computational resources. Importantly, DropKick does not require users to have their own PQ-safe UTXOs but instead enables them to use third-party aggregators who manage these commitments collectively.

In comparison to Tadge Dryja’s Lifeboat/Lifejacket protocols, DropKick opts for a simpler implementation with potentially lower security due to its relaxed commitment ordering requirement. Unlike Lifeboat, where validators must index all commitments to establish a chronological order, DropKick leverages merkle trees to embed commitments indirectly through blocks, thus eliminating the need for a centralized index database and reducing visibility of commitments on-chain.

This approach introduces a novel role for aggregators and removes the necessity for individual PQ-UTXOs, broadening the range of scenarios in which users can be rescued. However, it demands a longer delay between the commit and reveal phases, proportional to the value of the UTXO at stake. Despite these trade-offs, DropKick presents a versatile and efficient solution aimed at enhancing user experience and flexibility in post-quantum cryptocurrency transactions. For more detailed insights into the proving and verifying steps involved in DropKick, please visit conduition.io/bitcoin/dropkick.