Paper 2023/062

Post-Quantum Secure Deterministic Wallet: Stateless, Hot/Cold Setting, and More Secure

Abstract

Since the invention of Bitcoin, cryptocurrencies have gained huge popularity. Crypto wallet, as the tool to store and manage the cryptographic keys, is the primary entrance for the public to access cryptocurrency funds. Deterministic wallet is an advanced wallet mech- anism that has been proposed to achieve some appealing virtues, such as low-maintenance, easy backup and recovery, supporting functionali- ties required by cryptocurrencies, and so on. But deterministic wallets still have a long way to be practical in quantum world, and there are also some gaps in the classic world, since there are the following prob- lems waiting to be solved. Firstly, the relying on the state, i.e., stateful. The stateful deterministic wallet scheme must internally maintain and keep refreshing synchronously a state which makes the implementation in practice become more complex. And once one of the states is leaked, thereafter the security notion of unlinkability is cannot be guaranteed (referred to as the weak security notion of forward unlinkability). The second problem is vulnerable. There are security shortfalls in previous works, they suffer a vulnerability when a minor fault happens (say, one derived key is compromised somehow), then the damage is not limited to the leaked derived key, instead, it spreads to the master key and the whole system collapses. Thirdly, the falling short in supporting hot/cold setting. The hot/cold setting is a widely adopted method to effectively reduce the exposure chance of secret keys and hence improving the se- curity of the deterministic wallet system. The last problem is the relying on the weak security notion of unforgeability, in which the adversary is only allowed to query and forge the signatures w.r.t. the public keys that were assigned by the challenger. In this work, we present a new deterministic wallet scheme in quantum world, which is stateless, supports hot/cold setting, satisfiies stronger security notions, and is more efficient. In particular, we reformalize the syntax and security models for deterministic wallets, capturing the func- tionality and security requirements imposed by the practice in cryptocur- rency. Then we propose a deterministic wallet construction and prove its security in the quantum random oracle model. Finally, we show our wal- let scheme is more practicable by analyzing an instantiation of our wallet scheme based on the signature scheme Falcon.