Proof-of-useful-work (PoUW), an alternative to the widely used proof-of-work (PoW), aims to re-purpose the network’s computing power. Namely, users evaluate meaningful computational problems, e.g., solving optimization problems, instead of computing numerous hash function values as in PoW. A recent approach utilizes the training process of deep learning as “useful work”. However, these works lack security analysis when deploying them with blockchain-based protocols, let alone the informal and over-complicated system design. This work proposes a distributed proof-of-deep-learning (D-PoDL) scheme concerning PoUW’s requirements. With a novel hash-traininßg-hash structure and model-referencing mechanism, our scheme is the first deep learning-based PoUW scheme that enables achieving better accuracy distributively. Next, we introduce a transformation from the D-PoDL scheme to a generic D-PoDL blockchain protocol which can be instantiated with two chain selection rules, i.e., the longest-chain rule and the weight-based blockchain framework (LatinCrypt’ 21). This work is the first to provide formal proofs for deep learning-involved blockchain protocols concerning the robust ledger properties, i.e., chain growth, chain quality, and common prefix. Finally, we implement the D-PoDL scheme to discuss the effectiveness of our design.

Hot/cold wallet refers to a widely used paradigm to enhance the security level of cryptocurrency applications that was proposed on Bitcoin Improvement Proposal 32. In a nutshell, after performing an initial setup in which the hot wallet receives partial information of the cold wallet in order to hierarchically generate (transaction receiving) addresses, the cold wallet stays offline, whereas the hot wallet is kept online. The initial transferred information enables the hot wallet to generate receiving addresses for both wallets, but it can only spend its own funds, i.e., it cannot spend the funds in the cold wallet. This design conveniently mimics money storage in daily life: pocket money is kept in a less safe location, e.g., a regular wallet, while life savings are kept in a more safe environment, e.g., banking account. Note that the funds that land in offline addresses cannot be spent if the cold wallet is kept permanently offline. We propose a protocol and a technical solution to spend funds from a cold wallet without physically connecting it to any network. We designed and implemented a prototype for a system based on Optical Camera Communication (OCC) in a screen to camera setting, which can receive messages from a computer screen at the rate of over 150kB per second. Our system consists of a sequence of QR codes – a QR video. Our solution minimizes the possible attack vectors, including malware, by relying on optical communication yet providing a larger bandwidth than regular QR code based solutions.