The offline cash puzzle is the challenge of designing digital money that should behave like physical cash and, simultaneously, avoid double-spending and cloning. The puzzle is solved by minting a serialized coin in a local blockchain, which is designed in a two-stage approval protocol. The offline cash can be either minted as a hot coin, which expires and can be retrieved in case of loss, or minted as a cold coin, which is like physical cash.

With the rapid application of consortium chains in various industries, supervising these systems has become a challenge for governments. It is a promising way to govern the chains by a chain, but the existing cross-chain technologies cannot support perfect supervision. Aiming at the shortcomings of previous work, ChainKeeper, a cross-chain scheme for governing the chain by chain, is proposed. The innovation of ChainKeeper lies in three points. First, a modular proxy program is designed to be compatible with various implementations of consortium chains. Second, a verifiable node random selection method is proposed to improve the throughput of cross-chain data transmission. Finally, a verifiable identity threshold signature method is put forward to prevent the cheating behaviour of malicious nodes.

A novel vulnerability detection method based on transformer is proposed by constructing the control flow graph (CFG) of smart contracts operation codes (opcodes), which shields the difference of various versions of program language. Extensive experiments are conducted to evaluate the effectiveness of the proposed method on the authors' own collected dataset. The experimental results show that the proposed method achieves 94.36% accuracy in vulnerability detection, which performs better than other state-of-the-art methods