  Mobile app markets are emerging with the popularity of smartphones. However,
they fall short in several aspects, including no transparent app listing, no
world-wide app access, and even insecure app downloading. To address these
problems, we propose a novel blockchain-based gateway, AGChain, to bridge end
users and app markets so that existing app markets could still provide services
while users enjoy permanent, distributed, and secure app delegation from
AGChain. To this end, we identify two previously under-estimated challenges and
propose mechanisms to significantly reduce gas costs in our smart contract and
make IPFS (Inter-planetary File System) based file storage really distributed.
We also address three AGChain-specific system challenges to make it secure and
sustainable. We have implemented an AGChain prototype
(https://www.agchain.ltd/) on Ethereum. The evaluation shows that it achieves
security and decentralization with minimal gas costs and reasonable
performance.
