  An enormous amount of energy is wasted in Proofof-Work (PoW) mechanisms
adopted by popular blockchain applications (e.g., PoW-based cryptocurrencies),
because miners must conduct a large amount of computation. Owing to this, one
serious rising concern is that the energy waste not only dilutes the value of
the blockchain but also hinders its further application. In this paper, we
propose a novel blockchain design that fully recycles the energy required for
facilitating and maintaining it, which is re-invested to the computation of
deep learning. We realize this by proposing Proof-of-Deep-Learning (PoDL) such
that a valid proof for a new block can be generated if and only if a proper
deep learning model is produced. We present a proof-of-concept design of PoDL
that is compatible with the majority of the cryptocurrencies that are based on
hash-based PoW mechanisms. Our benchmark and simulation results show that the
proposed design is feasible for various popular cryptocurrencies such as
Bitcoin, Bitcoin Cash, and Litecoin.
