This is using the hashcash PoW. The use of scrypt as underlying hash function is a rather poor choice though, as scrypt's memory hardness makes PoW verification

This is using the hashcash PoW. The use of scrypt as underlying hash function is a rather poor choice though, as scrypt's memory hardness makes PoW verification unnecessarily expensive. To limit the damage, a rather small memory footprint is used for scrypt. It's perfectly possible to make a memory hard PoW that's instantly verifiable, by using something other than hashcash. Examples include Cuckoo Cycle [1], and Equihash [2]. These can easily be made to use hundreds of MB in solving, while verification is memory less. [1] https://github.com/tromp/cuckoo https://github.com/tromp/cuckoo [2] https://en.wikipedia.org/wiki/Equihash https://en.wikipedia.org/wiki/Equihash