CSW on double hash - scaleable ASICs
…”If you start to think about it, you will see that where:
A == Hash(X),
B == Hash(A)
allows us to have the value (A) sent to a miner in a way that doesn’t allow them to broadcast a block without individual transactions. In a Merkle tree structure, we could have all of the block sent and solved apart from a single transaction. Doing so would allow us to construct an ASIC mining facility that does not host the data in blocks. The miner is now a distributed function.
As such, the proof-of-work and the verification can be handed off to specialised entities. The ASIC facility can pay the verification facility upon discovery of valid blocks, and yet the system allows them to interact without being able to cheat either party. In fact, they can even have agreements with different miners and pools and allow it to occur without worry: if one party cheats, both lose out.”…
P.S. sha256d does not add to security of the hash as such.