[bitcoin-dev] A solution may solve Block Withholding Attack

[潘志彪]

Here is a solution may solve Block Withholding Attack. The general idea is
came from Aviv Zohar(avivz at cs.huji.ac.il), I made it work for Bitcoin.
Anyway, thanks Aviv.

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DIFF_1 = 0x00000000FFFF0000000000000000000000000000000000000000000000000000;

Diff = DIFF_1 / target

this is equal to

Diff = DIFF_1 / (target - 0) or Diff = DIFF_1 / abs(target - 0)

now, we change diff algo to below:

New_Diff = DIFF_1 / abs(target - offset)

Offset is 32 bytes, like uint256 in Bitcoin, range is [0, 2^256),
define: offset_hash = DSHA256(offset).

we need to do a little change to the merkle root hash algo, put the
offset_hash as a tx hash in the front of tx hashes.

[offset_hash, coinbase_tx_hash, tx01_hash, tx02_hash, … , tx_n_hash]

Actually could put offset_hash in any place in the array of hashes.

network_hash_range = network_hash_end - network_hash_begin

miner_hash_range = miner_hash_end - miner_hash_begin

The offset value MUST between network_hash_begin/end or
miner_hash_begin/end.

https://user-images.githubusercontent.com/514951/31133378-e00d9ca2-a891-11e7-8c61-73325f59f6ed.JPG

When mining pool send a job to miners, put the PoW hash range
(miner_hash_begin/end) in the job. So if the miners find a hash which value
is between [miner_hash_begin, miner_hash_end], means it's SHOULD be a
valid share, could submit the share to the pool. If the hash value is
between [network_hash_begin, network_hash_end] means find a valid block.

The network_diff is much much high than the miner's diff, means the
network_hash_range is much much smaller than miner_hash_range. By now,
a typical miner's pool diff is around 16K, network diff is 1123863285132,
so miner_hash_range is at least million times bigger than
network_hash_range.
The miners only know miner_hash_range, it's impossible for cheat miners
to find out which share could make a valid block or not.

Problems:
1. it's a hard fork.
2. will make existed asic dsha256 chips useless, but I think it's only a
small change to make new asic chips based on existed tech.
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