One masternode is randomly selected to announce each block.
masternode = regular node + deposit

256 randomly selected masternodes sign this block.

The node issues receipts for fast transaction confirmation.

The committee will reject a block if it is missing transactions.

Once signatures are collected, the block is confirmed.

Nodes have a hard limit of 2 hours to provide their signature.

The chain will usually have all the signatures,
so an attack would require much more than 50%.

Any double-signing can be penalized, and lose the deposit.

Implementation details outlined in the whitepaper.