Glossary

What is GHOSTDAG?

The consensus protocol Kaspa uses today to order blocks in its blockDAG.

GHOSTDAG is the consensus protocol Kaspa runs today. It takes the blockDAG of parallel blocks and turns it into a single agreed order of transactions.

Blue and red blocks

GHOSTDAG colours each block blue or red. Blue blocks belong to a well-connected cluster: they were mined by miners who could see each other's blocks quickly, which is what honest miners look like. Blocks that don't fit that cluster are coloured red.

Blue blocks are ordered first and carry the weight of consensus. Red blocks are still kept and their non-conflicting transactions still count, but they come later in the order.

The k parameter

How many parallel blocks count as normal is set by a fixed parameter, k, chosen from an assumed worst-case network delay. A block can be blue only if it has at most k blue blocks it couldn't have seen when it was mined.

This fixed k is GHOSTDAG's main limitation, and it is exactly what DAGKnight removes.

Origins

GHOSTDAG comes from the PHANTOM research by Yonatan Sompolinsky, Shai Wyborski and Aviv Zohar. PHANTOM describes the ideal ordering rule and GHOSTDAG is the efficient, practical version. Read the paper.