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GHOST Protocol

Ethereum uses the GHOST (Greedy Heavies Observed Subtree) protocol to solve the problem of stale blocks that are created simultaneously but can’t connect to the main. The more uncle blocks are created, the less secure the blockchain network will be, and the wasted computer resources due to the unconnected blocks will occur and the monopoly of mining. Unlike the Bitcoin, Ethereum is solving the problem of blocks created at the same time while maintaining the block generation cycle of 15 seconds using GHOST protocol. Several issues arising from Ethereum's block generation cycle, which is only 15 seconds, are addressed using the GHOST protocol.

Since GHOST also includes an uncle block when calculating which chain is the longest chain, up to two uncle blocks can be added to one normal block at the time of block creation and compensation is given to the uncle block and normal block. The GHOST protocol used in Ethereum can be defined as follows.


  • One block must specify one parent block and zero or more blocks of uncle.
  • The uncle block included in block #N connected to the main chain must have the following attributes:
  • - the direct descendant of the kth ancestor of block #N (2 <= k <= 7)
    - It should not be the ancestor of block #N.
  • It must be different from all uncle blocks contained in the previous block or from the uncle block included in the same block.
  • It must be a valid block header, but it does not have to be validated.