How Cardano protects itself from 51% attack?

Cardano’s PoS works in many ways very similarly to Bitcoin’s PoW. You may be surprised to learn that when a blockchain forks, Cardano applies the longest chain rule similar to Bitcoin. It doesn’t take a lot of energy to create a PoS block, so there must be some additional rules in the Cardano protocol. Let’s explain some of them and show how the rules protect Cardano from the 51% attack.


  • Cardano uses the longest chain rule that is similar to Bitcoin’s rule.
  • The Plenitude rule is used against long-range attacks.
  • If private keys used to sign blocks are erased, attempting to overwrite the history of the blockchain is impossible.

The protocols are about the rules

A blockchain is a chain of blocks. The network adds new blocks to the end of the chain. Occasionally, two blocks may be produced by two (or more) independent nodes simultaneously. This event is called a fork. It means that two new blocks follow the previous block. Some rule is required to ensure that one block is a winner and stays forever in the blockchain, while the other block is discarded (orphaned forever). You can see the fork in the picture below. The node that is going to produce the next block must choose between block A or B.

This article was prepared by Cardanians with support from Cexplorer.

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