Dash uses a two-tier network to secure its transactions. The first tier consists of nodes that carry out mining operations under a proof-of-work [consensus](https://coinmarketcap.com/alexandria/glossary/consensus) protocol, meaning that they compete to solve complex cryptographic problems and at least 51% of nodes must approve a transaction for it to be added to the blockchain.
The PoW algorithm used by Dash is called "X11" — a custom hashing algorithm developed by Dash founder Duffield that uses a sequence of 11 hashing algorithms. According to Dash's [documentation](https://docs.dash.org/en/stable/introduction/features.html#x11-hash-algorithm), X11 is "one of the safest and more sophisticated cryptographic hashes in use by modern cryptocurrencies."
The second tier consists of masternodes operating under a proof-of-service consensus algorithm in which masternodes are rated based on their history of providing good services to the network. Masternodes oversee the network and have the power to reject new blocks added by nodes if they were approved improperly. They also enable Dash's ChainLocks feature, which increases security because every 12 hours, a rotating group of masternodes observe and confirm all new blocks added to the blockchain. Dash's developers have [stated](https://blog.dash.org/mitigating-51-attacks-with-llmq-based-chainlocks-7266aa648ec9) that this protects the network against [51% attacks](https://coinmarketcap.com/alexandria/glossary/51-attack).