Consensus is the process of reaching a majority opinion by everyone involved in running the blockchain. Agreement must be made on which blocks to produce, which chain to adopt, and to determine the single state of the network. The consensus protocol determines how individual nodes assess the current state of the ledger system and reach a consensus.
The protocol has three main responsibilities -Perform a leader check and decide if a block should be produced -Handle chain selection -Verify produced blocks
Blockchains create consensus by allowing participants to bundle transactions that others have submitted to the system in blocks, and add them to their chain (sequence of blocks). Determining who is allowed to produce a block when, and what to do in case of conflicts, (such as two participants adding different blocks at the same point of the chain), is the purpose of the different consensus protocols.
Ouroboros, our ground-breaking proof-of-stake consensus protocol, is proven to have the same security guarantees as proof-of-work. Ouroboros establishes security guarantees, and the protocol was delivered with several peer-reviewed papers presented in top-tier conferences and publications in the area of cybersecurity and cryptography. Different implementations of Ouroboros have been developed. For further details on each flavour of Ouroboros, you can read the technical specifications for Classic, Byzantine Fault Tolerance (BFT), Genesis, Praos, and more recently the scalability solution Hydra.