An environmentally sustainable, verifiably secure proof-of-stake protocol with rigorous security guarantees.
The Blockchain Revolution Started With Bitcoin. It Continues Now With Ouroboros:
A proof-of-stake protocol that provides and improves the security guarantees of proof-of-work at a fraction of the energy cost. Ouroboros applies cryptography, combinatorics, and mathematical game theory to guarantee the protocol's integrity, longevity, and performance, and that of the distributed networks that depend upon it.
What Is Ouroboros?
Ouroboros is the first provably secure proof-of-stake protocol, and the first blockchain protocol to be based on peer-reviewed research. It combines cryptography with mathematically verified mechanisms that draw on game theory and economics to keep the blockchains that depend on it secure and sustainable. The result is a protocol with proven security guarantees that supports global, permissionless networks with minimal energy requirements. Cardano was the first of them.
At the heart of Ouroboros is the concept of infinity. Global networks must be able to grow sustainably and ethically: to provide greater opportunities to the world while also preserving it. This becomes possible with Ouroboros.
Ouroboros facilitates the creation and fruition of distributed, permissionless networks capable of sustainably supporting new markets.
Ouroboros exists to define the parameters of the new world: a protocol more secure, scalable, and energy-efficient than anything that has come before.
Explore the research
Provably Secure
Ouroboros features mathematically verifiable security against attackers.
The protocol is proven secure as long as more than half of the stake, in the case of Cardano ada, is held by honest participants. One of the mechanisms behind this is random leader selection. The protocol continues to evolve through new iterations and rigorous security analysis.
Incentives & Rewards
To ensure the sustainability of the blockchain networks using Ouroboros, the protocol features an incentive mechanism that rewards network participants for their participation.
This can either be operating a stake pool or delegating a stake in ada to a stake pool. Rewards (in the form of ada) can be earned by completing either of these activities.
Stake Delegation And Stake Pools
Ouroboros is a proof-of-stake protocol. It distributes network control across stake pools: node operators with the infrastructure required to ensure a consistent and reliable connection to the network.
In every slot, each stake pool has a chance to become slot leader in proportion to its stake. On average only one slot in twenty has a leader, who adds a block to the chain. Ada holders may delegate their stake to a stake pool, which increases its chance of being elected, and share in the rewards the protocol pays out every epoch. How Cardano works explains the details.
Energy Efficient
Ouroboros addresses one of the biggest challenges of proof-of-work blockchains: the need for more and more energy to reach consensus. Block producers do not compete on computing power, so Cardano runs on ordinary servers and can scale securely and sustainably.
Which version of Ouroboros does Cardano run?
Ouroboros is a family of protocols. Cardano mainnet runs Ouroboros Praos, which elects slot leaders privately using verifiable random functions. Ouroboros Genesis lets a new node find the honest chain without trusted checkpoints and is available in the node as an opt-in setting on mainnet. Peras and Leios are newer members of the family that target faster settlement and higher throughput. The Ouroboros glossary entry describes each variant.
Back to the big picture: What is Cardano?, or see how Cardano works end to end.
Attack the protocol or fork the blockchain? Explore the Ouroboros protocol firsthand in this interactive simulation.
Proof of stake and proof of work
There are two main blockchain protocols: proof-of-stake (PoS) and proof-of-work (PoW). These protocols are consensus algorithms for distributed networks: rulesets that dictate how networks, made up of thousands of nodes, agree on new additions (blocks) in a permissionless setting.
Proof-of-work is the blockchain protocol used by bitcoin. Proof-of-work began a revolution: it enabled the creation of secure, permissionless, distributed networks. But to achieve consensus for each new block, proof-of-work requires an enormous amount of energy: an amount so large that the supported blockchains struggle to sustain and scale to the performance requirements of global networks.
Proof-of-stake answers the performance and energy-use challenges of proof-of-work, and arrives at a more sustainable solution. Instead of relying on 'miners' to solve computationally complex equations to create new blocks, and rewarding the first to do so, proof of stake selects participants (in the case of Cardano, stake pools) to create new blocks based on the stake they control in the network.
Because block producers do not compete on computing power, a proof-of-stake network needs only a small fraction of the energy that proof-of-work uses to secure itself. Networks that add capacity on top of Cardano are listed on the layer 2 page.
How Ouroboros Works
Ouroboros processes transaction blocks by dividing chains into epochs, which are further divided into time slots. In each slot, every stake pool has a chance to be elected slot leader in proportion to its stake, and on average one slot in twenty has a leader, who adds a block to the chain. To protect against adversarial attempts to subvert the protocol, each new slot leader is required to consider the last few blocks of the received chain as transient: only the chain that precedes a prespecified number of transient blocks is considered settled. This is also referred to as the settlement delay, and is the mechanism through which the ledger is securely passed between participants.
Ouroboros is a meld of innovative technology and philosophy. Its research explores how we behave as a society, to discover an ideal balance, defined through game theory, between individual and collective interests. The Ouroboros incentive mechanism rewards participants for their honest participation, and disincentivizes dishonest actors. It is a stable and sustainable foundation for permissionless networks that are built to endure: the infrastructure of the future.