# Consensus

## Overview

In the Filecoin blockchain, network *consensus* is achieved using the Expected Consensus (EC) algorithm, a probabilistic, *Byzantine fault-tolerant* consensus protocol. At a high level, EC achieves consensus by running a secret, fair, and verifiable *leader election* at every [epoch](/reference/general/glossary.md#epoch) where a set number of participants may become eligible to submit a block to the chain based on fair and verifiable criteria.

## Properties

Expected Consensus (EC) has the following properties:

* Each epoch has potentially multiple elected leaders who may propose a block.
* A winner is selected randomly from a set of network participants weighted according to the respective storage power they contribute to the Filecoin network.
* All blocks proposed are grouped together in a *tipset*, from which the final chain is selected.
* A block producer can be verified by any participant in the network.
* The identity of a block producer is anonymous until they release their block to the network.

## Steps

In summary, EC involves the following steps at each *epoch*:

1. A storage provider checks to see if they are elected to propose a block by generating an *election proof*.
2. Zero, one, or multiple storage providers may be elected to propose a block. This does not mean that an elected participant is guaranteed to be able to submit a block. In the case where:
   * **No storage providers are elected to propose a block in a given epoch**; a new election is run in the next epoch to ensure that the network remains live.
   * **One or more storage providers are elected to propose a block in a given epoch**; each must generate a *WinningPoSt proof-of-storage* to be eligible to actually submit a block.
3. Each potential block producer elected generates a storage proof using [WinningPoSt](/reference/general/glossary.md#winning-proof-of-spacetime-winningpost) for a randomly selected [*sector*](/reference/general/glossary.md#sector) within in short window of time. Potential block producers that fail this step are not eligible to produce a block. In this step, the following could occur:
   * **All potential block producers fail WinningPoSt**, in which case EC returns to step 1 (described above).
   * **One or more potential block producers pass WinningPoSt**, which means they are eligible to submit that block to the epochs tipset.
4. Blocks generated by block producers are grouped into a [tipset](/reference/general/glossary.md#tipset).
5. The tipset that reflects the biggest amount of committed storage on the network is selected.
6. Using the selected tipset, the chain state is propagated.
7. EC returns to step 1 in the next epoch.

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