Nimiq Proof-of-Stake ​

Welcome to the Nimiq Proof-of-Stake documentation! This section introduces our consensus protocol, Albatross, and provides a comprehensive overview of our protocol's unique features.

• Blockchain Structure

  Everything about micro and macro blocks

• Staking Contract

  The repository of data for validators, stakers, and staking

• Validators

  Explore the pillars of Albatross PoS

• Slots

  Learn how slots are assigned to validators

• Stakers

  Learn about delegation and staking participation

What is Albatross? ​

Albatross is Nimiq's innovative Proof-of-Stake consensus algorithm designed for speed, security, and efficiency. Unlike traditional PoS systems, Albatross combines the best of Byzantine Fault Tolerance (BFT) protocols with probabilistic finality, achieving thousands of transactions per second while maintaining robust security guarantees.

Validators and Stakers ​

Validators play a crucial role in the Proof-of-Stake consensus mechanism as block producers. In our algorithm, we assume that out of 3f+1 validators, at most f are malicious. This assumption ensures valid and accurate performance of the blockchain, even if up to f validators fail to respond or act maliciously. Validators signal their participation by allocating stake, which increases their chances of being elected. The stake amount influences the number of slots assigned to a validator. Slots determine block producers, with random selection ensuring fairness.

Any node in Nimiq's network can propose to become a validator by staking coins as a deposit. The higher the stake a node has, the higher the chances of being selected to produce blocks and joining the validator list. Validators are selected according to the validator selection rules. We have 512 slots per batch ready to produce blocks.

Participants lacking the resources or expertise to become validators can delegate funds as stakers. Validators produce and validate blocks on behalf of stakers, who receive rewards even when offline. Validator rewards for stakers are processed off-chain. Stakers face the same punishment as their validator in case of misbehavior.

Blockchain Structure ​

Epochs and Batches ​

The Nimiq PoS blockchain is organized into epochs and batches. An epoch, comprising multiple batches, ends with a closing election macro block. While validators remain constant within an epoch, the election macro block selects new validators for the next epoch.

Micro Blocks ​

Produced by selected validators, micro blocks contain user transactions. A skip block may replace a delayed micro block, signed by over two-thirds of validators in the current epoch.

Macro Blocks ​

After a set number of micro blocks, a macro block finalizes the batch. Randomly proposed by a leader, macro blocks undergo a two-step voting process. Election blocks provide periodic finality, renewing the validator set, while checkpoint blocks retain the validator set.

Consensus Mechanism ​

Tendermint Integration ​

Albatross uses Tendermint for macro block consensus, ensuring Byzantine fault tolerance. The process involves:

1. Proposal Phase: A leader validator proposes a macro block
2. Pre-vote Phase: Validators vote on the proposal
3. Pre-commit Phase: Validators commit to the final decision
4. Finality: 2f+1 validators must agree for consensus out of a maximum of 512 available slots

Skip Block Protocol ​

When a validator fails to produce a micro block on time, any validator can produce a skip block. This ensures network continuity and prevents malicious validators from halting the network.

Dealing with Malicious Behavior ​

Validators earn rewards for contributions and face punishments for consensus violations, with severity varying by offense type. Minor offenses lead to deactivation of the responsible slot and burned rewards. Severe offenses result in a jail state, where the validator, including all slots, is locked for an extended period, with burned rewards and an inability to be re-elected. The jailing period also affects stakers, as their stake is locked for the duration of the jailing period.

Punishment Types ​

Network Security ​

Getting Started ​

Ready to dive deeper into the Nimiq protocol? Explore these key areas:

• Block Format: Understand how blocks are structured
• Validators: Learn about becoming a validator
• Staking Contract: The central hub for validator and staker data
• Network Sync: Learn about different synchronization methods

Technical Resources ​

• RPC: Integrate with the blockchain
• Web Client: Build browser-based applications