Blockchain Fundamentals in Filecoin

The Filecoin blockchain is an intricate distributed database shared among a network of computer nodes. Each node holds a copy of the blockchain, ensuring that every transaction and contractual obligation in the network is recorded and immutable. This provides a reliable and secure ledger of all activities within the Filecoin ecosystem.

Actors: The Workhorses of Filecoin’s Blockchain

Actors on Filecoin’s blockchain serve as the equivalent of smart contracts in the Ethereum Virtual Machine. Each actor encapsulates a set of state variables and methods to interact with the Filecoin network. They are essentially the agents that perform actions on the blockchain, such as managing storage deals or facilitating transactions.

Built-in System Actors

Filecoin’s network is powered by several built-in system actors that handle essential functions:

• System Actor: Executes general network operations.
• Init Actor: Responsible for initializing new actors and managing network naming conventions.
• Cron Actor: Acts as the network’s scheduler, triggering essential functions at each epoch.
• Account Actor: Manages user accounts beyond the scope of the singleton pattern.
• Storage Miner Actor: Coordinates storage mining operations and validates proofs of storage.
• Storage Market Actor: Manages storage deals within the network’s marketplace.
• Multisig Actor: Handles operations involving Filecoin’s multi-signature wallet.
• Payment Channel Actor: Manages the establishment and settlement of payment channels.
• Datacap Actor: Oversees the allocation and management of datacap tokens.
• Verified Registry Actor: Manages verified clients within the network.
• EVM Account Actor: Represents external Ethereum identities, facilitating interoperability with Ethereum-based systems.

User-Programmable Actors

As the Filecoin Virtual Machine (FVM) matures, developers have the opportunity to write and deploy their own actors, similar to smart contracts on other blockchains. These user-programmable actors can interact with the built-in actors through exported APIs, enabling a wide range of applications and services to be built on top of the Filecoin network.

Distributed Randomness in Filecoin

Filecoin utilizes a distributed and publicly verifiable randomness protocol known as Drand as the source of randomness for leader election during block production. This randomness is essential to ensure that the process is unpredictable, unbiased, and verifiable, maintaining the fairness and security of the mining process.

Nodes and Their Roles

Nodes on the Filecoin network are primarily classified by the services they provide:

• Chain Verifier Nodes: Validate the blockchain and enforce consensus rules.
• Client Nodes: Interact with the network to store and retrieve data.
• Storage Provider Nodes: Offer storage capacity to the network and prove continued storage.
• Retrieval Provider Nodes: Serve stored data quickly and reliably when requested.
• Multiple implementations of the Filecoin protocol coexist to enhance the network’s security and resilience, ensuring no single point of failure and promoting healthy decentralization.

Addresses: Identifying Actors in Filecoin

Addresses in Filecoin are alphanumeric strings that uniquely identify actors or users on the network, facilitating interactions such as transactions and smart contract executions. These addresses come in several forms, reflecting the different types of actors they represent:

• ID Addresses (f0): Numerical identifiers for actors, providing a human-readable way to reference network participants.
• Secp256k1 Addresses (f1): Derived from public keys using the secp256k1 encryption standard, commonly used for wallets.
• Actor Addresses (f2): Assigned to smart contracts and remain robust across network forks.
• BLS Addresses (f3): Generated from BLS public keys and used for wallets with BLS encryption.
• User-Defined Actor Addresses (f4): Flexible addresses that can be assigned by user-definable address management actors, allowing for custom and extensible addressing schemes.
• Each address type serves a specific purpose within Filecoin’s ecosystem, from facilitating transactions to managing smart contracts and user interactions.

Tipsets and Blocks

Filecoin’s blockchain deviates from the norm of a linear sequence of blocks. Here, blocks are grouped into ‘tipsets’, which can be thought of as snapshots of the network state at each epoch, or a fixed time interval in blockchain parlance. This model allows for a more flexible and efficient blockchain by enabling multiple valid blocks to be produced at the same time.

The Anatomy of a Filecoin Block

Each block in Filecoin is a bundle containing a header and a series of messages that represent the actions taken by actors, such as transactions or contractual agreements. The block header includes metadata like the miner’s address, the ticket (proof of work), and the parent blocks’ CIDs. The messages are the meat of the block, recording state changes such as token transfers and contract calls. Blocks are linked to at least one parent block, forming a continuous chain back to the genesis block.

Blocktime: Synchronizing the Network’s Pulse

Blocktime in Filecoin is set at an average of 30 seconds. This interval was strategically chosen to balance between the responsiveness of the network and the practicalities of its operation. A shorter blocktime could increase the speed of the network, but it would also impose greater hardware demands and could lead to more frequent blocktime failures. The 30-second blocktime allows storage providers sufficient time to perform necessary operations, such as sealing sectors and generating proofs, without overtaxing their hardware.

Tipsets: Maximizing Efficiency and Reward

In a given epoch, it’s possible for multiple storage providers to successfully mine blocks. Filecoin’s tipset structure accommodates this by bundling all valid blocks with the same height and parent into a single group. This means that all valid work contributes to the network’s state and is rewarded, an important feature that encourages participation and collaboration among miners. It also ensures that the network can efficiently handle forks, rapidly reaching consensus on the canonical chain.

The tipset system provides several advantages over traditional blockchains:

• Increased Network Throughput: By using all valid blocks to determine the network state, Filecoin can process more data and transactions in each epoch.
• Rewarding Valid Work: Every storage provider that produces a valid block receives a reward, thus incentivizing miners to contribute to the network and discouraging centralization.
• Collaboration Over Competition: Potential block producers are encouraged to collaborate, as the tipset structure disincentivizes the withholding of blocks that could be beneficial to the network’s growth.
• Resilience to Forks: With the tipset architecture, Filecoin achieves quicker convergence during forks, ensuring network stability.
• The Ethereum JSON-RPC and Filecoin

It’s worth noting that with the integration of the Filecoin EVM runtime and the adoption of Ethereum JSON-RPC standards, the notion of ‘tipset’ becomes even more user-friendly. In this context, when we talk about a ‘block hash’ in the Ethereum JSON-RPC, we’re actually referring to the hash of a tipset, which encompasses the combined state changes from all blocks within that tipset.

As we continue to explore Filecoin’s blockchain, we’ll see how these components interplay to create a decentralized storage network that is robust, efficient, and poised for future growth.

Filecoin Consensus

Filecoin’s consensus mechanism, known as Expected Consensus (EC), represents a cornerstone in its decentralized storage network. This chapter aims to provide an introduction to EC, delving into its operational principles, technical specifications, and the role it plays in maintaining the integrity and reliability of the Filecoin network.

Filecoin operates on a unique consensus mechanism termed Expected Consensus (EC). Unlike traditional blockchain protocols that often rely on Proof of Work (PoW) or Proof of Stake (PoS), EC blends elements of randomness, storage power, and probabilistic Byzantine fault tolerance. At its core, EC is designed to align incentives with the primary objective of Filecoin: to efficiently and reliably store data.

The Essence of EC

• Decentralization and Reliability: EC’s primary aim is to foster a decentralized environment where data storage and retrieval are both reliable and verifiable.
• Storage-Centric Approach: Unlike traditional blockchains focusing on computational power or coin holdings, Filecoin’s EC prioritizes storage power - the capacity to store data.

Core Mechanics of Expected Consensus

EC’s operational framework revolves around several key components, each playing a vital role in the network’s functionality.

1. Probabilistic Byzantine Fault Tolerance:

• EC incorporates Byzantine fault tolerance mechanisms, making it resilient to a range of adversarial conditions, including nodes acting maliciously or going offline.

1. Leader Election and Block Production:

• At the heart of EC is a leader election process. Unlike deterministic processes seen in other blockchains, EC employs a probabilistic method to select leaders or miners responsible for block creation.

1. Anonymity until Proven Elected:

• Miners within EC remain anonymous until they can prove their election status through an ‘ElectionProof’. This proof is pivotal to ensuring fairness and unpredictability in block production.

1. Proof of Storage:

• Miners are required to submit a ‘WinningPoSt’ (Proof of Spacetime), validating their contribution to the network’s storage capacity.

Technical Specifications of EC

The technical underpinnings of EC are where its innovative nature truly shines. Here, we explore some of the key specifications that define this consensus mechanism:

Randomness via DRAND:

• EC uses DRAND, an external, unbiasable randomness beacon, to facilitate various aspects of the protocol, including leader election.

Verifiable Random Function (VRF):

• Miners utilize a VRF, alongside randomness obtained from DRAND, to generate their ElectionProof.

ElectionProof and VRF Chain:

• The ElectionProof is crucial for miners to demonstrate they have been rightfully elected to produce a block.
• A continuous VRF chain is maintained, extending with each new block produced.

Storage Power and WinCount:

• A miner’s power in the network is proportional to their storage capacity.
• WinCount determines the number of blocks a miner can produce, based on their storage power and the outcome of their VRF.
• Consensus Security and Fairness

Security and fairness are paramount in EC, with several mechanisms in place to safeguard these principles:

Consensus Faults and Penalties:

EC defines specific types of consensus faults (e.g., Double-Fork Mining, Time-Offset Mining) and imposes penalties to deter malicious behavior.

Source of the images: Filecoin’s Documentation here: https://spec.filecoin.io/algorithms/expected_consensus/

Chain Weighting and Selection:

• The protocol employs a unique chain weighting system, where the ‘heaviest’ chain, indicative of the most cumulative storage power, is favored.

Soft Finality:

• EC employs a form of soft finality, rejecting blocks that deviate significantly from the chain, thereby enforcing network stability.

Drand: Distributed Randomness in Filecoin

Drand (Distributed Randomness) is a critical component of Filecoin’s consensus mechanism, providing an unbiasable source of entropy essential for the network’s secret leader election process. It’s a publicly verifiable random beacon protocol designed to generate a series of deterministic, verifiable random values.

How Drand Works

• Multi-Party Computations (MPCs): Drand runs a series of MPCs to produce random values. After a trusted setup phase, a group of known drand nodes sign a given message using threshold BLS signatures in successive rounds occurring at regular intervals.
• Threshold BLS Signatures: The process requires a minimum number of nodes (t-of-n) to sign a message. Any node with t of the signatures can reconstruct the full BLS signature. This signature, when hashed, produces a collective random value that can be verified against the public key from the setup phase.
• Security Assumptions: Drand assumes at least t of the n nodes are honest and online. If this threshold is broken, the adversary can halt randomness production but cannot bias the randomness.

Drand Randomness Outputs

Drand Value Format: Filecoin nodes obtain drand values in a specific format. Key components include:

• Signature: A BLS signature on the previous signature value and the current round number.
• PreviousSignature: The BLS signature from the previous Drand round.
• Round: The index of randomness in the sequence produced by the Drand network.

Using Drand in Filecoin

• Leader Election: Drand is used for leader election in Filecoin, providing a random value at each epoch. This randomness is critical for the Expected Consensus (EC) algorithm, ensuring fair and unpredictable leader selection.
• Fetching Drand Values: Filecoin nodes retrieve the latest randomness value from Drand using specific endpoints. This information is then integrated with on-chain data to support Filecoin’s consensus mechanism.

Proofs: Ensuring Integrity and Trust

Proofs in Filecoin serve to validate that storage providers are properly storing data as per the network’s standards. These proofs are critical for maintaining the integrity and trustworthiness of the decentralized storage system.

Types of Proofs in Filecoin

• Proof-of-Replication (PoRep): Used at the time of initial data storage, PoRep verifies that a storage provider has created and is storing a unique copy of the data.
• Proof-of-Spacetime (PoSt): Continuously verifies that the storage provider is maintaining the stored data over time. PoSt is further divided into WinningPoSt and WindowPoSt, serving different validation purposes in the network.

Role of PoRep and PoSt

• PoRep: Validates the initial replication of data by a storage provider, ensuring that the data is uniquely encoded and sealed.
• PoSt: WinningPoSt is used in the block consensus process, while WindowPoSt audits storage providers continuously, ensuring ongoing compliance with storage agreements.

Filecoin’s consensus mechanism, with its unique blend of EC, Drand, and cryptographic proofs, forms the backbone of a robust and reliable decentralized storage network. These elements work in concert to ensure that the network remains secure, efficient, and fair, fostering an environment where data integrity is paramount. As we delve deeper into the nuances of Filecoin’s blockchain, the ingenuity and sophistication of its consensus model become increasingly evident, underscoring the network’s potential to revolutionize the landscape of digital storage.