Definitions

Definitions / Glossary

Updates to definitions

To make any updates to these definitions please submit a pull request with the changes, or open an issue and one of the maintainers will do it for you.

Notes

  • Want to split all repair stuff to separate doc
  • Let’s refer to Filecoin system rather than network. In a sense, the network is an instantiation of the system (this protocol). We can however refer to the Filecoin VM separately which means the system by which we apply changes to the state of the system at a point in time.
  • Asterisks indicate that the definition requires updating by any affected party.

Definitions

Actor

An actor is an on-chain object with its own state and set of methods. An actors state is persisted on-chain in the state tree, keyed by its address. All actors (miner actors, the storage market actor, account actors) have an address. Actors methods are invoked by crafting messages and getting miners to include them in blocks.

Actors are very similar to smart contracts in Ethereum.

Address

An address is an identifier that refers to an actor in the Filecoin state.

Ask

Bid

Block

A block in the Filecoin blockchain is a chunk of data appended to the shared history of the network including transactions, messages, etc. and representing the state of the storage network at a given point in time.

See [Data Structures]()

Bootstrapping

Chain weight

Challenge sampling

Cid

CID is short for Content Identifier, a self describing content address used throughout the ipfs ecosystem. For more detailed information, see the github documentation for it.

Client

A client is any user with an account who wishes to store data with a miner. A client’s account is used to pay for the storage, and helps to prove the clients ability to pay.

Collateral

Collateral is Filecoin tokens pledged by an actor as a commitment to a promise. If the promise is respected, the collateral is returned. If the promise is broken, the collateral is not returned in full. For instance:

  • In becoming a Filecoin storage miner: the miner will put up collateral alongside their SEAL to
  • In a Filecoin deal: both the miner and client put up collateral to ensure their respect of deal terms.

Commitment

See Filecoin Proofs

Confirmation

Consensus

Deal

*** *A deal in a Filecoin market is made when a bid and ask are matched, corresponding to an agreement on a service and price between a miner and client.

Election Proof

An ElectionProof is derived from a past ticket and is included in every block header. The ElectionProof proves that the miner was eligible to mine a block at that height.

Erasure coding

Erasure coding is a strategy through which messages can be lengthened so as to be made recoverable in spite of errors.

See Wikipedia

Fault

A fault occurs when a proof is not posted in the Filecoin system within the proving period, denoting another malfunction such as loss of network connectivity, storage malfunction, malicious miner, etc.

Fair

File

Files are what clients bring to the filecoin system to store. A file is split up into pieces, which are what is actually stored by the network.

Finality

Piece Inclusion Proof

See Filecoin Proofs

Gas, Fees, Prices

Generation Attack Threshold

Security parameter. Number of rounds within which a new Proof-of-Storage must be submitted in order for a miner to retain power in the network (and avoid getting slashed). This number must be be smaller than the minimum time it takes for an adversarial miner to generate a replica of the data (thereby not storing it undetectably for some period of time).

The Generation Attack Threshold is equal to the Polling Time + some Grace Period after which miners get slashed.

GHOST

GHOST is an acronym for Greedy Heaviest Observable SubTree, a class of blockchain structures in which multiple blocks can validly be included in the chain at any given height or round. GHOSTy protocols produce blockDAGs rather than blockchains and use a weighting function for fork selection, rather than simply picking the longest chain.

Height

Height and round are synonymous and used interchangeably in this spec.

Height refers to the number of tickets generated between this TipSet and the genesis block (height 0), counting only the tickets of the block in a TipSet whose final ticket – the one generated alongside the ElectionProof – is the smallest.

If a TipSet contains multiple blocks, each block in the TipSet will have the same height. Put another way, there is a new round of leader election attempts at each height. Typically, such an attempt will find a single leader. If a single leader is found, that leader can generate a single block. If multiple leaders are found, they can each generate multiple blocks in the given round. If no leader is found, no block is generated (but a ticket is).

Leader

A leader, in the context of Filecoin consensus, is a node that is chosen to propose the next block in the blockchain.

Leader election

Leader election is the process by which the Filecoin network agrees who gets to create the next block.

Message

A message is a call to an actor in the Filecoin VM.

Miner

A miner is an actor in the Filecoin system performing a service in the network for a reward.

There are multiple types of miners in Filecoin:

  • Storage miners - storage miners
  • Retrieval miners:
  • Repair miners (to be split out):

Node

*** *A node is a communication endpoint that implements the Filecoin protocol. (also mention IPLD Node?)

On-chain/off-chain

Online/offline

Payment Channel

A payment channel is set up between actors in the Filecoin system to enable off-chain payments with on-chain guarantees, making settlement more efficient.

Piece

A piece is a portion of a file that gets fitted into a sector.

Pledge

****The initial commitment of a storage miner to provide a number of sectors to the system.

Polling Time

Security Parameter. Polling time is the time between two online PoReps in a PoSt proof.

Power

See Power Fraction.

Power Fraction

A miner’s Power Fraction or Power is the ratio of their committed storage as of their last PoSt submission over Filecoin’s total committed storage as of the current block. It is used in leader election.

Power table

The power table is an abstraction provided by the Filecoin storage market that lists the power of every miner in the system.

Protocol

Proving Period

The period of time during which storage miners must compute Proofs of Spacetime. At the end of the period they must submit their PoSt. Put another way, it is the duration of a PoSt.

Proving Set

The elements used as input by a proof of Spacetime to enable a proof to be generated.

**** elements necessary to generate a SEAL, or elements necessary to generate a proof

Proof of Replication

Proof that a unique encoding of data exists in physical storage.

Used in the Filecoin system to generate SEALed sectors through which storage miners prove they hold client data.

Proof of Spacetime

Proof that a given encoding of data existed in physical storage continuously over a period of time.

Used in the Filecoin system by a storage miner to prove that client data was kept over the contract duration.

Random(ness)

****Source of unpredictability used in the Filecoin system to ensure fairness and prevent malicious actors from gaining an advantage over the system.

TODO add a note to distinguish predictability from randomness

Election Randomness Lookback

Security parameter. A number of rounds to sample back from when choosing randomness for use in leader election. A higher number turns a more localized lottery into a more global one since a miner wins or loses on all descendants of a given randomness, but enables miners to look-ahead and know whether they will be elected in the future.

Also referred to as K in consensus settings.

Repair

Repair refers to the processes and protocols by which the Filecoin network ensures that data that is partially lost (by, for example, a miner disappearing) can be re-constructed and re-added to the network.

Round

See Height for definition. They are synonymous.

SEAL/UNSEAL

See Filecoin Proofs

Sector

A sector is a contiguous array of bytes that a miner puts together, seals, and performs Proofs of Spacetime on.

Slashing

Smart contracts

Storage

Storage widely refers to a place in which to store data in a given system.

In the context of:

  • The Filecoin miner: sotrage refers to disk sectors made available to the network.
  • The Filecoin chain: storage refers to the way in which system state is tracked through time on-chain through blocks.
  • Actor: the struct that defines an actor.

State

****Refers to The shared history of the Filecoin system contains actors and their storage, deals, etc. State is deterministically generated from the initial state and the set of messages generated by the system.

Ticket

A ticket is used as a source of randomness in EC leader election. Every block depends on an ElectionProof derived from a ticket. At least one new ticket is produced with every new block. Ticket creation is described here.

Ticket Chain

Each chain in Filecoin can be associated to a given ticket chain. The ticket chain is assembled by taking the tickets (usually one) contained by the block with the smallest final ticket in each of the chain’s TipSets.

Ticket comparison is done by interpreting the tickets’ Bytes as unsigned integers (little endian representation).

TipSet

A TipSet is a set of blocks that have the same parent set and same number of tickets, which implies they will have been mined at the same height. A TipSet can contain multiple blocks if more than one miner successfully mines a block at the same height as another miner.

Verifiable

Something that is verifiable can be checked for correctness by a third party.

VDF

A verifiable function that guarantees a time delay given some hardware assumptions and a small set of requirements. These requirements are efficient proof verification, random output, and strong sequentiality. Verifiable delay functions are formally defined by [[BBBF]](https://eprint.iacr.org/2018/601).

{proof, value} <—- VDF(public parameters, seed)

VM

Virtual Machine. The Filecoin VM refers to the system by which changes are applied to the Filecoin system’s state. The VM takes messages as input, and outputs state.

Voucher

Held by an actor as part of a payment channel to complete settlement when the counterparty defaults.

VRF

A verifiable random function that receives {Secret Key (SK), seed} and outputs {proof of correctness, output value}. VRFs must yield a proof of correctness and a unique & efficiently verifiable output.

{proof, value} <-- VRF(SK, seed)

Weight

Every mined block has a computed weight. Together, the weights of all the blocks in a branch of the chain determines the cumulative weight of that branch. Filecoin’s Expected Consensus is a GHOSTy or heaviest-chain protocol, where chain selection is done on the basis of an explicit weighting function. Filecoin’s weight function currently seeks to incentivize collaboration amongst miners as well as the addition of storage to the network. The specific weighting function is defined in Chain Weighting.

zkSNARK

Zero Knowledge Succinct ARguments of Knowledge. A way of producing a small ‘proof’ that convinces a ‘verifier’ that some computation was done correctly.

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