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zkVerify Mainchain API

Mainchain nodes expose some APIs to provide information about the chain status and endpoints to send commands (e.g. to create a new transaction).

APIs follow the Substrate typical format, and for this reason, they are categorized using the following categories:

Runtime​

Some calls are available to interact directly with the Mainchain runtime. All the standard calls are available in the official documentation. Availability of these calls may vary depending on the Mainchain runtime configuration and pallet integration.

JSON-RPC​

RPC methods can be used to query the Mainchain node for information or to submit commands. All the standard calls are available in the official documentation. Mainchain nodes currently expose only a subset of the Substrate RPC methods, in particular, the ones from the following pallets:

  • author
  • chain
  • childstate
  • offchain
  • payment
  • rpc
  • state
  • system

In addition to these, nodes expose the following custom commands:

poe​

poe_proofPath​

Given the hash of a proof and the id of the attestation in which it is included, returns the path of the proof in the Merkle tree. In case the proof is not found, an error is returned.

Parameters

attestation_id: u64

proof_hash: H256

Returns

MerkleProof

Constants​

All the standard constants are available in the official documentation. Mainchain nodes currently use only a subset of the Substrate constants, in particular, the ones from the following pallets:

  • balances
  • grandpa
  • imOnline
  • staking
  • system
  • timestamp
  • transactionPayment

Storage​

The node's storage can be queried to retrieve information about the current chain state. Some endpoints may return also historical data (e.g. the list of validators at a specific block), but availability depends on the specific query and the configuration of the node (e.g. standard vs archive node). Standard methods are available in the official documentation. Mainchain nodes currently use only a subset of these methods, in particular, the ones from the following pallets:

  • authorship
  • babe
  • balances
  • grandpa
  • imOnline
  • offences
  • session
  • staking
  • substrate
  • sudo
  • system
  • timestamp
  • transactionPayment

In addition to them, the following custom methods are available:

poe​

firstInsertionTime​

Returns the timestamp of the first insertion of a proof into the Merkle tree of the latest attestation.

Returns

Option<u64>

nextAttestation​

Returns the ID of the next attestation.

Returns

u64

palletVersion​

Returns the software version of the pallet.

Returns

u16

values​

Queries the storage looking for the proofs included in the Merkle tree of an attestation. The return value depends on the presence of the optional parameter proof_hash:

  • If the parameter is not provided, the method returns the list of all the proofs included in the Merkle tree of the requested attestation (if any)
  • If the parameter is provided, the method returns null if the proof is found in the attestation, None otherwise

Parameters

attestation_id: u64

proof_hash: Option<H256>

Returns

Option<null>

Extrinsics​

Mainchain nodes support some of the most common extrinsics provided by Substrate (see the official documentation). The pallet currently included in the runtime are:

  • balances
  • grandpa
  • imOnline
  • session
  • staking
  • sudo
  • system
  • timestamp

In addition to them, the following custom extrinsics are available:

poe​

publishAttestation​

Creates an extrinsic to trigger the finalization of an attestation containing the proofs submitted in the current window. If no proof is currently available, the attestation is empty but still published.

Verifier Pallets​

All verifier pallets share the following interface and define its types for: verification key, proof and public inputs. Anyway the available exstrinsics are:

submitProof​

Submit a Proof and verify it against the verification key Vk and public inputs Pubs. If the proof is valid it'll be included in the next attestation. The extrinsic fails in the case of an invalid proof.

Parameters

vkOrHash: VkOrHash indicates the verification key (the pallet's Vk) or the hash (H256) of a preregistered one.

proof: Proof the proof to be verified.

Pubs: [u8;32] The byte array representing the public inputs.

registerVk​

Register a verification key that can be used later in submit proof calls and emit a RegisteredVk event with the verification key hash.

Parameters

vk: Vk the verification key that should be registered.

Available Verifier Pallets​

settlementGroth16Pallet Types​

Support is provided for both the BN254 curve used in Ethereum, and the BLS12-381 curve. The details about how G1/G2 elliptic curve points and scalars are actually encoded can be found in the Groth16 pallet documentation

pub enum Curve {
    Bn254,
    Bls12_381,
}

pub struct G1(pub Vec<u8>); // 64 bytes for Bn256 and 96 for Bls12381
pub struct G2(pub Vec<u8>); // 128 bytes for Bn256 and 192 for Bls12381
pub struct Scalar(pub Vec<u8>); // 32 bytes

pub struct ProofInner {
    pub a: G1,
    pub b: G2,
    pub c: G1,
}

pub struct Vk {
    pub curve: Curve,
    pub alpha_g1: G1,
    pub beta_g2: G2,
    pub gamma_g2: G2,
    pub delta_g2: G2,
    pub gamma_abc_g1: Vec<G1>,
}
pub struct Proof {
    pub curve: Curve,
    pub proof: ProofInner,
}
pub type Pubs = Vec<Scalar>;
settlementRisc0Pallet Types​
pub type Proof = Vec<u8>; // Limited on a configurable max size
pub type Pubs = Vec<u8>;  // Limited on a configurable max size
pub type Vk = H256;
settlementFFlonkPallet Types​
pub struct Vk {
    power: u8,
    k1: Fr,
    k2: Fr,
    w: Fr,
    w3: Fr,
    w4: Fr,
    w8: Fr,
    wr: Fr,
    x2: G2,
    c0: G1, 
}
pub type Proof = [768; u8]
pub type Pubs = [32; u8]
settlementzksyncPallet Types​
pub type Vk = (); // zksync verifier doesn't have any verification key
pub type Proof = [1408; u8]
pub type Pubs = [32; u8]

Events​

The Mainchain leverages the standard Events provided by Substrate (see the official documentation). In addition to them, the following custom events are available:

poe​

NewElement​

Emitted when a new ZK proof is submitted, successfully verified, and included in the Merkle tree for the currently pending attestation.

Fields​
  • value: H256 The hash of the proof that has been included in the Merkle tree (i.e. the value of the leaf of the tree)
  • attestationId: u64 The ID of the attestation in which the proof has been included

NewAttestation​

Emitted when a new attestation is finalized and published. It may contain 0 or more proofs.

Fields​
  • id: u64 The ID of the attestation that has been finalized
  • attestation: H256 The root of the Merkle tree of the attestation

Verifier Pallets​

VkRegistered​

Fields​
  • hash: H256 The hash of the registered verification key that can be used later in the submitProof exstrinsic calls of the same verifier pallet

Errors​

The Mainchain nodes throw the standard errors provided by Substrate (see the official documentation).

In addition to them, the following custom errors have been defined:

poe​

TooEarlyForASmallTree​

Error thrown when a validator submits a block containing an attestation with too few proofs in the Merkle tree (the minimum and maximum number are configured in the runtime).

Note: the "sudo" account can override this behavior and submit an attestation whose size is lower than the minimum threshold.

Verifier Pallets​

InvalidInput​

Error thrown when the submitted public inputs are invalid (i.e. it was not possible to deserialize the raw bytes).

InvalidProofData​

Error thrown when the submitted proof is invalid (i.e. it was not possible to deserialize the raw bytes).

VerifyError​

Error thrown when the submitted proof is processed but the verification fails.

InvalidVerificationKey​

Error thrown when the submitted verification key is invalid.

VerificationKeyNotFound​

Error thrown when submitting a vk hash that is not related to any registered verification key.