Powers of Tau Specification

These documents comprise a specification for Ethereum's Powers of Tau (PoT) setup for use in KZG commitments in EIP-4844 (Proto-Danksharding) and ultimately Full Danksharding.

The ceremony takes place between participants and the coordinator. Participants are the entities that contribute their secret randomness to the final output $\tau$ s. The roll of the coordinator it to act as the common point of interaction for all participants as well as verifying participants' contribution as the ceremony progresses.

10'000 ft Overview

We are performing a ceremony to generate Powers of Tau for KZG proofs on Ethereum. The output of the ceremony consists of 4 (distinct) sets of Powers of Tau each with a different maximum power:

1. $([\tau_1^0]_1, [\tau_1^1]_1, \dots, [\tau_1^{2^{12}-1}]_1])$, $([\tau_1^0]_2, [\tau_1^1]_2, \dots, [\tau_1^{64}]_2])$
2. $([\tau_2^0]_1, [\tau_2^1]_1, \dots, [\tau_2^{2^{13}-1}]_1])$, $([\tau_2^0]_2, [\tau_2^1]_2, \dots, [\tau_2^{64}]_2])$
3. $([\tau_3^0]_1, [\tau_3^1]_1, \dots, [\tau_3^{2^{14}-1}]_1])$, $([\tau_3^0]_2, [\tau_3^1]_2, \dots, [\tau_3^{64}]_2])$
4. $([\tau_4^0]_1, [\tau_4^1]_1, \dots, [\tau_4^{2^{15}-1}]_1])$, $([\tau_4^0]_2, [\tau_4^1]_2, \dots, [\tau_4^{64}]_2])$

BLS Cryptography

Due to a lack of standardisation for a complete API for BLS curves, we define our own in BLS.md.

contribution.json

Due to the simplicity of this PoT setup, the full contribution is sent as a json file between the coordinator & participants. This allows the use of a RESTful API between the two and verification of certain aspects of the contribution.json file via the contributionSchema.json JSON schema.

Contribution object

We define a Contribution object for ease of specification the structure of which is identical to that of the initialContribution.json.

PowersOfTau

@dataclass
class PowersOfTau:
    g1_powers: List[bls.G1Point]
    g2_powers: List[bls.G2Point]

SubContribution

@dataclass
class SubContribution:
    num_g1_powers: int
    num_g2_powers: int
    powers_of_tau: PowersOfTau
    pot_pubkey: bls.G2Point

Contribution

@dataclass
class Contribution
    sub_contribution: List[SubContribution]

Initialization

The ceremony is initialized to initialContribution.json.