What Is KZG Commitment?
Also known as: Kate Commitment, Kate-Zaverucha-Goldberg, Polynomial Commitment, KZG Polynomial Commitment
In short
A KZG commitment is a polynomial commitment scheme, proposed by Kate, Zaverucha and Goldberg in 2010, that lets a party commit to a polynomial with a single small value and verify the polynomial's value at any point with a short proof.
Commitment schemes make it possible to bind oneself to a piece of data without revealing it, and later prove that the commitment has not changed. In KZG, data is expressed as a polynomial and reduced to a single elliptic curve point using elliptic curve pairings. A verifier can check that the polynomial's value at a given point is correct with a proof of constant size, regardless of the data size, without downloading all the data.
On Ethereum, KZG commitments form the basis of EIP-4844 (Proto-Danksharding), which arrived with the Dencun upgrade in March 2024. Data that layer 2 networks send to Ethereum is carried in structures called “blobs,” and each blob is represented by a KZG commitment. This design also lays the groundwork for data availability sampling and full danksharding in the future. KZG is also used in some zero-knowledge proof systems and in Verkle tree designs.
An important limitation of the scheme is that it requires a trusted setup. The secret value generated during the setup must be destroyed; otherwise, fake proofs could be produced. To reduce this risk, Ethereum held a setup ceremony with many participants; it is enough for only one of the participants to honestly destroy their share for the system to be secure.
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