KZG / EIP-4844

EIP-4844 ("blobs") attaches large data blobs to a transaction, each committed to with a KZG commitment and proven with a KZG proof. eth.kzg provides real, spec-correct KZG over the vendored c-kzg-4844 reference implementation and its blst dependency. The mainnet trusted setup (the KZG ceremony output) is embedded in the library via @embedFile, so you do not need to ship or locate an external setup file.

Initialize the trusted setup

Load the trusted setup once at startup and free it at shutdown. init is idempotent and thread-safe (guarded by an atomic once-flag), so calling it more than once is harmless.

const eth = @import("eth");

try eth.kzg.init(allocator);
defer eth.kzg.deinit();

Build a blob sidecar

The common task is turning raw blob bytes into a sidecar: the blob plus its KZG commitment and proof. blob.buildSidecar does exactly that.

// `raw_blob` is [131072]u8 (128 KiB = 4096 field elements x 32 bytes).
// Each 32-byte field element must be a canonical BLS12-381 scalar (< modulus).
var raw_blob: eth.blob.Blob = @splat(0);
// ... fill raw_blob with your data ...

const sidecar = try eth.blob.buildSidecar(allocator, raw_blob);
// sidecar.blob, sidecar.commitment ([48]u8), sidecar.proof ([48]u8)

The blob-transaction versioned hash that goes on-chain is derived from the commitment:

const versioned_hash = eth.blob.computeVersionedHash(sidecar.commitment);
// versioned_hash[0] == 0x01 (the KZG version byte)

Lower-level API

If you want the individual operations rather than a full sidecar:

const commitment = try eth.kzg.blobToKzgCommitment(&raw_blob); // [48]u8
const proof = try eth.kzg.computeBlobKzgProof(&raw_blob, commitment); // [48]u8

const ok = try eth.kzg.verifyBlobKzgProof(&raw_blob, commitment, proof);
// ok == true

// Batch verification over equal-length slices of blobs/commitments/proofs:
const all_ok = try eth.kzg.verifyBlobKzgProofBatch(blobs, commitments, proofs);

Errors map c-kzg's C_KZG_RET codes onto a Zig KzgError set (BadArgs, Internal, OutOfMemory), plus NotInitialized if you call an operation before kzg.init.

Correctness

The bindings are verified byte-for-byte against the official ethereum/c-kzg-4844 test vectors (the same blob_to_kzg_commitment, compute_blob_kzg_proof, and verify_blob_kzg_proof vectors used by the reference implementation), in addition to round-trip and lifecycle tests. The vendored versions are pinned in src/crypto/c-kzg/VENDOR.md (c-kzg-4844 v2.1.1, blst v0.3.14, built in blst's portable no-assembly C mode for robustness across targets).