> ## Documentation Index
> Fetch the complete documentation index at: https://voltaire.tevm.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Commitments

> Creating KZG commitments from blobs for EIP-4844

<Warning>
  **This page is a placeholder.** All examples on this page are currently AI-generated and are not correct. This documentation will be completed in the future with accurate, tested examples.
</Warning>

# KZG Commitments

Convert 128 KB blobs into succinct 48-byte commitments using polynomial commitments.

## Overview

KZG commitments represent a blob as a polynomial commitment on the BLS12-381 curve. The commitment is binding (cannot change blob after commitment) and enables efficient verification.

## API

<Tabs>
  <Tab title="Standard API">
    ```typescript theme={null}
    import { Kzg, Blob } from '@tevm/voltaire';

    // Load trusted setup (required once)
    Kzg.loadTrustedSetup();

    // Create blob
    const blob = Blob(131072); // 131,072 bytes
    // ... fill with data

    // Generate commitment
    const commitment = Kzg.Commitment(blob);
    // Returns: Uint8Array (48 bytes)
    ```
  </Tab>

  <Tab title="Factory API">
    ```typescript theme={null}
    import { Kzg, Blob } from '@tevm/voltaire';
    import * as ckzg from 'c-kzg';

    // Load trusted setup
    Kzg.loadTrustedSetup();

    // Create factory with c-kzg dependency injection
    const Commitment = Kzg.CommitmentFactory({
      blobToKzgCommitment: ckzg.blobToKzgCommitment
    });

    // Use factory
    const blob = Blob(131072);
    const commitment = Commitment(blob);
    // Returns: Uint8Array (48 bytes)
    ```

    **Benefits**: Tree-shakeable, testable with mock c-kzg implementations
  </Tab>
</Tabs>

## Blob Format

**Size**: 131,072 bytes (128 KB exactly)
**Structure**: 4,096 field elements × 32 bytes
**Constraint**: Each field element must have top byte = 0 (\< BLS12-381 modulus)

```typescript theme={null}
// Valid blob
const blob = Blob(131072);
for (let i = 0; i < 4096; i++) {
  blob[i * 32] = 0; // Top byte must be 0
  // ... fill remaining 31 bytes
}
```

## Error Handling

```typescript theme={null}
try {
  const commitment = Kzg.Commitment(blob);
} catch (error) {
  if (error instanceof KzgNotInitializedError) {
    // Trusted setup not loaded
    Kzg.loadTrustedSetup();
  } else if (error instanceof KzgInvalidBlobError) {
    // Invalid blob format
    console.error('Blob validation failed:', error.message);
  } else if (error instanceof KzgError) {
    // Commitment computation failed
    console.error('KZG error:', error.message);
  }
}
```

## Related

* [KZG Overview](./index)
* [Proofs](./proofs)
* [EIP-4844](./eip-4844)