> ## 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.

# Hash (Moved to Keccak256)

> Hash has moved to crypto/keccak256 as Keccak256Hash

## Overview

The `Hash` primitive has been moved to `crypto/keccak256` as `Keccak256Hash`. This change reflects that Hash was specifically for Keccak256 hashing and belongs semantically under cryptographic operations rather than general primitives.

## Why the Change

**Better Organization**

* Hash was Keccak256-specific, not a general hash primitive
* Cryptographic operations belong in the crypto module
* Clearer semantic organization of the codebase

**Semantic Clarity**

* `Keccak256Hash` explicitly names what it is
* Separates hash algorithm (Keccak256) from hash type (Keccak256Hash)
* Aligns with other crypto primitives (Secp256k1Signature, BlsSignature, etc.)

## Migration Guide

### Import Changes

```typescript theme={null}
// Old
import { Hash } from '@tevm/voltaire'
import * as Hash from '@tevm/voltaire/primitives/Hash'

// New
import { Keccak256 } from '@tevm/voltaire/Keccak256'
import * as Keccak256 from '@tevm/voltaire/Keccak256'
```

### Hashing Methods

```typescript theme={null}
// Old - Hash.keccak256()
const hash = Hash.keccak256(data)
const hashFromHex = Hash.keccak256Hex('0x1234...')
const hashFromString = Hash.keccak256String('hello')

// New - Keccak256.hash()
const hash = Keccak256.hash(data)
const hashFromHex = Keccak256.hashHex('0x1234...')
const hashFromString = Keccak256.hashString('hello')
```

### Type Changes

```typescript theme={null}
// Old - HashType
import type { HashType } from '@tevm/voltaire'

function processHash(hash: HashType): void {
  // ...
}

// New - Keccak256Hash (extends Bytes32)
import type { Keccak256Hash } from '@tevm/voltaire/Keccak256'

function processHash(hash: Keccak256Hash): void {
  // ...
}
```

### Constructor Changes

```typescript theme={null}
// Old
const hash = Hash.from('0x1234...')
const hash = Hash.fromHex('0x1234...')
const hash = Hash.fromBytes(bytes)

// New - Use Keccak256Hash namespace
import * as Keccak256Hash from '@tevm/voltaire/Keccak256/Keccak256Hash'

const hash = Keccak256Hash.from('0x1234...')
const hash = Keccak256Hash.fromHex('0x1234...')
const hash = Keccak256Hash.fromBytes(bytes)
```

### Complete Example

```typescript theme={null}
// Old approach
import * as Hash from '@tevm/voltaire/primitives/Hash'

const data = new Uint8Array([1, 2, 3, 4])
const hash = Hash.keccak256(data)
const hex = hash.toHex()
const isValid = Hash.isHash(hash)

// New approach
import * as Keccak256 from '@tevm/voltaire/Keccak256'
import * as Keccak256Hash from '@tevm/voltaire/Keccak256/Keccak256Hash'

const data = new Uint8Array([1, 2, 3, 4])
const hash = Keccak256.hash(data)
const hex = Keccak256Hash.toHex(hash)
const isValid = Keccak256Hash.isKeccak256Hash(hash)
```

## Type Hierarchy

`Keccak256Hash` extends `Bytes32`, inheriting all Bytes32 methods while adding Keccak256-specific semantics:

```typescript theme={null}
type Keccak256Hash = Bytes32 & { readonly __tag: "Keccak256Hash" }
```

This means all `Bytes32` operations work on `Keccak256Hash`:

* Construction: `Bytes32.from()`, `Bytes32.fromHex()`
* Conversion: `Bytes32.toHex()`, `Bytes32.toBytes()`
* Validation: `Bytes32.equals()`, `Bytes32.isZero()`
* Utilities: `Bytes32.slice()`, `Bytes32.concat()`

## Where to Find

### Keccak256Hash Type

**[/crypto/keccak256/hash](/crypto/keccak256/hash)** - Type definition, branded type system, constructor methods

### Hashing Methods

**[/crypto/keccak256/index](/crypto/keccak256/index)** - Main hashing functions: `hash()`, `hashHex()`, `hashString()`

### Implementations

**[/crypto/keccak256/implementations](/crypto/keccak256/implementations)** - Native (keccak-asm), WASM (ReleaseSmall/ReleaseFast), JavaScript fallback

## Related

* [Bytes32](/primitives/bytes/bytes32) - Base type for 32-byte values
* [Keccak256](/crypto/keccak256/index) - Keccak256 hashing functions
* [Keccak256Hash](/crypto/keccak256/hash) - Keccak256Hash type documentation