# sha384.select

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## Purpose

`sha384.select.ts` is the build-time primitive selector for the SHA-384 implementation. It is a generated file that re-exports exactly one concrete implementation — either `sha384.noble.ts` (the audited `@noble/hashes` backend) or `sha384.native.ts` (the in-house native backend) — based on the setting in `crypto.config.ts`.

Consumers import SHA-384 through the stable public entry point, which resolves here; they are insulated from backend changes. Regenerating this file via `bun scripts/gen-crypto-selects.ts` is the only step required to swap implementations.

## Features

- Single-symbol re-export of `sha384(data: Uint8Array): Uint8Array`.
- Generated by `bun scripts/gen-crypto-selects.ts` — never hand-edited.
- Controlled by `crypto.config.ts`: set `sha384` to `'noble'` or `'native'`.
- Maintains a stable public API across backend switches.
- Enables static dead-code elimination of the unused backend.

## Usage: Basic Example

```ts
import { sha384 } from "@suaveplan/crypto-hash/primitives/sha384/sha384";

const digest = sha384(new TextEncoder().encode("hello"));
console.log(digest.length); // 48
```

## Usage: Advanced Example

```ts
import { sha384 } from "@suaveplan/crypto-hash/primitives/sha384/sha384";

// Compute a commitment to a serialised record.
function commit(record: Record<string, string>): Uint8Array {
    const encoded = new TextEncoder().encode(JSON.stringify(record));
    return sha384(encoded);
}

const hash = commit({ userId: "u_123", action: "login" });
console.log(hash.length); // 48
```

## API Reference

Re-exports the following from the active implementation:

### `sha384(data: Uint8Array): Uint8Array`

One-shot SHA-384 digest.

| Parameter | Type | Description |
|-----------|------|-------------|
| `data` | `Uint8Array` | Arbitrary byte sequence to hash. |

**Returns:** Fresh 48-byte `Uint8Array` containing the SHA-384 digest.

## Implementation Notes

SHA-384 is a truncation of SHA-512 that shares the same 64-bit word operations and block size. It is preferred over SHA-256 in environments that process large amounts of data on 64-bit processors because the 64-bit arithmetic is natively fast, and the truncation provides a modest reduction in output size relative to SHA-512. The Noble backend delegates to `@noble/hashes/sha2` without any added overhead. The native stub throws `PrimitiveNotImplemented("sha384")` until the in-house implementation is ready and has passed the NIST CAVP test vectors.