# p256

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  - [p256.native](./impl/p256.native/p256.native.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256.noble](./impl/p256.noble/p256.noble.md) — <!-- begin:auto-docs --> _(no submodules)_  - [p256.noble](./impl/p256.noble/p256.noble.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256.select](./p256.select/p256.select.md) — <!-- begin:auto-docs --> _(no submodules)_  - [p256.select](./p256.select/p256.select.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256](./p256.md) — <!-- begin:auto-docs --> _(no submodules)_- p256.native — <!-- begin:auto-docs --> _(no submodul…
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- [p256.native](./impl/p256.native/p256.native.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256.noble](./impl/p256.noble/p256.noble.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256.noble](./impl/p256.noble/p256.noble.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256.select](./p256.select/p256.select.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256.select](./p256.select/p256.select.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256](./p256.md) — <!-- begin:auto-docs --> _(no submodules)_- p256.native — <!-- begin:auto-docs --> _(no submodu…
- [p256.native](./impl/p256.native/p256.native.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256.noble](./impl/p256.noble/p256.noble.md) — <!-- begin:auto-docs --> _(no submodules)_  - [p256.noble](./impl/p256.noble/p256.noble.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256.select](./p256.select/p256.select.md) — <!-- begin:auto-docs --> _(no submodules)_  - [p256.select](./p256.select/p256.select.md) — <!-- begin:auto-docs --> _(no submodules)_- [p256](./p256.md) — <!-- begin:auto-docs --> _(no submodules)_
## Purpose

`p256.ts` is the stable public entry point for the NIST P-256 elliptic-curve primitive in `@suaveplan/crypto-curve`. It re-exports everything from `p256.select.ts`, which forwards to either the Noble-backed or native implementation based on `crypto.config.ts`.

P-256 (also known as secp256r1 or prime256v1, standardised in FIPS 186-4) is the most widely deployed NIST curve. It is mandatory in TLS 1.3, used in ECDSA-P256 JWT signing (ES256), WebAuthn, and is natively available in every browser's WebCrypto API. Callers import from this file and remain insulated from implementation changes.

## Features

- `getPublicKey(privateKey)` — 33-byte compressed public key.
- `sign(digest, privateKey)` — compact 64-byte ECDSA signature (r ‖ s). Caller pre-hashes.
- `verify(signature, digest, publicKey)` — boolean; never throws on malformed inputs.
- `randomPrivateKey()` — rejection-sampled 32-byte private key.

## Usage: Basic Example

```ts
import * as p256 from "@suaveplan/crypto-curve/p256";
import { sha256 } from "@suaveplan/crypto-hash/hash";

const sk = p256.randomPrivateKey();
const pk = p256.getPublicKey(sk);
const msg = new TextEncoder().encode("hello P-256");
const sig = p256.sign(sha256(msg), sk);
console.log(p256.verify(sig, sha256(msg), pk)); // true
```

## Usage: Advanced Example

```ts
import * as p256 from "@suaveplan/crypto-curve/p256";
import { sha256 } from "@suaveplan/crypto-hash/hash";
import { toHex } from "@suaveplan/crypto-hash/encoding";

// Sign a JSON payload and produce a JWS-style compact token.
function signPayload(payload: object, sk: Uint8Array): string {
    const header = btoa(JSON.stringify({ alg: "ES256" }));
    const body = btoa(JSON.stringify(payload));
    const sigInput = new TextEncoder().encode(`${header}.${body}`);
    const sig = p256.sign(sha256(sigInput), sk);
    return `${header}.${body}.${toHex(sig)}`;
}
```

## API Reference

All symbols re-exported from `p256.select.ts`:

- `getPublicKey(privateKey: Uint8Array): Uint8Array`
- `sign(digest: Uint8Array, privateKey: Uint8Array): Uint8Array`
- `verify(signature: Uint8Array, digest: Uint8Array, publicKey: Uint8Array): boolean`
- `randomPrivateKey(): Uint8Array`

## Implementation Notes

This file is a zero-logic re-export barrel. Its sole purpose is the stable import path `@suaveplan/crypto-curve/p256`. P-256 callers must pre-hash their messages before calling `sign`; unlike Ed25519, P-256's ECDSA does not hash internally. Use SHA-256 for ES256 compatibility.