ecdh.ts

import { buf } from './buffer'

export async function generateKeyPair(): Promise<CryptoKeyPair> {
  return crypto.subtle.generateKey(
    { name: 'ECDH', namedCurve: 'P-256' },
    true,
    ['deriveBits']
  )
}

export async function exportPublicKey(key: CryptoKey): Promise<Uint8Array> {
  const raw = await crypto.subtle.exportKey('raw', key)
  return new Uint8Array(raw)
}

export async function importPublicKey(raw: Uint8Array): Promise<CryptoKey> {
  return crypto.subtle.importKey(
    'raw',
    buf(raw),
    { name: 'ECDH', namedCurve: 'P-256' },
    true,
    []
  )
}

export async function deriveSharedSecret(
  privateKey: CryptoKey,
  publicKey: CryptoKey,
): Promise<Uint8Array> {
  const bits = await crypto.subtle.deriveBits(
    { name: 'ECDH', public: publicKey },
    privateKey,
    256
  )
  return new Uint8Array(bits)
}