/*
 * Copyright 2024 The Matrix.org Foundation C.I.C.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// salt for HKDF, with 8 bytes of zeros
const zeroSalt = new Uint8Array(8);

/**
 * Derive AES and HMAC keys from a master key.
 *
 * This is used for deriving secret storage keys: see https://spec.matrix.org/v1.11/client-server-api/#msecret_storagev1aes-hmac-sha2 (step 1).
 *
 * @param key
 * @param name
 */
export async function deriveKeys(key, name) {
  const hkdfkey = await globalThis.crypto.subtle.importKey("raw", key, {
    name: "HKDF"
  }, false, ["deriveBits"]);
  const keybits = await globalThis.crypto.subtle.deriveBits({
    name: "HKDF",
    salt: zeroSalt,
    // @ts-ignore: https://github.com/microsoft/TypeScript-DOM-lib-generator/pull/879
    info: new TextEncoder().encode(name),
    hash: "SHA-256"
  }, hkdfkey, 512);
  const aesKey = keybits.slice(0, 32);
  const hmacKey = keybits.slice(32);
  const aesProm = globalThis.crypto.subtle.importKey("raw", aesKey, {
    name: "AES-CTR"
  }, false, ["encrypt", "decrypt"]);
  const hmacProm = globalThis.crypto.subtle.importKey("raw", hmacKey, {
    name: "HMAC",
    hash: {
      name: "SHA-256"
    }
  }, false, ["sign", "verify"]);
  return Promise.all([aesProm, hmacProm]);
}
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