libsignal/node/ts/zkgroup/groupsend/GroupSendDerivedKeyPair.ts

//
// Copyright 2024 Signal Messenger, LLC.
// SPDX-License-Identifier: AGPL-3.0-only
//

import ByteArray from '../internal/ByteArray.js';
import * as Native from '../../Native.js';
import ServerSecretParams from '../ServerSecretParams.js';

// For docs
import type GroupSendEndorsementsResponse from './GroupSendEndorsementsResponse.js';

/**
 * The key pair used to issue and verify group send endorsements.
 *
 * Group send endorsements use a different key pair depending on the endorsement's expiration (but
 * not the user ID being endorsed). The server may cache these keys to avoid the (small) cost of
 * deriving them from the root key in {@link ServerSecretParams}. The key object stores the
 * expiration so that it doesn't need to be provided again when issuing endorsements.
 *
 * @see {@link GroupSendEndorsementsResponse.issue}
 * @see {@link GroupSendFullToken#verify}
 */
export default class GroupSendDerivedKeyPair extends ByteArray {
  constructor(contents: Uint8Array<ArrayBuffer>) {
    super(contents, Native.GroupSendDerivedKeyPair_CheckValidContents);
  }

  /**
   * Derives a new key for group send endorsements that expire at `expiration`.
   *
   * `expiration` must be day-aligned as a protection against fingerprinting by the issuing server.
   */
  public static forExpiration(
    expiration: Date,
    params: ServerSecretParams
  ): GroupSendDerivedKeyPair {
    return new GroupSendDerivedKeyPair(
      Native.GroupSendDerivedKeyPair_ForExpiration(
        Math.floor(expiration.getTime() / 1000),
        params
      )
    );
  }
}