Method _deriveSecrets

src/node/security/SecretRotator.ts:130–166

(p: any, now: number)

  }

  async _deriveSecrets(p: any, now: number) {
    this._logger.debug('deriving secrets from', p);
    if (!p.interval) return [await algorithms[p.algId].derive(p.algParams, null)];
    const t0 = intervalStart(now, p.interval);
    // Start of the first interval covered by these params. To accommodate clock skew, p.interval is
    // subtracted. If we did not do this, then the following could happen:
    //   1. Instance (A) starts up and publishes params starting at the current interval.
    //   2. Instance (B) starts up with a clock that is in the previous interval.
    //   3. Instance (B) reads the params published by instance (A) and sees that there's no
    //      coverage of what it thinks is the current interval.
    //   4. Instance (B) generates and publishes new params that covers what it thinks is the
    //      current interval.
    //   5. Instance (B) starts generating MACs from a secret derived from the new params.
    //   6. Instance (A) fails to validate the MACs generated by instance (B) until it re-reads
    //      the published params, which might take as long as interval.
    // An alternative approach is to backdate p.start by p.interval when creating new params, but
    // this could affect the end time of legacy secrets.
    const tA = intervalStart(p.start - p.interval, p.interval);
    const tZ = intervalStart(p.end - 1, p.interval);
    this._logger.debug('now:', now, 't0:', t0, 'tA:', tA, 'tZ:', tZ);
    // Starts of intervals to derive keys for.
    const tNs = [];
    // Whether the derived secret for the interval starting at tN is still relevant. If there was no
    // clock skew, a derived secret is relevant until p.lifetime has elapsed since the end of the
    // interval. To accommodate clock skew, this end time is extended by p.interval.
    const expired = (tN:number) => now >= tN + (2 * p.interval) + p.lifetime;
    // Walk from t0 back until either the start of coverage or the derived secret is expired. t0
    // must always be the first entry in case p is the current params. (The first derived secret is
    // used for generating MACs, so the secret derived for t0 must be before the secrets derived for
    // other times.)
    for (let tN = Math.min(t0, tZ); tN >= tA && !expired(tN); tN -= p.interval) tNs.push(tN);
    // Include a future derived secret to accommodate clock skew.
    if (t0 + p.interval <= tZ) tNs.push(t0 + p.interval);
    this._logger.debug('deriving secrets for intervals with start times:', tNs);
    return await Promise.all(
        tNs.map(async (tN) => await algorithms[p.algId].derive(p.algParams, `${tN}`)));
  }

  async _update() {
    const now = this._t.now();