// getEntropy is very slow (~500µs), so we don't want it on the hot path. // We keep both a persistent DRBG instance and a pool of additional instances. // Occasional uses will use drbgInstance, even if the pool was emptied since the // last use. Frequent concurrent uses will fill the pool and use it. var drbgInstance atomic.Pointer[Counter] var drbgPool = sync.Pool{ New: func() any { return NewCounter(getEntropy()) }, } // Read fills b with cryptographically secure random bytes. In FIPS mode, it...