safing-portbase/rng/tickfeeder.go

package rng

import (
	"time"
)

var (
	tickDuration = 1 * time.Millisecond
)

func getTickDuration() time.Duration {

	// be ready in 1/10 time of reseedAfterSeconds
	msecsAvailable := reseedAfterSeconds() * 100
	// ex.: reseed after 10 minutes: msecsAvailable = 36000
	// have full entropy after 5 minutes

	// one tick generates 0,125 bits of entropy
	ticksNeeded := minFeedEntropy() * 8
	// ex.: minimum entropy is 256: ticksNeeded = 2048

	// msces between ticks
	tickMsecs := msecsAvailable / ticksNeeded
	// ex.: tickMsecs = 17(,578125)

	// use a minimum of 10 msecs per tick for good entropy
	// it would take 21 seconds to get full 256 bits of entropy with 10msec ticks
	if tickMsecs < 10 {
		tickMsecs = 10
	}

	return time.Duration(tickMsecs * int64(time.Millisecond))
}

// tickFeeder is a really simple entropy feeder that adds the least significant bit of the current nanosecond unixtime to its pool every time it 'ticks'.
// The more work the program does, the better the quality, as the internal schedular cannot immediately run the goroutine when it's ready.
func tickFeeder() {

	var value int64
	var pushes int
	feeder := NewFeeder()

	for {
		select {
		case <-time.After(tickDuration):

			value = (value << 1) | (time.Now().UnixNano() % 2)

			pushes++
			if pushes >= 64 {
				feeder.SupplyEntropyAsInt(value, 8)
				pushes = 0
			}

			tickDuration = getTickDuration()

		case <-shutdownSignal:
			return
		}
	}
}