github.com/safing/portbase@v0.19.5/rng/tickfeeder.go (about)

     1  package rng
     2  
     3  import (
     4  	"context"
     5  	"encoding/binary"
     6  	"time"
     7  )
     8  
     9  func getTickFeederTickDuration() time.Duration {
    10  	// be ready in 1/10 time of reseedAfterSeconds
    11  	msecsAvailable := reseedAfterSeconds * 100
    12  	// ex.: reseed after 10 minutes: msecsAvailable = 60000
    13  	// have full entropy after 5 minutes
    14  
    15  	// one tick generates 0,125 bits of entropy
    16  	ticksNeeded := minFeedEntropy * 8
    17  	// ex.: minimum entropy is 256: ticksNeeded = 2048
    18  
    19  	// msces between ticks
    20  	tickMsecs := msecsAvailable / ticksNeeded
    21  	// ex.: tickMsecs = 29(,296875)
    22  
    23  	// use a minimum of 10 msecs per tick for good entropy
    24  	// it would take 21 seconds to get full 256 bits of entropy with 10msec ticks
    25  	if tickMsecs < 10 {
    26  		tickMsecs = 10
    27  	}
    28  
    29  	return time.Duration(tickMsecs) * time.Millisecond
    30  }
    31  
    32  // 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'.
    33  // The more work the program does, the better the quality, as the internal schedular cannot immediately run the goroutine when it's ready.
    34  func tickFeeder(ctx context.Context) error {
    35  	var value int64
    36  	var pushes int
    37  	feeder := NewFeeder()
    38  	defer feeder.CloseFeeder()
    39  
    40  	tickDuration := getTickFeederTickDuration()
    41  
    42  	for {
    43  		// wait for tick
    44  		time.Sleep(tickDuration)
    45  
    46  		// add tick value
    47  		value = (value << 1) | (time.Now().UnixNano() % 2)
    48  		pushes++
    49  
    50  		if pushes >= 64 {
    51  			// convert to []byte
    52  			b := make([]byte, 8)
    53  			binary.LittleEndian.PutUint64(b, uint64(value))
    54  			// reset
    55  			pushes = 0
    56  
    57  			// feed
    58  			select {
    59  			case feeder.input <- &entropyData{
    60  				data:    b,
    61  				entropy: 8,
    62  			}:
    63  			case <-ctx.Done():
    64  				return nil
    65  			}
    66  		} else {
    67  			// check if are done
    68  			select {
    69  			case <-ctx.Done():
    70  				return nil
    71  			default:
    72  			}
    73  		}
    74  	}
    75  }