crng.go

package main

import (
	"fmt"
	"io/ioutil"
	"os"
	"strconv"
	"syscall"
	"time"
	"unsafe"

	"golang.org/x/sys/unix"
)

type entropy struct {
	bitCount  int /* number of bits of entropy in data */
	byteCount int /* number of bytes of data in array */
	buf       []byte
}

func main() {
	start := time.Now()
	for avail() < 2048 {
		urnd, err := os.Open("/dev/urandom")
		check(err)
		rnd, err := os.Open("/dev/random")
		check(err)
		d := make([]byte, 512)
		_, err = urnd.Read(d)
		check(err)
		e := entropy{4 * len(d), len(d), d}
		ioctl(rnd.Fd(), unix.RNDADDENTROPY, uintptr(unsafe.Pointer(&e)))
	}
	elapsed := time.Since(start)
	fmt.Printf("Finished entropizing with %d of bad entropy. took %s\n", avail(), elapsed)
}

func avail() int {
	f, err := os.Open("/proc/sys/kernel/random/entropy_avail")
	check(err)
	r, err := ioutil.ReadAll(f)
	check(err)
	i, err := strconv.Atoi(string(r[:len(r)-1]))
	check(err)
	return i
}

func check(e error) {
	if e != nil {
		panic(e)
	}
}

func ioctl(fd, op, arg uintptr) error {
	_, _, ep := syscall.Syscall(syscall.SYS_IOCTL, fd, op, arg)
	if ep != 0 {
		return syscall.Errno(ep)
	}
	return nil
}