Go: Cryptographically secure random numbers

Go has two packages for random numbers:

The two packages can be combined by calling rand.New in package math/rand with a source that gets its data from crypto/rand.

import (
        crand "crypto/rand"
        rand "math/rand"


func main() {
        var src cryptoSource
        rnd := rand.New(src)
        fmt.Println(rnd.Intn(1000)) // a random number from 0 to 999

type cryptoSource struct{}

func (s cryptoSource) Seed(seed int64) {}

func (s cryptoSource) Int63() int64 {
        return int64(s.Uint64() & ^uint64(1<<63))

func (s cryptoSource) Uint64() (v uint64) {
        err := binary.Read(crand.Reader, binary.BigEndian, &v)
        if err != nil {
        return v

The crand.Reader returns an error if the underlying system call fails. For instance if the runtime can't read /dev/urandom on a *nix system or if CryptAcquireContext fails on a Windows system.


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