Package rand


Package rand implements a cryptographically secure random number generator.




Package files

eagain.go rand.go rand_batched.go rand_linux.go rand_unix.go util.go


Reader is a global, shared instance of a cryptographically secure random number generator.

On Linux and FreeBSD, Reader uses getrandom(2) if available, /dev/urandom otherwise. On OpenBSD, Reader uses getentropy(2). On other Unix-like systems, Reader reads from /dev/urandom. On Windows systems, Reader uses the CryptGenRandom API. On Wasm, Reader uses the Web Crypto API.

var Reader io.Reader

func IntSource

func Int(rand io.Reader, max *big.Int) (n *big.Int, err error)

Int returns a uniform random value in [0, max). It panics if max <= 0.

func PrimeSource

func Prime(rand io.Reader, bits int) (p *big.Int, err error)

Prime returns a number, p, of the given size, such that p is prime with high probability. Prime will return error for any error returned by rand.Read or if bits < 2.

func ReadSource

func Read(b []byte) (n int, err error)

Read is a helper function that calls Reader.Read using io.ReadFull. On return, n == len(b) if and only if err == nil.


This example reads 10 cryptographically secure pseudorandom numbers from rand.Reader and writes them to a byte slice.

package main

import (

func main() {
	c := 10
	b := make([]byte, c)
	_, err := rand.Read(b)
	if err != nil {
		fmt.Println("error:", err)
	// The slice should now contain random bytes instead of only zeroes.
	fmt.Println(bytes.Equal(b, make([]byte, c)))


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