rand - ActiveState ActiveGo 1.8

Package rand

import "crypto/rand"

Overview ▾

Package rand implements a cryptographically secure pseudorandom number generator.


Reader is a global, shared instance of a cryptographically strong pseudo-random generator.

On Linux, 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.

var Reader io.Reader

func Int

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 Prime

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 Read

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.


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)))