syncthing/lib/rand/random.go

76 lines
2.1 KiB
Go
Raw Normal View History

// Copyright (C) 2014 The Syncthing Authors.
//
2015-03-07 20:36:35 +00:00
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
// Package rand implements functions similar to math/rand in the standard
// library, but on top of a secure random number generator.
package rand
import (
"io"
mathRand "math/rand"
"reflect"
"strings"
)
// Reader is the standard crypto/rand.Reader with added buffering.
var Reader = defaultSecureSource
func Read(p []byte) (int, error) {
return io.ReadFull(defaultSecureSource, p)
}
2020-03-30 21:26:28 +00:00
// randomCharset contains the characters that can make up a rand.String().
const randomCharset = "2345679abcdefghijkmnopqrstuvwxyzACDEFGHJKLMNPQRSTUVWXYZ"
var (
// defaultSecureSource is a concurrency-safe, cryptographically secure
// math/rand.Source.
2020-03-30 21:26:28 +00:00
defaultSecureSource = newSecureSource()
// defaultSecureRand is a math/rand.Rand based on the secure source.
2020-03-30 21:26:28 +00:00
defaultSecureRand = mathRand.New(defaultSecureSource)
)
// String returns a cryptographically secure random string of characters
// (taken from randomCharset) of the specified length. The returned string
// contains ~5.8 bits of entropy per character, due to the character set used.
func String(l int) string {
var sb strings.Builder
sb.Grow(l)
for i := 0; i < l; i++ {
sb.WriteByte(randomCharset[defaultSecureRand.Intn(len(randomCharset))])
}
return sb.String()
}
// Int63 returns a cryptographically secure random int63.
func Int63() int64 {
2020-03-30 21:26:28 +00:00
return defaultSecureSource.Int63()
}
// Uint64 returns a cryptographically secure strongly random uint64.
func Uint64() uint64 {
return defaultSecureSource.Uint64()
}
// Intn returns, as an int, a cryptographically secure non-negative
// random number in [0,n). It panics if n <= 0.
func Intn(n int) int {
return defaultSecureRand.Intn(n)
}
2020-03-30 21:26:28 +00:00
// Shuffle the order of elements in slice.
func Shuffle(slice interface{}) {
rv := reflect.ValueOf(slice)
swap := reflect.Swapper(slice)
length := rv.Len()
if length < 2 {
return
}
defaultSecureRand.Shuffle(length, swap)
}