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- // Copyright (C) 2014 The Syncthing Authors.
- //
- // 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)
- }
- // 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.
- defaultSecureSource = newSecureSource()
- // defaultSecureRand is a math/rand.Rand based on the secure source.
- 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 {
- 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)
- }
- // 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)
- }
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