syncthing/lib/rand/random.go

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// Copyright (C) 2014 The Syncthing Authors.
//
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// 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 (
cryptoRand "crypto/rand"
mathRand "math/rand"
"reflect"
)
// Reader is the standard crypto/rand.Reader, re-exported for convenience
var Reader = cryptoRand.Reader
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// 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.
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defaultSecureSource = newSecureSource()
// defaultSecureRand is a math/rand.Rand based on the secure source.
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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 {
bs := make([]byte, l)
for i := range bs {
bs[i] = randomCharset[defaultSecureRand.Intn(len(randomCharset))]
}
return string(bs)
}
// Int63 returns a cryptographically secure random int63.
func Int63() int64 {
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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)
}
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// 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)
}