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