65 lines
1.6 KiB
Go
65 lines
1.6 KiB
Go
// Copyright (C) 2016 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
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import (
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"bufio"
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"crypto/rand"
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"encoding/binary"
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"io"
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"sync"
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)
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// The secureSource is a math/rand.Source + io.Reader that reads bytes from
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// crypto/rand.Reader. It means we can use the convenience functions
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// provided by math/rand.Rand on top of a secure source of numbers. It is
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// concurrency safe for ease of use.
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type secureSource struct {
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rd io.Reader
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mut sync.Mutex
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}
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func newSecureSource() *secureSource {
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return &secureSource{
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// Using buffering on top of the rand.Reader increases our
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// performance by about 20%, even though it means we must use
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// locking.
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rd: bufio.NewReader(rand.Reader),
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}
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}
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func (s *secureSource) Seed(int64) {
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panic("SecureSource is not seedable")
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}
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func (s *secureSource) Int63() int64 {
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return int64(s.Uint64() & (1<<63 - 1))
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}
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func (s *secureSource) Read(p []byte) (int, error) {
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s.mut.Lock()
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defer s.mut.Unlock()
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return s.rd.Read(p)
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}
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func (s *secureSource) Uint64() uint64 {
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var buf [8]byte
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// Read eight bytes of entropy from the buffered, secure random number
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// generator. The buffered reader isn't concurrency safe, so we lock
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// around that.
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s.mut.Lock()
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_, err := io.ReadFull(s.rd, buf[:])
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s.mut.Unlock()
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if err != nil {
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panic("randomness failure: " + err.Error())
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}
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// Grab those bytes as an uint64
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return binary.BigEndian.Uint64(buf[:])
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}
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