libgo/go/crypto/rand/rand_unix.go

   1 // Copyright 2010 The Go Authors.  All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // +build darwin dragonfly freebsd linux nacl netbsd openbsd plan9 solaris
   6
   7 // Unix cryptographically secure pseudorandom number
   8 // generator.
   9
  10 package rand
  11
  12 import (
  13         "bufio"
  14         "crypto/aes"
  15         "crypto/cipher"
  16         "io"
  17         "os"
  18         "runtime"
  19         "sync"
  20         "time"
  21 )
  22
  23 // Easy implementation: read from /dev/urandom.
  24 // This is sufficient on Linux, OS X, and FreeBSD.
  25
  26 func init() {
  27         if runtime.GOOS == "plan9" {
  28                 Reader = newReader(nil)
  29         } else {
  30                 Reader = &devReader{name: "/dev/urandom"}
  31         }
  32 }
  33
  34 // A devReader satisfies reads by reading the file named name.
  35 type devReader struct {
  36         name string
  37         f    io.Reader
  38         mu   sync.Mutex
  39 }
  40
  41 func (r *devReader) Read(b []byte) (n int, err error) {
  42         r.mu.Lock()
  43         defer r.mu.Unlock()
  44         if r.f == nil {
  45                 f, err := os.Open(r.name)
  46                 if f == nil {
  47                         return 0, err
  48                 }
  49                 if runtime.GOOS == "plan9" {
  50                         r.f = f
  51                 } else {
  52                         r.f = bufio.NewReader(f)
  53                 }
  54         }
  55         return r.f.Read(b)
  56 }
  57
  58 // Alternate pseudo-random implementation for use on
  59 // systems without a reliable /dev/urandom.
  60
  61 // newReader returns a new pseudorandom generator that
  62 // seeds itself by reading from entropy.  If entropy == nil,
  63 // the generator seeds itself by reading from the system's
  64 // random number generator, typically /dev/random.
  65 // The Read method on the returned reader always returns
  66 // the full amount asked for, or else it returns an error.
  67 //
  68 // The generator uses the X9.31 algorithm with AES-128,
  69 // reseeding after every 1 MB of generated data.
  70 func newReader(entropy io.Reader) io.Reader {
  71         if entropy == nil {
  72                 entropy = &devReader{name: "/dev/random"}
  73         }
  74         return &reader{entropy: entropy}
  75 }
  76
  77 type reader struct {
  78         mu                   sync.Mutex
  79         budget               int // number of bytes that can be generated
  80         cipher               cipher.Block
  81         entropy              io.Reader
  82         time, seed, dst, key [aes.BlockSize]byte
  83 }
  84
  85 func (r *reader) Read(b []byte) (n int, err error) {
  86         r.mu.Lock()
  87         defer r.mu.Unlock()
  88         n = len(b)
  89
  90         for len(b) > 0 {
  91                 if r.budget == 0 {
  92                         _, err := io.ReadFull(r.entropy, r.seed[0:])
  93                         if err != nil {
  94                                 return n - len(b), err
  95                         }
  96                         _, err = io.ReadFull(r.entropy, r.key[0:])
  97                         if err != nil {
  98                                 return n - len(b), err
  99                         }
 100                         r.cipher, err = aes.NewCipher(r.key[0:])
 101                         if err != nil {
 102                                 return n - len(b), err
 103                         }
 104                         r.budget = 1 << 20 // reseed after generating 1MB
 105                 }
 106                 r.budget -= aes.BlockSize
 107
 108                 // ANSI X9.31 (== X9.17) algorithm, but using AES in place of 3DES.
 109                 //
 110                 // single block:
 111                 // t = encrypt(time)
 112                 // dst = encrypt(t^seed)
 113                 // seed = encrypt(t^dst)
 114                 ns := time.Now().UnixNano()
 115                 r.time[0] = byte(ns >> 56)
 116                 r.time[1] = byte(ns >> 48)
 117                 r.time[2] = byte(ns >> 40)
 118                 r.time[3] = byte(ns >> 32)
 119                 r.time[4] = byte(ns >> 24)
 120                 r.time[5] = byte(ns >> 16)
 121                 r.time[6] = byte(ns >> 8)
 122                 r.time[7] = byte(ns)
 123                 r.cipher.Encrypt(r.time[0:], r.time[0:])
 124                 for i := 0; i < aes.BlockSize; i++ {
 125                         r.dst[i] = r.time[i] ^ r.seed[i]
 126                 }
 127                 r.cipher.Encrypt(r.dst[0:], r.dst[0:])
 128                 for i := 0; i < aes.BlockSize; i++ {
 129                         r.seed[i] = r.time[i] ^ r.dst[i]
 130                 }
 131                 r.cipher.Encrypt(r.seed[0:], r.seed[0:])
 132
 133                 m := copy(b, r.dst[0:])
 134                 b = b[m:]
 135         }
 136
 137         return n, nil
 138 }