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Source file
src/crypto/rand/rand_unix.go
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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 const urandomDevice = "/dev/urandom"
24
25
26
27
28 func init() {
29 if runtime.GOOS == "plan9" {
30 Reader = newReader(nil)
31 } else {
32 Reader = &devReader{name: urandomDevice}
33 }
34 }
35
36
37 type devReader struct {
38 name string
39 f io.Reader
40 mu sync.Mutex
41 }
42
43
44
45 var altGetRandom func([]byte) (ok bool)
46
47 func (r *devReader) Read(b []byte) (n int, err error) {
48 if altGetRandom != nil && r.name == urandomDevice && altGetRandom(b) {
49 return len(b), nil
50 }
51 r.mu.Lock()
52 defer r.mu.Unlock()
53 if r.f == nil {
54 f, err := os.Open(r.name)
55 if f == nil {
56 return 0, err
57 }
58 if runtime.GOOS == "plan9" {
59 r.f = f
60 } else {
61 r.f = bufio.NewReader(hideAgainReader{f})
62 }
63 }
64 return r.f.Read(b)
65 }
66
67 var isEAGAIN func(error) bool
68
69
70
71 type hideAgainReader struct {
72 r io.Reader
73 }
74
75 func (hr hideAgainReader) Read(p []byte) (n int, err error) {
76 n, err = hr.r.Read(p)
77 if err != nil && isEAGAIN != nil && isEAGAIN(err) {
78 err = nil
79 }
80 return
81 }
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94
95 func newReader(entropy io.Reader) io.Reader {
96 if entropy == nil {
97 entropy = &devReader{name: "/dev/random"}
98 }
99 return &reader{entropy: entropy}
100 }
101
102 type reader struct {
103 mu sync.Mutex
104 budget int
105 cipher cipher.Block
106 entropy io.Reader
107 time, seed, dst, key [aes.BlockSize]byte
108 }
109
110 func (r *reader) Read(b []byte) (n int, err error) {
111 r.mu.Lock()
112 defer r.mu.Unlock()
113 n = len(b)
114
115 for len(b) > 0 {
116 if r.budget == 0 {
117 _, err := io.ReadFull(r.entropy, r.seed[0:])
118 if err != nil {
119 return n - len(b), err
120 }
121 _, err = io.ReadFull(r.entropy, r.key[0:])
122 if err != nil {
123 return n - len(b), err
124 }
125 r.cipher, err = aes.NewCipher(r.key[0:])
126 if err != nil {
127 return n - len(b), err
128 }
129 r.budget = 1 << 20
130 }
131 r.budget -= aes.BlockSize
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138
139 ns := time.Now().UnixNano()
140 r.time[0] = byte(ns >> 56)
141 r.time[1] = byte(ns >> 48)
142 r.time[2] = byte(ns >> 40)
143 r.time[3] = byte(ns >> 32)
144 r.time[4] = byte(ns >> 24)
145 r.time[5] = byte(ns >> 16)
146 r.time[6] = byte(ns >> 8)
147 r.time[7] = byte(ns)
148 r.cipher.Encrypt(r.time[0:], r.time[0:])
149 for i := 0; i < aes.BlockSize; i++ {
150 r.dst[i] = r.time[i] ^ r.seed[i]
151 }
152 r.cipher.Encrypt(r.dst[0:], r.dst[0:])
153 for i := 0; i < aes.BlockSize; i++ {
154 r.seed[i] = r.time[i] ^ r.dst[i]
155 }
156 r.cipher.Encrypt(r.seed[0:], r.seed[0:])
157
158 m := copy(b, r.dst[0:])
159 b = b[m:]
160 }
161
162 return n, nil
163 }
164
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