1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
|
// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package chacha8rand implements a pseudorandom generator
// based on ChaCha8. It is used by both runtime and math/rand/v2
// and must have no dependencies.
package chacha8rand
const (
ctrInc = 4 // increment counter by 4 between block calls
ctrMax = 16 // reseed when counter reaches 16
chunk = 32 // each chunk produced by block is 32 uint64s
reseed = 4 // reseed with 4 words
)
// block is the chacha8rand block function.
func block(seed *[4]uint64, blocks *[32]uint64, counter uint32)
// A State holds the state for a single random generator.
// It must be used from one goroutine at a time.
// If used by multiple goroutines at a time, the goroutines
// may see the same random values, but the code will not
// crash or cause out-of-bounds memory accesses.
type State struct {
buf [32]uint64
seed [4]uint64
i uint32
n uint32
c uint32
}
// Next returns the next random value, along with a boolean
// indicating whether one was available.
// If one is not available, the caller should call Refill
// and then repeat the call to Next.
//
// Next is //go:nosplit to allow its use in the runtime
// with per-m data without holding the per-m lock.
//go:nosplit
func (s *State) Next() (uint64, bool) {
i := s.i
if i >= s.n {
return 0, false
}
s.i = i + 1
return s.buf[i&31], true // i&31 eliminates bounds check
}
// Init seeds the State with the given seed value.
func (s *State) Init(seed [32]byte) {
s.Init64([4]uint64{
leUint64(seed[0*8:]),
leUint64(seed[1*8:]),
leUint64(seed[2*8:]),
leUint64(seed[3*8:]),
})
}
// Init64 seeds the state with the given seed value.
func (s *State) Init64(seed [4]uint64) {
s.seed = seed
block(&s.seed, &s.buf, 0)
s.c = 0
s.i = 0
s.n = chunk
}
// Refill refills the state with more random values.
// After a call to Refill, an immediate call to Next will succeed
// (unless multiple goroutines are incorrectly sharing a state).
func (s *State) Refill() {
s.c += ctrInc
if s.c == ctrMax {
// Reseed with generated uint64s for forward secrecy.
// Normally this is done immediately after computing a block,
// but we do it immediately before computing the next block,
// to allow a much smaller serialized state (just the seed plus offset).
// This gives a delayed benefit for the forward secrecy
// (you can reconstruct the recent past given a memory dump),
// which we deem acceptable in exchange for the reduced size.
s.seed[0] = s.buf[len(s.buf)-reseed+0]
s.seed[1] = s.buf[len(s.buf)-reseed+1]
s.seed[2] = s.buf[len(s.buf)-reseed+2]
s.seed[3] = s.buf[len(s.buf)-reseed+3]
s.c = 0
}
block(&s.seed, &s.buf, s.c)
s.i = 0
s.n = uint32(len(s.buf))
if s.c == ctrMax-ctrInc {
s.n = uint32(len(s.buf)) - reseed
}
}
// Reseed reseeds the state with new random values.
// After a call to Reseed, any previously returned random values
// have been erased from the memory of the state and cannot be
// recovered.
func (s *State) Reseed() {
var seed [4]uint64
for i := range seed {
for {
x, ok := s.Next()
if ok {
seed[i] = x
break
}
s.Refill()
}
}
s.Init64(seed)
}
// Marshal marshals the state into a byte slice.
// Marshal and Unmarshal are functions, not methods,
// so that they will not be linked into the runtime
// when it uses the State struct, since the runtime
// does not need these.
func Marshal(s *State) []byte {
data := make([]byte, 6*8)
copy(data, "chacha8:")
used := (s.c/ctrInc)*chunk + s.i
bePutUint64(data[1*8:], uint64(used))
for i, seed := range s.seed {
lePutUint64(data[(2+i)*8:], seed)
}
return data
}
type errUnmarshalChaCha8 struct{}
func (*errUnmarshalChaCha8) Error() string {
return "invalid ChaCha8 encoding"
}
// Unmarshal unmarshals the state from a byte slice.
func Unmarshal(s *State, data []byte) error {
if len(data) != 6*8 || string(data[:8]) != "chacha8:" {
return new(errUnmarshalChaCha8)
}
used := beUint64(data[1*8:])
if used > (ctrMax/ctrInc)*chunk-reseed {
return new(errUnmarshalChaCha8)
}
for i := range s.seed {
s.seed[i] = leUint64(data[(2+i)*8:])
}
s.c = ctrInc * (uint32(used) / chunk)
block(&s.seed, &s.buf, s.c)
s.i = uint32(used) % chunk
s.n = chunk
if s.c == ctrMax-ctrInc {
s.n = chunk - reseed
}
return nil
}
// binary.bigEndian.Uint64, copied to avoid dependency
func beUint64(b []byte) uint64 {
_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
}
// binary.bigEndian.PutUint64, copied to avoid dependency
func bePutUint64(b []byte, v uint64) {
_ = b[7] // early bounds check to guarantee safety of writes below
b[0] = byte(v >> 56)
b[1] = byte(v >> 48)
b[2] = byte(v >> 40)
b[3] = byte(v >> 32)
b[4] = byte(v >> 24)
b[5] = byte(v >> 16)
b[6] = byte(v >> 8)
b[7] = byte(v)
}
// binary.littleEndian.Uint64, copied to avoid dependency
func leUint64(b []byte) uint64 {
_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
}
// binary.littleEndian.PutUint64, copied to avoid dependency
func lePutUint64(b []byte, v uint64) {
_ = b[7] // early bounds check to guarantee safety of writes below
b[0] = byte(v)
b[1] = byte(v >> 8)
b[2] = byte(v >> 16)
b[3] = byte(v >> 24)
b[4] = byte(v >> 32)
b[5] = byte(v >> 40)
b[6] = byte(v >> 48)
b[7] = byte(v >> 56)
}
|
