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
|
/*
* Copyright (c) 2014, Yawning Angel <yawning at torproject dot org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
// Package drbg implements a minimalistic DRBG based off SipHash-2-4 in OFB
// mode.
package drbg
import (
"encoding/binary"
"encoding/hex"
"fmt"
"hash"
"github.com/dchest/siphash"
"github.com/OperatorFoundation/obfs4/common/csrand"
)
// Size is the length of the HashDrbg output.
const Size = siphash.Size
// SeedLength is the length of the HashDrbg seed.
const SeedLength = 16 + Size
// Seed is the initial state for a HashDrbg. It consists of a SipHash-2-4
// key, and 8 bytes of initial data.
type Seed [SeedLength]byte
// Bytes returns a pointer to the raw HashDrbg seed.
func (seed *Seed) Bytes() *[SeedLength]byte {
return (*[SeedLength]byte)(seed)
}
// Hex returns the hexdecimal representation of the seed.
func (seed *Seed) Hex() string {
return hex.EncodeToString(seed.Bytes()[:])
}
// NewSeed returns a Seed initialized with the runtime CSPRNG.
func NewSeed() (seed *Seed, err error) {
seed = new(Seed)
if err = csrand.Bytes(seed.Bytes()[:]); err != nil {
return nil, err
}
return
}
// SeedFromBytes creates a Seed from the raw bytes, truncating to SeedLength as
// appropriate.
func SeedFromBytes(src []byte) (seed *Seed, err error) {
if len(src) < SeedLength {
return nil, InvalidSeedLengthError(len(src))
}
seed = new(Seed)
copy(seed.Bytes()[:], src)
return
}
// SeedFromHex creates a Seed from the hexdecimal representation, truncating to
// SeedLength as appropriate.
func SeedFromHex(encoded string) (seed *Seed, err error) {
var raw []byte
if raw, err = hex.DecodeString(encoded); err != nil {
return nil, err
}
return SeedFromBytes(raw)
}
// InvalidSeedLengthError is the error returned when the seed provided to the
// DRBG is an invalid length.
type InvalidSeedLengthError int
func (e InvalidSeedLengthError) Error() string {
return fmt.Sprintf("invalid seed length: %d", int(e))
}
// HashDrbg is a CSDRBG based off of SipHash-2-4 in OFB mode.
type HashDrbg struct {
sip hash.Hash64
ofb [Size]byte
}
// NewHashDrbg makes a HashDrbg instance based off an optional seed. The seed
// is truncated to SeedLength.
func NewHashDrbg(seed *Seed) (*HashDrbg, error) {
drbg := new(HashDrbg)
if seed == nil {
var err error
if seed, err = NewSeed(); err != nil {
return nil, err
}
}
drbg.sip = siphash.New(seed.Bytes()[:16])
copy(drbg.ofb[:], seed.Bytes()[16:])
return drbg, nil
}
// Int63 returns a uniformly distributed random integer [0, 1 << 63).
func (drbg *HashDrbg) Int63() int64 {
block := drbg.NextBlock()
ret := binary.BigEndian.Uint64(block)
ret &= (1<<63 - 1)
return int64(ret)
}
// Seed does nothing, call NewHashDrbg if you want to reseed.
func (drbg *HashDrbg) Seed(seed int64) {
// No-op.
}
// NextBlock returns the next 8 byte DRBG block.
func (drbg *HashDrbg) NextBlock() []byte {
drbg.sip.Write(drbg.ofb[:])
copy(drbg.ofb[:], drbg.sip.Sum(nil))
ret := make([]byte, Size)
copy(ret, drbg.ofb[:])
return ret
}
|
