main
1// Copyright 2017 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
5package blake2b
6
7import (
8 "encoding/binary"
9 "errors"
10 "io"
11)
12
13// XOF defines the interface to hash functions that
14// support arbitrary-length output.
15type XOF interface {
16 // Write absorbs more data into the hash's state. It panics if called
17 // after Read.
18 io.Writer
19
20 // Read reads more output from the hash. It returns io.EOF if the limit
21 // has been reached.
22 io.Reader
23
24 // Clone returns a copy of the XOF in its current state.
25 Clone() XOF
26
27 // Reset resets the XOF to its initial state.
28 Reset()
29}
30
31// OutputLengthUnknown can be used as the size argument to NewXOF to indicate
32// the length of the output is not known in advance.
33const OutputLengthUnknown = 0
34
35// magicUnknownOutputLength is a magic value for the output size that indicates
36// an unknown number of output bytes.
37const magicUnknownOutputLength = (1 << 32) - 1
38
39// maxOutputLength is the absolute maximum number of bytes to produce when the
40// number of output bytes is unknown.
41const maxOutputLength = (1 << 32) * 64
42
43// NewXOF creates a new variable-output-length hash. The hash either produce a
44// known number of bytes (1 <= size < 2**32-1), or an unknown number of bytes
45// (size == OutputLengthUnknown). In the latter case, an absolute limit of
46// 256GiB applies.
47//
48// A non-nil key turns the hash into a MAC. The key must between
49// zero and 32 bytes long.
50func NewXOF(size uint32, key []byte) (XOF, error) {
51 if len(key) > Size {
52 return nil, errKeySize
53 }
54 if size == magicUnknownOutputLength {
55 // 2^32-1 indicates an unknown number of bytes and thus isn't a
56 // valid length.
57 return nil, errors.New("blake2b: XOF length too large")
58 }
59 if size == OutputLengthUnknown {
60 size = magicUnknownOutputLength
61 }
62 x := &xof{
63 d: digest{
64 size: Size,
65 keyLen: len(key),
66 },
67 length: size,
68 }
69 copy(x.d.key[:], key)
70 x.Reset()
71 return x, nil
72}
73
74type xof struct {
75 d digest
76 length uint32
77 remaining uint64
78 cfg, root, block [Size]byte
79 offset int
80 nodeOffset uint32
81 readMode bool
82}
83
84func (x *xof) Write(p []byte) (n int, err error) {
85 if x.readMode {
86 panic("blake2b: write to XOF after read")
87 }
88 return x.d.Write(p)
89}
90
91func (x *xof) Clone() XOF {
92 clone := *x
93 return &clone
94}
95
96func (x *xof) Reset() {
97 x.cfg[0] = byte(Size)
98 binary.LittleEndian.PutUint32(x.cfg[4:], uint32(Size)) // leaf length
99 binary.LittleEndian.PutUint32(x.cfg[12:], x.length) // XOF length
100 x.cfg[17] = byte(Size) // inner hash size
101
102 x.d.Reset()
103 x.d.h[1] ^= uint64(x.length) << 32
104
105 x.remaining = uint64(x.length)
106 if x.remaining == magicUnknownOutputLength {
107 x.remaining = maxOutputLength
108 }
109 x.offset, x.nodeOffset = 0, 0
110 x.readMode = false
111}
112
113func (x *xof) Read(p []byte) (n int, err error) {
114 if !x.readMode {
115 x.d.finalize(&x.root)
116 x.readMode = true
117 }
118
119 if x.remaining == 0 {
120 return 0, io.EOF
121 }
122
123 n = len(p)
124 if uint64(n) > x.remaining {
125 n = int(x.remaining)
126 p = p[:n]
127 }
128
129 if x.offset > 0 {
130 blockRemaining := Size - x.offset
131 if n < blockRemaining {
132 x.offset += copy(p, x.block[x.offset:])
133 x.remaining -= uint64(n)
134 return
135 }
136 copy(p, x.block[x.offset:])
137 p = p[blockRemaining:]
138 x.offset = 0
139 x.remaining -= uint64(blockRemaining)
140 }
141
142 for len(p) >= Size {
143 binary.LittleEndian.PutUint32(x.cfg[8:], x.nodeOffset)
144 x.nodeOffset++
145
146 x.d.initConfig(&x.cfg)
147 x.d.Write(x.root[:])
148 x.d.finalize(&x.block)
149
150 copy(p, x.block[:])
151 p = p[Size:]
152 x.remaining -= uint64(Size)
153 }
154
155 if todo := len(p); todo > 0 {
156 if x.remaining < uint64(Size) {
157 x.cfg[0] = byte(x.remaining)
158 }
159 binary.LittleEndian.PutUint32(x.cfg[8:], x.nodeOffset)
160 x.nodeOffset++
161
162 x.d.initConfig(&x.cfg)
163 x.d.Write(x.root[:])
164 x.d.finalize(&x.block)
165
166 x.offset = copy(p, x.block[:todo])
167 x.remaining -= uint64(todo)
168 }
169 return
170}
171
172func (d *digest) initConfig(cfg *[Size]byte) {
173 d.offset, d.c[0], d.c[1] = 0, 0, 0
174 for i := range d.h {
175 d.h[i] = iv[i] ^ binary.LittleEndian.Uint64(cfg[i*8:])
176 }
177}