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
|
// Copyright 2014 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 hkdf implements the HMAC-based Extract-and-Expand Key Derivation
// Function (HKDF) as defined in RFC 5869.
//
// HKDF is a cryptographic key derivation function (KDF) with the goal of
// expanding limited input keying material into one or more cryptographically
// strong secret keys.
//
// RFC 5869: https://tools.ietf.org/html/rfc5869
package hkdf // import "golang.org/x/crypto/hkdf"
import (
"crypto/hmac"
"errors"
"hash"
"io"
)
type hkdf struct {
expander hash.Hash
size int
info []byte
counter byte
prev []byte
cache []byte
}
func (f *hkdf) Read(p []byte) (int, error) {
// Check whether enough data can be generated
need := len(p)
remains := len(f.cache) + int(255-f.counter+1)*f.size
if remains < need {
return 0, errors.New("hkdf: entropy limit reached")
}
// Read from the cache, if enough data is present
n := copy(p, f.cache)
p = p[n:]
// Fill the buffer
for len(p) > 0 {
f.expander.Reset()
f.expander.Write(f.prev)
f.expander.Write(f.info)
f.expander.Write([]byte{f.counter})
f.prev = f.expander.Sum(f.prev[:0])
f.counter++
// Copy the new batch into p
f.cache = f.prev
n = copy(p, f.cache)
p = p[n:]
}
// Save leftovers for next run
f.cache = f.cache[n:]
return need, nil
}
// New returns a new HKDF using the given hash, the secret keying material to expand
// and optional salt and info fields.
func New(hash func() hash.Hash, secret, salt, info []byte) io.Reader {
if salt == nil {
salt = make([]byte, hash().Size())
}
extractor := hmac.New(hash, salt)
extractor.Write(secret)
prk := extractor.Sum(nil)
return &hkdf{hmac.New(hash, prk), extractor.Size(), info, 1, nil, nil}
}
|
