1 package concatkdf
2
3 import (
4 "crypto"
5 "encoding/binary"
6
7 "github.com/pkg/errors"
8 )
9
10 type KDF struct {
11 buf []byte
12 otherinfo []byte
13 z []byte
14 hash crypto.Hash
15 }
16
17 func ndata(src []byte) []byte {
18 buf := make([]byte, 4+len(src))
19 binary.BigEndian.PutUint32(buf, uint32(len(src)))
20 copy(buf[4:], src)
21 return buf
22 }
23
24 func New(hash crypto.Hash, alg, Z, apu, apv, pubinfo, privinfo []byte) *KDF {
25 algbuf := ndata(alg)
26 apubuf := ndata(apu)
27 apvbuf := ndata(apv)
28
29 concat := make([]byte, len(algbuf)+len(apubuf)+len(apvbuf)+len(pubinfo)+len(privinfo))
30 n := copy(concat, algbuf)
31 n += copy(concat[n:], apubuf)
32 n += copy(concat[n:], apvbuf)
33 n += copy(concat[n:], pubinfo)
34 copy(concat[n:], privinfo)
35
36 return &KDF{
37 hash: hash,
38 otherinfo: concat,
39 z: Z,
40 }
41 }
42
43 func (k *KDF) Read(out []byte) (int, error) {
44 var round uint32 = 1
45 h := k.hash.New()
46
47 for len(out) > len(k.buf) {
48 h.Reset()
49
50 if err := binary.Write(h, binary.BigEndian, round); err != nil {
51 return 0, errors.Wrap(err, "failed to write round using kdf")
52 }
53 if _, err := h.Write(k.z); err != nil {
54 return 0, errors.Wrap(err, "failed to write z using kdf")
55 }
56 if _, err := h.Write(k.otherinfo); err != nil {
57 return 0, errors.Wrap(err, "failed to write other info using kdf")
58 }
59
60 k.buf = append(k.buf, h.Sum(nil)...)
61 round++
62 }
63
64 n := copy(out, k.buf[:len(out)])
65 k.buf = k.buf[len(out):]
66 return n, nil
67 }
68
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