1// Copyright 2012 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 ssh
 6
 7// Message authentication support
 8
 9import (
10	"crypto/hmac"
11	"crypto/sha1"
12	"crypto/sha256"
13	"crypto/sha512"
14	"hash"
15)
16
17type macMode struct {
18	keySize int
19	etm     bool
20	new     func(key []byte) hash.Hash
21}
22
23// truncatingMAC wraps around a hash.Hash and truncates the output digest to
24// a given size.
25type truncatingMAC struct {
26	length int
27	hmac   hash.Hash
28}
29
30func (t truncatingMAC) Write(data []byte) (int, error) {
31	return t.hmac.Write(data)
32}
33
34func (t truncatingMAC) Sum(in []byte) []byte {
35	out := t.hmac.Sum(in)
36	return out[:len(in)+t.length]
37}
38
39func (t truncatingMAC) Reset() {
40	t.hmac.Reset()
41}
42
43func (t truncatingMAC) Size() int {
44	return t.length
45}
46
47func (t truncatingMAC) BlockSize() int { return t.hmac.BlockSize() }
48
49var macModes = map[string]*macMode{
50	"hmac-sha2-512-etm@openssh.com": {64, true, func(key []byte) hash.Hash {
51		return hmac.New(sha512.New, key)
52	}},
53	"hmac-sha2-256-etm@openssh.com": {32, true, func(key []byte) hash.Hash {
54		return hmac.New(sha256.New, key)
55	}},
56	"hmac-sha2-512": {64, false, func(key []byte) hash.Hash {
57		return hmac.New(sha512.New, key)
58	}},
59	"hmac-sha2-256": {32, false, func(key []byte) hash.Hash {
60		return hmac.New(sha256.New, key)
61	}},
62	"hmac-sha1": {20, false, func(key []byte) hash.Hash {
63		return hmac.New(sha1.New, key)
64	}},
65	"hmac-sha1-96": {20, false, func(key []byte) hash.Hash {
66		return truncatingMAC{12, hmac.New(sha1.New, key)}
67	}},
68}