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
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
|
// Modifications by 42wim
//
// Copyright 2021 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package sshsig
import (
"crypto/rand"
"crypto/sha256"
"crypto/sha512"
"errors"
"hash"
"io"
"golang.org/x/crypto/ssh"
"golang.org/x/crypto/ssh/agent"
)
// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.sshsig#L81
type MessageWrapper struct {
Namespace string
Reserved string
HashAlgorithm string
Hash string
}
// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.sshsig#L34
type WrappedSig struct {
MagicHeader [6]byte
Version uint32
PublicKey string
Namespace string
Reserved string
HashAlgorithm string
Signature string
}
const (
magicHeader = "SSHSIG"
defaultHashAlgorithm = "sha512"
)
var supportedHashAlgorithms = map[string]func() hash.Hash{
"sha256": sha256.New,
"sha512": sha512.New,
}
func wrapData(m io.Reader, ns string) ([]byte, error) {
hf := sha512.New()
if _, err := io.Copy(hf, m); err != nil {
return nil, err
}
mh := hf.Sum(nil)
sp := MessageWrapper{
Namespace: ns,
HashAlgorithm: defaultHashAlgorithm,
Hash: string(mh),
}
dataMessageWrapper := ssh.Marshal(sp)
dataMessageWrapper = append([]byte(magicHeader), dataMessageWrapper...)
return dataMessageWrapper, nil
}
func sign(s ssh.AlgorithmSigner, m io.Reader, ns string) (*ssh.Signature, error) {
dataMessageWrapper, err := wrapData(m, ns)
if err != nil {
return nil, err
}
// ssh-rsa is not supported for RSA keys:
// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.sshsig#L71
// We can use the default value of "" for other key types though.
algo := ""
if s.PublicKey().Type() == ssh.KeyAlgoRSA {
algo = ssh.SigAlgoRSASHA2512
}
return s.SignWithAlgorithm(rand.Reader, dataMessageWrapper, algo)
}
func signAgent(pk ssh.PublicKey, ag agent.Agent, m io.Reader, ns string) (*ssh.Signature, error) {
dataMessageWrapper, err := wrapData(m, ns)
if err != nil {
return nil, err
}
var sigFlag agent.SignatureFlags
if pk.Type() == ssh.KeyAlgoRSA {
sigFlag = agent.SignatureFlagRsaSha512
}
agExt, ok := ag.(agent.ExtendedAgent)
if !ok {
return nil, errors.New("couldn't cast to ExtendedAgent")
}
return agExt.SignWithFlags(pk, dataMessageWrapper, sigFlag)
}
// SignWithAgent asks the ssh Agent to sign the data with the signer matching the given publicKey and returns an armored signature.
// The purpose of the namespace value is to specify a unambiguous
// interpretation domain for the signature, e.g. file signing.
// This prevents cross-protocol attacks caused by signatures
// intended for one intended domain being accepted in another.
// If empty, the default is "file".
// This can be compared with `ssh-keygen -Y sign -f keyfile -n namespace data`
func SignWithAgent(publicKey []byte, ag agent.Agent, data io.Reader, namespace string) ([]byte, error) {
pk, _, _, _, err := ssh.ParseAuthorizedKey(publicKey)
if err != nil {
return nil, err
}
if namespace == "" {
namespace = defaultNamespace
}
sig, err := signAgent(pk, ag, data, namespace)
if err != nil {
return nil, err
}
armored := Armor(sig, pk, namespace)
return armored, nil
}
// Sign signs the data with the given private key in PEM format and returns an armored signature.
// The purpose of the namespace value is to specify a unambiguous
// interpretation domain for the signature, e.g. file signing.
// This prevents cross-protocol attacks caused by signatures
// intended for one intended domain being accepted in another.
// If empty, the default is "file".
// This can be compared with `ssh-keygen -Y sign -f keyfile -n namespace data`
func Sign(pemBytes []byte, data io.Reader, namespace string) ([]byte, error) {
s, err := ssh.ParsePrivateKey(pemBytes)
if err != nil {
return nil, err
}
as, ok := s.(ssh.AlgorithmSigner)
if !ok {
return nil, err
}
if namespace == "" {
namespace = defaultNamespace
}
sig, err := sign(as, data, namespace)
if err != nil {
return nil, err
}
armored := Armor(sig, s.PublicKey(), namespace)
return armored, nil
}
|
