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
|
//
// 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 ssh implements signing with SSH keys
package ssh
import (
"encoding/pem"
"errors"
"fmt"
"golang.org/x/crypto/ssh"
)
const (
namespace = "file"
pemType = "SSH SIGNATURE"
)
// Signature encapsulates an SSH Signature object for verification.
type Signature struct {
signature *ssh.Signature
pk ssh.PublicKey
hashAlg string
}
// Armor generates a PEM armored signature block.
func Armor(s *ssh.Signature, p ssh.PublicKey) []byte {
sig := wrappedSig{
Version: 1,
PublicKey: string(p.Marshal()),
Namespace: namespace,
HashAlgorithm: defaultHashAlgorithm,
Signature: string(ssh.Marshal(s)),
}
copy(sig.MagicHeader[:], magicHeader)
enc := pem.EncodeToMemory(&pem.Block{
Type: pemType,
Bytes: ssh.Marshal(sig),
})
return enc
}
// Decode parses a PEM armored signature block.
func Decode(b []byte) (*Signature, error) {
pemBlock, _ := pem.Decode(b)
if pemBlock == nil {
return nil, errors.New("unable to decode pem file")
}
if pemBlock.Type != pemType {
return nil, fmt.Errorf("wrong pem block type: %s. Expected SSH-SIGNATURE", pemBlock.Type)
}
// Now we unmarshal it into the Signature block
sig := wrappedSig{}
if err := ssh.Unmarshal(pemBlock.Bytes, &sig); err != nil {
return nil, err
}
if sig.Version != 1 {
return nil, fmt.Errorf("unsupported signature version: %d", sig.Version)
}
if string(sig.MagicHeader[:]) != magicHeader {
return nil, fmt.Errorf("invalid magic header: %s", sig.MagicHeader[:])
}
if sig.Namespace != "file" {
return nil, fmt.Errorf("invalid signature namespace: %s", sig.Namespace)
}
if _, ok := supportedHashAlgorithms[sig.HashAlgorithm]; !ok {
return nil, fmt.Errorf("unsupported hash algorithm: %s", sig.HashAlgorithm)
}
// Now we can unpack the Signature and PublicKey blocks
sshSig := ssh.Signature{}
if err := ssh.Unmarshal([]byte(sig.Signature), &sshSig); err != nil {
return nil, err
}
pk, err := ssh.ParsePublicKey([]byte(sig.PublicKey))
if err != nil {
return nil, err
}
return &Signature{
signature: &sshSig,
pk: pk,
hashAlg: sig.HashAlgorithm,
}, nil
}
|
