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
|
// Copyright 2011 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 ssh
import (
"crypto/aes"
"crypto/cipher"
"crypto/rc4"
)
// streamDump is used to dump the initial keystream for stream ciphers. It is a
// a write-only buffer, and not intended for reading so do not require a mutex.
var streamDump [512]byte
// noneCipher implements cipher.Stream and provides no encryption. It is used
// by the transport before the first key-exchange.
type noneCipher struct{}
func (c noneCipher) XORKeyStream(dst, src []byte) {
copy(dst, src)
}
func newAESCTR(key, iv []byte) (cipher.Stream, error) {
c, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
return cipher.NewCTR(c, iv), nil
}
func newRC4(key, iv []byte) (cipher.Stream, error) {
return rc4.NewCipher(key)
}
type cipherMode struct {
keySize int
ivSize int
skip int
createFn func(key, iv []byte) (cipher.Stream, error)
}
func (c *cipherMode) createCipher(key, iv []byte) (cipher.Stream, error) {
if len(key) < c.keySize {
panic("ssh: key length too small for cipher")
}
if len(iv) < c.ivSize {
panic("ssh: iv too small for cipher")
}
stream, err := c.createFn(key[:c.keySize], iv[:c.ivSize])
if err != nil {
return nil, err
}
for remainingToDump := c.skip; remainingToDump > 0; {
dumpThisTime := remainingToDump
if dumpThisTime > len(streamDump) {
dumpThisTime = len(streamDump)
}
stream.XORKeyStream(streamDump[:dumpThisTime], streamDump[:dumpThisTime])
remainingToDump -= dumpThisTime
}
return stream, nil
}
// Specifies a default set of ciphers and a preference order. This is based on
// OpenSSH's default client preference order, minus algorithms that are not
// implemented.
var DefaultCipherOrder = []string{
"aes128-ctr", "aes192-ctr", "aes256-ctr",
"arcfour256", "arcfour128",
}
var cipherModes = map[string]*cipherMode{
// Ciphers from RFC4344, which introduced many CTR-based ciphers. Algorithms
// are defined in the order specified in the RFC.
"aes128-ctr": &cipherMode{16, aes.BlockSize, 0, newAESCTR},
"aes192-ctr": &cipherMode{24, aes.BlockSize, 0, newAESCTR},
"aes256-ctr": &cipherMode{32, aes.BlockSize, 0, newAESCTR},
// Ciphers from RFC4345, which introduces security-improved arcfour ciphers.
// They are defined in the order specified in the RFC.
"arcfour128": &cipherMode{16, 0, 1536, newRC4},
"arcfour256": &cipherMode{32, 0, 1536, newRC4},
}
|
