forked from zmap/zgrab
-
Notifications
You must be signed in to change notification settings - Fork 1
/
kex_gex.go
289 lines (246 loc) · 7.45 KB
/
kex_gex.go
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
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
package xssh
import (
"crypto"
"crypto/rand"
"encoding/binary"
"encoding/json"
"fmt"
"io"
"math/big"
ztoolsKeys "github.com/zmap/zgrab/ztools/keys"
)
const (
kexAlgoDHGEXSHA1 = "diffie-hellman-group-exchange-sha1"
kexAlgoDHGEXSHA256 = "diffie-hellman-group-exchange-sha256"
)
// Messages
type kexDHGexGroupMsg struct {
P *big.Int `sshtype:"31"`
G *big.Int
}
type kexDHGexInitMsg struct {
X *big.Int `sshtype:"32"`
}
type kexDHGexReplyMsg struct {
HostKey []byte `sshtype:"33"`
Y *big.Int
Signature []byte
}
type kexDHGexRequestMsg struct {
MinBits uint32 `sshtype:"34"`
PreferedBits uint32
MaxBits uint32
}
type gexJsonLog struct {
Parameters *ztoolsKeys.DHParams `json:"parameters,omitempty"`
ServerSignature []byte `json:"server_signature,omitempty"`
ServerHostKey *ServerHostKeyJsonLog `json:"server_host_key,omitempty"`
}
type dhGEXSHA struct {
g, p *big.Int
hashFunc crypto.Hash
JsonLog *gexJsonLog
}
func (gex *dhGEXSHA) GetNew(keyType string) kexAlgorithm {
switch keyType {
case kexAlgoDHGEXSHA1:
ret := new(dhGEXSHA)
ret.hashFunc = crypto.SHA1
ret.JsonLog = new(gexJsonLog)
ret.JsonLog.Parameters = new(ztoolsKeys.DHParams)
return ret
case kexAlgoDHGEXSHA256:
ret := new(dhGEXSHA)
ret.hashFunc = crypto.SHA256
ret.JsonLog = new(gexJsonLog)
ret.JsonLog.Parameters = new(ztoolsKeys.DHParams)
return ret
default:
panic("Unimplemented GEX selected")
}
}
func (gex *dhGEXSHA) MarshalJSON() ([]byte, error) {
return json.Marshal(gex.JsonLog)
}
func (gex *dhGEXSHA) diffieHellman(theirPublic, myPrivate *big.Int) (*big.Int, error) {
if theirPublic.Sign() <= 0 || theirPublic.Cmp(gex.p) >= 0 {
return nil, fmt.Errorf("ssh: DH parameter out of bounds")
}
return new(big.Int).Exp(theirPublic, myPrivate, gex.p), nil
}
func (gex *dhGEXSHA) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) {
// Send GexRequest
kexDHGexRequest := kexDHGexRequestMsg{
MinBits: uint32(pkgConfig.GexMinBits),
PreferedBits: uint32(pkgConfig.GexPreferredBits),
MaxBits: uint32(pkgConfig.GexMaxBits),
}
if err := c.writePacket(Marshal(&kexDHGexRequest)); err != nil {
return nil, err
}
// *Receive GexGroup*
packet, err := c.readPacket()
if err != nil {
return nil, err
}
var kexDHGexGroup kexDHGexGroupMsg
if err = Unmarshal(packet, &kexDHGexGroup); err != nil {
return nil, err
}
if gex.JsonLog != nil {
gex.JsonLog.Parameters.Prime = kexDHGexGroup.P
gex.JsonLog.Parameters.Generator = kexDHGexGroup.G
}
// reject if p's bit length < pkgConfig.GexMinBits or > pkgConfig.GexMaxBits
if kexDHGexGroup.P.BitLen() < int(pkgConfig.GexMinBits) || kexDHGexGroup.P.BitLen() > int(pkgConfig.GexMaxBits) {
return nil, fmt.Errorf("Server-generated gex p (dont't ask) is out of range (%d bits)", kexDHGexGroup.P.BitLen())
}
gex.p = kexDHGexGroup.P
gex.g = kexDHGexGroup.G
// *Send GexInit
x, err := rand.Int(randSource, gex.p)
if err != nil {
return nil, err
}
X := new(big.Int).Exp(gex.g, x, gex.p)
kexDHGexInit := kexDHGexInitMsg{
X: X,
}
if gex.JsonLog != nil && pkgConfig.Verbose {
gex.JsonLog.Parameters.ClientPrivate = x
gex.JsonLog.Parameters.ClientPublic = X
}
if err := c.writePacket(Marshal(&kexDHGexInit)); err != nil {
return nil, err
}
// Receive GexReply
packet, err = c.readPacket()
if err != nil {
return nil, err
}
var kexDHGexReply kexDHGexReplyMsg
if err = Unmarshal(packet, &kexDHGexReply); err != nil {
return nil, err
}
if gex.JsonLog != nil {
gex.JsonLog.Parameters.ServerPublic = kexDHGexReply.Y
gex.JsonLog.ServerSignature = kexDHGexReply.Signature
gex.JsonLog.ServerHostKey = LogServerHostKey(kexDHGexReply.HostKey)
}
kInt, err := gex.diffieHellman(kexDHGexReply.Y, x)
if err != nil {
return nil, err
}
h := gex.hashFunc.New()
magics.write(h)
writeString(h, kexDHGexReply.HostKey)
binary.Write(h, binary.BigEndian, uint32(pkgConfig.GexMinBits))
binary.Write(h, binary.BigEndian, uint32(pkgConfig.GexPreferredBits))
binary.Write(h, binary.BigEndian, uint32(pkgConfig.GexMaxBits))
writeInt(h, gex.p)
writeInt(h, gex.g)
writeInt(h, X)
writeInt(h, kexDHGexReply.Y)
K := make([]byte, intLength(kInt))
marshalInt(K, kInt)
h.Write(K)
return &kexResult{
H: h.Sum(nil),
K: K,
HostKey: kexDHGexReply.HostKey,
Signature: kexDHGexReply.Signature,
Hash: gex.hashFunc,
}, nil
}
func (gex *dhGEXSHA) Server(c packetConn, randSource io.Reader, magics *handshakeMagics, priv Signer) (result *kexResult, err error) {
// *Receive GexRequest*
packet, err := c.readPacket()
if err != nil {
return
}
var kexDHGexRequest kexDHGexRequestMsg
if err = Unmarshal(packet, &kexDHGexRequest); err != nil {
return
}
// smoosh the user's preferred size into our own limits
if kexDHGexRequest.PreferedBits > uint32(pkgConfig.GexMaxBits) {
kexDHGexRequest.PreferedBits = uint32(pkgConfig.GexMaxBits)
}
if kexDHGexRequest.PreferedBits < uint32(pkgConfig.GexMinBits) {
kexDHGexRequest.PreferedBits = uint32(pkgConfig.GexMinBits)
}
// fix min/max if they're inconsistent. technically, we could just pout
// and hang up, but there's no harm in giving them the benefit of the
// doubt and just picking a bitsize for them.
if kexDHGexRequest.MinBits > kexDHGexRequest.PreferedBits {
kexDHGexRequest.MinBits = kexDHGexRequest.PreferedBits
}
if kexDHGexRequest.MaxBits < kexDHGexRequest.PreferedBits {
kexDHGexRequest.MaxBits = kexDHGexRequest.PreferedBits
}
// *Send GexGroup*
// generate prime
// TODO: Not implemented yet, should load primes from /etc/ssh/moduli
gex.p, _ = new(big.Int).SetString("D1391174233D315398FE2830AC6B2B66BCCD01B0A634899F339B7879F1DB85712E9DC4E4B1C6C8355570C1D2DCB53493DF18175A9C53D1128B592B4C72D97136F5542FEB981CBFE8012FDD30361F288A42BD5EBB08BAB0A5640E1AC48763B2ABD1945FEE36B2D55E1D50A1C86CED9DD141C4E7BE2D32D9B562A0F8E2E927020E91F58B57EB9ACDDA106A59302D7E92AD5F6E851A45FA1CFE86029A0F727F65A8F475F33572E2FDAB6073F0C21B8B54C3823DB2EF068927E5D747498F96361507", 16)
gex.g = big.NewInt(5)
kexDHGexGroup := kexDHGexGroupMsg{
P: gex.p,
G: gex.g,
}
if err := c.writePacket(Marshal(&kexDHGexGroup)); err != nil {
return nil, err
}
// *Receive GexInit
packet, err = c.readPacket()
if err != nil {
return
}
var kexDHGexInit kexDHGexInitMsg
if err = Unmarshal(packet, &kexDHGexInit); err != nil {
return
}
y, err := rand.Int(randSource, gex.p)
if err != nil {
return
}
Y := new(big.Int).Exp(gex.g, y, gex.p)
kInt, err := gex.diffieHellman(kexDHGexInit.X, y)
if err != nil {
return nil, err
}
hostKeyBytes := priv.PublicKey().Marshal()
h := gex.hashFunc.New()
magics.write(h)
writeString(h, hostKeyBytes)
binary.Write(h, binary.BigEndian, uint32(pkgConfig.GexMinBits))
binary.Write(h, binary.BigEndian, uint32(pkgConfig.GexPreferredBits))
binary.Write(h, binary.BigEndian, uint32(pkgConfig.GexMaxBits))
writeInt(h, gex.p)
writeInt(h, gex.g)
writeInt(h, kexDHGexInit.X)
writeInt(h, Y)
K := make([]byte, intLength(kInt))
marshalInt(K, kInt)
h.Write(K)
H := h.Sum(nil)
// H is already a hash, but the hostkey signing will apply its
// own key-specific hash algorithm.
sig, err := signAndMarshal(priv, randSource, H)
if err != nil {
return nil, err
}
kexDHGexReply := kexDHGexReplyMsg{
HostKey: hostKeyBytes,
Y: Y,
Signature: sig,
}
packet = Marshal(&kexDHGexReply)
err = c.writePacket(packet)
return &kexResult{
H: H,
K: K,
HostKey: hostKeyBytes,
Signature: sig,
Hash: gex.hashFunc,
}, nil
}