1 // Copyright 2011 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.
19 // These are string constants in the SSH protocol.
21 compressionNone = "none"
22 serviceUserAuth = "ssh-userauth"
23 serviceSSH = "ssh-connection"
26 // supportedCiphers specifies the supported ciphers in preference order.
27 var supportedCiphers = []string{
28 "aes128-ctr", "aes192-ctr", "aes256-ctr",
29 "aes128-gcm@openssh.com",
30 "arcfour256", "arcfour128",
33 // supportedKexAlgos specifies the supported key-exchange algorithms in
35 var supportedKexAlgos = []string{
36 kexAlgoCurve25519SHA256,
37 // P384 and P521 are not constant-time yet, but since we don't
38 // reuse ephemeral keys, using them for ECDH should be OK.
39 kexAlgoECDH256, kexAlgoECDH384, kexAlgoECDH521,
40 kexAlgoDH14SHA1, kexAlgoDH1SHA1,
43 // supportedKexAlgos specifies the supported host-key algorithms (i.e. methods
44 // of authenticating servers) in preference order.
45 var supportedHostKeyAlgos = []string{
46 CertAlgoRSAv01, CertAlgoDSAv01, CertAlgoECDSA256v01,
47 CertAlgoECDSA384v01, CertAlgoECDSA521v01, CertAlgoED25519v01,
49 KeyAlgoECDSA256, KeyAlgoECDSA384, KeyAlgoECDSA521,
50 KeyAlgoRSA, KeyAlgoDSA,
55 // supportedMACs specifies a default set of MAC algorithms in preference order.
56 // This is based on RFC 4253, section 6.4, but with hmac-md5 variants removed
57 // because they have reached the end of their useful life.
58 var supportedMACs = []string{
59 "hmac-sha2-256-etm@openssh.com", "hmac-sha2-256", "hmac-sha1", "hmac-sha1-96",
62 var supportedCompressions = []string{compressionNone}
64 // hashFuncs keeps the mapping of supported algorithms to their respective
65 // hashes needed for signature verification.
66 var hashFuncs = map[string]crypto.Hash{
67 KeyAlgoRSA: crypto.SHA1,
68 KeyAlgoDSA: crypto.SHA1,
69 KeyAlgoECDSA256: crypto.SHA256,
70 KeyAlgoECDSA384: crypto.SHA384,
71 KeyAlgoECDSA521: crypto.SHA512,
72 CertAlgoRSAv01: crypto.SHA1,
73 CertAlgoDSAv01: crypto.SHA1,
74 CertAlgoECDSA256v01: crypto.SHA256,
75 CertAlgoECDSA384v01: crypto.SHA384,
76 CertAlgoECDSA521v01: crypto.SHA512,
79 // unexpectedMessageError results when the SSH message that we received didn't
80 // match what we wanted.
81 func unexpectedMessageError(expected, got uint8) error {
82 return fmt.Errorf("ssh: unexpected message type %d (expected %d)", got, expected)
85 // parseError results from a malformed SSH message.
86 func parseError(tag uint8) error {
87 return fmt.Errorf("ssh: parse error in message type %d", tag)
90 func findCommon(what string, client []string, server []string) (common string, err error) {
91 for _, c := range client {
92 for _, s := range server {
98 return "", fmt.Errorf("ssh: no common algorithm for %s; client offered: %v, server offered: %v", what, client, server)
101 type directionAlgorithms struct {
107 // rekeyBytes returns a rekeying intervals in bytes.
108 func (a *directionAlgorithms) rekeyBytes() int64 {
109 // According to RFC4344 block ciphers should rekey after
110 // 2^(BLOCKSIZE/4) blocks. For all AES flavors BLOCKSIZE is
113 case "aes128-ctr", "aes192-ctr", "aes256-ctr", gcmCipherID, aes128cbcID:
114 return 16 * (1 << 32)
118 // For others, stick with RFC4253 recommendation to rekey after 1 Gb of data.
122 type algorithms struct {
125 w directionAlgorithms
126 r directionAlgorithms
129 func findAgreedAlgorithms(clientKexInit, serverKexInit *kexInitMsg) (algs *algorithms, err error) {
130 result := &algorithms{}
132 result.kex, err = findCommon("key exchange", clientKexInit.KexAlgos, serverKexInit.KexAlgos)
137 result.hostKey, err = findCommon("host key", clientKexInit.ServerHostKeyAlgos, serverKexInit.ServerHostKeyAlgos)
142 result.w.Cipher, err = findCommon("client to server cipher", clientKexInit.CiphersClientServer, serverKexInit.CiphersClientServer)
147 result.r.Cipher, err = findCommon("server to client cipher", clientKexInit.CiphersServerClient, serverKexInit.CiphersServerClient)
152 result.w.MAC, err = findCommon("client to server MAC", clientKexInit.MACsClientServer, serverKexInit.MACsClientServer)
157 result.r.MAC, err = findCommon("server to client MAC", clientKexInit.MACsServerClient, serverKexInit.MACsServerClient)
162 result.w.Compression, err = findCommon("client to server compression", clientKexInit.CompressionClientServer, serverKexInit.CompressionClientServer)
167 result.r.Compression, err = findCommon("server to client compression", clientKexInit.CompressionServerClient, serverKexInit.CompressionServerClient)
175 // If rekeythreshold is too small, we can't make any progress sending
177 const minRekeyThreshold uint64 = 256
179 // Config contains configuration data common to both ServerConfig and
182 // Rand provides the source of entropy for cryptographic
183 // primitives. If Rand is nil, the cryptographic random reader
184 // in package crypto/rand will be used.
187 // The maximum number of bytes sent or received after which a
188 // new key is negotiated. It must be at least 256. If
189 // unspecified, 1 gigabyte is used.
190 RekeyThreshold uint64
192 // The allowed key exchanges algorithms. If unspecified then a
193 // default set of algorithms is used.
194 KeyExchanges []string
196 // The allowed cipher algorithms. If unspecified then a sensible
200 // The allowed MAC algorithms. If unspecified then a sensible default
205 // SetDefaults sets sensible values for unset fields in config. This is
206 // exported for testing: Configs passed to SSH functions are copied and have
207 // default values set automatically.
208 func (c *Config) SetDefaults() {
212 if c.Ciphers == nil {
213 c.Ciphers = supportedCiphers
216 for _, c := range c.Ciphers {
217 if cipherModes[c] != nil {
218 // reject the cipher if we have no cipherModes definition
219 ciphers = append(ciphers, c)
224 if c.KeyExchanges == nil {
225 c.KeyExchanges = supportedKexAlgos
229 c.MACs = supportedMACs
232 if c.RekeyThreshold == 0 {
233 // RFC 4253, section 9 suggests rekeying after 1G.
234 c.RekeyThreshold = 1 << 30
236 if c.RekeyThreshold < minRekeyThreshold {
237 c.RekeyThreshold = minRekeyThreshold
241 // buildDataSignedForAuth returns the data that is signed in order to prove
242 // possession of a private key. See RFC 4252, section 7.
243 func buildDataSignedForAuth(sessionId []byte, req userAuthRequestMsg, algo, pubKey []byte) []byte {
266 func appendU16(buf []byte, n uint16) []byte {
267 return append(buf, byte(n>>8), byte(n))
270 func appendU32(buf []byte, n uint32) []byte {
271 return append(buf, byte(n>>24), byte(n>>16), byte(n>>8), byte(n))
274 func appendU64(buf []byte, n uint64) []byte {
276 byte(n>>56), byte(n>>48), byte(n>>40), byte(n>>32),
277 byte(n>>24), byte(n>>16), byte(n>>8), byte(n))
280 func appendInt(buf []byte, n int) []byte {
281 return appendU32(buf, uint32(n))
284 func appendString(buf []byte, s string) []byte {
285 buf = appendU32(buf, uint32(len(s)))
286 buf = append(buf, s...)
290 func appendBool(buf []byte, b bool) []byte {
292 return append(buf, 1)
294 return append(buf, 0)
297 // newCond is a helper to hide the fact that there is no usable zero
298 // value for sync.Cond.
299 func newCond() *sync.Cond { return sync.NewCond(new(sync.Mutex)) }
301 // window represents the buffer available to clients
302 // wishing to write to a channel.
305 win uint32 // RFC 4254 5.2 says the window size can grow to 2^32-1
310 // add adds win to the amount of window available
312 func (w *window) add(win uint32) bool {
313 // a zero sized window adjust is a noop.
323 // It is unusual that multiple goroutines would be attempting to reserve
324 // window space, but not guaranteed. Use broadcast to notify all waiters
325 // that additional window is available.
331 // close sets the window to closed, so all reservations fail
333 func (w *window) close() {
340 // reserve reserves win from the available window capacity.
341 // If no capacity remains, reserve will block. reserve may
342 // return less than requested.
343 func (w *window) reserve(win uint32) (uint32, error) {
348 for w.win == 0 && !w.closed {
363 // waitWriterBlocked waits until some goroutine is blocked for further
364 // writes. It is used in tests only.
365 func (w *window) waitWriterBlocked() {
367 for w.writeWaiters == 0 {