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.
20 // These are string constants in the SSH protocol.
22 compressionNone = "none"
23 serviceUserAuth = "ssh-userauth"
24 serviceSSH = "ssh-connection"
27 // supportedCiphers specifies the supported ciphers in preference order.
28 var supportedCiphers = []string{
29 "aes128-ctr", "aes192-ctr", "aes256-ctr",
30 "aes128-gcm@openssh.com",
31 "arcfour256", "arcfour128",
34 // supportedKexAlgos specifies the supported key-exchange algorithms in
36 var supportedKexAlgos = []string{
37 kexAlgoCurve25519SHA256,
38 // P384 and P521 are not constant-time yet, but since we don't
39 // reuse ephemeral keys, using them for ECDH should be OK.
40 kexAlgoECDH256, kexAlgoECDH384, kexAlgoECDH521,
41 kexAlgoDH14SHA1, kexAlgoDH1SHA1,
44 // supportedHostKeyAlgos specifies the supported host-key algorithms (i.e. methods
45 // of authenticating servers) in preference order.
46 var supportedHostKeyAlgos = []string{
47 CertAlgoRSAv01, CertAlgoDSAv01, CertAlgoECDSA256v01,
48 CertAlgoECDSA384v01, CertAlgoECDSA521v01, CertAlgoED25519v01,
50 KeyAlgoECDSA256, KeyAlgoECDSA384, KeyAlgoECDSA521,
51 KeyAlgoRSA, KeyAlgoDSA,
56 // supportedMACs specifies a default set of MAC algorithms in preference order.
57 // This is based on RFC 4253, section 6.4, but with hmac-md5 variants removed
58 // because they have reached the end of their useful life.
59 var supportedMACs = []string{
60 "hmac-sha2-256-etm@openssh.com", "hmac-sha2-256", "hmac-sha1", "hmac-sha1-96",
63 var supportedCompressions = []string{compressionNone}
65 // hashFuncs keeps the mapping of supported algorithms to their respective
66 // hashes needed for signature verification.
67 var hashFuncs = map[string]crypto.Hash{
68 KeyAlgoRSA: crypto.SHA1,
69 KeyAlgoDSA: crypto.SHA1,
70 KeyAlgoECDSA256: crypto.SHA256,
71 KeyAlgoECDSA384: crypto.SHA384,
72 KeyAlgoECDSA521: crypto.SHA512,
73 CertAlgoRSAv01: crypto.SHA1,
74 CertAlgoDSAv01: crypto.SHA1,
75 CertAlgoECDSA256v01: crypto.SHA256,
76 CertAlgoECDSA384v01: crypto.SHA384,
77 CertAlgoECDSA521v01: crypto.SHA512,
80 // unexpectedMessageError results when the SSH message that we received didn't
81 // match what we wanted.
82 func unexpectedMessageError(expected, got uint8) error {
83 return fmt.Errorf("ssh: unexpected message type %d (expected %d)", got, expected)
86 // parseError results from a malformed SSH message.
87 func parseError(tag uint8) error {
88 return fmt.Errorf("ssh: parse error in message type %d", tag)
91 func findCommon(what string, client []string, server []string) (common string, err error) {
92 for _, c := range client {
93 for _, s := range server {
99 return "", fmt.Errorf("ssh: no common algorithm for %s; client offered: %v, server offered: %v", what, client, server)
102 type directionAlgorithms struct {
108 // rekeyBytes returns a rekeying intervals in bytes.
109 func (a *directionAlgorithms) rekeyBytes() int64 {
110 // According to RFC4344 block ciphers should rekey after
111 // 2^(BLOCKSIZE/4) blocks. For all AES flavors BLOCKSIZE is
114 case "aes128-ctr", "aes192-ctr", "aes256-ctr", gcmCipherID, aes128cbcID:
115 return 16 * (1 << 32)
119 // For others, stick with RFC4253 recommendation to rekey after 1 Gb of data.
123 type algorithms struct {
126 w directionAlgorithms
127 r directionAlgorithms
130 func findAgreedAlgorithms(clientKexInit, serverKexInit *kexInitMsg) (algs *algorithms, err error) {
131 result := &algorithms{}
133 result.kex, err = findCommon("key exchange", clientKexInit.KexAlgos, serverKexInit.KexAlgos)
138 result.hostKey, err = findCommon("host key", clientKexInit.ServerHostKeyAlgos, serverKexInit.ServerHostKeyAlgos)
143 result.w.Cipher, err = findCommon("client to server cipher", clientKexInit.CiphersClientServer, serverKexInit.CiphersClientServer)
148 result.r.Cipher, err = findCommon("server to client cipher", clientKexInit.CiphersServerClient, serverKexInit.CiphersServerClient)
153 result.w.MAC, err = findCommon("client to server MAC", clientKexInit.MACsClientServer, serverKexInit.MACsClientServer)
158 result.r.MAC, err = findCommon("server to client MAC", clientKexInit.MACsServerClient, serverKexInit.MACsServerClient)
163 result.w.Compression, err = findCommon("client to server compression", clientKexInit.CompressionClientServer, serverKexInit.CompressionClientServer)
168 result.r.Compression, err = findCommon("server to client compression", clientKexInit.CompressionServerClient, serverKexInit.CompressionServerClient)
176 // If rekeythreshold is too small, we can't make any progress sending
178 const minRekeyThreshold uint64 = 256
180 // Config contains configuration data common to both ServerConfig and
183 // Rand provides the source of entropy for cryptographic
184 // primitives. If Rand is nil, the cryptographic random reader
185 // in package crypto/rand will be used.
188 // The maximum number of bytes sent or received after which a
189 // new key is negotiated. It must be at least 256. If
190 // unspecified, a size suitable for the chosen cipher is used.
191 RekeyThreshold uint64
193 // The allowed key exchanges algorithms. If unspecified then a
194 // default set of algorithms is used.
195 KeyExchanges []string
197 // The allowed cipher algorithms. If unspecified then a sensible
201 // The allowed MAC algorithms. If unspecified then a sensible default
206 // SetDefaults sets sensible values for unset fields in config. This is
207 // exported for testing: Configs passed to SSH functions are copied and have
208 // default values set automatically.
209 func (c *Config) SetDefaults() {
213 if c.Ciphers == nil {
214 c.Ciphers = supportedCiphers
217 for _, c := range c.Ciphers {
218 if cipherModes[c] != nil {
219 // reject the cipher if we have no cipherModes definition
220 ciphers = append(ciphers, c)
225 if c.KeyExchanges == nil {
226 c.KeyExchanges = supportedKexAlgos
230 c.MACs = supportedMACs
233 if c.RekeyThreshold == 0 {
234 // cipher specific default
235 } else if c.RekeyThreshold < minRekeyThreshold {
236 c.RekeyThreshold = minRekeyThreshold
237 } else if c.RekeyThreshold >= math.MaxInt64 {
238 // Avoid weirdness if somebody uses -1 as a threshold.
239 c.RekeyThreshold = math.MaxInt64
243 // buildDataSignedForAuth returns the data that is signed in order to prove
244 // possession of a private key. See RFC 4252, section 7.
245 func buildDataSignedForAuth(sessionId []byte, req userAuthRequestMsg, algo, pubKey []byte) []byte {
268 func appendU16(buf []byte, n uint16) []byte {
269 return append(buf, byte(n>>8), byte(n))
272 func appendU32(buf []byte, n uint32) []byte {
273 return append(buf, byte(n>>24), byte(n>>16), byte(n>>8), byte(n))
276 func appendU64(buf []byte, n uint64) []byte {
278 byte(n>>56), byte(n>>48), byte(n>>40), byte(n>>32),
279 byte(n>>24), byte(n>>16), byte(n>>8), byte(n))
282 func appendInt(buf []byte, n int) []byte {
283 return appendU32(buf, uint32(n))
286 func appendString(buf []byte, s string) []byte {
287 buf = appendU32(buf, uint32(len(s)))
288 buf = append(buf, s...)
292 func appendBool(buf []byte, b bool) []byte {
294 return append(buf, 1)
296 return append(buf, 0)
299 // newCond is a helper to hide the fact that there is no usable zero
300 // value for sync.Cond.
301 func newCond() *sync.Cond { return sync.NewCond(new(sync.Mutex)) }
303 // window represents the buffer available to clients
304 // wishing to write to a channel.
307 win uint32 // RFC 4254 5.2 says the window size can grow to 2^32-1
312 // add adds win to the amount of window available
314 func (w *window) add(win uint32) bool {
315 // a zero sized window adjust is a noop.
325 // It is unusual that multiple goroutines would be attempting to reserve
326 // window space, but not guaranteed. Use broadcast to notify all waiters
327 // that additional window is available.
333 // close sets the window to closed, so all reservations fail
335 func (w *window) close() {
342 // reserve reserves win from the available window capacity.
343 // If no capacity remains, reserve will block. reserve may
344 // return less than requested.
345 func (w *window) reserve(win uint32) (uint32, error) {
350 for w.win == 0 && !w.closed {
365 // waitWriterBlocked waits until some goroutine is blocked for further
366 // writes. It is used in tests only.
367 func (w *window) waitWriterBlocked() {
369 for w.writeWaiters == 0 {