--- /dev/null
+// 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"
+ "crypto/rand"
+ "fmt"
+ "io"
+ "math"
+ "sync"
+
+ _ "crypto/sha1"
+ _ "crypto/sha256"
+ _ "crypto/sha512"
+)
+
+// These are string constants in the SSH protocol.
+const (
+ compressionNone = "none"
+ serviceUserAuth = "ssh-userauth"
+ serviceSSH = "ssh-connection"
+)
+
+// supportedCiphers specifies the supported ciphers in preference order.
+var supportedCiphers = []string{
+ "aes128-ctr", "aes192-ctr", "aes256-ctr",
+ "aes128-gcm@openssh.com",
+ "arcfour256", "arcfour128",
+}
+
+// supportedKexAlgos specifies the supported key-exchange algorithms in
+// preference order.
+var supportedKexAlgos = []string{
+ kexAlgoCurve25519SHA256,
+ // P384 and P521 are not constant-time yet, but since we don't
+ // reuse ephemeral keys, using them for ECDH should be OK.
+ kexAlgoECDH256, kexAlgoECDH384, kexAlgoECDH521,
+ kexAlgoDH14SHA1, kexAlgoDH1SHA1,
+}
+
+// supportedHostKeyAlgos specifies the supported host-key algorithms (i.e. methods
+// of authenticating servers) in preference order.
+var supportedHostKeyAlgos = []string{
+ CertAlgoRSAv01, CertAlgoDSAv01, CertAlgoECDSA256v01,
+ CertAlgoECDSA384v01, CertAlgoECDSA521v01, CertAlgoED25519v01,
+
+ KeyAlgoECDSA256, KeyAlgoECDSA384, KeyAlgoECDSA521,
+ KeyAlgoRSA, KeyAlgoDSA,
+
+ KeyAlgoED25519,
+}
+
+// supportedMACs specifies a default set of MAC algorithms in preference order.
+// This is based on RFC 4253, section 6.4, but with hmac-md5 variants removed
+// because they have reached the end of their useful life.
+var supportedMACs = []string{
+ "hmac-sha2-256-etm@openssh.com", "hmac-sha2-256", "hmac-sha1", "hmac-sha1-96",
+}
+
+var supportedCompressions = []string{compressionNone}
+
+// hashFuncs keeps the mapping of supported algorithms to their respective
+// hashes needed for signature verification.
+var hashFuncs = map[string]crypto.Hash{
+ KeyAlgoRSA: crypto.SHA1,
+ KeyAlgoDSA: crypto.SHA1,
+ KeyAlgoECDSA256: crypto.SHA256,
+ KeyAlgoECDSA384: crypto.SHA384,
+ KeyAlgoECDSA521: crypto.SHA512,
+ CertAlgoRSAv01: crypto.SHA1,
+ CertAlgoDSAv01: crypto.SHA1,
+ CertAlgoECDSA256v01: crypto.SHA256,
+ CertAlgoECDSA384v01: crypto.SHA384,
+ CertAlgoECDSA521v01: crypto.SHA512,
+}
+
+// unexpectedMessageError results when the SSH message that we received didn't
+// match what we wanted.
+func unexpectedMessageError(expected, got uint8) error {
+ return fmt.Errorf("ssh: unexpected message type %d (expected %d)", got, expected)
+}
+
+// parseError results from a malformed SSH message.
+func parseError(tag uint8) error {
+ return fmt.Errorf("ssh: parse error in message type %d", tag)
+}
+
+func findCommon(what string, client []string, server []string) (common string, err error) {
+ for _, c := range client {
+ for _, s := range server {
+ if c == s {
+ return c, nil
+ }
+ }
+ }
+ return "", fmt.Errorf("ssh: no common algorithm for %s; client offered: %v, server offered: %v", what, client, server)
+}
+
+type directionAlgorithms struct {
+ Cipher string
+ MAC string
+ Compression string
+}
+
+// rekeyBytes returns a rekeying intervals in bytes.
+func (a *directionAlgorithms) rekeyBytes() int64 {
+ // According to RFC4344 block ciphers should rekey after
+ // 2^(BLOCKSIZE/4) blocks. For all AES flavors BLOCKSIZE is
+ // 128.
+ switch a.Cipher {
+ case "aes128-ctr", "aes192-ctr", "aes256-ctr", gcmCipherID, aes128cbcID:
+ return 16 * (1 << 32)
+
+ }
+
+ // For others, stick with RFC4253 recommendation to rekey after 1 Gb of data.
+ return 1 << 30
+}
+
+type algorithms struct {
+ kex string
+ hostKey string
+ w directionAlgorithms
+ r directionAlgorithms
+}
+
+func findAgreedAlgorithms(clientKexInit, serverKexInit *kexInitMsg) (algs *algorithms, err error) {
+ result := &algorithms{}
+
+ result.kex, err = findCommon("key exchange", clientKexInit.KexAlgos, serverKexInit.KexAlgos)
+ if err != nil {
+ return
+ }
+
+ result.hostKey, err = findCommon("host key", clientKexInit.ServerHostKeyAlgos, serverKexInit.ServerHostKeyAlgos)
+ if err != nil {
+ return
+ }
+
+ result.w.Cipher, err = findCommon("client to server cipher", clientKexInit.CiphersClientServer, serverKexInit.CiphersClientServer)
+ if err != nil {
+ return
+ }
+
+ result.r.Cipher, err = findCommon("server to client cipher", clientKexInit.CiphersServerClient, serverKexInit.CiphersServerClient)
+ if err != nil {
+ return
+ }
+
+ result.w.MAC, err = findCommon("client to server MAC", clientKexInit.MACsClientServer, serverKexInit.MACsClientServer)
+ if err != nil {
+ return
+ }
+
+ result.r.MAC, err = findCommon("server to client MAC", clientKexInit.MACsServerClient, serverKexInit.MACsServerClient)
+ if err != nil {
+ return
+ }
+
+ result.w.Compression, err = findCommon("client to server compression", clientKexInit.CompressionClientServer, serverKexInit.CompressionClientServer)
+ if err != nil {
+ return
+ }
+
+ result.r.Compression, err = findCommon("server to client compression", clientKexInit.CompressionServerClient, serverKexInit.CompressionServerClient)
+ if err != nil {
+ return
+ }
+
+ return result, nil
+}
+
+// If rekeythreshold is too small, we can't make any progress sending
+// stuff.
+const minRekeyThreshold uint64 = 256
+
+// Config contains configuration data common to both ServerConfig and
+// ClientConfig.
+type Config struct {
+ // Rand provides the source of entropy for cryptographic
+ // primitives. If Rand is nil, the cryptographic random reader
+ // in package crypto/rand will be used.
+ Rand io.Reader
+
+ // The maximum number of bytes sent or received after which a
+ // new key is negotiated. It must be at least 256. If
+ // unspecified, a size suitable for the chosen cipher is used.
+ RekeyThreshold uint64
+
+ // The allowed key exchanges algorithms. If unspecified then a
+ // default set of algorithms is used.
+ KeyExchanges []string
+
+ // The allowed cipher algorithms. If unspecified then a sensible
+ // default is used.
+ Ciphers []string
+
+ // The allowed MAC algorithms. If unspecified then a sensible default
+ // is used.
+ MACs []string
+}
+
+// SetDefaults sets sensible values for unset fields in config. This is
+// exported for testing: Configs passed to SSH functions are copied and have
+// default values set automatically.
+func (c *Config) SetDefaults() {
+ if c.Rand == nil {
+ c.Rand = rand.Reader
+ }
+ if c.Ciphers == nil {
+ c.Ciphers = supportedCiphers
+ }
+ var ciphers []string
+ for _, c := range c.Ciphers {
+ if cipherModes[c] != nil {
+ // reject the cipher if we have no cipherModes definition
+ ciphers = append(ciphers, c)
+ }
+ }
+ c.Ciphers = ciphers
+
+ if c.KeyExchanges == nil {
+ c.KeyExchanges = supportedKexAlgos
+ }
+
+ if c.MACs == nil {
+ c.MACs = supportedMACs
+ }
+
+ if c.RekeyThreshold == 0 {
+ // cipher specific default
+ } else if c.RekeyThreshold < minRekeyThreshold {
+ c.RekeyThreshold = minRekeyThreshold
+ } else if c.RekeyThreshold >= math.MaxInt64 {
+ // Avoid weirdness if somebody uses -1 as a threshold.
+ c.RekeyThreshold = math.MaxInt64
+ }
+}
+
+// buildDataSignedForAuth returns the data that is signed in order to prove
+// possession of a private key. See RFC 4252, section 7.
+func buildDataSignedForAuth(sessionId []byte, req userAuthRequestMsg, algo, pubKey []byte) []byte {
+ data := struct {
+ Session []byte
+ Type byte
+ User string
+ Service string
+ Method string
+ Sign bool
+ Algo []byte
+ PubKey []byte
+ }{
+ sessionId,
+ msgUserAuthRequest,
+ req.User,
+ req.Service,
+ req.Method,
+ true,
+ algo,
+ pubKey,
+ }
+ return Marshal(data)
+}
+
+func appendU16(buf []byte, n uint16) []byte {
+ return append(buf, byte(n>>8), byte(n))
+}
+
+func appendU32(buf []byte, n uint32) []byte {
+ return append(buf, byte(n>>24), byte(n>>16), byte(n>>8), byte(n))
+}
+
+func appendU64(buf []byte, n uint64) []byte {
+ return append(buf,
+ byte(n>>56), byte(n>>48), byte(n>>40), byte(n>>32),
+ byte(n>>24), byte(n>>16), byte(n>>8), byte(n))
+}
+
+func appendInt(buf []byte, n int) []byte {
+ return appendU32(buf, uint32(n))
+}
+
+func appendString(buf []byte, s string) []byte {
+ buf = appendU32(buf, uint32(len(s)))
+ buf = append(buf, s...)
+ return buf
+}
+
+func appendBool(buf []byte, b bool) []byte {
+ if b {
+ return append(buf, 1)
+ }
+ return append(buf, 0)
+}
+
+// newCond is a helper to hide the fact that there is no usable zero
+// value for sync.Cond.
+func newCond() *sync.Cond { return sync.NewCond(new(sync.Mutex)) }
+
+// window represents the buffer available to clients
+// wishing to write to a channel.
+type window struct {
+ *sync.Cond
+ win uint32 // RFC 4254 5.2 says the window size can grow to 2^32-1
+ writeWaiters int
+ closed bool
+}
+
+// add adds win to the amount of window available
+// for consumers.
+func (w *window) add(win uint32) bool {
+ // a zero sized window adjust is a noop.
+ if win == 0 {
+ return true
+ }
+ w.L.Lock()
+ if w.win+win < win {
+ w.L.Unlock()
+ return false
+ }
+ w.win += win
+ // It is unusual that multiple goroutines would be attempting to reserve
+ // window space, but not guaranteed. Use broadcast to notify all waiters
+ // that additional window is available.
+ w.Broadcast()
+ w.L.Unlock()
+ return true
+}
+
+// close sets the window to closed, so all reservations fail
+// immediately.
+func (w *window) close() {
+ w.L.Lock()
+ w.closed = true
+ w.Broadcast()
+ w.L.Unlock()
+}
+
+// reserve reserves win from the available window capacity.
+// If no capacity remains, reserve will block. reserve may
+// return less than requested.
+func (w *window) reserve(win uint32) (uint32, error) {
+ var err error
+ w.L.Lock()
+ w.writeWaiters++
+ w.Broadcast()
+ for w.win == 0 && !w.closed {
+ w.Wait()
+ }
+ w.writeWaiters--
+ if w.win < win {
+ win = w.win
+ }
+ w.win -= win
+ if w.closed {
+ err = io.EOF
+ }
+ w.L.Unlock()
+ return win, err
+}
+
+// waitWriterBlocked waits until some goroutine is blocked for further
+// writes. It is used in tests only.
+func (w *window) waitWriterBlocked() {
+ w.Cond.L.Lock()
+ for w.writeWaiters == 0 {
+ w.Cond.Wait()
+ }
+ w.Cond.L.Unlock()
+}
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