rebase: bump the golang-dependencies group with 1 update

Bumps the golang-dependencies group with 1 update: [golang.org/x/crypto](https://github.com/golang/crypto).


Updates `golang.org/x/crypto` from 0.16.0 to 0.17.0
- [Commits](https://github.com/golang/crypto/compare/v0.16.0...v0.17.0)

---
updated-dependencies:
- dependency-name: golang.org/x/crypto
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: golang-dependencies
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/golang.org/x/crypto/ssh/handshake.go

@@ -35,6 +35,16 @@ type keyingTransport interface {
 	// direction will be effected if a msgNewKeys message is sent
 	// or received.
 	prepareKeyChange(*algorithms, *kexResult) error
+
+	// setStrictMode sets the strict KEX mode, notably triggering
+	// sequence number resets on sending or receiving msgNewKeys.
+	// If the sequence number is already > 1 when setStrictMode
+	// is called, an error is returned.
+	setStrictMode() error
+
+	// setInitialKEXDone indicates to the transport that the initial key exchange
+	// was completed
+	setInitialKEXDone()
 }
 
 // handshakeTransport implements rekeying on top of a keyingTransport
@@ -100,6 +110,10 @@ type handshakeTransport struct {
 
 	// The session ID or nil if first kex did not complete yet.
 	sessionID []byte
+
+	// strictMode indicates if the other side of the handshake indicated
+	// that we should be following the strict KEX protocol restrictions.
+	strictMode bool
 }
 
 type pendingKex struct {
@@ -209,7 +223,10 @@ func (t *handshakeTransport) readLoop() {
 			close(t.incoming)
 			break
 		}
-		if p[0] == msgIgnore || p[0] == msgDebug {
+		// If this is the first kex, and strict KEX mode is enabled,
+		// we don't ignore any messages, as they may be used to manipulate
+		// the packet sequence numbers.
+		if !(t.sessionID == nil && t.strictMode) && (p[0] == msgIgnore || p[0] == msgDebug) {
 			continue
 		}
 		t.incoming <- p
@@ -441,6 +458,11 @@ func (t *handshakeTransport) readOnePacket(first bool) ([]byte, error) {
 	return successPacket, nil
 }
 
+const (
+	kexStrictClient = "kex-strict-c-v00@openssh.com"
+	kexStrictServer = "kex-strict-s-v00@openssh.com"
+)
+
 // sendKexInit sends a key change message.
 func (t *handshakeTransport) sendKexInit() error {
 	t.mu.Lock()
@@ -454,7 +476,6 @@ func (t *handshakeTransport) sendKexInit() error {
 	}
 
 	msg := &kexInitMsg{
-		KexAlgos:                t.config.KeyExchanges,
 		CiphersClientServer:     t.config.Ciphers,
 		CiphersServerClient:     t.config.Ciphers,
 		MACsClientServer:        t.config.MACs,
@@ -464,6 +485,13 @@ func (t *handshakeTransport) sendKexInit() error {
 	}
 	io.ReadFull(rand.Reader, msg.Cookie[:])
 
+	// We mutate the KexAlgos slice, in order to add the kex-strict extension algorithm,
+	// and possibly to add the ext-info extension algorithm. Since the slice may be the
+	// user owned KeyExchanges, we create our own slice in order to avoid using user
+	// owned memory by mistake.
+	msg.KexAlgos = make([]string, 0, len(t.config.KeyExchanges)+2) // room for kex-strict and ext-info
+	msg.KexAlgos = append(msg.KexAlgos, t.config.KeyExchanges...)
+
 	isServer := len(t.hostKeys) > 0
 	if isServer {
 		for _, k := range t.hostKeys {
@@ -488,17 +516,24 @@ func (t *handshakeTransport) sendKexInit() error {
 				msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, keyFormat)
 			}
 		}
+
+		if t.sessionID == nil {
+			msg.KexAlgos = append(msg.KexAlgos, kexStrictServer)
+		}
 	} else {
 		msg.ServerHostKeyAlgos = t.hostKeyAlgorithms
 
 		// As a client we opt in to receiving SSH_MSG_EXT_INFO so we know what
 		// algorithms the server supports for public key authentication. See RFC
 		// 8308, Section 2.1.
+		//
+		// We also send the strict KEX mode extension algorithm, in order to opt
+		// into the strict KEX mode.
 		if firstKeyExchange := t.sessionID == nil; firstKeyExchange {
-			msg.KexAlgos = make([]string, 0, len(t.config.KeyExchanges)+1)
-			msg.KexAlgos = append(msg.KexAlgos, t.config.KeyExchanges...)
 			msg.KexAlgos = append(msg.KexAlgos, "ext-info-c")
+			msg.KexAlgos = append(msg.KexAlgos, kexStrictClient)
 		}
+
 	}
 
 	packet := Marshal(msg)
@@ -604,6 +639,13 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error {
 		return err
 	}
 
+	if t.sessionID == nil && ((isClient && contains(serverInit.KexAlgos, kexStrictServer)) || (!isClient && contains(clientInit.KexAlgos, kexStrictClient))) {
+		t.strictMode = true
+		if err := t.conn.setStrictMode(); err != nil {
+			return err
+		}
+	}
+
 	// We don't send FirstKexFollows, but we handle receiving it.
 	//
 	// RFC 4253 section 7 defines the kex and the agreement method for
@@ -679,6 +721,12 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error {
 		return unexpectedMessageError(msgNewKeys, packet[0])
 	}
 
+	if firstKeyExchange {
+		// Indicates to the transport that the first key exchange is completed
+		// after receiving SSH_MSG_NEWKEYS.
+		t.conn.setInitialKEXDone()
+	}
+
 	return nil
 }