diff --git a/phpseclib/Net/SFTP.php b/phpseclib/Net/SFTP.php
index 0c0bac49..b50adf99 100644
--- a/phpseclib/Net/SFTP.php
+++ b/phpseclib/Net/SFTP.php
@@ -349,8 +349,6 @@ class SFTP extends SSH2
      */
     private function partial_init_sftp_connection(): bool
     {
-        $this->window_size_server_to_client[self::CHANNEL] = $this->window_size;
-
         $response = $this->openChannel(self::CHANNEL, true);
         if ($response === true && $this->isTimeout()) {
             return false;
diff --git a/phpseclib/Net/SSH2.php b/phpseclib/Net/SSH2.php
index 4d73bd7d..ff374ccb 100644
--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -2754,6 +2754,10 @@ class SSH2
      */
     public function read(string $expect = '', int $mode = self::READ_SIMPLE, int $channel = null)
     {
+        if (!$this->isAuthenticated()) {
+            throw new InsufficientSetupException('Operation disallowed prior to login()');
+        }
+
         $this->curTimeout = $this->timeout;
         $this->is_timeout = false;
 
@@ -2761,7 +2765,7 @@ class SSH2
             $channel = $this->get_interactive_channel();
         }
 
-        if (!$this->isInteractiveChannelOpen($channel) && empty($this->channel_buffers[$channel])) {
+        if (!$this->is_channel_status_data($channel) && empty($this->channel_buffers[$channel])) {
             if ($channel != self::CHANNEL_SHELL) {
                 throw new InsufficientSetupException('Data is not available on channel');
             } elseif (!$this->openShell()) {
@@ -2809,11 +2813,15 @@ class SSH2
      */
     public function write(string $cmd, int $channel = null): void
     {
+        if (!$this->isAuthenticated()) {
+            throw new InsufficientSetupException('Operation disallowed prior to login()');
+        }
+
         if ($channel === null) {
             $channel = $this->get_interactive_channel();
         }
 
-        if (!$this->isInteractiveChannelOpen($channel)) {
+        if (!$this->is_channel_status_data($channel)) {
             if ($channel != self::CHANNEL_SHELL) {
                 throw new InsufficientSetupException('Data is not available on channel');
             } elseif (!$this->openShell()) {