diff --git a/phpseclib/Crypt/Common/AsymmetricKey.php b/phpseclib/Crypt/Common/AsymmetricKey.php
index 28ced301..f85cad4c 100644
--- a/phpseclib/Crypt/Common/AsymmetricKey.php
+++ b/phpseclib/Crypt/Common/AsymmetricKey.php
@@ -80,22 +80,6 @@ abstract class AsymmetricKey
      */
     private static $invisiblePlugins = [];
 
-    /**
-     * Supported signature formats (lower case)
-     *
-     * @see self::initialize_static_variables()
-     * @var array
-     */
-    private static $signatureFormats = [];
-
-    /**
-     * Supported signature formats (original case)
-     *
-     * @see self::initialize_static_variables()
-     * @var array
-     */
-    private static $signatureFileFormats = [];
-
     /**
      * Available Engines
      *
diff --git a/phpseclib/Crypt/Common/Formats/Keys/OpenSSH.php b/phpseclib/Crypt/Common/Formats/Keys/OpenSSH.php
index 7711cf39..8763f791 100644
--- a/phpseclib/Crypt/Common/Formats/Keys/OpenSSH.php
+++ b/phpseclib/Crypt/Common/Formats/Keys/OpenSSH.php
@@ -129,7 +129,7 @@ abstract class OpenSSH
 
         if (!isset($parts[1])) {
             $key = base64_decode($parts[0]);
-            $comment = $parts[1] ?? false;
+            $comment = false;
         } else {
             $asciiType = $parts[0];
             self::checkType($parts[0]);
diff --git a/phpseclib/Crypt/EC/BaseCurves/Base.php b/phpseclib/Crypt/EC/BaseCurves/Base.php
index 8aebf78b..325b9a64 100644
--- a/phpseclib/Crypt/EC/BaseCurves/Base.php
+++ b/phpseclib/Crypt/EC/BaseCurves/Base.php
@@ -24,20 +24,6 @@ use phpseclib3\Math\BigInteger;
  */
 abstract class Base
 {
-    /**
-     * Doubles
-     *
-     * @var object[]
-     */
-    protected $doubles;
-
-    /**
-     * NAF Points
-     *
-     * @var int[]
-     */
-    private $naf;
-
     /**
      * The Order
      *
diff --git a/phpseclib/Crypt/RC2.php b/phpseclib/Crypt/RC2.php
index 446a8b15..47795259 100644
--- a/phpseclib/Crypt/RC2.php
+++ b/phpseclib/Crypt/RC2.php
@@ -71,14 +71,6 @@ class RC2 extends BlockCipher
      */
     private $orig_key;
 
-    /**
-     * Don't truncate / null pad key
-     *
-     * @see \phpseclib3\Crypt\Common\SymmetricKey::clearBuffers()
-     * @var bool
-     */
-    private $skip_key_adjustment = true;
-
     /**
      * Key Length (in bytes)
      *
diff --git a/phpseclib/File/X509.php b/phpseclib/File/X509.php
index b9346a7c..017e2738 100644
--- a/phpseclib/File/X509.php
+++ b/phpseclib/File/X509.php
@@ -161,14 +161,6 @@ class X509
      */
     private $privateKey;
 
-    /**
-     * Object identifiers for X.509 certificates
-     *
-     * @var array
-     * @link http://en.wikipedia.org/wiki/Object_identifier
-     */
-    private $oids;
-
     /**
      * The certificate authorities
      *
diff --git a/phpseclib/System/SSH/Agent.php b/phpseclib/System/SSH/Agent.php
index a65eecf9..d89f7fae 100644
--- a/phpseclib/System/SSH/Agent.php
+++ b/phpseclib/System/SSH/Agent.php
@@ -109,13 +109,6 @@ class Agent
      */
     private $expected_bytes = 0;
 
-    /**
-     * The current request channel
-     *
-     * @var int
-     */
-    private $request_channel;
-
     /**
      * Default Constructor
      *