stream ciphers don't use IVs

phpseclib/Crypt/Common/StreamCipher.php

@@ -24,4 +24,14 @@ namespace phpseclib3\Crypt\Common;
  */
 abstract class StreamCipher extends SymmetricKey
 {
+    /**
+     * Stream ciphers not use an IV
+     *
+     * @access public
+     * @return bool
+     */
+    public function usesIV()
+    {
+        return false;
+    }
 }

phpseclib/Crypt/RC4.php

@@ -161,17 +161,6 @@ class RC4 extends StreamCipher
         return parent::isValidEngineHelper($engine);
     }
 
-    /**
-     * RC4 does not use an IV
-     *
-     * @access public
-     * @return bool
-     */
-    public function usesIV()
-    {
-        return false;
-    }
-
     /**
      * Sets the key length
      *

phpseclib/Crypt/Salsa20.php

@@ -107,16 +107,6 @@ class Salsa20 extends StreamCipher
         parent::__construct('stream');
     }
 
-    /**
-     * Salsa20 does not use an IV
-     *
-     * @return bool
-     */
-    public function usesIV()
-    {
-        return false;
-    }
-
     /**
      * Salsa20 uses a nonce
      *