remove the option [regular] from the mathastext function

bib.bib

@@ -19,14 +19,15 @@
         year = "2016",
 }
 @misc{ref4,
-        author = "Whitfield Diffie, Martin Hellman",
-        title = "New Directions in Cryptographie",
+        author = "Whitfield Diffie  Martin Hellman",
+        title = {New Directions in Cryptographie},
         note = "\url{https://www-ee.stanford.edu/\%7Ehellman/publications/24.pdf}",
         year = "1976",
 }
 @misc{ref5,
-        author = "R.L. Rivest, A. Shamir, and L. Adleman",
-        title = "A Method for Obtaining Digital Signatures and Public-Key Cryptosystems",
+        author = "R.L. Rivest und A. Shamir und L. Adleman",
+        title = "A Method for Obtaining Digital Signatures and Public-Key 
+                 Cryptosystems",
         note = "\url{https://people.csail.mit.edu/rivest/Rsapaper.pdf}",
         year = "1978",
 }

math_rsa.cls

@@ -8,7 +8,7 @@
 %Enable Mathsupport
 \RequirePackage{mathtools}
 %Use normal font for math
-\RequirePackage[Regular]{mathastext}
+\RequirePackage{mathastext}
 
 %Support for German
 \RequirePackage[utf8]{inputenc}