public static byte[] FromBase64StringNoPadding(this String base64String) { ArgumentUtility.CheckStringForNullOrEmpty(base64String, "base64String"); string s = base64String; s = s.Replace('-', '+'); // 62nd char of encoding s = s.Replace('_', '/'); // 63rd char of encoding switch (s.Length % 4) // Pad with trailing '='s { case 0: break; // No pad chars in this case case 2: s += "=="; break; // Two pad chars case 3: s += "="; break; // One pad char default: throw new ArgumentException(CommonResources.IllegalBase64String(), "base64String"); } return(Convert.FromBase64String(s)); // Standard base64 decoder }