While applications could simply require users to use a computer-generated password, it is inconvenient for people to remember. User-made passwords and the ability to change one's password are important for making an application user-friendly, so many schemes work to accommodate the characteristic. Researchers note that a password based protocol with mutual authentication is important because user identities and passwords are still protected, as the messages are only readable to the two parties involved. However, a negative aspect about password-based authentication is that password tables can take up a lot of memory space. One way around using a lot of memory during a password-based authentication scheme is to implement one-time passwords (OTP), which is a password sent to the user via SMS or email. OTPs are time-sensitive, which means that they will expire after a certain amount of time and that memory does not need to be stored. Multi-factor authentication Recently, more schemes have higher level authentication than password based schemes. While password-based authentication is considered as "single-factor authentication," schemes are beginning to implement smart card (two-factor) or biometric-based (three-factor) authentication schemes. Smart cards are simpler to implement and easy for authentication, but still have risks of being tampered with. Biometrics have grown more popular over password-based schemes because it is more difficult to copy or guess session keys when using biometrics, but it can be difficult to encrypt noisy data. Due to these security risks and limitations, schemes can still employ mutual authentication regardless of how many authentication factors are added. Certificate based schemes and system applications Mutual authentication is often found in schemes employed in the Internet of Things (IoT), where physical objects are incorporated into the Internet and can communicate via IP address. Authentication schemes can be applied to many types of systems that involve data transmission. As the Internet's presence in mechanical systems increases, writing effective security schemes for large numbers of users, objects, and servers can become challenging, especially when needing schemes to be lightweight and have low computational costs. Instead of password-based authentication, devices will use certificates to verify each other's identities. Radio networks Mutual authentication can be satisfied in radio network schemes, where data transmissions through radio frequencies are secure after verifying the sender and receiver. Radio frequency identification (RFID) tags are commonly used for object detection, which many manufacturers are implementing into their warehouse systems for automation. This allows for a faster way