# Lightweight Sensor Authentication Scheme for Energy Efficiency in Ubiquitous Computing Environments
## 2 Related Work
### Previous Crypto Technology  
The RSA algorithm, which is widely used for the safe distribution of encryption keys and other key management problems, is an encryption method based on the theory that generally, multiplying two prime numbers with a large difference between them is easy, but factoring the two numbers once multiplied is difficult [28]. However, the algorithm places a large operational demand on devices during the encryption and decoding processes; if it were applied in IoT environments, the network may become overloaded.  
Elliptic curve cryptosystems (ECCs), based on the discrete logarithm in the elliptic curve group defined in finite fields, is a public key encryption algorithm suggested independently by [PERSON] and [PERSON] in 1985. It has been studied in number theory and algebraic geometry for over 150 years. In recent encryption research, the elliptic curve method (ECM) has been utilized in factorization problems, primality tests, and public key encryption, which are crucial for RSA encryption [29].  
Currently, public key encryption utilizes intractability; that is, the calculation is possible, but takes significant time to calculate, according to computational complexity theory. The early stages of public key encryption are based on prime factorization with random positive integers, which requires significant time to perform. Elliptic curve encryption relies on the long time needed to find the discrete log of a random elliptic curve at a specific known point. For encryption purposes, an elliptic curve is a type of plane curve and is the set of points that meet the equation \(y^{2}=x^{3}+ax+b\). (To simplify the curve, the point characteristics are fixed finite fields). The above set forms the Avenlan group, having the infinite point as the identity element together with the computation of the elliptic curve group. The structure of the group follows the factor of the underlying algebraic variety [30; 31].  
Kerberos authentication is composed of a Kerberos server, ticket, and authenticator. After the Kerberos server and Ticket Granting Server (TGS) generate a ticket, the ticket is used in communication between the client and TGS, and between TGS and the server. The authenticator is generated by the client, can be used only once and includes the client name, workstation IP address, and the current time as authentication information [32]. When the client request a login to request a server access ticket, and authentication is completed by transmitting the required information, the ticket is generated and sent to the client; then it verifies whether the client is authorized from the server. The user saves the ticket and accesses TGS using this ticket when requesting access to the service. To prevent ticket interception, it includes the ticket issuance time and valid time. The AS verifies the ID by providing the session key between client and TGS and between client and server, and prevents the risk of intercept by limiting the valid time [33]. Despite this, intercept and replay attacks are possible using the weak point in that time. Although user authentication is realized by issuing the ticket, a digital signature is not provided. In addition, due to security problems in the Kerberos server, it should be constructed with perfect confidence between client and server, as well as between servers. That is, it should be used with encryption technology such as SSL [34] or Diffie-Hellman [35], though these can cause network overloading when applied to IoT environments [36].