Review on Public Key Cryptography Scheme-Based Performance Metrics

ABSTRACT


INTRODUCTION
Cryptography is the study of mathematical schemes that handle privacy and authentication issues in data security [1]. It is also defined as a technique to secure personal data from unauthorized users [2]. It was applied to send unreadable form of message over the transmission medium. Generally, cryptography uses keys to encrypt and decrypt the message. Cryptographic key is divided into two classes; private key cryptography and public key cryptography. Private key cryptography, where the sender and recipient share the same key to encrypt and decrypt the plain text and ciphertext accordingly. The main advantage of private key cryptography is that it is relatively fast. This is because of only one key involved in encryption and decryption. However, by using the same key it will lead the damage to the ciphertext because of if the key is known by third party, he or she will easily decrypt the ciphertext. Thus, public key cryptography was introduced to solve the weakness of private key cryptography. It requires two different keys; public key and private key. The key used to encrypt the plaintext and can share among everyone is called public key. While another pair of key which used to decrypt the ciphertext is kept secret and it is called private key. According to [3] the private key will only be secured as long as it is kept private. Other than that, the ciphertext that was encrypted using public key can be decrypted only with corresponding private key [4]. In public key cryptography, the recipient"s public key is used to encrypt the plain text to the ciphertext while the recipient"s private key is used to decrypt the ciphertext to the original plain text. These two keys must match and agreed each other to ensure authorize sender and recipient are in the communication process. Public key cryptography can solve the problems in private key cryptography which use same key to encrypt and decrypt  [5]. However, public key cryptography works based on different schemes. Each scheme applies their own techniques to achieve the cryptography goal. The literature has shown a significant contribution to different schemes since it was invented in the last four decades. The schemes are evaluated based on different performance metrics in achieving the cryptography goal which to send data securely from sender to receiver through public network with high speed and efficient. Performance analysis is important in evaluating the strength and the efficiency of the proposed schemes. Even the cryptography concern is security; however speed and space are also the factors that effected the strength of the schemes proposed. This paper is established to review the different public key cryptography scheme based on performance analysis used to see research patterns for the last 40 years since they were invented. Meanwhile, this study had been conducted based on several steps which includes gathering the data, pre-processing data, classify the previous study based on metrics performance, evaluate data based on metrics performance classification and obtain the results.

PUBLIC KEY CRYPTOGRAPHY PERFORMANCE METRICS ON DIFFERENT PKC SCHEME
This section presents the performance metrics in evaluating the public key cryptography scheme.  Generally, each scheme was developed to offer facilities for users in data communication and transmission as well as to save the capacity, the computational time and to ensure the data protection will always be reliable. Thus, public key cryptography (PKC) is evaluated by these performance metrics to make sure the cryptanalysis is performing well in delivering secured data from sender to receiver through public networks. There are three performance metrics of PKC, which are security, speed and space [6][7]. According to [8] security is defined as all about confidentiality, integrity and availability. Other than that, computer and network security is about concerning in protecting the systems. Increasing the security usually will also increase the size of key that will use more space. The more space used, the slower the algorithm. In line with [2] an efficient cryptography algorithm probably uses less space after the encryption process in order to have fast processing. As stated by [9] fast processing is about the time needed in generating key, encrypting and decrypting process.
However, there are also integrated performance metrics that had been highlighted by the previous researchers which applied for different schemes; security and speed; security and space; speed and space; and security, speed and space. These performance metrics are used to evaluate the performance of the PKC schemes as shown in Figure 2. It also shows that most of the schemes including Diffie Hellman, RSA, McEliece, ElGamal, Elliptic Curve and GGH are more focused on security. Other than that, most of the scheme also shows attention on the integration of security and speed (digital signature and hybrid scheme); and security and space (lattices and fully homomorphic scheme). Only a few of the schemes focused on speed and space separately. On the other hand, GGH and lattices paid attention on space as the evaluation criteria for the scheme performance metrics as these schemes applied small key size and small ciphertext [10][11].

RELATED WORKS ON PERFORMANCE METRICS OF PKC SCHEMES
Basically, the main concern of PKC is the security itself where it must make sure that data transmit securely from sender to receiver over public networks. According to [2] cryptography provide a technique to secure personal data from unauthorized users. Other than that, the speed also plays the important roles as to ensure users can encrypt and decrypt faster. Moreover, not only security and speed, space also should be counted in the concern of PKC for the usage of devices that has limited space and resources. Some of the previous studies not only focused on security, speed and space separately, but they integrate the performance metrics for their schemes evaluation criteria for example security and speed; security and space; speed and space; and security, speed and space. Table 1 shows the previous research that focussing in different performance metrics that can be classified as single performance metrics and integrated performance metrics. Other than that, it also shows the schemes that are are divided into three categories which are conventional, trans-contemporary and contemporary schemes based on the year proposed. [96] [97 -99] Referring to Table 1, a few researches were implemented in the conventional years and almost no difference in the next trans-contemporary years. However, from the whole table it shows that most of the studies were concentrate in the contemporary years. On the other hand, almost all the research that focuses on single performance metrics paid attention on security. Only a few of the research look at the speed and space as their performance metrics in their proposed schemes. From the integrated performance metrics perspective, it also shows the same view where most of the research were done aggressively in the contemporary years and focused on the integration with the security performance metrics, which are security and speed; and security and space.

PREFERRED PERFORMANCE METRICS
From the seven performance-metrics discussed previously, it shows that there are three highest performance metrics popular in the previous studies which are security (44.44%); security and speed (20%); and security and space (14.44%). From the top three performance metrics, security shows the highest performance metrics that are popular among researchers which take 44.4% out of total research. On the other hand, space (2.22%), speed (5.56%), speed and space (5.56%) and security, speed and space (7.78%) shows the lowest percentage among the total previous studies. This is because, to upgrade the security, the key size and the ciphertext size will expand. Thus, it will affect the space. According to [100] if the space used is more where the block size and key size are larger, it will affect the speed of the algorithm and become slower.
From literature survey, in public key cryptography, these are the significant findings that are made based on the seven-performance metrics. Figure 3 shows the preferred performance metrics of PKC scheme which are security, then followed by security and speed; and security and space.

CONCLUSION
This paper studied an overview of seven performance-metrics for public key encryption; security; speed; space; security and speed; security and space; speed and space; and security, speed and space. They have their own strength to support the achieving of cryptography goal such as secured [23] [24] [25] [26] [27], fast [57] [58] and efficient [59]. Most of the previous researchers focus on security [33 -53]; security and speed [67 -76]; and security and space [80 -88] as their scheme performance metrics. Other than that, from the previous sections, it shows that most of the research were done aggressively in the contemporary years. However, lack of research focus on space alone because of high security and speed will lead of using more space. The findings clearly showed that the security; security and speed; security and space are the key performance metrics which addressed by the researchers in previous studies. Overall, this paper contributes suggestions and guidelines for future researchers in PKC field to choose and use the appropriate schemes based on the performance metrics that had been concentrated by the previous researchers.