1. Introduction
    In this era, technology has become an important aspect of human needs. Almost all their activities have been facilitated by technology, especially communication technology. Communication technology has always evolved over timeandthemostcommonlyusedcommunicationtechnologytodayissmartphones.Thesmartphoneisatelecommunication device with a touch screen function that offers more capabilities than simply calling and sending messages, which also works as a portable computer that can be carried anywhere. Due to the capabilities of the smartphone, peopledonothavetorelyoncallandshortmessageservices(SMS)featuresanymore.Theycanusechatapplications tocommunicatewitheachother.Asitiseasierandmoreconvenienttocommunicatewithsmartphones,therearealso new threats to digital data that raise issues related to security in online data exchange. This security effort is carried out with the aim of preserving the integrity and confidentiality of any information that stored or transmitted by one party to another. To maintain the security of the current data transmission in the communication process, there is an algorithm that usually handles the situation, i.e., cryptography. Cryptography is a field of study that studies the schemes of data encryptionsanddecryptions.Theseschemesarecalledcryptographicsystemsorciphers.Encryptionoralsoknownas encipheringisaprocessoftransformingarawdataortheoriginalmessage,i.e.plaintext,intoacodedmessagecalled ciphertext. Moreover, the decryption (deciphering) is the inverse process of encryption that converts the ciphertext backtotheplaintext.Cryptographyitselfconsistsofseveralalgorithmsthatdevelopedbyresearchers,suchasCaesar cipher,RivestShamirAdleman(RSA),dataencryptionstandard(DES),tripledataencryptionstandard(3DES),elliptic curve cryptography (ECC), and advanced encryption standard (AES). These algorithms can improve the security of a system with the objective of providing a level of complexity that is required by a specific program to safeguard the integrity and confidentiality of the data. Nowadays, among all the cryptography algorithms, only ECC and RSA are the most common algorithms for information security. The RSA algorithm was first introduced by Ron Rivest, Adi Shamir, and Leonard Adleman in 19782. RSA is motivated by the published works of Diffie and Hellman in 19763. However, to obtain the best algorithm for information security, Chandraseka et al.4 have compared the ECC and RSA algorithms based on the size of encryption results at the same level of security. The comparison outcomes show the ECC has smaller sizes than RSA algorithm. In Lenstra and Verheul5 it also state that ECC can offer equivalent security with substantially smaller key sizes. Therefore, many researchers focus on studying the behaviors of the ECC algorithm. Elliptic curve cryptography (ECC) is a public key cryptographic algorithm that uses elliptic curves and finite fields. Elliptic Curve Cryptography (ECC) was first proposed by victor Miller6 in 1986 and independently by Neal Koblitz7 in 1987. With its advantage in the key sizes, the ECC algorithm can be implemented for devices with limited resources, such as smartphones. In this paper, we implement the ECC algorithm to encrypt and decrypt text messages in chat applications of a smartphone. Currently, there are two kinds of platforms that usually installed and popularly used in smartphones, i.e., Android and iOS. Based on the Statista survey8 that conducted in December 2017, Android has dominated the smartphone market which its percentage had reached 88.37% compared to the other platforms. Therefore, our chat application is built on an Android smartphone with the help of Android Studio, the real-time database firebase, and the local storage room persistence library. Two novelties given in this article are first we implement the algorithm thatSingh1 usesinSmartphones.Secondlywevalidatetheencryptionanddecryptionalgorithmsthatarenotgivenin Singh1. So this article is a support for the algorithm created in Singh1. The rest of this paper is organized as follows. Section 2 describes any prior works that related to ours. Next, our proposed system and the ECC algorithm will be explained in Section 3. Afterward, the experimental and result will be discussed further in Section 4. Finally, Section 5 concludes this paper and describes future improvements. Elliptical curve cryptography (ECC) is a trending cryptography scheme that currently many researchers1,9,10 experiment about. The key size and security level of ECC are the factor which motivates many researchers to learn and explore it to know its strength and limit. The ECC is suitable for mobile devices since it is relatively small key size compared to other cryptography schemes such as RSA and Diffie Hellman. Below is a table from the NSA(Nasional Security Agency)s Case for Elliptic Cryptography showing the disparity In2015,L.D.SinghandK.M.Singh1 offeredthefastermethodtoencryptanddecryptdatausingECCratherthan commonlookuptableintheirresearchtitled”ImplementationofTextEncryptionusingEllipticCurveCryptography”. The ECC was used in the process of transforming plaintext into coordinates to be encrypted with the help of ASCII code. This research showed that their method is effective to encrypt and decrypt text data. Moreover, in their research titled ”Design of an Android Application for Secure Chatting”, Ammar H. Ali and Ali M. Sagheer11 implemented many algorithms such as Elliptic Curve Diffie Hellman (ECDH), AES, and RC4 in their chatting application with Android platform. Elliptic Curve was used as the key exchange protocol which will be mixedintoothersymmetricalgorithms,AESandRC4.ThisresearchprovedthatECDH,AES,andRC4canbehybrid

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