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This research examines the application of the Elliptic Curve Digital Signature Algorithm (ECDSA) in a blockchain system as a security solution for digital payment systems in Indonesia. Using a descriptive-qualitative approach based on literature review and conceptual simulations using Python, this study discusses the working principles of ECDSA, its advantages over other digital signature algorithms, and the challenges of its adoption in Indonesia. The results show that ECDSA provides high cryptographic efficiency, maintains transaction authenticity and integrity, and supports a transparent decentralized system. The academic simulations include not only KYC processes, top-ups, transactions, validation by validators, and block recording, but also demonstrates the formation of an interconnected multi-level blockchain and tests scenarios for rejecting manipulated or invalid transactions. The contribution of this research lies not only in the theoretical review but also in the implementation illustrations that can be used as a basis for education and the initial development of blockchain-based digital payment systems. The research results show that ECDSA is capable of providing a high level of efficiency in the encryption and transaction verification process, maintaining data integrity and authenticity, and supporting a decentralized and transparent system. The academic simulations included the KYC process, wallet creation using ECDSA keys, balance top-ups through bank integration, transaction creation and validation, and block recording in the blockchain. Specifically, the simulations successfully demonstrated how new blocks are added to the chain by referencing the previous block's hash, as well as how transactions with corrupted signatures, manipulated amounts, or insufficient balances are automatically rejected by the validator consensus mechanism, maintaining system integrity. This research contributes not only theoretically, but also through conceptual representations that can be used as an educational foundation and for the initial development of blockchain-based digital payment systems in Indonesia.

Bitcoin sebagai salah satu cryptocurrency paling populer yang menawarkan peluang investasi besar namun disertai dengan volatilitas harga yang tinggi. Penelitian ini bertujuan untuk memprediksi harga Bitcoin menggunakan model Support Vector Machine (SVM) dan menganalisis risiko pasar yang melekat. Dataset historis Bitcoin digunakan untuk melatih model dengan fitur seperti harga pembukaan, harga tertinggi, harga terendah, dan volume perdagangan. Penelitian menggunakan model SVM yang dioptimalkan melalui tuning parameter untuk meningkatkan akurasi prediksi. Evaluasi model dilakukan menggunakan metrik Mean Absolute Error (MAE) dan Root Mean Squared Error (RMSE). Hasil evaluasi menunjukkan performa model yang baik dengan MAE sebesar 0,0036 dan RMSE sebesar 0,0050. Korelasi fitur menunjukkan hubungan yang kuat antara harga penutupan dengan variabel harga lainnya, sementara volume memiliki hubungan moderat. Analisis risiko menggunakan pengembalian harian mengidentifikasi volatilitas signifikan, yang menjadi tantangan dalam pengambilan keputusan investasi. Penelitian ini menyimpulkan bahwa model SVM efektif dalam memprediksi tren harga Bitcoin. Namun, analisis risiko tetap penting untuk mendukung strategi investasi yang lebih bijaksana.    

In order to send data or information  processed by using cryptography people can use XML(eXtensible Markup Language). XML data are general texts file which consist of several different tagswhich are defined by the XML document maker. In this research, the XML data were processed by usingPassword Based Encryption cryptography. This method consists of encryption and decryption meant toalter plaintext into chipertext which in turn creates chipertext from plaintext by using password key.²The implementation of the program in this research is a prototype of Hospital’s web facilitated withencyption menus and decryption data which are meant to protect the saved data which are in turn accessedand processed by authorized people. The implementation of the program is built as a web application withJava Server Page (JSP) in NetBeans 6.0 with Password Based Encryption cryptography provided by JavaCryptography Extension (JCE).

Kriptografi berasal dari kata crypto yang berarti rahasia dan graphy yang berarti tulisan. Jadikriptografi dapat diartikan sebagai tulisan rahasia. Secara istilah dapat didefinisikan sebagai studi tentangteknik-teknik matematika yang berhubungan dengan keamanan informasi.Playfair merupakan digraphs cipher, artinya setiap proses enkripsi dilakukan pada setiap dua huruf.Adapun tujuan yang akan di capai adalah membuat aplikasi untuk pengamanan pada file text denganmenggunakan metode Playfair yang dapat mendukung proses perlindungan data yang tidak mudahdicuri dan tidak mudah dipecahkan yang dapat digunakan sebagai keamanan pada data-data yang sangatpenting.

Cryptography is a science which studying about safety of messages, so it makes themessages cannot be read by unauthorized persons. Cryptography have two kinds of algorithmfirst is encryption algorithm, that is algorithm altering plaintext become the ciphertext, and thesecond is decryption algorithm that is algorithm altering ciphertext become the plaintext,  thatconducive of message can only be made and read by authorized persons. Plaintext represent themessage able to be read,  while ciphertext is message which have pass by the encryption process,so that order the ciphertext difficult to be translated or read. And method of substitution andtranspotition method are some of conventional technique able to be used to protect the picturesfiles, so that produce the pictures files which do not easy to to be read. The conventionaltechnique basically use a same key to do the encryption  and decryption process.

Kriptografi (cryptography) merupakan ilmu dan seni untuk menjaga pesan agar aman. (Cryptography is the art and science of keeping messages secure) “Crypto” berarti “secret” (rahasia) dan “graphy” berarti “writing” (tulisan). Para pelaku atau praktisi kriptografi disebut cryptographers. Sebuah algoritma kriptografik (cryptographic algorithm), disebut cipher, merupakan persamaan matematik yangdigunakan untuk proses enkripsi dan dekripsi. Biasanya kedua persamaan matematik (untuk enkripsi dan dekripsi) tersebut memiliki hubungan matematis yang cukup erat. Enkripsi digunakan untuk menyandikan data-data atau informasi sehingga tidak dapat dibaca oleh orang yang tidak berhak. Dengan enkripsi data disandikan (encrypted) dengan menggunakan sebuah kunci (key). Untuk membuka (decrypt) data tersebut digunakan juga sebuah kunci yang sama dengan kunci untuk mengenkripsi (untuk kasus private key cryptography) atau dengan kunci yang berbeda (untuk kasus public key cryptography).