International Journal of Electrical and Computer Engineering (IJECE) Vol. 12, No. 4, August 2022, pp. 3960~3969 ISSN: 2088-8708, DOI: 10.11591/ijece.v12i4.pp3960-3969  3960 Journal homepage: http://ijece.iaescore.com Stream-keys generation based on graph labeling for strengthening Vigenere encryption Antonius Cahya Prihandoko 1 , Dafik 2 , Ika Hesti Agustin 3 1 Department of Informatics, Faculty of Computer Science, University of Jember, Jember, Indonesia 2 Department Mathematics Education, Faculty of Teacher Training and Education, University of Jember, Jember, Indonesia 3 Department of Mathematics, Faculty of Mathematics and Natural Science, University of Jember, Jember, Indonesia Article Info ABSTRACT Article history: Received May 4, 2021 Revised Dec 19, 2021 Accepted Jan 26, 2022 This paper address the cryptographic keys management problem: how to generate the cryptographic keys and apply them to secure encryption. The purpose of this research was to study on utilizing graph labeling for generating stream-keys and implementing the keys for strengthening Vigenere encryption. To achieve this objective, the research was carried out in four stages: developing an algorithm for generating stream-keys, testing the randomness of the constructed keys, implementing the eligible keys in a modified Vigenere encryption and, finally, analyzing the security of the encryption. As the result, most of stream-keys produced by the algorithm are random, and the implementation of the stream keys to the modified Vigenere cipher achieve good security. The contributions of this research are utilizing graph labeling to generate stream-keys and providing different encryption keys for different blocks in a block based cipher with low storage capacity. The novel technical results yielded from this research are the algorithm of developing the source of the stream-keys based on graph labeling, the algorithm of constructing the initial block keys, and the protocol of a modified Vigenere encryption using stream-keys and operated in cipher block chaining mode. Keywords: Cipher block chaining Encryption algorithm Graph labeling Stream-keys Vigenere cipher This is an open access article under the CC BY-SA license. Corresponding Author: Antonius Cahya Prihandoko Department of Information Technology, University of Jember Kalimantan Street No. 37, Jember-68121, East Java, Indonesia Email: antoniuscp.ilkom@unej.ac.id 1. INTRODUCTION A critical characteristic of information is confidentiality. Information is said to be confidential when it is kept secret to unauthorized parties [1]. Confidentiality guarantees that only those who have rights for accessing information are able to do so. Cryptography is a well-known method to achieve information confidentiality. In this method, information is encrypted before being distributed over an insecure networks. With this capability, cryptography has a widely range of applications: securing content distribution systems [2], improving digital rights management systems [3]-[4], establishing speech encryption [5]-[6], tracing traitor in a content distribution system [7], solving security problem in mobile computing [8]-[9], and many more. The strength of cryptography protocols relies on the encryption-decryption keys management: how to protect the keys from disclose to unauthorized parties. Without a doubt, it is the biggest challenge for many cryptographic methods. Investigations on the keys management are unceasingly carried out and are concentrated to accomplish information confidentiality in accordance with the level of security required. To address the keys management problem, many researchers focused on keys generation. This aspect is the most strongly part of encryption technique [10]. Many keys generation techniques have been