Putro, Sewindu, Sumbogo Wisnu Pamungkas, and Dony Ariyus. 2020. “Modification of Two Algorithms Playfair And Caesar Chiper Al-Gorithm Using Postal Code City: Modification of Two Algorithms Playfair And Caesar Chiper Al-Gorithm Using Postal Code City”. Jurnal Mantik 3 (4):412-19. https://www.iocscience.org/ejournal/index.php/mantik/article/view/584.