National Cryptography Day, or Hari Persandian Nasional, is observed in Indonesia every April 4 to honor cyber security professionals and commemorate the establishment of the Code Service in 1946. The day highlights the contributions of Lieutenant Colonel Roebiono Kertopati, who was tasked with forming an Indonesian signal intelligence unit during the Indonesian National Revolution. Despite lacking formal training in intelligence or cryptography, Kertopati and his team developed effective cryptographic techniques for securing communications in various critical situations. The Code Service was later renamed the Crypto Bureau and eventually became the National Crypto Agency in 1972. In 2017, the agency merged with the Cyber Information Defense and Security Desk to form the National Cyber and Crypto Agency, which oversees cyber intelligence and defense. National Cryptography Day serves to recognize the vital role of signal and cyber intelligence specialists in national defense.