Study of how to use cryptography to break the public key of crypto virus is called?

Cryptovirology is the study of cryptography from an attacker's perspective, including how malware can use cryptography (like ransomware encrypting files) and how to attack cryptographic systems. Kleptography is the study of stealing information securely using subliminal channels, cryptology is the broader field encompassing both cryptography and cryptanalysis, and cryptography is the practice of secure communication.