A method for defending a computing system against ransomware attacks is disclosed. In one embodiment, such a method includes identifying, on a computing system, files to be protected against ransomware attacks. The method appends a public key to each of the files. Upon receiving a request to modify a specific file, the method reads the public key appended to the file, requests an authentication token from a user, and computes a private key associated with the files. The method combines the public key, authentication token, and private key to generate an unlock key. This unlock key is compared to a validation key. The method authorizes modification of the file in the event the unlock key matches the validation key. A corresponding system and computer program product are also disclosed.