a cybersecurity analyst is applying for a new job with a penetration testing firm. he received the job application as a secured adobe pdf file, but unfortunately, the firm locked the file with a password so the potential employee could not fill in the application. instead of asking for an unlocked copy of the document, the analyst decides to write a script in python to attempt to unlock the pdf file by using passwords from a list of commonly used passwords until he can find the correct password or attempts every password in his list. based on this description, what kind of cryptographic attack did the analyst perform?