This is where the real magic happens. Only root can read this file. Arena spends 15 pages on password hashing algorithms (MD5, SHA-512, yescrypt). He urges administrators to audit this file weekly:
Using chage :
Arena famously writes: “En Linux, hasta el proceso más humilde debe tener un dueño.” (In Linux, even the humblest process must have an owner.) This philosophy ensures accountability. Every file, every running program (process), and every scheduled task belongs to a user. Users - La Biblia De Linux - Hector Facundo Arena