Unixlösenordssystemet

The Unix password system, often referred to as the shadow password system, is a fundamental component of Unix-like operating systems responsible for managing user authentication. It originally stored user account information, including encrypted passwords, in a file called /etc/passwd. This file was world-readable, meaning any user on the system could view it.

The primary drawback of this initial approach was that the encrypted passwords, while not the plain text themselves, could be subjected to brute-force attacks or dictionary attacks offline if an attacker gained access to the /etc/passwd file. This posed a significant security risk.

To address this vulnerability, the shadow password system was introduced. In this improved system, the encrypted password hashes are moved from the world-readable /etc/passwd file to a new, more protected file, typically named /etc/shadow. The /etc/shadow file is only readable by the root user.

The /etc/passwd file in the shadow system still contains essential user account information such as username, user ID, group ID, home directory, and default shell, but it omits the password field, often replacing it with an 'x' or another placeholder. This separation ensures that sensitive password data is not exposed to regular users.

The shadow password system significantly enhances system security by making it much harder for attackers to obtain and attempt to crack user passwords, even if they manage to access the system's file structure.