Analysis of user password storage mechanism in Linux system

Analysis of user password storage mechanism in Linux system

In Linux system, the storage of user password is one of the very important security mechanisms. This article will analyze the storage mechanism of user passwords in Linux systems, including the encrypted storage of passwords, the password verification process, and how to securely manage user passwords. At the same time, specific code examples will be used to demonstrate the actual operation process of password storage.

1. Encrypted storage of passwords

In the Linux system, user passwords are not stored in the system in plain text, but are encrypted and saved. The commonly used password encryption algorithm in Linux systems is SHA-512 (SHA-256 can also be used). In the Linux system, the user's password is stored in the /etc/shadow file, which stores the user's account information, including the encrypted password, password expiration time, password last modification time, etc.

The following is the content of an example /etc/shadow file:

root:$6$xld94ij$BW0RfSx9WLNAWia7D5PQwx/dNnhTgy8f3W6/vobqEmmhVUISZoL5EwrF8RTXA8xRztRGtUjLzxyBnUqVoJk7Z.:18474:0:99 999:7:::
user1:$6$du065TO$9v6.LU3F8JbLVQ7FEQEfkrQ.Zd8dxR.Vl5ohZ9uiXG4lF8k1OHkRTrqtzc5RpaC2mvM5KpIe7YH2zUL3MOUEO1:18474:0:99999:7:::

Among them, the first field represents the user name, and the second field is Encrypted password. It can be seen that the password has been encrypted into a garbled code, so even if the /etc/shadow file is leaked, it will be difficult for hackers to restore the user's password.

2. Password verification process

When a user logs in to the system, the system will verify whether the password entered by the user is correct. The process of verifying the password is actually to encrypt the password entered by the user according to the same encryption algorithm, and then compare it with the password in the /etc/shadow file. If the two are consistent, the verification is successful and the user is allowed to log in; otherwise, the verification fails and the user is refused to log in.

The following is a simple password verification code example, written in Python:

import crypt
import getpass

def validate_password(username, password):
    with open('/etc/shadow', 'r') as f:
        for line in f:
            if line.startswith(username ':'):
                shadow_entry = line.split(':')
                encrypted_password = shadow_entry[1]
                salt = encrypted_password.split('$')[2]
                new_encrypted_password = crypt.crypt(password, '$6$' salt '$')
                if new_encrypted_password == encrypted_password:
                    return True
                else:
                    return False
    return False

username = input("Enter username: ")
password = getpass.getpass("Enter password: ")

if validate_password(username, password):
    print("Password is correct. Logging in...")
else:
    print("Password is incorrect. Please try again.")

3. Securely manage user passwords

Managing user passwords is a very important security issue. First, simple passwords should be avoided and complex passwords containing uppercase and lowercase letters, numbers, and special characters are recommended. Secondly, change your password regularly to avoid using the same password for a long time. Also, passwords should not be stored in clear text anywhere, including in code.

In Linux systems, administrators can use the passwd command to modify the user password. This command will automatically encrypt the user password and store it in the /etc/shadow file. In addition, you can use some specialized password management tools to help manage user passwords, such as KeePass, LastPass, etc.

Summary:
The user password storage mechanism in the Linux system is a very important security mechanism. Through encrypted storage and strict verification process, the user password is protected from being easily leaked. Administrators need to regularly review password policies to ensure the security of user passwords. At the same time, users also need to pay attention to the security of their passwords and avoid using simple passwords and storing plain text passwords in unsafe places.

Through the analysis and code examples of this article, I hope readers will have a deeper understanding of the storage mechanism of user passwords in Linux systems to improve system security.

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