Shadow Password File

What is a shadow password file?

As /etc/shadow is a system file found in the Linux operating system where encrypted user passwords are stored for added security. Access to this file is restricted to the root user, limiting unauthorized access and reducing the risk of intrusion by malicious entities.

The conventional way of storing passwords in the /etc/passwd file is vulnerable to security loopholes this is what makes Linux systems possible targets of unauthorized access attempts. The way of avoiding this risk is that modern Linux system now utilizes /etc/shadow files in storing passwords of the user in a significantly secure manner.

Encrypted passwords are traditionally stored in /etc/shadow, while /etc/passwd typically stores user account information without passwords.

Authentication with /etc/passwd and /etc/shadow

Authentication violations in Linux systems can be prevented through the use of the /etc/shadow file, which reinforces access controls at the account level. This file serves as the authoritative source for secure passwords, storing their hashed values along with additional password-related elements.

In any cryptography system, the plain text is first converted (one-way function) to hashed data by means of the hash function. Stored as long strings which are passwords, this contains the hashing algorithm, the hashed password, and an optional salt used for throwing off the possibility of learning the hashed password.

Under the old way of Linux systems, passwords are written in a file called /etc/passwd, and it includes usernames and passwords. This Linux AS thus provides servants, which, as default, are a to-do list, buddies, contacts, and appointment tracking. It is belong to root account therefore changes to this file can be made only by root or users who are given sudo permissions and their content can be read by all the system users.

Within the /etc/passwd file is the representation of each password stored as an encrypted string. These keys undergo hashing using a hash function with no key feature embedded, making them impossible to decode. In this regard, on login, the system compares the content of the /etc/password file to encryption of password using a key or salt and password hashing.

If another user attempts to access the system when the capacity limit is reached, the system automatically denies access to additional users. Therefore, addressing the chronic security issue of password reuse and the increasing use of rainbow tables by malicious actors to crack password hashes is crucial. Users must stay informed about solutions to mitigate these risks and prevent potential security breaches.

The/etc/shadow file, which is an essential tool for authentication mechanism level accounts, influences stricter access controls at the file level. Herein the full actual set of passwords is safely kept in encrypted form with the provision of auxiliary password data like tips for complex and capitals passwords.

Hash functions make this possible using one-way hashing of the plain text passwords. The stored passwords are the character strings of lengthy problem, each of which address the mathematical algorithm, the mathematical solution of this password, and, optionally, salt, which in the addressing process introduces additional randomness.

/etc/shadow only the root user, who can be called either linux administrator or superuser account, own this and their group shadow has the permission to access it. On the contrary, /etc/passwd is a commonly acknowledged as a file that can be accessed by the whole world, which it used by various tools to verify the ownership, and authentication dating.

On the contrary, decrypting passwords since they are not stored in clear text calls for awareness of both the hash string and the hashing algorithm involved. A bad guy will consequently have to be doing brute-force attacks where he tries every combination one at a time shifting proportionally with each one, and as soon as a suitable hash value is obtained, it should match with that stored hashed in the database.

The need for a shadow password file

This is one of the most tedious and intricate methods that serve as a feature to stop illegal access, to a great extent undermining the capability of the old '/etc/passwd' file unauthorized deletions.

A secure mechanism to store password information is already present in the /etc/passwd file itself. The need for a shadow password file comes from the risk associated with storing passwords in this file. Although passwords in /etc/passwd get encrypted with a randomly generated key or encryption, this key can be stored beside the encoded password alongside the hash function along with a total of one or 4096-byte keys.

Nevertheless, /etc/passwd remains vulnerable to unauthorized changes despite its efforts to improve security. Most important rules are done via password hashing. But the /etc/passwd file, which is world-readable, becomes attractive for hackers. Even more, the (DES) algorithm used for encryption is a basic one that was put also in the past, pushing aside the main security issues.

If working with password-cracking tools, hackers are able to recognize DES password vulnerabilities, particularly when they are the result of poor or simple password usage. Using elements like dictionary attacks, they use a hard guessing strategy that covers all possible hash variants of equally common passwords, which are converted and have had 2,197 times.

When hackers perform attacks on systems that use weak passwords just like "1234567" or "password", they are able to log in within hours.

To all the lessen the risks, runmers can use the /etc/passwd-file and transfer their passwords to /etc/shadow infinite, which is only permitted to individuals that have access to the system root directory Traditional /etc/passwd file will be retained for it is the file with the lots of information of users such as username, user identifier, group identifier and absolute path to the user's home directory.

As a part of this discussion, the next point is the case of encrypted passwords along with additional details, including password validity dates, a minimum number of days between password changes, and the maximum validity period of the passwords, which are also stored in the shadow password file.

The root user and the processes, which are owned by this user, can access the shadow password file as well as from the private companies to the locations elsewhere. This stringent security protocol strengthens the firewalls against breaking into//tampering with //lookup I//IP address list of the user pointing at /etc/passwd.

Format of a shadow password file:

The Shadow Password file structure is one password line (per user account) per line, which is analogous to the user password file on /etc/passwd. Usually, the leading sentence concerns the founder's account, then followed by the operating system, regular users' accounts, and others.

Each line within the file encompasses nine fields separated by colons:

Username: This stands for the actual user account and the so-called name that the system identifies.
Encrypted password: This symbolizes the hashed password stored in the format $type$salt$hashed, with it resembling the lengths ranging from eight to twelve characters.
Last password change: Shows that it was the last time the password was changed - as of Jan. 1, 1970. The display of age and that date is a convenient way to identify the strength of a password.
Minimum password age: It represents the number of days needed to prevent unauthorized use of the account after the password was changed.
Maximum password age: States the number they were counted up to, days after which the user had to change their password.
Warning period: Specifies the login date of the password from when the user gets the reminder to change the password within days until expiration.
Inactivity period: Deduce the number of days which had expired after Jan. 1, 1970. Subtract this from the count where the user's account is inactive.
Expiration date: Indicates the day of expiry or closure of the account.
Unused: The area is labeled empty, while the doing so in the future is possible.

One should pay attention to the fact that changes in the shadow password file, such as manual editing, should be avoided.
Below is a detailed explanation of each field in the shadow password file format.

The format of the /etc/shadow file is structured with each line representing an individual user account and comprising nine fields separated by colons

Let's delve into each field of the /etc/shadow file in detail. These fields include:

Username
Encrypted password
Frequency of password change.
The minimum period during which the device will not require a password change.
Number of days after which password is not permitted updating.
More days are displayed to remind users their passwords are about to expire.
Days before password automatic expiration, the account will be deactivated.
Account expiration date
Reserved field

1. Username:

Such field represents the login field and the one that links the one /etc/shadow file and /etc/passwd file.
Other login information pertaining to the user is encoded and stored under the /etc/passwd field but not passwords.
When a new user account is created, they have their username information that are included simultaneously in both the /etc/passwd and /etc/shadow files.

2. Encrypted Password:

This store is password protected by the encoding in an encrypted form.
The hashing algorithm employed for password encryption in the /etc/shadow file is commonly SHA-512, although the specific algorithm may vary depending on system configurations and security policies.
SHA-512 hashes the password along with a randomly generated salt, a process akin to an ancient language technique, ensuring that even identical passwords result in unique encrypted hashes

3. Controlling Login:

Linux, the system, won't let you enter the blank password while you log in. In case there is any unauthorized user or service tries to log in without password authentication or having a empty password, then the system will deny access to that user. This field can be solely employed to represent the user login by a value which is not a password. The latter is an encrypted one. Such as, if this attribute contains a token such as a value of (!) the corresponding account will be explicitly locked and therefore the user or service will be unable to log into the resource or location.

And as the two lines of the code suggest their roles, (they is written as character ! and line *) depict an open password. However, there is a distinction between them: misunderstandings of global issues might lead to international frictions and possibly even war conflicts. As the precaution is frequent occurrence of the user account unlock, setting a password for this optional field through passwd command is possible.

Locked Services Accounts

Date of last password change

The information regarding the last password change for each user is stored in the /etc/shadow file, encrypted in the number of days that have elapsed since the user's password was updated on January 1, 1970. Changing the password to a user on 10th March 2022, the number of days recorded in the timestamp field would by 18979 (this is calculated from the subtraction of 10th March 22 from 1 January 70).

To change from a date to days or to walking backwards from days to date, the command you will use is OS-dependent.

This command washes away all arguments, completely delivers the date at present instantaneously.

To calculate the number of days from 1 January 1970 to the current date, you can use this command on Unix/Linux system

The following figure shows the above commands with output:

Minimum required days between password changes

The "Set Minimum Number of Required Days between Password Changes" field determines the minimum number of days a user's password cannot be altered. The login form app provides expiration term in case the users are not allowed to change passwords within the duration specified here. Thus, if the value is set to 0(zero), the user will be offered the opportunity to change their password immediately.

Maximum allowed days between password changes

The "Maximum allowed days between password changes" parameter sets the maximum duration acceptable between a password's modification. After the user makes a change of their password, he/she has to change it again before the period which is stipulated in the field allotted for this purpose expires. It literally means a limited duration which a password can grant access to a website/application. It will lead to no forced restriction for the user to retain a password for a certain predetermined amount.

Days before displaying password expiration message

This parameter functions as a cut-off marker by popping out the expiration message of a password a specific number of days in advance. When the days of changing a password equaled or are lower than the number of days specified in the current field, the user receives a popup window reminding him/her to change the password.

Days after password expiration an account can be disabled

The former one will conclude with the months a password is considered to be valid for the account to be disabled. The system does not allow user to use an old password after 7 days without changing, instead the old password is marked as expired password. Such user accounts with expired passwords shall be automatically disabled by the system after this time of inactivity has elapsed. This will help to prevent unauthorized access to data and apps.

Account expiration date

This variable is for the termination of account at the specified time. Date transferred, the user can no longer login starting from this field. The date is expressed as an absolute value from a base year which is 1 January 1970. The like, the date-setting to the account expiration of 28 June 2018 will be through the number 17710. If no expiration date is set the account will remain active.

Reserve field

The final field serves as a placeholder for potential future use. Although it currently remains empty, it is included in the file structure for accommodating any forthcoming data or features. Typically left blank during file formatting, this field maintains flexibility for system enhancements or updates in the future.

Typically used commands within shadow password files include-

The contact of support group and Psychiatrist will be established to ensure a sustainable recovery.

To build a password expiration, the "root" user utilizes the command "chage."

We use the pwck utility to check for the authenticity of the password files of our users. This command performs the following tasks:

Assures that the data is generated from authorized users and authenticated human beings.
Makes sure that those entries in /etc/passwd and /etc/shadow keeping the normal format and may contain the right information.
Calls for removal of log entries that are in the incorrect format or contain factual mistakes from which there is no cure.

/etc/shadow file in Linux Explained with Examples

This document covers a general outline explanation of /etc/shadow file in Linux, with examples given. It explains the concepts of /etc/shadow file and what does it exactly store. Getting in tune with the /etc/shadow file is an essential building block to perform the account management in Linux efficiently.

In the past, the '/etc/passwd' file was a place where all login information was kept on Linux systems which worked by themself. However, due to several reasons, this practice was superseded by the adoption of the /etc/shadow file.

Limitations of /etc/passwd

However, the /etc/passwd file merely conducts one field for password data; thereby, more space for accommodation of other password-related information is hindered.
As a matter of fact, the scratching out of basic encryption techniques like DES is available, which can be despoiled by the password, gaining from hackers.
The sensitive information of users is exposed as the /etc/passwd file is open for viewing by any local user, which in essence means that all these users could peek into encrypted passwords.

Advantages of /etc/shadow

The /etc/shadow file is more robust than the two-field /etc/passwd structure because it is able to store nine fields worth of encrypted passwords and another password information instead.
Through the its implementation of advanced cryptography algorithms and feature of updatable feature it ensures safe and secure transactions and services.
One of the most essential parts is that the /etc/shadow file is readable only by the root user, so that password data are protected and cannot be accessed by unauthorized users.

The /etc/shadow file permission

A distinction lies in the set of permissions for the /etc/shadow file compared to the /etc/passwd file. Users can edit information in /etc/passwd, but the /etc/shadow file is not even accessible to all users. It is restricted to the root user or superuser only. Among these restrictions, an individual enjoys the right of the root shell and executes the following commands.

In Ubuntu Linux, the permanent lock for a root account is enabled by default. Therefore, in the case of a basic command, access to a superuser hull by executing the commands below is required, provided that if you are following a script on Ubuntu Linux.

Part of the attack, the malicious script trying to access the/etc/shadow file, which is the file where the passwords are encrypted, fails the shell. Furthermore, this step even serves as a remarkable security feature, that makes sure, that intruders and software password breakers can't access sensitive digital information, e.g. the passwords. But granting an analogous title is allowed when done from a root user or a superuser, the accounts with extended powers. The system architecture is advantageous over unprivileged users since it offers limited access to the /etc/shadow file. hence, the risk of unauthorized access is more malicious and overall security posture can be strengthened.

How do I change my account password?

Use the below syntax to change your own password:

First, you need to provide the old password. Then, you can enter a new password twice, as shown in the figure below:

The passwd command shows the SUID setting (safe user id). This causes the event that when the execution of the passwd command is done, the active EUID at that moment is copied to the saved user ID that usually belongs to the root. Therefore this ability increases the chances of a regular user attempting to their password update via this technique. There are tutors available which would further guide you on usage of command.

Conclusion

To sum up, the /etc/shadow file can be regarded as the foundation one in Linux which is used during user authentication and password security. It solves the dilemmas of a /etc/passwd file's classical characteristics by utilizing encryption techniques of a greater capacity and also providing access restrictions. Basing on hash algorithms and specifying permission settings systemically, the etc/shadow file guarantees information about sensitive password stays undecrypted and out of the reach of unprivileged users.

Through illustrating the structure as well as the objectives which each of the fields within the /etc/shadow file has, the user clearly comes to know how the password handling is carried out in the case of the linux operating systems. Alongside the last password change date through to account expiration date, every parameter contributes a small part of the mechanisms that ensures the system security through implementing password policies.

Moreover, the process of password storage in /etc/shadow file among other security benefits enables in protecting against unauthorized access to the data and password related weaknesses. Acting in a way that is much pro-active, its usage reflects the development of tools that protect sensitive information and prevent wrongful entries.

By and large, it is the /etc/shadow file that shows the way in the realm of user authentication in Linux as it brings in to light strong encryption techniques and the necessary controls to preserve user passwords confidentiality and indivisibility.

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