计算机代写 FIT2093 Week 9 Lab – cscodehelp代写
Monash University – FIT2093 Week 9 Lab
Access Control and Password Management
IMPORTANT NOTES: Study lecture materials at least 1 hour and attempt task 3 (Users and Access Con- trol) prior to the lab session. Prepared questions will be discussed in the lab session.
1 Overview
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The objective of this lab is to understand the access control and password management in UNIX. Optional worksheet will further explore the techniques that an attackers can use to crack the password in UNIX. In this lab, students are required to create users and groups in UNIX. Unix stores hashes of all its accounts’ passwords in a single file i.e. /etc/passwd on old systems and /etc/shadow on new ones. In the optional worksheet, students can further explore set-UID and crack the passwords by a tool called ”John the Ripper” to crack the passwords stored in a file. Students will recover passwords using different techniques.
2 Lab Environment
Virtual Machine. Cloud Ubuntu VM.
User Accounts Information. crack-these.txt is in the /srv/fit2093files/fit2093lab/ folder for the lab optional worksheet.
Lab Task: Users and Access Control
adduser addgroup usermod
su [username] passwd
add a user to the system
add a user group to the system modify a user account
change user ID or become superuser change user password
change file mode bits
Table 1: User manipulation and access control commands
1. Create a new user account for one of your group members and give it a default login password. Add the user to the sudo group. Create a new user group named fitstudents and add the user to the group. Use the terminal to login to the new user account. Change the password of the user.
In order to create a new user or change its password, we need to temporarily disable some – tication Modules (PAM) in the cloud VM. Run sudo pam-auth-update –force in a terminal and disable the following options:
• Pwquality password strength checking
• Kerberos authentication
• Support for authentication by external scripts
If the Kerberos password is required during any steps in this lab exercise, please re-run the above steps. 1
Monash University – FIT2093 Week 9 Lab
2. Avoid other users from listing or writing to the new user’s home directory by assigning proper permissions to the user’s home directory. However, anyone from the sudo group should be able to access the new user’s files if they know the file name and where it is located at. Add your authcate user to the sudo group. Logout and relogin to the cloud VM to make the change of authcate user’s group effective, and try this.
4 Understanding UNIX password handling
Files shadow and passwd contain user’s accounts information, shadow has more restrictive permissions than the passwd file. Run following commands and examine both files, note the permission restrictions and compare the contents of the files. Why do you think shadow file is more restricted than passwd?
Monash University – FIT2093
Week 9 Lab
% ls -l /etc/passwd
% ls -l /etc/shadow
% sudo cat /etc/passwd
% sudo cat /etc/shadow
In shadow file, find your user name and hashed password, an example is shown below ahsan:$6$ViV1fAdR$7J7WsQhS7DpqPqGQQtYqnoLsOm4J0Ixd0WLnU0EN5
jywHCsdhk2qAEgfWdUOso4Hy0VElMsZklDeZlGN3ZG.Q1:16579:0:99999:7:::
We are looking for hash of the password, which is second field.
$6$ViV1fAdR$7J7WsQhS7DpqPqGQQtYqnoLsOm4J0Ixd0WLnU0EN5jywHCsdhk2qAEg
fWdUOso4Hy0VElMsZklDeZlGN3ZG
1. The first field (numerical number) indicates the type of hashing algorithm used
$2 = Blowfish
$2a = eksblowfish $5 = SHA-256
$6 = SHA-512
2. The second field is the salt value
The salt is used to ensure that users with the same password will most likely not have the same hashed password, and it also strengthen the password.
3. The last field is the hash value of salt + user password
To complete this task: identify number of users in your system (you can add more users with adduser command), what hashing algorithms they are using and what are hashed salt and password values.
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