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Chapter 7: Passwords
Cracking UNIX/Linux passwords with John the Ripper
John the Ripper can also crack UNIX/Linux passwords. You need root access
to your system and to the password (/etc/passwd) and shadow password
(/etc/shadow) files. Perform the following steps for cracking UNIX/Linux
passwords:
1. Download the UNIX source files from www.openwall.com/john.
2. Extract the program by entering the following command:
[root@localhost kbeaver]#tar -zxf john-1.7.9.tar.gz
or whatever the current filename is.
You can also crack UNIX or Linux passwords on a Windows system by
using the Windows/DOS version of John the Ripper.
3. Change to the /src directory that was created when you extracted the
program and enter the following command:
make generic
4. Change to the /run directory and enter the following command to use
the unshadow program to combine the passwd and shadow files and
copy them to the file cracked.txt:
./unshadow /etc/passwd /etc/shadow > cracked.txt
The unshadow process won’t work with all UNIX variants.
5. Enter the following command to start the cracking process:
./john cracked.txt
When John the Ripper is complete (and this could take some time), the
output is similar to the results of the preceding Windows process. (Refer
to Figure 7-3.)
After completing the preceding Windows or UNIX steps, you can either force
users to change passwords that don’t meet specific password policy requirements,
you can create a new password policy, or you can use the information
to update your security awareness program. Just do something.
Be careful handling the results of your password cracking. You create an
accountability issue because more than one person now knows the passwords.
Always treat the password information of others as strictly confidential.
If you end up storing them on your test system, make sure it’s extra
secure. If it’s a laptop, encrypting the hard drive is the best defense.
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