John the Ripper
John the Ripper is an excellent password cracker available at http://www.openwall.com/john/
This program will help system and network administrators identify users with weak passwords, and illustrate the need for secure password practices (e.g. MD5 passwords, shadow passwords, and NIS passwd maps that do not contain the password hash).
Installing on Linux:
1. wget http://openwall.com/john/john-1.6.tar.gz
2. tar zxvf john-1.6.tar.gz
3. cd john-1.6/src
4. make linux-x86-any-elf
5. cd ../run (change to directory containing john executable)
Note: if you are using shadow passwords (very
likely on any modern UNIX system), you will need access to the /etc/shadow
file on the target system. /etc/shadow contains the password hash
needed to crack the password and is by default only readable and writable
by the root user.
To crack a UNIX shadow file named shadow using John's default order of cracking modes:
or run John in the background with a very low priority:
nice -n 20 ./john shadow &
Cracked passwords will be displayed on STDOUT (if running interactively) as well as stored in a file named john.pot. To display passwords already cracked by John, use the following command (assuming a password file named shadow):
./john -show shadow
Please employ the secure password practices listed above, and educate users on choosing strong passwords.
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Last modified: 01/02/2003