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Analyze the composition about the password under the Ubuntu and RHEL


Hello everyone, it’s time to post a rubbish. The topic of today is about analyzing the composition about the password under the Linux OS. We have known about the file of password that’s in the /etc/shadow, but how to produce these passwords after we created these accounts? John the ripper? Let’s keep reading:

1) Explanation about the file of /etc/shadow
#cat /etc/shadow
aychedee:$6$vb1tLY1qiY$M.1ZCqKtJBxBtZm1gRi8Bbkn39KU0YJW1cuMFzTRANcNKFKR4RmAQVk4rqQQCkaJT6wXqjUkFcA/qNxLyqW.U/:15405:0:99999:7:::
a.The local username.
b.The password hash, more on this later.
c.Number of days since the start of unix time (01/01/1970) that the password was last changed.
d.Minimum number of days before the password can be changed.
e.Maximum number of days before the password must be changed. 99999 means that the user will not be forced to change their password.
f.Number of days before forcing the password change that the user will be warned.
g.The number of days after expiration that the account will be disabled.
h.Days since the start of unix time that the account has been disabled.
i.Currently unused but reserved for future use.

2) Explanation about the hash of password
a.$1$ -> md5.
b.$2a$ -> Blowfish.
c.$2y$ -> Blowfish, with correct handling of 8 bit characters.
d.$5$ -> sha-256.
e.$6$ -> sha-512.

3) Produce the password w/ salt and sha-512 through mkpasswd under the Ubuntu
#mkpasswd -m sha-512
$6$$
#cat /etc/shadow
yozloy:$6$$:...

4) Produce the password w/ salt and sha-512 through grub-crypt or the script of python
#grub-crypt --sha-512
#echo 'import crypt,getpass; print crypt.crypt(getpass.getpass(), "$6$16_CHARACTER_SALT_HERE")' | python -
perl -e 'print crypt("password","\$6\$saltsalt\$") . "\n"'

◎、Above information is about analyzing the composition about the password under the Ubuntu and RHEL, and I have referred the article of aychedee, superuser and ThorneLabs, so you can google it for more detail information if you have more interesting. That’s all for today, see you next time!

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