[ILUG] password & shadow

[Colm MacCarthaigh]

On Fri, Nov 16, 2001 at 10:28:16PM -0800, saeed babadi nia wrote:
> 
>  Hi all
> 
>  I want to know how someone can find the password
>  with having password and shadow files ?

assuming you are reffering to /etc/passwd and /etc/shadow
and the system is configured (as is the default configuration)
to use /etc/shadow for authentication there are several methods.

/etc/shadow typically stores passwords as the result of  a one way hash
function , usually DES or MD5, it's pretty much impossible to take a hash 
and find out what the corresponding password is. You can however try a 
dictionary attack, whereby you hash the entire contents of a sophisticated
dictionary, reversing each word, replacing certain letters with numbers,
adding numbers, trying certain capitalisations .. etc. In in a large
shadow file it is common to get quiet a few weak passwords this way.
There are numerous utilites available to help with this task.

In a small shadow file, with sensible passphrase choices you havnt a 
hope.

-- 
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colmmacc at redbrick.dcu.ie