UNIX for Dummies Questions & Answers

Can i get back the clear text password by copy the encrypted value from /etc/passwd and put this value in the function 'decrypt()'......is that possible ???

No. crypt() is actually a bad name, since it doesn't do any encryption, but only runs your password through a hashing function (MD5/Blowfish/...).

Is there any way to get back clear text password from /etc/shadow encrypted data ??

Yeah, there are several programs that do this. The best available is called "john the ripper", JtR for short. It works by trying all possible passwords until it hits a match. Last November I started JtR running to try and crack a list of 168 passwords. (This is a security test and its part of my job. My manager knows I am doing this.) So far it has broken 9 passwords. It is slowing down. It breaks the easy passwords first. It's been over a month since password 9 was broken. My guess it that it will take several decades to break all 168. I'm using a somewhat souped up sunblade-1000. With a top of the line overclocked quad extreme rig, it could probably crack them all in under a decade.