ok, but if we knows, that there is a way to crack the shadow file, why don't we use a secure algorithm ? (triple DES or AES) Are there no implementation for this algorithms ? (a DES cracker-maschine costs about 100.000 $)
Wait! and read aloud after me: "The password is *not* encrypted." Take a deep breath. Now repeat it, please. The password is in fact hashed. The resulting hash is stored in /etc/shadow. The password is gone after that, there's no trace of it left. What then happens, when you login, is that the password you supply to the system is hashed and the hash is compared to the one stored in /etc/shadow. If they match, you're in, if they don't, you're not. As Olaf has repeatedly said, in the case where DES is used, the salt is encrypted using the password as a key to get the 'hash'. However, if you're using 'MD5 passwords' (which is something of a misnomer, of course), DES isn't involved. Someone correct me if I'm wrong. Cheers Tobias