UNIX for Dummies Questions & Answers

Hi, lads. Good day.

I have one question to ask.

I read on the Internet, for the SUSE system, the password is encrypted into 13 characters, and the first 2 characters are called salt characters? Is there any special meaning for salt? Why we need these salt characters?

And, I have a look at the shadow file in the system, I found there is no rules on the salt character at all. And I also found the encrypted password for the root is much longer than the other users (about 50 characters). Why is it so long? Just to make the system safer? However, if the hacker can decode a 13 characters password, 50 characters password is only a matter of time to be decoded, isn't?

Thanks in advance

In general, salt is random data used in encryption. In the case of the traditional unix scheme the salt is 2 characters selected from the set: "./0-9a-zA-Z" In this case, the salt means that each password has 4096 different representations. This makes it harder to build a list of all possible encrypted passwords. It also means that you can't as easily tell if two accounts have the same password.

No one has ever found a way to to decode the encrypted password when the standard unix algorithm is used. And some very smart people have been trying for decades. The only way is to try all possible passwords until you find one that encrypts to same value in the encrypted field. The weakness of the standard scheme is that it is limited to passwords of 8 characters or less. That's not enough, we need longer passwords. So new scheme are being used that provide long passwords. That's what you must see in your root account.

It is not strictly correct to call the passwords "encrypted" since no decryption algorithm exists. But people commonly do anyway.