问题
I am debating using user-names as a means to salt passwords, instead of storing a random string along with the names. My justification is that the purpose of the salt is to prevent rainbow tables, so what makes this realistically less secure than another set of data in there?
For example,
hash( md5(johnny_381@example.com), p4ss\/\/0rD)
vs
hash( md5(some_UUID_value), p4ss\/\/0rD)
Is there a real reason I couldn't just stick with the user name and simplify things? The only thing my web searching resulted was debates as to how a salt should be like a password, but ended without any reasoning behind it, where I'm under the impression this is just to prevent something like a cain-and-able cracker to run against it without being in the range of a million years. Thinking about processing limitations of reality, I don't believe this is a big deal if people know the hash, they still don't know the password, and they've moved into the super-computer range to brute force each individual hash.
Could someone please enlighten me here?
回答1:
You'll run into problems, when the username changes (if it can be changed). There's no way you can update the hashed password, because you don't store the unsalted, unhashed password.
回答2:
I don't see a problem with utilizing the username as the salt value.
A more secure way of storing passwords involves using a different salt value for each record anyway.
If you look at the aspnet_Membership table of the asp.net membership provider you'll see that they have stored the password, passwordsalt, and username fields in pretty much the same record. So, from that perspective, there's no security difference in just using the username for the salt value.
Note that some systems use a single salt value for all of the passwords, and store that in a config file. The only difference in security here is that if they gained access to a single salt value, then they can more easily build a rainbow table to crack all of the passwords at once...
But then again, if they have access to the encrypted form of the passwords, then they probably would have access to the salt value stored in the user table right along with it... Which might mean that they would have a slightly harder time of figuring out the password values.
However, at the end of the day I believe nearly all applications fail on the encryption front because they only encrypt what is ostensibly one of the least important pieces of data: the password. What should really be encrypted is nearly everything else.
After all, if I have access to your database, why would I care if the password is encrypted? I already have access to the important things...
There are obviously other considerations at play, but at the end of the day I wouldn't sweat this one too much as it's a minor issue compared others.
回答3:
If you use the username as password and there are many instances of your application, people may create rainbow tables for specific users like "admin" or "system" like it is the case with Oracle databases or with a whole list of common names like they did for WPA (CowPatty)
You better take a really random salt, it is not that difficult and it will not come back haunting you.
回答4:
This method was deemed secure enough for the working group that created HTTP digest authentication which operates with a hash of the string "username:realm:password".
I think you would be fine seeing as this decision is secret. If someone steals your database and source code to see how you actually implemented your hashing, well what are they logging in to access at that point? The website that displays the data in the database that they've already stolen?
In this case a salt buys your user a couple of security benefits. First, if the thief has precomputed values (rainbow tables) they would have to recompute them for every single user in order to do their attack; if the thief is after a single user's password this isn't a big win.
Second, the hashes for all users will always be different even if they share the same password, so the thief wouldn't get any hash collisions for free (crack one user get 300 passwords).
These two benefits help protect your users that may use the same password at multiple sites even if the thief happens to acquire the databases of other sites.
So while a salt for password hashing is best kept secret (which in your case the exact data used for the salt would be) it does still provide benefits even if it is compromised.
回答5:
Random salting prevents comparison of two independently-computed password hashes for the same username. Without it, it would be possible to test whether a person's password on one machine matched the one on another, or whether a password matched one that was used in the past, etc., without having to have the actual password. It would also greatly facilitate searching for criteria like the above even when the password is available (since one could search for the computed hash, rather than computing the hash separately for each old password hash value).
As to whether such prevention is a good thing or a bad thing, who knows.
回答6:
I know this is an old question but for anyone searching for a solution based on this question.
If you use a derived salt (as opposed to random salt), the salt source should be strengthened by using a key derivation function like PBKDF2.
Thus if your username is "theunhandledexception" pass that through PBKDF2 for x iterations to generate a 32 bit (or whatever length salt you need) value.
Make x pseudo random (as opposed to even numbers like 1,000) and pass in a static site specific salt to the PBKDF2 and you make it highly improbable that your username salt will match any other site's username salt.
来源：https://stackoverflow.com/questions/3347035/salting-is-it-reasonable-to-use-the-user-name