Any value in salting an already “strong” password?

Question

Is there any benefit in salting passwords for a strong, unique (not used for other applications by the user) password?

Salting (as I am aware) protects against rainbow tables generated with a dictionary or common passwords. It also protects against an attacker noticing a user with the same hash in another application.

Seeing as a strong password will (likely) not appear on a generated rainbow table, and a smart user will use unique passwords for each application he wants to protect, does salting protect an already "smart" user?

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this is theoretical. i have no inclination to stop salting.

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in essence, doesn't the salt just become part of the password? it just happens to be supplied by the gatekeeper rather than the user.

Answer 1

If you can guarantee that all users will never reuse passwords, and that none of their passwords will ever be of a form that it is computationally feasible to precalculate colliding hashes for, then indeed the salt is little additional benefit.

However, the salt is also of little additional cost; while these premises are very hard indeed to guarantee, and the cost of being wrong about them is high. Keep the salt.

Answer 2

Apart from rainbow tables there are also bruteforce tools to resolve a hash. This doesn't prevent unsalted hashes from being resolved. It only takes a longer as stronger the password is. Salting would certainly still make sense.

Answer 3

This feels like you want to make an assumption, then base your security on that assumption. When you assumption becomes bad, for whatever reason, then your security becomes bad.

So how might your assumption (that strong passwords don't need salting) become invalid?

1) Over time, larger, more comprehensive rainbow tables are generated. This is something I would worry about if it is up to your user to choose a strong password. They might think they have done a good job, and you and your safety checking might think they have done a good job too, but later it turns out their thought process creating the password was easily duplicated by stringing a few words and numbers together.

2) If users cannot choose their password, your strong password generation process might, due to bug or whatever, turn out to be not as strong as you want.

3) Your user might be too lazy to come up with a site-unique/strong password! This is surely the most important problem. Do you really want to generate a system which is usable only by cryptographic experts? :)

Answer 4

Rainbow tables are most definitely not restricted to dictionary passwords or the like. Most tend to include every character combination up to some max length - after all, it's a one time cost for generation. Do your users all use 12+ character passwords? Unlikely.