Using a random salt in password encryption?

Question

I've seen a few other threads about this topic, but I can't seem to find a few answers to some questions involving the use of a random salt in password encryption. To my understanding, the steps go something like this:

1. Generate a random salt for the user.
2. Append the salt to their password.
3. Use something like SHA-2 to hash the result.
4. Store both the salt and hashed password in the database.

How does this method work when retrieving the user's password and verifying log-in? One response says that the user's salt should be retrieved, appended to their inputted password, hashed, and then compared to the stored hash, but doesn't this raise some issues? Namely:

• How do you retrieve the salt without compromising that user? If someone wanted to brute-force a certain account's password, wouldn't they be able to retrieve the salt that was sent back from the server to hash the inputted password, thereby eliminating the security that having a salt adds?
• If we avoid the previous problem by doing the salt retrieval server-side, then won't we be sending the user's inputted password unencrypted at one point or another (so that it may later be appended to the retrieved salt)?

Answer 1

The salt should never be exposed outside of the service - your instinct is right that this would be exposing the salt and introducing risk.

Any communication between your client and server should occur over an SSL connection - or at least using some kind of encryption of the interaction.

Keep in mind the purpose of the salt: to make it harder for someone to precalculate hash codes and therefore be able to look up passwords in the case of the database being compromised. An 8 bit salt makes the hash space 256 times bigger, making precalculation that much harder. The salt isn't about securing communication - there are other solutions for that.

Answer 2

You have to use random salt because of goal of using it is protecting against some types of attacks such as dictionary attack, brute-force attack and rainbow attack. thus it's so important to generate random salt for each password and store hashed password and salt in user table or attached to user profile. When you want to validate user password it's enough to hash entered password with stored salt and compare with stored hash value. I don't believe @cherouvim advise because it seems he doesn't care about above attacks. For more information i suggest an amazing, simple and understandable article by Defuse Security

Good luck.