Is it safe to store usernames and passwords in the database?

The process for storing passwords with a basic measure of security is fairly simple:

• Hash the passwords with salt
• Use a different salt for each user/password
• Store the salt with the hashed password in the DB
• When they try to log in, run what the attempted PW thru the same method; compare the result.

If they entered the correct password, the hashed PWs will match. Hashing protects the users from attacks as well as the janitor walking by a screen with the members table on display.

Creating Salt and Hashing the PW

' salt size is 32 (0-31
Private Const SaltSize As Integer = 31
...

Dim dbPW As String = TextBox1.Text
Dim dbSalt = CreateNewSalt(SaltSize)
' eg: "dsEGWpJpwfAOvdRZyUo9rA=="

Dim SaltedPWHash As String = GetSaltedHash(dbPW, dbSalt)
' examples:
' using SHA256: bbKN8wYYgoZmNaG3IsQ2DPS2ZPIOnenl6i5NwUmrGmo=
' using SHA512: 
' 0vqZWBIbOlyzL25l9iWk51CxxJTiEM6QUZEH1ph+/aNp+lk4Yf8NYv8RLhYtbqCNpOqO3y8BmM+0YWtbAhE+RA=="

Store the PW hash and the salt as part of the user’s record. The salt is not secret, but change it when/if the user changes their password.

Comparing a Login attempt

' check if PW entered equals DB
Dim pwTry = TextBox2.Text
' hash the login attempt using the salt stored in the DB
Dim pwLogin = GetSaltedHash(pwTry, dbSalt)

' compare the hash of what they entered to whats in the DB:
If String.Compare(SaltedPWHash, pwLogin, False) = 0 Then
    ' okay!
    Console.Beep()
End If

If the user enters the same PW, it should result in the same hash, it is as simple as that. The hashing code is not all that complicated:

Hash Methods

Private Function GetSaltedHash(pw As String, salt As String) As String
    Dim tmp As String = pw & salt

    ' or SHA512Managed
    Using hash As HashAlgorithm = New SHA256Managed()
        ' convert pw+salt to bytes:
        Dim saltyPW = Encoding.UTF8.GetBytes(tmp)
        ' hash the pw+salt bytes:
        Dim hBytes = hash.ComputeHash(saltyPW)
        ' return a B64 string so it can be saved as text 
        Return Convert.ToBase64String(hBytes)
    End Using

End Function

Private Function CreateNewSalt(size As Integer) As String
    ' use the crypto random number generator to create
    ' a new random salt 
    Using rng As New RNGCryptoServiceProvider
        ' dont allow very small salt
        Dim data(If(size < 7, 7, size)) As Byte
        ' fill the array
        rng.GetBytes(data)
        ' convert to B64 for saving as text
        Return Convert.ToBase64String(data)
    End Using
End Function

• It is tempting to use something like a GUID (System.Guid.NewGuid.ToString) as the salt, but it just isn’t all that hard to use the cryptographic random number generator.
• As with the hashed password, the return string is longer due to the encoding.
• Create a new salt every time the user changes their password. Don’t use a global salt, it defeats the purpose.
• You can also hash the PW multiple times. Part of the key is to make it take a long time to try all various combinations if/when attacked.
• The functions are ideal candidates for Shared / static class members.

Note also, the article linked to by Kenneth is well worth reading.

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Note that the article mentions The salt should be stored in the user account table alongside the hash This doesn’t mean you must have a Salt column in the DB. You can see the following being done in the linked article:

Dim dbPW As String = TextBox1.Text
Dim dbSalt = CreateNewSalt(SaltSize)

' get the salted PW hash
Dim SaltedPWHash As String = GetSaltedHash(dbPW, dbSalt)
' store salt with the hash:
SaltedPWHash = String.Format("{0}:{1}", dbSalt, dbPW)
' salt + ":" + hashed PW now ready to store in the db

To split the salt from the hashed password:

Dim SaltAndPWHash = rdr.Item("PWHash").ToString()

Dim split = SaltAndPWHash.Split(":"c)    ' split on ":"
Dim Salt = split(0)                      ' element(0) == salt
Dim StoredPWHash = split(1)              ' element(1) == hashed PW

You need both parts: after you hash the attempted log in PW, compare it to split(1).