Question

I’m having a dilemma. I have a field hashedX that is a hashed/salted value and the salt is saved in the same row in the mysql database as is common practice.

hashedX      saltX
------       ------
hashed1      ssai3
hashed2      woddp
hashed3      92ofu

When I receive inputX, I need to know if it matches any of the values in hashedX such as hashed1 hashed2 or hashed3. So typically I would take my input, hash/salt it, and compare it to the values of hashedX. Pseudo code:

$hashed_input = hash ($input with $salt );
select * from tablename where $hashed_input is hashedX

The problem is I don’t know which saltX I need to even get to the $hashed_input before I can do any select.

I could go through the database rows, one by one, try that salt on my input, then check if the input as hashed/salted with this salt matches hashedX of that same row. If I have a 100,000 records, my guess is that this would be painfully slow. I have no idea how slow since I’m not that great at databases.

• Is there a better way to do this, than selecting all rows, looping through them, using that row’s salt to hash input, then comparing again to the hashed value in the db?

Answer 1

If it is possible (depends on your hash formula) define a MySQL User Defined Function database side for the hash formula (see CREATE FUNCTION). This way you will be able to get your results in one simple request:

SELECT hashedX, saltX FROM tablename WHERE UDFhash(input, saltX) = hashedX ;