Question

I have a table called,tblClient with an encrypted column called SSN.

Due to company policy, we encrypted SSN using a symmetric key (chosen over asymmetric key due to performance reasons) using a password.

Here is a partial LIKE search on SSN
declare @SSN varchar(11)
set @SSN = ‘111-22-%’

open symmetric key SSN_KEY decrypt by password = 'secret'

    select  Client_ID
    from    tblClient (nolock)
    where   convert(nvarchar(11), DECRYPTBYKEY(SSN)) like @SSN

close symmetric key SSN_KEY

Before encryption, searching thru 150,000 records took less than 1 second.
but with the mix of decryption, the same search takes around 5 seconds.

What strategy can I apply to try to optimize searching thru encrypted column?

Answer 1

The simple solution is to add an unencrypted column for first characters of SSN. And this is the hard one.