Re: Why the index is not used ?

Additionally it is not clear why you want to search in table on encrypted
data. Usually you match user with it's unpersonalized data (such as login,
user ID) and then decrypt personalized data. If you need to store user
identifying data encrypted as well (e.g. bank account number) you can use a
deterministic algorithm for it (without salt) because it is guaranteed to
be unique and you don't need to have different encrypted data for two same
input strings.

Vlad