is_unique for encrypted data

Hi to all...
I decide to encrypt user's sensitive data (tel, address,...) using CI encryption library. In form validation rules, for some fields like mobile number, I used is_unique[table.field]. But for encrypted data, it is useless!
Is there anyway to solve this or I must write a callback function in form validation rules (a function that get a field, encrypted it and then compare it to all records)?
I want to know also your opinion for encrypting these data.

thanks.