We have ideas how to make relational databases secure while running everything server-side, thanks to recent research publications [notably CipherBase from Microsoft Research http://www.cidrdb.org/cidr2013/Papers/CIDR13_Paper33.pdf] and advances in CPU hardware. Early days, but we'll probably test it first in the open source ZeroDB database [https://opensource.zerodb.com] and then apply the same method to existing relational databases.

I think, you may have the application with a different cloud provider or even in a different geographic location, so that you can keep keys away from the data. In this case you sort of distribute trust.