  In encrypted databases, sensitive data is protected from an untrusted server
by encrypting columns using partially homomorphic encryption schemes, and
storing encryption keys in a trusted client. However, encrypting columns and
protecting encryption keys does not ensure confidentiality - sensitive data can
leak during query processing due to information flows through the trusted
client. In this paper, we propose SecureSQL, an encrypted database that
partitions query processing between an untrusted server and a trusted client
while ensuring the absence of information flows. Our evaluation based on OLTP
benchmarks suggests that SecureSQL can protect against explicit flows with low
overheads (< 30%). However, protecting against implicit flows can be expensive
because it precludes the use of key databases optimizations and introduces
additional round trips between client and server.
