Semi-order preserving encryption

To study the relationship among precision, security and ciphertext expansion, we introduce semi-order preserving degree d, which measures the difference between SOPE and OPE. The theoretical derivation shows that security will increase with d, while precision and ciphertext expansion will decrease with d. Thus SOPE can balance precision, security and ciphertext expansion by adjusting semi-order preserving degree d according to a concrete condition. Finally, we present an implementation of SOPE.