Numerical SQL Value Expressions Over Encrypted Cloud Databases

Cloud databases often need client-side encryption. Encryption however impairs queries, especially with numerical SQL value expressions. Fully homomorphic encryption scheme could suffice, but known schemes remain impractical. Partially homomorphic encryption suffices for specific expressions only. The additively homomorphic Paillier scheme appears the most practical. We propose the homomorphic encryption for standard SQL expressions over a practical domain of positive values. The scheme uses a version of Paillier’s formulae and auxiliary tables at the cloud that are conceptually the traditional mathematical tables. They tabulate encrypted log and antilog functions and some others over the domain. The choice of functions is extensible. We rewrite the expressions with any number of SQL operators ‘*’, ‘/’ ‘^’ and of standard aggregate functions so they compute over encrypted data using the tables and Paillier’s formulae only. All calculations occur at the cloud. We present our scheme, show its security, variants and practicality.

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