An efficient search algorithm for large encrypted data by homomorphic encryption

The purpose of this study is to provide an efficient search function over a large amount of encrypted data, where the bit length of each item is several tens of bits. For this purpose, we have improved the existing hybrid homomorphic encryption by enabling the longer data items to be stored while using multiple encrypted databases and by suggesting an improved search method working on top of the multiple instances of the database. Further, we found the optimal number of databases to be needed when 40‐bit information, such as social security number, is stored after encryption. Through experiments, we were able to check the existence of a given (Korean) social security number of 13 decimal digits in approximately 12 s from a database that has 10 million encrypted social security numbers over a typical personal computer environment. The outcome of this research can be used to build a large‐scale, practical encrypted database in order to support the search operation. In addition, it is expected to be used as a method for providing both security and practicality to the industry dealing with credit information evaluation and personal data requiring privacy.