Homomorphic encryption is a type of cryptography that allows computations to be performed on encrypted data. For instance, such a scheme can be used in a cloud environment to query encrypted data without decrypting that data, avoiding privacy issues that plague online setting.
A fully homomorphic encryption (FHE) supports arbitrary computation on encrypted data. This offers a very powerful capability, however at present, it is computationally too intense for practical use. Partially homomorphic encryption only allows some operations to be preserved in ciphertexts, such as additions, multiplications, or quadratic functions. These schemes are becoming practical with today’s computing resources.
Homomorphic encryption is powerful tool that can be leveraged in many application. One such application is Private Information Retrieval (PIR). Private Information retrieval is a protocol whereby a user can retrieve an item from a database without revealing which item is retrieved. Under the guise of homomorphic encryption, one can search encrypted data without ever decrypting. PIR has been in the making for many years and now it is on the horizon of practicality!