Schemes of homomorphic re-encryption

Method and apparatus are disclosed for homomorphic re-encryption schemes in a system comprising a cloud service provider (CSP), a third authorized party (TAP), a data requestor (DR) and a plurality of data providers (DPs). According to an embodiment, a method implemented at a CSP comprises: in response to a request from a TAP, obtaining from a plurality of DPs cipher texts of their respective data, based on the request, wherein each DP is able to homomorphically encrypt its data; analyzing the cipher texts; and sending the analyzing result to the TAP, wherein the TAP is able to re-encrypt the analyzing result, such that a DR can decrypt the re-encrypted analyzing result with the DR's secret key. According to another embodiment, a method implemented at a CSP comprises: collecting from a plurality of DPs cipher texts of their respective data, wherein each DP is able to homomorphically encrypt its data; analyzing the cipher texts; in response to a request from a TAP, encrypting the analyzing result; and sending the encrypted analyzing result to the TAP, wherein the TAP is able to re-encrypt the encrypted analyzing result, such that a DR can decrypt the re-encrypted analyzing result with the DR's secret key.