In this paper, we propose a secure protocol that allows processing encrypted data emitted by a medical IOT device. Its originality stands on a new fast algorithm which makes possible the conversion of Combined Linear Congruential Generator (CLCG) encrypted data into data homomorphically encrypted with the Damgard-Jurik (D-J) cryptosystem. By doing so, an honest-but-curious third party, like a smartphone, can process data issued from the IOT devices (e.g. raising a health alert) without endangering data privacy while CLCG can be integrated in an IOT of low computation capabilities. Moreover, in order to reduce communication and computation complexities compared to existing solutions and to achieve a real time solution, we further propose a secure packed version of CLCG in the D-J domain. With it a medical IOT can encrypt several pieces of data at once while allowing a third party to independently convert and process them in their D-J homomorphic encrypted form. We theoretically and experimentally demonstrate the performance of our solution in the case of a connected knee prosthesis, the data of which are processed for patient monitoring.

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In this paper, we propose a secure protocol that allows processing encrypted data emitted by an IOT device with low computational capabilities. Its originality is threefold. It first relies on a new fast algorithm which makes possible the conversion of Combined Linear Congruential Generator (CLCG) encrypted IOT data into data homomorphically encrypted with the Damgard-Jurik (D-J) cryptosystem. In second, an original data packing strategy is given so as to reduce communication and computation complexity as well as process several D-J encrypted data at once by means of matrix operations. In third, we introduce a crypto-watermarking based integrity control mechanism. This one combines the lightweight hash function Quark with LSB substitution so as to offer the capability to check the integrity of CLCG encrypted data. We illustrate the deployment of our protocol, in the case an honest-but-curious or malicious third party wants to process encrypted data issued from a real connected knee prosthesis. We theoretically and experimentally demonstrate the performance of our solution. This one can nearly process 500 samples every second. Beyond, our proposal is suited to the general case of IOT.