A Fast and Secure Approach for the Transmission of Monitoring Data over MultiRATs
Authors: Yaacoub Elias , Diba Rida , Noura Hassan 
Published: June 2019

In an mHealth remote patient monitoring scenario, usually control units/data aggregators receive data from the body area network (BAN) sensors then send it to the network or “cloud”. The control unit would have to transmit the measurement data to the home access point (AP) using WiFi for example, or directly to a cellular base station (BS), e.g. using the long-term evolution (LTE) technology, or both (e.g. using multi-homing to transmit over multiple radio access technologies (Multi-RATs). Fast encryption or physical layer security techniques are needed to secure the data. In fact, during normal conditions, monitoring data can be transmitted using best effort transmission. However, when real-time processing detects an emergency situation, the current monitoring data should be transmitted real-time to the appropriate medical personnel in emergency response teams. The proposed approach consists of benefiting of the presence of multi-RATs in order to exchange the secrecy information more efficiently while optimizing the transmission time. It can be summarized as follows (assuming there are two RATs):1) The first step is to determine the proportion of data bits to be transmitted over each RAT in order to minimize the transmission time, given the data rates achievable on each RAT. Denoting the data rates by R1, and R2, and the total number of bits to be transmitted by D =  SUM(D1,D2), where D1 and D2 are the number of bits to be transmitted over RAT1 and RAT2 respectively, then they should be selected such that D1/R1 = D2/R22) Then, the exchange of the secrecy parameters between sender and receiver is done over the two RATs in order to maintain the security of the transmission. To avoid the complexity of public key cryptography, a three way handshake can be used: 2-1) The sender decides to divide the data into n parts, with a fraction n1 sent on RAT1 and a fraction n2 sent on RAT2, according to the ratios determined in 1) above (i.e. the sum of the bits in the n1 parts should be close to D1 bits, and the sum of the n2 parts should be close to D2 bits) 2-2) The sender generates a scrambling vector P(D,n) to scramble the n data parts and transmit them out of order. 2-3) The sender groups the secret information consisting of S =  {n, n1, n2, P(D,n)}, and could add additional information to protect against replay attacks, e.g. timestamp, nonce, etc., and sends this information on the two RATs, encrypted by a different key: K11 on RAT1 and K12 on RAT2. Thus, {S}_K11 is sent on RAT1 and {S}_K12 is sent on RAT2. 2-4) The receiver does not know K11 and K12. Thus, it encrypts the received information with two other keys K21 (over RAT1) and K22 (over RAT2) and sends them back: {{S}_K11,K21} is sent on RAT1 and {{S}_K12,K22} is sent on RAT2. 2-5) The sender decodes the received encrypted vectors using his keys and sends back {S}_K21 on RAT1 and {S}_K22 on RAT2. The secret information is still securely encoded by the receiver's secret keys K21 and K22. 2-6) The receiver can now decrypt the information and obtain S. 3. The two parties can now communicate using the secret scrambling approach provided by S. This information can be changed periodically as needed. For example, if the data is subdivided over 10 parts, with 40% to be sent over LTE and 60% to be sent over WiFi, according to the scrambling vector P(D,n) = {4,1,10,7,3,9,5,2,6}, then parts {4,1,10,7} are sent over LTE and parts {7,3,9,5,2,6} are sent over WiFi. The receiver will sort them out in the correct order.