A Secure Recommendation System for Providing Context-Aware Physical Activity Classification for Users

Algorithm 1

Homomorphic user correlation operations.

	Input: , the set of HE user correlations between user k and other users , the set of data vectors of other users of application “i” at context “c,” secured by Enc(s1)
	Output: {M, N}: the data to calculate final recommendations
(1)	WhileDo
(2)	For Each activity “a” performed by “p” and “j,” Do
(3)	Measure M: the resultant value from the equations below steps (4) and (5)
(4)	Measure the value as
(5)	Measure N: the resultant value as
(6)	End For
(7)	End Do
(8)	Return (M, N)
(9)	End