“…If S satisfies (A, ρ), U utilizes his secret key SK U and LSSS scheme to decrypt Υ and recover M .Otherwise, the algorithm outputs ⊥.Algorithm 11: EHR Decryption AlgorithmInput: P KP A, SKU with attribute set S, CT with access policy (A, ρ).Output: M/⊥. 1 if S satisfies (A, ρ) then 2Data user utilizes the LSSS scheme to find {λi ∈ Zp} i∈[n 1 ] such that i∈[n 1 ] λiAi = (1, 0, · · · , 0);3 Calculate Υ = C0/[e(C1, dU,4) · e(wP A,3, i∈[n 1 ] (dU,5,i) C 2,i ·λ i )]; M = SDec(CM , H0(Υ)); Return M/⊥.4.12. Keyword Match based Policy Update QueryIf the patient P A wants to update the access policy of the EHR ciphertext that are stored in the e-health big data system, he runs the keyword match based policy update query algorithm (shown in Algorithm 12) to generate a policy update query P U Q, which is submitted to the cloud platform.Suppose that the original access policy is (A, ρ) with A ∈ Z n1×n2 p and the update access policy is (A , ρ ) with A ∈ Z n 1 ×n 2 p…”