Atomic upload: User Ui first encrypts and then uploads its sensor data to S as the transaction ti ::=
{update(s j,Ui, cj)| j = 1 · · · n} where cj = ENC(Uipb , vj).
(The actual process of recording sensor data is described later in Section 5.1). On receiving the
transaction ti, S performs conflict detection (the conflict detection logic is given later in Step 4).
For now, we assume that the conflict detection was successful, leading to update of the Ui rows in
si, · · · , sn tables and commit of ti.