(a) The county election board shall deliver the keys, which unlock the operating mechanism and the registering counters or counter compartment of the voting machine, to the judge of election, not earlier than the Saturday preceding an election, nor later than three-quarters of an hour before the time set for the opening of the polls, and shall take his receipt therefor. The keys shall be enclosed in a sealed envelope, on which shall be written or printed: (1) the number of the voting machine; (2) the name or designation of the election district; (3) the number of the seal; (4) the number registered on the protective counter or device as reported by the custodian: Provided, however, That if the type of voting machine used requires the simultaneous use of three keys to unlock the registering counters or counter compartment, only two of said keys shall be enclosed in said sealed envelope, the third key being retained by the custodian, the county election board, or such other person as they shall have authorized.

(b) No election officer shall open an envelope so delivered, until the minority inspector shall be present in the polling place, and shall have examined the envelope to see that it has not been opened.