No permission for doing any street work by private contract under and pursuant to the provisions of this Article shall become effective until the contractor covenanting to perform the same shall have executed to the City and County of San Francisco, and delivered to the Secretary of the Department of Public Works a bond in such amount as may have been fixed in the order of the said Director, granting such permission, with some surety company authorized to do business in the State of California as surety thereon, conditioned for the faithful performance of the contract, or shall have deposited with the said Secretary a certified check upon some solvent bank for the said amount as a guaranty for such performance. Before entering upon the performance of any work in this Article provided for, the contractor covenanting to do such work shall also file with the Director of Public Works a bond, with some surety company authorized to do business in the State of California, as surety thereon, to be satisfactory in all respects to said Director, in a sum not less than ½ of the total amount payable by the terms of the contract, conditioned for the payment of all materialmen and employees under the contract. In lieu of such bonds or certified check, any contractor may deliver to said Secretary a bond in the sum of $25,000, with some surety company authorized to do business in the State of California, as surety thereon, conditioned for faithful performance of any and all private contracts authorized to be performed by him in pursuance of the provisions of this Article, and for the payment of all materialmen and employees under such contracts. Such last-mentioned bond must be satisfactory in all respects to said Director and shall be renewed annually.