The certificates shall be authorized by resolutions of the board, and shall bear such dates, mature at such time or times not exceeding 25 years from their respective dates, bear interest at such rate or rates agreed upon between the board and the investing agency, not exceeding 6 percent per year, payable semiannually, be in such denominations and in such form, be payable in such medium of payment and at such place or places, and subject to such terms of redemption at such prices not exceeding 106 percent of the principal amount as the resolutions provide.