United States within one year after the date of issue of the obligation. (4) Interest rate Any obligation issued under paragraph (1) shall bear interest at a rate determined by the Secretary, taking into consideration the current average market yield on outstanding marketable obligations of the United States of comparable maturities during the month preceding the issuance of any obligation authorized by this subsection. (5) Purchase The Secretary shall purchase any obligation of the Corporation issued under paragraph (1), and for such purchase the Secretary may use as a public debt transaction the proceeds of the sale of any securities issued under chapter 31 of title 31, United States Code. The purpose for which securities may be issued under such chapter shall include any such purchase. (6) Funding There are hereby authorized to be appropriated to the Secretary for fiscal year 2018 and each fiscal year thereafter such sums as may be necessary to carry out this subsection. (f) Fees (1) In general Fees may be charged for providing services and for transaction costs incurred by the Corporation in amounts to be determined by the Corporation. (2) Use of fees All fees under paragraph (1) paid for transaction costs and other costs associated with services provided shall be available for obligation for the purposes for which such fees were collected. (g) Income and revenue in general In order to carry out the purposes of the Corporation, all funds, fees, revenues, and income transferred to or earned by the Corporation, from whatever source derived, shall be held by the Corporation and shall be available to carry out the purposes of the Corporation, including— (1) payment of all expenses of the Corporation