The right of any person to any benefit under subchapter I shall not be transferable or assignable at law or in equity except to the United States, and none of the moneys paid or payable (except money paid hereunder as reimbursement for funeral expenses or as reimbursement with respect to payments of workmen's compensation or in the nature of workmen's compensation benefits), or rights existing under said subchapter, shall be subject to execution, levy, attachment, garnishment, or other legal process or to the operation of any bankruptcy or insolvency law.