25 U.S.C. § 1951
Any State court entering a final decree or order in any Indian child adoptive placement after November 8, 1978, shall provide the Secretary with a copy of such decree or order together with such other information as may be necessary to show-
Where the court records contain an affidavit of the biological parent or parents that their identity remain confidential, the court shall include such affidavit with the other information. The Secretary shall insure that the confidentiality of such information is maintained and such information shall not be subject to the Freedom of Information Act ( 5 U.S.C. 552 ), as amended.
Upon the request of the adopted Indian child over the age of eighteen, the adoptive or foster parents of an Indian child, or an Indian tribe, the Secretary shall disclose such information as may be necessary for the enrollment of an Indian child in the tribe in which the child may be eligible for enrollment or for determining any rights or benefits associated with that membership. Where the documents relating to such child contain an affidavit from the biological parent or parents requesting anonymity, the Secretary shall certify to the Indian child's tribe, where the information warrants, that the child's parentage and other circumstances of birth entitle the child to enrollment under the criteria established by such tribe.
25 U.S.C. § 1951