47 CFR § 90.553 - Encryption.
(a) Encryption is permitted on all but the two nationwide Interoperability calling channels. Radios employing encryption must have a readily accessible switch or other readily accessible control that permits the radio user to disable encryption.
(b) If encryption is employed, then transmitters manufactured after August 11, 2014 must use the Advanced Encryption Standard (AES) specified in ANSI/TIA–102.AAAD–A. Until 2030, manufacturers may also include the Digital Encryption Standard (DES) or Triple Data Encryption Algorithm (TDEA), in addition to but not in place of AES, for compatibility with legacy radios that lack AES capability.
(c) ANSI/TIA–102.AAAD–A: Project 25 Digital Land Mobile Radio-Block Encryption Protocol, approved August 20, 2009 is incorporated by reference into this section with the approval of the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. This incorporation by reference (IBR) material is available for inspection at the FCC and at the National Archives and Records Administration (NARA). Contact the FCC through the Federal Communications Commission's Reference Information Center, phone: (202) 418–0270. For information on the availability of this material at NARA, visit www.archives.gov/federal-register/cfr/ibr-locations.html or email fr.inspection@nara.gov. The material may be obtained from the following sources:
(1) Telecommunications Industry Association (TIA), 2500 Wilson Boulevard, Arlington, VA 22201; website: https://tiaonline.org.
(2) S&P Global Standards Store, 15 Inverness Way East, Englewood, CO 80112; website: https://global.ihs.com.
(3) American National Standards Institute (ANSI), 25 West 43rd Street, Fourth Floor, New York, NY 10036; website: www.ansi.org.