1. National Bureau of Standards (1977) Data Encryption Standard (DES) (U.S. Department of Commerce, Washington, DC), Federal Information Processing Standards Publication (FIPS) 46. https://csrc.nist.gov/publications/detail/fips/46/archive/1977-01-15
2. Federal Information Processing Standards Publication: escrowded encryption standard (EES)
3. National Security Agency (1998) SKIPJACK and KEA Algorithm Specifications, Version 2.0 (National Security Agency, Ft. Meade, MD), May 29, 1998. https://csrc.nist.gov/CSRC/media//Projects/Cryptographic-Algorithm-Validation-Program/documents/skipjack/skipjack.pdf
4. American National Standards Institute (1981) Data Encryption Algorithm (American National Standards Institute, Washington, DC), ANSI X3.92-1981 (R1998). https://webstore.ansi.org/standards/incits/ansix3921981r1998
5. Curtin M (2005) Brute Force: Cracking the Data Encryption Standard (Copernicus Books, Springer, New York), ISBN 0-387-20109-2. https://link.springer.com/book/10.1007/b138699