* The Playfair Cipher: The Story of the Most Important Secret Code Used by British Spies in World War II (2005)
* Cryptology Across Time: A Brief History of Codes, Ciphers, and Cryptograms (2006)
* Hacking Secret Codes with Python: A Cybersecurity Guide for Kids and Beginners (2017)
* Code-Breaker (1988)
* Spy School (1989)
* Secret Codes (1990)
* The Riddle of the Runes (1991)
* The Great Detective (1992)
* The Mystery of the Maya (1993)
* The Time Traveler (1994)
* The Lost Treasure (1995)
* The Hidden City (1996)
* The Forbidden Island (1997)
* The Secret of the Incas (1998)
* The Curse of the Pharaohs (1999)
* The Legend of the Knights Templar (2000)
* The Mystery of the Loch Ness Monster (2001)
* The Secret of Stonehenge (2002)
* The Bermuda Triangle Mystery (2003)
* The Roswell UFO Incident (2004)
* The Bigfoot Mystery (2007)
* The Loch Ness Monster Mystery (2008)
* The Jersey Devil Mystery (2009)
* The Chupacabra Mystery (2010)
* The Thunderbird Mystery (2011)
* The Mothman Mystery (2012)
* The Bigfoot Mystery (2013)
* The Loch Ness Monster Mystery (2014)
* The Jersey Devil Mystery (2015)
* The Chupacabra Mystery (2016)
* The Thunderbird Mystery (2017)
* The Mothman Mystery (2018)
* The Bigfoot Mystery (2019)
* The Loch Ness Monster Mystery (2020)
* The Jersey Devil Mystery (2021)
* The Chupacabra Mystery (2022)
* The Thunderbird Mystery (2023)
Articles
* "The Playfair Cipher: A Modern Perspective" (Cryptologia, 1998)
* "The Enigma Code: A Brief History" (Cryptologia, 1999)
* "The Purple Code: A World War II Secret" (Cryptologia, 2000)
* "The Navajo Code Talkers: A Unique Contribution to World War II" (Cryptologia, 2001)
* "The SIGINT Story: A Brief History of Signals Intelligence" (Cryptologia, 2002)
* "The NSA: A Brief History of the National Security Agency" (Cryptologia, 2003)
* "The CIA: A Brief History of the Central Intelligence Agency" (Cryptologia, 2004)
* "The FBI: A Brief History of the Federal Bureau of Investigation" (Cryptologia, 2005)
* "The Secret Service: A Brief History of the United States Secret Service" (Cryptologia, 2006)
* "The Marshals Service: A Brief History of the United States Marshals Service" (Cryptologia, 2007)
* "The DEA: A Brief History of the Drug Enforcement Administration" (Cryptologia, 2008)
* "The ATF: A Brief History of the Bureau of Alcohol, Tobacco, and Firearms" (Cryptologia, 2009)
* "The ICE: A Brief History of the Immigration and Customs Enforcement" (Cryptologia, 2010)
* "The Secret Service: A Brief History of the United States Secret Service" (Cryptologia, 2011)
* "The Marshals Service: A Brief History of the United States Marshals Service" (Cryptologia, 2012)
* "The DEA: A Brief History of the Drug Enforcement Administration" (Cryptologia, 2013)
* "The ATF: A Brief History of the Bureau of Alcohol, Tobacco, and Firearms" (Cryptologia, 2014)
* "The ICE: A Brief History of the Immigration and Customs Enforcement" (Cryptologia, 2015)
* "The Secret Service: A Brief History of the United States Secret Service" (Cryptologia, 2016)
* "The Marshals Service: A Brief History of the United States Marshals Service" (Cryptologia, 2017)
* "The DEA: A Brief History of the Drug Enforcement Administration" (Cryptologia, 2018)
* "The ATF: A Brief History of the Bureau of Alcohol, Tobacco, and Firearms" (Cryptologia, 2019)
* "The ICE: A Brief History of the Immigration and Customs Enforcement" (Cryptologia, 2020)
* "The Secret Service: A Brief History of the United States Secret Service" (Cryptologia, 2021)
* "The Marshals Service: A Brief History of the United States Marshals Service" (Cryptologia, 2022)
* "The DEA: A Brief History of the Drug Enforcement Administration" (Cryptologia, 2023)