Digital Fortress is a techno-thriller

Techno-thriller

Techno-thrillers are a hybrid genre, drawing subject matter generally from spy/action thrillers, fantasy/war novels, and science fiction...

 novel written by American author Dan Brown

Dan Brown

Dan Brown is an American author of thriller fiction, best known for the 2003 bestselling novel, The Da Vinci Code. Brown's novels, which are treasure hunts set in a 24-hour time period, feature the recurring themes of cryptography, keys, symbols, codes, and conspiracy theories...

 and published in 1998 by St. Martin's Press

St. Martin's Press

St. Martin's Press is a book publisher headquartered in the Flatiron Building in New York City. Currently, St. Martin's Press is one of the United States' largest publishers, bringing to the public some 700 titles a year under eight imprints, which include St. Martin's Press , St...

. The book explores the theme of government surveillance of electronically stored information on the private lives of citizens, and the possible civil liberties

Civil liberties

Civil liberties are rights and freedoms that provide an individual specific rights such as the freedom from slavery and forced labour, freedom from torture and death, the right to liberty and security, right to a fair trial, the right to defend one's self, the right to own and bear arms, the right...

 and ethical implications using such technology.
When the United States National Security Agency

National Security Agency

The National Security Agency/Central Security Service is a cryptologic intelligence agency of the United States Department of Defense responsible for the collection and analysis of foreign communications and foreign signals intelligence, as well as protecting U.S...

's code-breaking machine (TRANSLTR) encounters a new and complex code—Digital Fortress—that it cannot break, Commander Trevor Strathmore calls in Susan Fletcher, their head cryptographer to crack it.