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Digital Fortress
First edition cover
Author	Dan Brown
Country	United States
Language	English
Genre(s)	Science fiction, Techno-thriller novel
Publisher	St. Martin's Press
Publication date	1996
Media type	Print (Hardback & Paperback)
ISBN	ISBN 0-312-26312-0
Followed by	Angels & Demons

Digital Fortress is a techno-thriller novel by American author Dan Brown and published in 1996 by St. Martin's Press (ISBN 0-312-26312-0).

Plot summary

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Susan Fletcher, a brilliant mathematician and head of the National Security Agency's (NSA's) cryptography division, finds herself faced with an unbreakable code named "Digital Fortress", that TRANSLTR cannot break. TRANSLTR is the NSA's 3 million processor supercomputer that can crack encrypted data using the brute force method in a short amount of time, with some codes broken in more than 3 hours, others within minutes. The code of "Digital Fortress" is written by Japanese cryptographer Ensei Tankado, a fired employee of the NSA, who is displeased with the agency's intrusion into people's privacy. Tankado posts a copy of Digital Fortress on his website, encrypted with itself. Tankado auctions the passkey to unlock the algorithm on his website, threatening that his accomplice "North Dakota" will release the algorithm for free if he dies. Tankado is found dead in Seville, Spain. Fletcher, along with her fiancé, David Becker, a skilled linguist with eidetic memory, must find a solution to stop the spread of the code.

Characters

• Susan Fletcher - Head Cryptographer
• Commander Trevor Strathmore - Head of the Cryptography Department ('Crypto') and Deputy Director of the NSA and the main antagonist of the novel.
• David Becker - Susan Fletcher's fiance
• Ensei Tankado - Ex-NSA employee
• North Dakota (aka NDAKOTA) - A fictional accomplice of Ensei Tankado
• Hulohot - An NSA assassin (wearing wire-rim glasses)
• Midge Milken - Head of NSA internal security
• Phil Chartrukian - System security technician
• Jabba - Senior sys-sec officer who developed gauntlet, an anti-virus software.
• Soshi Kuta - Head techi after Jabba.
• Greg Hale - An employee of 'Crypto'
• Leland Fontaine - Director of the NSA
• Chad Brinkerhoff - PA to Director of the NSA
• Coliander, Smith - Agents of NSA sent to Spain to watch Hulohot's back.

The Digital Fortress

Digital Fortress is actually a computer worm designed with the intent to open the entire NSA databank to the world. Tankado knew that the NSA would use TRANSLTR to try and crack the Digital Fortress algorithm so they could decode all messages encrypted with it. In doing so, Digital Fortress would then gain access to the databank and open all its firewalls so that "Any 3rd grader with a modem would get access."

Themes & Issues

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This book deals with issues of civil rights, privacy from your government and the right to privacy in the internet. There are many discussions in the book concerning whether or not having access to everyone's information in order to secure their safety is ethical. Other books by Dan Brown are Angels and Demons, The Da Vinci Code, Deception Point, and The Solomon Key

Real life scenarios

The book is loosely based around recent history of cryptography. In 1976 the Data Encryption Standard (DES) was approved with a 56-bit key rather than the 64-bit key originally proposed. It was widely reckoned that the National Security Agency had pushed through this reduction in security on the assumption that it could crack codes before anyone else.

In fact the DES was first publicly broken in 1997, 96 days after the first of the DES Challenges. In 1998, the same year as Digital Fortress was published, the Electronic Frontier Foundation (featured in the book) built a piece of hardware costing less than $250,000 called the EFF DES cracker which broke it in 56 hours.

The brute force search used by TRANSLTR takes twice as long for each extra bit added to the key (if this is done sensibly), so the reaction of the industry has understandably been to lengthen the key. The Advanced Encryption Standard established in 2001 uses 128, 192 or 256 bits, which take at least 10²¹ times as long to solve by this technique.

Unbreakable codes are not new to the industry. The one-time pad, invented in 1917 and used for the cold-war era Moscow-Washington hotline, was proved to be unconditionally secure by Claude Shannon in 1949 when properly implemented. However it is inconvenient and expensive to use in practice and its use is generally limited to government and military agencies.

Public-key cryptography does not generally use fixed length keys and is not susceptible to the computer described in Digital Fortress although it is not unbreakable and may be broken in the future using quantum computing techniques.

Code solution

The code that appears in the end of the book

128-10-93-85-10-128-98-112-6-6-25-126-39-1-68-78

is decrypted by looking at the first letter of the chapter for each number. For example, chapter 128 starts 'When Susan awoke'. The resulting text is:

WECGEWHYAAIORTNU

Decryption is performed using a columnar transposition cipher, termed a "Caesar Square" cipher in the book (this is unrelated to the Caesar cipher). The letters are arranged into a square:

W E C G
E W H Y
A A I O
R T N U

and read from the top down.

WEAREWATCHINGYOU

Add spaces and you get the plaintext,

"We are watching you"

a reference to the NSA's monitoring systems.

Technical Errors

Although the book's website cites reviews lauding Digital Fortress for being extremely realistic, the book contains a number of technical errors and misunderstandings in computers, math and technology.

• Brown mentions a Hungarian mathematician, Josef Harne, who in 1987 proposed an encryption algorithm that, in addition to encrypting, shifted decrypted cleartext over a time variant. However, neither Harne nor the concept of rotating-cleartext ever existed.¹

Notes

1. ^ Digital Fortress: what Dan Brown got wrong » Becoming paranoid » Tips about computer security, privacy and staying safe online

• One briefly described character is mentioned as an alumnus of Amherst College, which Brown graduated in 1986.
• The assassin, Hulohot, is described as using a revolver with the finest silencer available. Except for the unusual Nagant 1895, revolvers don't benefit from a silencer because noise comes through the gap between the cylinder and the barrel of the gun. Even with the silencer on the Nagant, the gun makes a loud clicking noise, impractical for use in public areas (as described in the book).

External links

• Digital Fortress page at Mathematical Fiction Alex Kasman's site includes a forum, critique of the math/computing, and his solution to the code.
• Rob Slade's review of Digital Fortress The book is reviewed "on the basis of technology, including the fiction".
• (Spanish) Criticism in the Spanish-language Epoca of the book's description of locations in Seville
• Matt Crypto lists some errors in the book