Digital Fortress

Digital Fortress is a novel by American author Dan Brown and published in 1998 by St. Martin's Press (ISBN 0312263120).

Plot

Susan Fletcher, a brilliant mathematician and head of the National Security Agency's cryptography division, finds herself faced with an unbreakable code resistant to brute-force attacks by the NSA's 3 million processor supercomputer. The code is written by Japanese cryptographer Ensei Tankado, a sacked employee of the NSA, who is displeased with the agency's intrusion into people's privacy. Tankado auctions the algorithm on his website, threatening that his accomplice, "NDakota", 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.

Main characters

Susan Fletcher: Mathematician, NSA's head cryptographer
David Becker: Professor of Linguistics at Georgetown University and Susan's fiancé
Commander Trevor Strathmore: Deputy Director of the NSA, head of Crypto
Ensei Tankado: Japanese ex-NSA cryptographer, creator of Digital Fortress
Greg Hale: NSA cryptographer, former Marine
Leland Fontaine: Director of the NSA
Midge Milken: NSA's Internal security analyst
Hulohot: A deaf assassin hired to hunt down Ensei Tankado and take the ring. After killing Tankado, his new mission was to retrieve the ring before David Becker gets it.
Chad Brinkerhoff: PA of the NSA Director's Office
Phil Chartrukian: NSA Sys-sec
Tokugen Numataka: Japanese businessman, Ensei Tankado's reluctant father
"Jabba": Resident Sys-sec Chief, anti-hacker computer expert

Artistic license

Cryptography and computers

The main premise of the book is that there exists a supercomputer that can decrypt any encrypted message through brute force, no matter which algorithm was used to encrypt the message. No exotic cryptographic breakthroughs are mentioned. In reality this is a flawed premise, and one which characters repeatedly describe as being based on the "Bergofsky Principle". In fact, no such principle exists. Some algorithms such as the one-time pad are decisively impossible to decrypt through brute force alone. While there are widely used encryption methods that can be defeated through brute force attacks, most of them require decryption systems that have several orders of magnitude more computing power than that described in the novel, if the messages are to be decrypted in such a short timespan. The author also fails to account for exponential increases in difficulty as the key length increases.

It is possible to examine even an executable program without running it; as such, in reality viruses pose no problem to decryption systems, since they will never be running the text being decrypted. Since viruses are one of the key dangers in the book and a major plot point, this forms another major use of artistic license. One explanation for this is that the computer was testing to see if the key was a self modifying program, and through a flaw in security, accidentally let the virus take it over.

The novel states that "Enigma was history’s most famous code-writing machine—the Nazis’ twelve-ton encryption beast." In reality, the Wehrmacht Enigma weighed only around twelve kilograms.

The author has also stated that the ASCII consists of 256 characters, when it actually consists of 128 characters. He also stated that a 64-bit integer would make 64 characters. In reality, it can hold an integer value from 0 - 18,446,744,073,709,551,615 (2⁶⁴ - 1), or a string of only eight characters. Although ASCII only needs 7 bits per character, in practice an extra bit per character is left unused, so each ASCII character effectively consumes 8 bits.

The author uses some concepts as if they were encryption algorithms that can be broken by brute force: PGP, Diffie-Hellman, ZIP, IDEA, and ElGamal. Of these, Diffie-Hellman is a key exchange protocol which allows two parties to establish a shared secret key over an insecure communications channel. ZIP is a file format for data compression. PGP is an e-mail security program which uses the IDEA encryption algorithm, among others. The only two encryption algorithms of the list are IDEA, a symmetric encryption algorithm, and ElGamal, an asymmetric encryption algorithm.

The book also employs invented and undefined encryption technologies such as "mutation strings." Where real terms are used, they are thrown about without regard for their actual meaning. One section describes public-key encryption as using an agreed-upon key phrase, when in fact the defining feature of public-key systems is that they do not require shared secrets.

Contrary to the book's claim, it is not possible to trace the address to which an email is forwarded once it is sent (at least, not without cooperation from the recipient).

Five-character alphanumeric passwords are not considered secure. While an NSA cryptographer might use a weak password under some circumstances, she certainly would be aware of its weakness, and not be especially surprised if someone broke it.

Once a file has been downloaded, changing the contents of the file at the website will not normally affect any downloaded copies; this makes Strathmore's plan unworkable.

If they had the source-code of the virus (which they clearly did since they were able to find 'orphans' in the code) then finding the kill-switch code would be easier than cracking a serial number in a demo program.

Seville

The book's generous use of artistic license also extends to its depiction of the places, buildings, and populace of Seville. To wit, Plaza de España does not have the city hall but rather the Government Delegation, Subdelegation and other public buildings; the Spanish do not venerate Christopher Columbus as a saint; and his remains (which would be merely skeletal anyway; the scrotum disappears in a cadaver within six years after death) are buried, intact, in the Seville cathedral.

Practically all the book's notions of Spanish customs, religion, health care, telecommunications, transport, crime fighting and politics are inaccurate. The book is full of strange assertions: for example, that the Spanish national drink is cranberry juice with vodka, that Roman Catholic Spaniards take Communion at the start of the mass. Brown also confuses the Guardia Civil with the Spanish Urban Police (calling both "Guardia") and depicts its agents as highly corrupt and violent.

Even the time of construction and artistic style of several monuments in Seville are wrong. The most badly depicted is the Seville cathedral and its famous bell tower, the Giralda. The book claims that the Giralda is a Moorish tower from the 15th century with a height of 419 ft (140 m.). Inside the Giralda, there occurs a dangerous chase scene over supposedly steep stairs. In fact, the tower is an ancient minaret from the Almohad mosque, and was constructed in sections, the oldest part dating from 1184. The height of the tower is 320 ft (97.5 meters). The Giralda has no stairs; instead, 35 ramps are used to ascend the tower. Needless to say, no visitors or modern tourists have been killed in the building.

The Seville cathedral is depicted in the book as "the second largest cathedral in the world" (actually, it is St. Paul's Cathedral, in London) and a 11th century gothic structure, but it was actually built between 1433 and 1528 over the ruins of a mosque and has several baroque, neoclassic and neogothic parts due to subsequent reforms. Contrary to the book's description, the Cathedral has not merely one main gate "for protection against the Moors", but seven monumental gates and other minor exits. Moreover, at the time of the (actual) construction, there were no Moorish invasions in the Sevillian region because Al-Andalus was completely reduced to the tiny and weak Kingdom of Granada, tributary of Castile; and at the time of the (fictional) construction, in the 11th century, Seville was still under (strong) Muslim rule. In any case, it is illogical to construct a building with only one gate for protection because it would be a mortal trap in case the attackers set it on fire. No Spanish church is constructed as Brown says the Cathedral is.

Finally, the Alcázar Real was begun in the year 913 rather than the 15th century; and the Hotel Alfonso XIII is not a small 4-star hotel, but a large 5-star hotel that was built in 1928 with the intention of becoming the most luxurious hotel in Europe.^*

Japanese language

The first name "Ensei," though old fashioned, is acceptable, but the last name "Tankado" sounds more like the name of a street or a bar than a person and is not listed in the Japanese Name Dictionary (WWWJDIC) (it was written to be an anagram of "NDakota"). Likewise the name "Numataka" is probably fabricated. "Tokugen" is listed in the name dictionary.

At the end of the chapter 18, the book makes reference to "shichigosan, the seven deities of good luck" but shichigosan actually refers to a festival celebrating children's health at the ages of 7 (shichi), 5 (go) and 3 (san). The seven deities of luck are shichifukujin.

Others

Towards the end of the book there is a claim that Fat Man, the nuclear bomb dropped on Nagasaki, contained no plutonium but instead was a uranium-238 bomb. While U-238 was present in Fat Man, it was only used as a tamper with the plutonium providing the main nuclear reaction. Uranium-238 cannot be used alone for fission.

At one point, an underground chamber is described as having a 40-by-30 foot video wall at one end, and having been built by excavating 250 metric tons of earth. Assuming the earth to be of average density, the room would be less than 2 metres long.

Hulohot, an assassin in the story, is also noted several times as using a silenced revolver. Though the use of silencers on revolvers is possible and precedented, it is quite uncommon and far-fetched. A semi-automatic handgun would have suited the purpose better, not only for it generally being compatible with suppressors, but it would also justify the assassin's repeated use of his firearm: while it is never mentioned that he reloads his weapon, a revolver can only hold a maximum of eight bullets, while a semi-automatic could hold up to fifteen typically and even more with extended magazines.

The book describes Hulohot as a totally deaf man. However, he "hears steps" in one page. Hulohot is not a Portuguese name.

"Without wax" -the code which haunts Susan because she is unable to decrypt the phrase- is derived from Spanish "sin cera". In fact the adjective "sincerus" is Latin. Etymology: honey "sine cera" (without wax) was "pure" honey without any residue. It is unlikely that David, being a professor in linguistics, does not know this...

The director in the story, Leland Fontaine, is clearly a civilian, and we are told that he worked his way up through the ranks of the NSA. However, this would not occur in real life, as since the NSA was founded, the director has always been a military officer of three star rank. The novel makes no acknowledgement of this. The television series 24 makes a similar mistake in its depiction of NSA director Roger Stanton in its second season.

Spanish reaction

In Spain, the novel has been criticized for depicting the country as having substandard health care, corrupt security forces and poor telecommunications, among other things. Critics argue that this negative depiction of Spain is far from the truth, arguing that Spain's health service is, according to several criteria, one of the very best in the world; that the country does not suffer from high levels of corruption; and that the Spanish telephone infrastructure and public transport is not as unreliable as Brown suggests. The City Council of Seville, refusing to enter into polemics, has invited Brown to visit for a first-hand experience of the city.

The Spanish version of the book was released in February 2006 with the title Fortaleza Digital. It contains a prologue in which Dan Brown claims that Seville is his favourite city in the world and the place where he was inspired to write The Da Vinci Code. Ironically, the polemical and 'dreamy' description of the city helped the book to become a best-seller in Seville during its first month on sale (a similar event occurred in 2005 in Uruguay with Steven Seagal's film Submerged). ^*

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: WECG EWHY AAIO RTNU 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.

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.
(Spanish) Criticism in the Spanish-language Epoca of the book's description of locations in Seville

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