Digital Fortress is a science-fiction/suspense novel and author Dan Brown's first published work. It was published first as an ebook in 1996 and then as a paperback in 1998.
Plot
Susan Fletcher, a brilliant mathematician, head of National Security Agency's cryptography division, finds herself faced with an unbreakable code, resistant to brute-force attacks by a 3-million processor supercomputer. Along with her fiancé, a skilled linguist with eidetic memory, she must find a solution to stop the spreading of the code.
Criticism
The book has been criticized for its inaccurate depictions of cryptography. It has also been criticized for its short-attention-span writing style (128 chapters in 429 pages) and its unbelievable characters.
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 link