Table of Contents

Preface. 10

1.     How can I break an encrypted message? And other introductory questions. 13

  • What is this book about?
  • Which technical terms do I need to know?
  • How can I break an encrypted text?
  • How do I know what kind of encryption I am dealing with?
  • I have found an encrypted text in the attic; can you decipher it for me?
  • I have encrypted a text myself, can you break it?
  • I have invented a new encryption method; can you take a look at it?
  • I have solved a famous unsolved cryptogram, what shall I do?
  • What tools do I need for codebreaking?
  • How can I encrypt my files and emails?
  • I have a comment on this book, what shall I do?
  • Who contributed to this book? (Acknowledgements). 22

2.     The Caesar cipher

  • How the Caesar cipher works
  • How to detect a Caesar cipher
  • How to break a Caesar cipher
  • Success stories
    • A prison inmate cipher
    • A spy’s encrypted sheet
    • An encrypted journal from the movie “The Prestige”
  • Challenges
    • Herbert Yardley’s first challenge
    • A series of newspaper advertisements from 1900

. 25

3.     Simple substitution ciphers. 33

  • How simple substitution ciphers work
  • How to detect a simple substitution cipher
  • Example of a cipher that is not a simple substitution cipher
  • Index of coincidence technique
  • How to break a simple substitution cipher
  • Frequency analysis
  • Guessing frequent words
  • Guessing words with unusual letter patterns
  • Success stories
    • How Gary Klivans broke a prison inmate code
    • How Kent Boklan broke encrypted diary entries from theCivil War
    • Beatrix Potter’s diary
  • Challenges
    • Prison code
    • A postcard
    • Another postcard
    • Friedmans’ wedding centennial nickel
    • An Aristocrat from the ACA
  • Unsolved cryptograms
    • An encrypted newspaper ad from 1888
    • The Zodiac Celebrity Cypher

. 34

4.     Simple substitution ciphers without spaces between words: Patristocrats. 51

  • How a Patristocrat, a simple substitution cipher without spaces, works
  • How to detect a Patristocrat
  • How to break a Patristocrat
  • Frequency analysis and word guessing
  • Word guessing
  • Success stories
    • A prison message
    • The Cheltenham Number Stone
  • Challenges
    • Rudyard Kipling’s encrypted message
    • NSA’s second Monday challenge
  • Unsolved cryptograms
    • The Dorabella cryptogram
    • The Chinese gold bars mystery
    • James Hampton’s notebook

. 51

5.     Simple substitution ciphers in non-English languages. 63

  • Detecting the language used
  • How to break a non-English simple substitution cipher
  • Frequency analysis and word-guessing
  • Word pattern guessing
  • Success stories
    • How André Langie broke a pigpen cipher (Spanish)
    • The La Buse cryptogram (French)
    • A postcard with a love message (German)
    • A Mafia message (Italian)
  • Challenges
    • An encrypted postcard
    • The third NSA Monday Challenge
    • Christlieb Funk’s challenge cryptogram
  • Unsolved cryptograms
  • The Voynich Manuscript
  • Cigarette case cryptogram
  • NSA’s fourth Monday Challenge
  • Moustier altar inscriptions

. 64

6.     Homophonic ciphers. 80

  • How homophonic ciphers work
  • How to detect a homophonic cipher
  • How to break a homophonic cipher
  • Success stories
    • The first Zodiac message (Z408)
    • Ferdinand III’s letters
    • A postcard from Hawaii
  • Challenges
    • A message to the Zodiac Killer
    • Edgar Allan Poe’s second challenge
  • Unsolved cryptograms
    • Beale Papers #1 & #3
    • The Zodiac Killer’s second message (Z340)
    • The Zodiac Killer’s third message (Z13)
    • The Zodiac Killer’s fourth message (Z32)
    • Scorpion cryptograms
    • Henry Debosnys’ messages

. 82

7.     Codes and nomenclators. 99

  • Codes
  • The difference between codes and ciphers
  • Nomenclators
  • Terminology
  • History of codes and nomenclators
  • Super-encryption of codes and nomenclators
  • How to detect a code or nomenclator
  • How to break a code or nomenclator
  • Finding the nomenclator table or codebook
  • Exploiting weaknesses of codes and nomenclators
  • Solving codes and nomenclators with cribs
  • Success stories
    • A telegram sent to Tel Aviv
    • Mary, Queen of Scots
    • Lord Franklin search expedition
    • The Japanese JN-25 code
  • Challenges
    • Mount Everest telegram
  • Unsolved cryptograms
    • Silk dress cryptogram
    • The train station robbery cryptogram
    • Pollaky’s newspaper advertisement
    • Lord Manchester’s Letter

. 100

8.     Polyalphabetic ciphers. 125

  • How a polyalphabetic cipher works
  • Vigenère cipher
  • Polyalphabetic ciphers
  • One-time pad
  • How todetect a polyalphabetic cipher
  • How tobreak a polyalphabetic cipher
  • Word guessing
  • Checking for repeating patterns (Kasiski’s method)
  • Using the index of coincidence
  • Dictionary attack
  • Tobias Schrödel’s method
  • Other Vigenère breaking methods
  • How to break a one-time pad
  • Success stories
    • Diana Dors’ message
    • Kryptos 1 and 2
    • The Cyrillic Projector
    • Thouless’s second cryptogram from the crypt
    • The Smithy Code
  • Challenges
    • Schooling challenge
    • A German radio message from the Second World War
    • Unsolved cryptograms
    • Wood’s cryptogram from the crypt

. 125

9.     Complete columnar transposition ciphers. 149

  • How complete columnar transposition ciphers work
  • How to detect a complete columnar transposition
  • How to break a complete columnar transposition cipher
  • The arrange-and-read method
  • Vowel frequencies and multiple anagramming
  • Success stories
    • Donald Hill’s diary
    • The Pablo Waberski spy case
  • Challenges
    • Love in Code
    • The Friedmans’ love messages
    • Agony Column
    • Yardley’s 11th ciphergram
    • Edgar Allan Poe’s first challenge
    • IRA messages

. 150

10.       Incomplete columnar transposition ciphers  167

  • How an incomplete columnar transposition works
  • How to detect an incomplete columnar transposition
  • How to break an incomplete columnar transposition
  • Successs tories
  • Kryptos – K3
  • Antonio Marzi’s radio messages
  • Challenges
    • IRA
    • Double Columnar Transposition Reloaded
  • Unsolved cryptograms
    • Catokwacopa

. 167

11.       Turning grille transposition ciphers. 185

  • How turning grille encryption works
  • How to detect a turning grille encryption
  • How to break a turning grille encryption
  • Success stories
    • Paolo Bonavoglia’s solution of a turning grille
    • André Langie’s solution of a turning grille
    • Karl de Leeuw’s solution of a turning grille
    • The Mathias Sandorf cryptogram
  • Challenges
    • The Friedman’s Christmas card
    • Jew-Lee and Bill’s Cryptocablegram
    • MysteryTwister C3 challenge
    • Kerckhoffs’ cryptogram

. 186

12.       Digraph substitution. 205

  • How a digraph substitution works
  • General case
  • The Playfair cipher
  • How todetect a digraph substitution
  • General case
  • Detection of a Playfair cipher
  • How to break a digraph substitution
  • Frequency analysis
  • Dictionary attack
  • Manual attack on the Playfair cipher
  • Success stories
    • Thouless’s first message
    • Thouless’s third message
  • Challenges
    • National Treasure: Book of Secrets
    • Unsolved cryptograms
    • World record digraph challenge
    • World record Playfair challenge

. 205

13.       Abbreviation ciphers  229

  • How abbreviation ciphers work
  • How to detect an abbreviation cipher
  • How to break an abbreviation cipher
  • Success stories
    • Emil Snyder’s booklet
  • Challenges
    • A birthday card
  • Unsolved cryptograms
    • The Tamam Shud mystery
    • Two unsolved postcards

. 229

14.       Dictionary codes and book ciphers. 238

  • How dictionary codes and book ciphers work
  • How to detect a dictionary code or book cipher
  • How to break a dictionary code or book cipher
  • Identifying the book or dictionary
  • Reconstructing the dictionary
  • Treating a book cipher like a simple substitution cipher
  • Success stories
    • The FIDES ads
    • Nicolas Trist’s key book
    • William Friedman and the Hindu Conspiracy
    • A dictionary code message sent to Robert E. Lee
  • Challenges
    • Dan Brown’s book cipher challenge
    • Dictionary code challenge
  • Unsolved cryptograms
    • Two encrypted newspaper advertisements from 1873

. 239

15.       Additional encryption methods. 252

  • Cipher tools. 252
  • Voice encryption. 253
  • Code talking. 254
  • Shorthand (stenography) 255
  • Hidden messages (steganography)
    • Success story: How Elonka found a hidden message on a tombstone. 260
    • Success story: Deciphering Steganographia. 262
    • Success story: Mysterious Stranger message
  • Challenge: Another steganographic message by the Friedmans
  • Cipher machines. 268

16.       Solving ciphers with hill climbing. 273

  • Solving simple substitution ciphers with hill climbing
    • Success story: Bart Wenmecker’s solution of the Baring-Gould cryptogram
    • Success story: Florida murder case cryptogram
  • Solving a homophonic cipher with hill climbing
    • Success story: Dhavare, Low, and Stamp’s Zodiac Killer solutions
  • Solving a Vigenère cipher with hill climbing
    • Success story: Jim Gillogly’s solution of IRA Vigenère cryptograms
  • Solving a columnar transposition with hill climbing
    • Success story: Jim Gillogly’s solution of IRA transposition cryptograms
    • Success story: Richard Bean’s solution of the last unsolved IRA cryptogram
    • Success story: George Lasry’s solution of the doublecolumnar transposition challenge
  • Solving a turning grille cipher with hill climbing
    • Success story: Bart Wenmeckers’ solution of a turninggrille cryptogram
    • Success story: Armin Krauß’s solution of a turninggrille challenge
  • Solving a general digraph substitution with hill climbing
    • Success story: Digraph challenges
  • Solving a Playfair cipher with hill climbing
    • Success story: Dan Girard’s solution of the Cheltenham Letter Stone
    • Success story: Playfair challenges
  • Solving machine ciphers with hill climbing
  • Success story: Breaking the Enigma

. 274

17.       What next?. 297

  • More unsolved cryptograms
  • The fourth Kryptos message (K4)
  • The Rubin cryptogram
  • Ricky McCormick’s encrypted notes
  • The World War II carrier pigeon message
  • Even more unsolved cryptograms
  • Codebreaking tools
  • Other books about codebreaking (Recommended reading)
  • Websites about codebreaking (links)
  • Journals and newsletters
  • Events

. 297

Appendix A: Kryptos

. 311

Appendix B: Useful language statistics. 313

  • Letter frequencies
  • Most frequent digraphs
  • Most frequent doubled letters
  • Most frequent trigraphs
  • Most frequent words
  • Average word lengths in a text
  • Index of coincidence

. 313

Appendix C: Glossary. 318

Appendix D: Figure sources. 322

Index. 332

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