Slides from my recent talk at the 2015 Cryptologic History Symposium in Laurel, MD

1. The Zodiac Ciphers
What do we know? And
when can we stop trying
to solve them?
David Oranchak
http://zodiackillerciphers.com

2. December 20, 1968
Betty Lou Jensen, David Faraday
Lake Herman Road, Benicia
July 4, 1969
Darlene Ferrin, Michael Mageau
Blue Rock Springs Park, Vallejo
September 27, 1969,
Cecelia Shepard, Bryan Hartnell
Lake Berryessa
October 11, 1969
Paul Stine
Presidio Heights, San Francisco

4. The Ciphers
Z408 Z340
Z32
Z13

5. 13 symbols long
8 unique symbols in cipher alphabet

6. Names Phrases

7. Cipher is 32 symbols long
But there are 29 unique symbols!

9. I like killing people
because it is so much fun
it is more fun than killing
wild game in the forrest
because man is the most
dangerous animal of all to
kill something gives me the
most thrilling experience
it is even better than
getting your rocks off with
a girl the best part of it
is that when I die I will
be reborn in paradice and
all the I have killed will
become my slaves I will not
give you my name because
you will try to slow down
or stop my collecting of
slaves for my afterlife
ebeorietemethhpiti

11. EBEORIETEMETHHPITI
ROBE[R]T EM[M]ET THE HIP[P]IE
TIMOTHIE E. PHEIBERTE
I'M HERE TO BITE THE PIE
THE EERIE POET BIT HIM
I HOE THE TIBET EMPIRE
I BETTER HOPE I TEE HIM.
BE HERE. TIPTOE. TIE HIM.

12. EBEORIETEMETHHPITI
ROBE[R]T EM[M]ET THE HIP[P]IE
TIMOTHIE E. PHEIBERTE
I'M HERE TO BITE THE PIE
THE EERIE POET BIT HIM
I HOE THE TIBET EMPIRE
I BETTER HOPE I TEE HIM.
BE HERE. TIPTOE. TIE HIM.

14. PART
1:
PART
2:

19. Symbols in Z408 alphabet, not
in Z340 alphabet:
Symbols in Z340 alphabet, not
in Z408 alphabet:

21. Z408 Z340

22. 8.5” 8.5”
11”
11”

23. 8.5” 8.5”
11”
11”

25. 62 repeats 25 repeats

26. 11 repeats 2 repeats

27. Distance 19:
37 repeated bigrams
Distance 14, reading
right to left:
40 repeated bigrams
Distance 1:
25 repeated bigrams

28. 7 occurrences 6 occurrences

29. Plaintexts with
similar patterns:
1.5%
Chance of
preserving during
encipherment:
1 in 50,000

33. Prime positions:
2, 3, 5, 7, 11, 13, 17, 19,
23, 29, 31, 37, 41, 43, 47,
53, 59, 61, 67, 71, 73, 79,
83, 89, 97, 101, 103, 107,
109, 113, 127, 131, 137,
139, 149, 151, 157, 163,
167, 173, 179, 181, 191,
193, 197, 199, 211, 223,
227, 229, 233, 239, 241,
251, 257, 263, 269, 271,
277, 281, 283, 293, 307,
311, 313, 317, 331, 337

34. ODDS
EVENS

35. When can we stop trying to solve it?
● Someone solves it
● No message to find
● Better things to do
But we want to know the solution, so we keep trying.
Most commonly tested idea: Z340 was made like Z408.
A better question is: When can we move on to another idea?
Possible answer: Generate many test ciphers

36. “Z340 was made like Z408” hypothesis
● Homophonic substitution
● Normal reading direction
● English language
● Possible misspellings
● Omitted words
● Possible transcription errors
● Curious features are random accidents
● Filler

37. “Symbol confusion”
groups
Cipher generator
● Big pile of books
● Take random samples of length 340
● Generate random misspellings, omissions, filler
● Generate random keys
● Measure features
○ Symbol counts, ngram count, appearances of cycles,
prime phobia, transcription errors, even/odd
discrepancy, row randomness, appearances of
specific patterns, filler section, misspellings
● Use multiobjective optimization to find keys with
measurements most similar to Z340
○ Genetic algorithm

38. Sample generated ciphers -
Patterns similar to Z340
Gilbert and
Sullivan
Count of Monte
Cristo
Les Miserables

39. Z340 Generated

40. ● Improve codebreaking skills
○ Some plaintexts are harder than others
● Verify that hypothesis can make Z340-like
cipher
● Curious features may be phantoms
● Solving numerous test ciphers increases
confidence that hypothesis is wrong.
Nice parlor trick. But what’s the point?

41. Explore other hypotheses
● Dan Olson’s hypothesis
● Transpositions
● Wildcards/polyphones
● Ngram substitution
● Quadrants
● Home-grown modification to simple substitution
● Error in encipherment method
● And an infinite number of others

42. Future Work:
● Continue collecting observations, test results, and ruling out hypotheses
● Knight/Nuhn’s cipher type detection
○ Obtain/generate huge training set of ciphers
○ Better results are possible with ensemble classifiers
○ Example: “Netflix Prize” won by BellKor’s Pragmatic Chaos classifier
● How would Z340 be classified?
● Online workbench: Centralize autosolvers and statistical tools
More Info:
ZodiacKillerCiphers.Com
Thanks to: The many researchers and collaborators in the forums at ZodiacKillerSite.
com, ZodiacKillerFacts.com, and ZodiacKiller.com.