Presentation on theme: "Background on Unsolved 340-cipher Ryan Garlick"— Presentation transcript:
1 Background on Unsolved 340-cipher Ryan Garlick The Zodiac KillerBackground onUnsolved 340-cipherRyan Garlick
2 BackgroundThe Zodiac was a serial killer active in California during the late 1960’s and early 1970’s.He definitely killed 5 people and claimed 37 victims.He taunted the police in over 20 letters and ciphers
3 July 4, 1969 Mike Mageau and Darlene Ferrin Parked at a Lover’s Lane Darlene was killed and Mike seriously woundedGunman approached and shot without saying a word
4 July 31, 1969Zodiac mails very similar handwritten letters to 3 newspapers in northern California…
6 July 31, 1969 Each newspaper also received a different cipher Vallejo Times-Herald received
7 Solved by… CIA? NSA? The California Department of Justice? FBI? Office of Naval Intelligence?
8 Solved byHigh school history teacher Donald Harden and his wife Betty at their breakfast table.
9 Cipher Details The Cipher was a homophonic substitution cipher Δ = ‘S’, etc.Homophones – more than one symbol represents ‘S’.Throws off statistical analysis
10 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 DANGEROUE ANIMAL OF ALL TO KILL SOMETHING GIVES ME THE MOST THRILLING EXPERENCEIT IS EVEN BETTER THAN GETTING YOUR ROCKS OFF WITH A GIRLTHE BEST PART IS THAE WHEN I DIE I WILL BE REBORN IN PARADICE AND ALL THE I HAVE KILLED WILL BECOME MY SLAVESI WILL NOT GIVE YOU MY NAME BECAUSE YOU WILL TRY TO SLOI DOWN OR STOP MY COLLECTING OF SLAVES FOR MY AFTERLIFE EBEORIETEMETHHPITI
11 Oct. 11, 1969Cab driver Paul Stine killed in San Francisco
14 The “Dripping pen” card included this 340 character cipher
15 Assumptions Another substitution cipher? Left to right? Meaningless? Polyalphabetic?Symbols mean different things for each occurrence in the cipherBook cipher?
16 Naïve Brute Force 26^63 possible keys Then all possible word combinationsx = min number of words + 1, y = max + 1
17 We can do much better Not all symbols represent ‘A’ Max number of mappings per symbolDon’t need to generate every possible wordScan for digrams, trigramsTotal word countUse his previous vocabulary – 22 letters
18 Scoring What is a ‘good’ solution? Word count Bigrams and trigrams Frequency distribution – Zodiac may have thrown this off with junk at the end like on 408 (solved) cipherCombination
19 Still a lot of work Distribute the problem Other optimizations Your ideas
20 Genetic Algorithm Heuristic method Directed search “Evolve” the key Many parameters – population size, mutation rate, % of pop to discard, etc.
21 EM Algorithm Expectation Maximization Bigram probabilities for the entire cipher
22 Brute Force Intractable Many computers running keys The “testbed” for our key scoringKeeping good keys, return them to a key serverWe could get (very) lucky - stranger things have happened!
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