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Cryptography and Murder – The Zodiac Killer

Cryptography and Murder – The Zodiac Killer. The Case. Serial killer active in the San Francisco area 1967 – 1974 (at least) Linked to 7 murders, but claimed many more Never caught Police investigation closed in 2004 Lots of theories and speculations around the case.

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Cryptography and Murder – The Zodiac Killer

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  1. Cryptography and Murder –The Zodiac Killer

  2. The Case • Serial killer active in the San Francisco area • 1967 – 1974 (at least) • Linked to 7 murders, but claimed many more • Never caught • Police investigation closed in 2004 • Lots of theories and speculations around the case

  3. This is the Zodiac speaking... • Wrote many letters (at least 18) to the police and to newspapers in the SF area

  4. Ciphers • Four letters contained ciphers • Appear to be substitution ciphers, but with more cipher text symbols than ordinary letters • Two of them contain too little cipher text to be solved

  5. First cipher the Zodiac sent Was divided in three parts and sent to three different newspapers All three parts published on the front pages Solved in a week by a high school teacher and his wife 408 Cipher

  6. How Did They Do It? • Knew the killer had a big ego, assumed he would start with ’I’ • Assumed the word ’kill’ would appear several times • This was 1969 – only pencil and paper! Donald Harden http://www.zodiackiller.com/donaldharden.mp3

  7. Part 1 Character Cipher Cipher Key Cipher Solution

  8. Caesar Ciphers • Method used by Romans for hiding messages; called “Caesar Ciphers” • An easy way to hide messages is to shift each letter of the alphabet forward or backward a number of spaces. • Let’s shift the alphabet backward by three and code the following message: • FORENSIC SCIENCE USES CRYPTOGRAPHY TO SOLVE CRIMES.

  9. FORENSIC SCIENCE USES CRYPTOGRAPHY TO SOLVE CRIMES. Plain Cipher Solution: IRUHQVLF VFLHQFH XVHV FUBSWRJUDSKB WR VROYH FULPHV.

  10. Caesar Ciphers • Answer 3: • Do number four! • Answer 4: ZKBD YP DRO JYNSKM MYNO RKC LOOX LBYUOX The Zodiac killer is still at large.

  11. This is quite cumbersome so let’s look at letter frequencies to speed this up. • Most commonly used letters in descending order of frequency: • E-T-A-O-N-R-I-S-H-D-L-F-C-U- M-G-P-Y-W-B-V-K-X-J-Q-Z • Do number 5! • Answer 5: The Zodiac killer uses complex ciphers. HVS NCRWOQ YWZZSF IGSG QCADZSL QWDVSFG

  12. Substitution Ciphers • It would have been simple to break the code if the Zodiac killer had used a Ceasar cipher, but he didn’t. • He used a substitution cipher. In a substitution cipher, either the alphabet is not in order or each letter of the alphabet is represented by a symbol. • Do number 6! • Answer 6: Donald Harden solved a zodiac cipher.

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