Presentation on theme: "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."— Presentation transcript:
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
This is the Zodiac speaking... Wrote many letters (at least 18) to the police and to newspapers in the SF area
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
408 Cipher 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
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
Part 1 Character Cipher Cipher Key Cipher Solution
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.
Caesar Ciphers Answer 3: Do number four! Answer 4: ZKBD YP DRO JYNSKM MYNO RKC LOOX LBYUOX The Zodiac killer is still at large.
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
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.