The Index of Coincidence and the Somerton Man Code

The Index of Coincidence (IC) is a statistical tool used in cryptanalysis and linguistics to measure the likelihood that two randomly selected letters from a text are the same. It’s calculated by observing the frequency of each letter and comparing it to the expected frequency of a random distribution of letters.

Here’s why the IC is important:

1. Cryptanalysis: The IC helps in breaking ciphers, especially those based on substitution. It can indicate if a text is encoded with a simple substitution cipher (which would have an IC similar to the language it’s written in) or a more complex method like a polyalphabetic cipher (which would have a lower IC, closer to random text). This technique was used to help solve K1, K2 and K3 of the Kryptos puzzle.
2. Language Analysis: The IC can reveal characteristics about a language’s letter distribution. Languages with a higher IC tend to have more repeated letters, which can be useful in linguistic studies and language comparison.
3. Identifying Language: In a multilingual text, the IC can help determine which parts are in which language by comparing the IC values to known values for different languages.
   This equates to the following values:
   - English: 0.0667
   - French: 0.0694
   - German: 0.0734
   - Spanish: 0.0729
   - Portuguese: 0.0824

Overall, the IC is a valuable measure for both understanding language patterns and for practical applications in cryptography. It’s a key concept in the field of cryptology, providing insights into the structure and complexity of languages and codes.

Python Program to work out the Index of Coincidence for the Somerton Man code

from collections import Counter

def index_of_coincidence(text):
freqs = Counter(text)
length = len(text)
ioc = sum([value*(value-1) for value in freqs.values()]) / (length*(length-1))
return ioc

# Example usage:

#WRGOABABDWTBIMPANETPMLIABOAIAQCITTMTSAMSTGAB
text = “WRGOABABDWTBIMPANETPMLIABOAIAQCITTMTSAMSTGAB” # replace with your version of the 1948 Somerton Man code
print(index_of_coincidence(text))

This code can then be run using an online Python program:

This provides the following result when run. ??Is this correct??

This equates to the language of the Somerton Man code being German text as this IC value rounds to 0.074.

This article was created using MS Copilot

This link shows Genius mode in You.com repeating the same result:

https://you.com/search?q=can+you+check+the+code+WRGOABABD%0AWTBIMPANETP%0AMLIABOAIAQC%0AITTMTSAMSTGAB+for+the+index+of+coincidence...&cid=c1_0a6f7933-aefe-41d1-bd87-4d97aadcc59c&tbm=youchat

Recalculated a different answer was also provided.

See also:

Matching the Somerton Man