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4 votes
Accepted

Mutual Index of Coincidence

As defined e.g. in Stinson's Cryptography: Theory and Practice (1995, 1st ed.; the earliest source for the term I could find that has even excerpts online), the mutual index of coincidence of two ...
Ilmari Karonen's user avatar
3 votes
Accepted

K Friedman - two texts explanation

Just for simplicity lets assume that your short period "password" was just XORed with plaintext. So we have encryption procedure like: ...
CaptainRR's user avatar
  • 646
2 votes

How do I exactly use the Index of Coincidence in Cyphertext?

The index of coincidence is a measure of how different a collection of letters is from a random set based on repetitions. For an alphabet of 26 letters a completely random collection of letters will ...
Daniel S's user avatar
  • 24.1k
2 votes

What does the normalizing coefficient do in the Index of Coincidence?

The normalizing coefficient makes sure that for a random text the IC will be (close to) 1.0, independent of the size of the alphabet.
Jigg's user avatar
  • 21
1 vote

Index of Coincidence Averages List

The index of coincidence (IOC) measures the likelihood of drawing two matching characters by randomly selecting two characters from a given ciphertext. It also applies to digraphs, etc. So, the ...
Patriot's user avatar
  • 3,132
1 vote
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Checking if a sentence is English after decryption

Try tokenizing the plaintext using an English dictionary. Give higher scores to bigger words to prevent your analyzer from favoring a bunch of one to two letter words. Total the score up and take the ...
DCronce's user avatar
  • 26

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