# Tagged Questions

The Playfair cipher is a digraph substitution cipher. It employs a table where one letter of the alphabet is omitted, and the letters are arranged in a 5x5 grid.

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### What are the main weaknesses of a Playfair cipher, if any?

What are the main weaknesses of a Playfair cipher, if any? I know that they depend on none of the letters missing, but that is an easy fix if a letter gets dropped. Besides that, are there any other ...
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### How to attack a classical cipher using known partial plaintext?

I have a ciphertext generated by a classical cipher. I do not know what was cipher used to generate it. I do however have the beginning of the plaintext. What are the cryptanalysis approaches for ...
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### How does cryptanalysis of the Playfair cipher work?

I have a set of Playfair-enciphered data that I'm trying to crack without the key. I know I need to analyse bigrams; I've currently worked out what decrypts to th, <...
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### How many keys does the Playfair Cipher have?

I was just studying the Playfair cipher and from what I've understood, it is just a slightly better version of a Caesar cipher, in that it isn't actually mono-alphabetic but rather the 'digrams' are ...
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### Four-Square cipher and its keyspace

Am I thinking about this correctly? Consider that the keyspace of the Playfair cipher is equivalent to all permutations of the alphabet, e.g. the number of distinct permutations of 25 objects, and ...
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### How to find the keyword of the Playfair text knowing/not knowing the plaintext and having decrypted text?

I know how the Playfair cipher works. I would like to know how can I find the keyword of the play fair cipher in two cases: 1) knowing the plaintext 2) not knowing the plaintext? Some examples: <...
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### Decoding the Playfair cipher with a crib [duplicate]

I have a Playfair cipher text and I know a portion of the text (one world). How can I decode the cipher from here? Thanks.
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### Does the length of the keyword used for keytable for Playfair matter?

So for Playfair, we choose a keyword and put that in the keytable with no duplicates. Then, we fill the rest of the table with alphabets in order that are not in the keyword without 'J'. Does the ...
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### Multi-round Transposition/Playfair as a secure hand cipher in the computer age

Given that computers can be easily compromised, there is a need for a hand cipher that can withstand computer attack. Clearly the traditional hand ciphers fail. One time pads work. They also have ...
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### Playfair Cipher + Vigenere Cipher?

I'm researching cryptography for a school project, came across the above two ciphers, and something occurred to me. Would combining these two schemes give a considerably stronger encryption than ...
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### Encryption of numeric value using playfair

I am studying in CSE and in my recent exam paper, A question was asked as: Construct a playfair cipher for Plaintext: semester5 and key:technology. Generally as we are taught yet, there is no ...
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### Playfair Cipher Confusion with one column encryption

Recently I decided to learn "Playfair Cipher", and I have hit a road block. what do i substitute the letters for if they are on the same column? Here is an example: ...
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### How to create and validate potential grids when attacking a Playfair cipher?

First up: I am not asking you to decypher anything. This question is about attacking a Playfair cipher; more specifically – how to create potential grids when doing so. I'm currently working on a ...
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### Unicity-distance of Playfair

Given the classical scheme Playfair, say, for 5*5 matrices, I am interested to determine its unicity-distance. How should one proceed to properly do that? I should appreciate it, if I could obtain a ...