Cryptography Stack Exchange
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Questions tagged [playfair]

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.

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. To fit the grid, the J is removed from the alphabet and an I takes its place in the text that is to be encoded.

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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 problems with it?
Arlen Beiler
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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 mono-alphabetic. I believe that since it offers a…
GamingX
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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 classical ciphers? How do you suggest trying to…
Jake
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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, er, in, and he, and have figured out where th and he are in the grid. However, now…
helpneeded123
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Playfair cipher - questions about inserting 'X'

I'm implementing the Playfair cipher as part of a programming project. I realize there are different versions of the cipher - I've been asked to implement the version which treats the letters 'I' and 'J' as the same letter, and which inserts the…
user61891
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How to find the keyword of the Playfair cipher, given the plaintext and the ciphertext?

I know how the Playfair cipher works. I would like to know how to find the keyword of the Playfair cipher, given some ciphertext and the corresponding plaintext. For example: encrypted: gy mm ko kc gc plaintext: he ll ow or ld I searched all over…
Brian Brown
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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 is equal to $1.551 · 10^{25}$. (A lot!) 1) What…
user7538
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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 length of the keyword matter? I am wondering because…
whiteSkar
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Playfair Cipher + Vigenère 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 either one individually? Consider two encryption…
user2085590
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How to decode Playfair when only a small part of key is available?

How to decode Playfair when only a small part of key is available? What is the plain text for this message? Can someone explain how to recover the plain text for this message? Is there a program that I can download and execute on my PC to test…
Julio Doebeli
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How large is the Playfair cipher keyspace?

In the Playfair cipher, is the key space 5 x 5 = 25 or 25 x 25 = 625? I'm trying to work out the size of the key space if each set of equivalent keys is counted as one key.
hperm
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Decoding the Playfair cipher with a crib

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.
Robert Sandu
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Recommended puzzles?

I am beginning my journey into Cryptography, having studied a theory-heavy master's degree module, and I have also read The Code Book by Simon Singh, among many other online resources. What puzzle books would the community recommend, just so I can…
securityauditor
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Question about the Playfair cipher

The task: The Playfair cipher with $I = J, X$ added into two same letters and the key keep distance. The plaintext: CORONAVIRUS SPREADS FAST The whitespaces in plaintext and key are to be discarded. not sure what they mean by I = J, X The…
Papps
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Can I use a Friedman test when decrypting a Playfair cipher?

I’d like to decrypt a Playfair ciphertext; however, I need to find the key word first. Is it possible to use the Friedman test here to find the length of the key word? My cipher has no J’s in it would this mean my Ni for J would be 0, or would I…
Lauren Hosking
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