|Cryptography: Computer science|
"... and easier to explain and use than other polyalphabetic ciphers."
I thought this was supposed to be a monoalphabetic or an extension thereof. If this is monoalphabetic then by the same reasoning Hill's cypher would be as well (?) Can anyone clear this up? --.schwrz (talk) 05:45, 5 May 2009 (UTC)
- It should not be described as a polyalphabetic cipher. My exposure to the field would lead me to describe both Playfair and Hill as "polygraphic", as it is a single substitution applied to polygrams (i.e. blocks of letters) rather than a family of monoalphabetic substitutions. I suppose in a theoretical sense, one might think of it as a monoalphabetic substitution in a special formal language with 600 (or 626, or 26^n for general n-Hill ciphers) "letters" in its "alphabet", but that would be a very specialized distinction that I have not seen in the literature and probably has very limited utility. I couldn't decide how to change the sentence to be correct but still capture the message the editor intended, so I removed it entirely as the whole sentence seemed largely subjective and unsourced.MatthewDaly (talk) 21:07, 22 May 2009 (UTC)
The Playfair is thus significantly harder to break since straight frequency analysis doesn't work with it.
Well, that's simply not the case. Analysis of single letters doesn't work with Playfair, but if you do frequency analysis of digraphs it works ... well, not "fine" exactly, but it's the way to get results. True, there are roughly 600 of them (in English) as opposed to 26, and the distribution is flatter, but as written the article suggests that cryptanalysts faced with Playfair sit around scratching their heads, which I imagine they generally don't. --Calieber 15:31, 7 Oct 2003 (UTC)
600* possible digraphs
There is currently an asterisk after the 600 in the number of possible digraphs. In <a href="http://en.wikipedia.org/w/index.php?title=Playfair_cipher&diff=prev&oldid=53704799">this edit</url> the "footnote" of *600 = was removed. It is not clear to me why a non-standard footnote was used in the first place, nor exactly what this notation was supposed to mean (the combinations of 25 letters?), nor why 25 is used instead of 26, nor why 25^2=625 does not equal 600.
- The asterisk doesn't make sense. The number 600 however can be explained as follows. Because one uses I=J there are only 25 distinct letters. Because one replaces one of the letters with an X when the same letter appears twice in a digraph, it is not possible that a double letter occurs in the ciphertext (at least if one also assumes that XX does not occur in the plaintext). This implies that only 25*24 = 600 digraphs in the ciphertext are possible. 184.108.40.206 (talk) 20:50, 27 February 2008 (UTC)
Too difficult to understand
The article loses me at the point "To encrypt a message, one would break the message into digraphs (groups of 2 letters) such that, for example, "HelloWorld" becomes "HE LL OW OR LD", and map them out on the key table. The two letters of the digraph look like the corners of a rectangle in the key table. Note the relative position of the corners of this rectangle. Then apply the following 4 rules, in order, to each pair of letters in the plaintext." What does "map them out on the key table" mean? Wikipedia articles should be accessible to a general reader and not be a communication from those in the know to others in the know. APW (talk) 13:06, 24 May 2009 (UTC)
Moved from article
I removed the following suggestion from 220.127.116.11 from the Example section:
- ("// just i think j letter should has been used somewhere , maybe together with another letter, usually it goes together with i, who knows please try to correct it" with regards mike18 unipi //")..
"It became known as the Playfair cipher after Lord Playfair, who heavily promoted its use, despite its invention by Wheatstone." Did Playfair have some kind of grudge against Wheatstone? 18.104.22.168 (talk) 13:56, 24 May 2016 (UTC)
- You're misinterpreting the sentence. It doesn't mean that "Playfair promoted its use despite its invention by Wheatstone" but that "Playfair's promotion of the cipher led to its being known by his name rather than that of its creator, Wheatstone". --Khajidha (talk) 00:14, 11 June 2017 (UTC)
I re-worded this part to "Wheatstone invented the cipher for secrecy in telegraphy, but it carries the name of his friend Lord Playfair, first Baron Playfair of St. Andrews, who promoted its use" Romerojp (talk) 16:58, 9 January 2018 (UTC)
Not called the Wheatstone cipher
Wadsworth invented a cipher that became known as the Wheatstone cipher. Source: Secret History: The Story of Cryptology by Craig P. Bauer, Pg 168 I added the "not to be confused with" and got rid of the line that said that the Playfair cipher was known as the Wheatstone cipher.