24 lines
1.8 KiB
Text
24 lines
1.8 KiB
Text
;Description
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The [https://en.wikipedia.org/wiki/ADFGVX_cipher ADFGVX cipher] was a manually applied field cipher used by the German Army during World War I. It was broken in 1918 by the French cryptanalyst [https://en.wikipedia.org/wiki/Georges_Painvin Georges Painvin].
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The workings of the cipher are described in the Wikipedia article, linked to above, and so will not be repeated here.
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;Task
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Write routines, functions etc. in your language to:
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1. Encrypt ''suitable'' plaintext and decrypt the resulting cipher text using the ADFGVX cipher algorithm given a Polybius square (see 2. below) and a ''suitable'' key. For this purpose ''suitable'' means text consisting solely of ASCII upper case letters or digits.
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2. Create a 6 x 6 [https://en.wikipedia.org/wiki/Polybius_square Polybius square] using a random combination of the letters A to Z and the digits 0 to 9 and then display it.
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3. Given the number of letters (between 7 and 12 say) to use, create a key by selecting a ''suitable'' word at random from [http://wiki.puzzlers.org/pub/wordlists/unixdict.txt unixdict.txt] and then display it. The word selected should be such that none of its characters are repeated.
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Use these routines to create a Polybius square and a 9 letter key.
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These should then be used to encrypt the plaintext: '''ATTACKAT1200AM''' and decrypt the resulting cipher text. Display here the results of both operations.
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;Note
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As it's unclear from the Wikipedia article how to handle a final row with fewer elements than the number of characters in the key, either of the methods mentioned in [https://en.wikipedia.org/wiki/Transposition_cipher#Columnar_transposition Columnar transposition] may be used. In the case of the second method, it is also acceptable to fill any gaps after shuffling by moving elements to the left which makes decipherment harder.
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<br><br>
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