page_title: Grille (cryptography)
section_title: A Third-Party Grille: the crossword puzzle
hierarchical_section_title: Grille (cryptography) / Unusual possibilities / A Third-Party Grille: the crossword puzzle
caption_attribution_description: Italiano: Un cruciverba apparso su un giornale inglese del 1941
context_page_description: In the history of cryptography, a grille cipher was a technique for encrypting a plaintext by writing it onto a sheet of paper through a pierced sheet. The earliest known description is due to the polymath Girolamo Cardano in 1550. His proposal was for a rectangular stencil allowing single letters, syllables, or words to be written, then later read, through its various apertures. The written fragments of the plaintext could be further disguised by filling the gaps between the fragments with anodyne words or letters. This variant is also an example of steganography, as are many of the grille ciphers.
context_section_description: The distribution of grilles, an example of the difficult problem of key exchange, can be eased by taking a readily-available third-party grid in the form of a newspaper crossword puzzle.  Although this is not strictly a grille cipher, it resembles the chessboard with the black squares shifted and it can be used in the Cardan manner. The message text can be written horizontally in the white squares and the ciphertext taken off vertically, or vice versa.
  CTATI ETTOL TTOEH RRHEI MUCKE SSEEL AUDUE RITSC VISCH NREHE LEERD DTOHS ESDNN LEWAC LEONT OIIEA RRSET  LLPDR EIVYT ELTTD TOXEA E4TMI GIUOD PTRT1 ENCNE ABYMO NOEET EBCAL LUZIU TLEPT SIFNT ONUYK YOOOO
  Again, following Sacco's observation, this method disrupts a fractionating cipher such as Seriated Playfair. 
  Crosswords are also a possible source of keywords.  A grid of the size illustrated has a word for each day of the month, the squares being numbered.
caption: A crossword grid taken from a 1941 newspaper
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