Polygraphic Substitution Ciphers

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A list of Polygraphic Substitution ciphers

• Four-Square Cipher

  An algorithm invented by Felix Delastelle, published in 1902

• Hill Cipher

  An algorithm based on matrix theory. Very good at diffusion.

• Playfair Cipher

  The technique encrypts pairs of letters (digraphs), instead of single letters as in the simple substitution cipher. The Playfair cipher is thus significantly harder to break since the frequency analysis used for simple substitution ciphers does not work with it.