Hill Cipher

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Hill Cipher
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Hill Cipher

• Takes two or three or more letter combinations to
  the same size combinations, e.g. the ? rqv
• Uses simple linear equations
• An example of a block cipher encrypting a block
  of text at a time
• Numbered alphabet a 0, b 1, c 3, etc.(in
  CAP, use ASCII code)

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Example
C1 9p1 18p2 10p3 (mod 26) C2 16p1
21p2 1p3 (mod 26) C3 5p1 12p2 23p3
(mod 26)
C1 9 18 10 p1 C2 16 21 1 p2
(mod 26) C3 5 12 23 p3
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I cant do it 8 2 0 13 19 3 14 8 19
? EOM TMY SVJ
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Hill key is matrix

• k11 k12 k13
• k21 k22 k23
• k31 k32 k33
• Generalize to any size, larger blocks
• Matrix must be invertible

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Hill -- bad matrix
bcd ? XJR hfa ? XJR