1. Hill Cipher

2. 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)

3. Example C1 = 9*p1 + 18*p2 + 10*p3 (mod 26)
C2 = p2 (mod 26)
C p3

4.  EOM TMY SVJ I can’t do it 8 2 0 13 19 3 14 8 19 4 9 18 10 8
14 = (mod 26)
12 = (mod 26)
21 = (mod 26)

5. Hill – key is matrix k11 k12 k13 k21 k22 k23 k31 k32 k33
Generalize to any size, larger blocks
Matrix must be invertible

6. Hill -- bad matrix bcd  XJR hfa  XJR 23 9 18 10 1
9 = (mod 26)
9 = (mod 26)