ClassicCrypto

Note that we must try m3 x n 6 x 4 x 5 setting up the

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Unformatted text preview: e key sequence. 3. If not, try m =3 and so on… Setting up the Equations to Attack LFSR Setting This is best shown with an example. Example: Suppose we have the key sequence (011010111100) m=2: Recurrence is x n + 2 = c 0 x n + c1x n +1 Which yields the system of equations: 1 = c 0 ⋅ 0 + c1 ⋅1 0 = c 0 ⋅1 + c1 ⋅1 ⇒ Solve to get : c 0 = 1, c1 = 1. Try this out. Note that We must try m=3! x n +6 ≠ x 4 + x 5 Setting up the Equations to Attack LFSR, pg 2 Setting m=3: The recurrence is: x n +3 = c 0 x n + c1x n +1 + c 2 x n + 2 The system of equations we get is: ⎛ 0 1 1 ⎞⎛ c 0 ⎞ ⎛ 0 ⎞ ⎟⎜ ⎟ ⎜ ⎟ ⎜ ⎜ 1 1 0 ⎟⎜ c1 ⎟ = ⎜ 1 ⎟ ⎜ 1 0 1 ⎟⎜ c ⎟ ⎜ 0 ⎟ ⎠...
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