An 8-bit linear feedback shift register with connection polynomial C(X) = 1+aX +bX^2 +cX^3 +dX^4 +eX^5 + fX^6 +gX^7 +hX^8 is used to generate a pseudo-random binary sequence. This pseudo-random sequence is used as the enciphering key of a stream cipher. It is known that when the cipher is applied to the plaintext string [0,0,0,1,0,0,0,0,1,1,0,0,1,0,1,0,0,1,1,1,0,1,0,1,1,0,1,1,0,1] the corresponding ciphertext string is [0,1,0,0,0,1,1,0,0,0,0,0,0,0,1,0,1,1,1,0,0,1,1,1,0,1,0,0,1,1]. Determine the coefficients of the connection polynomial

  • $\begingroup$ How do I go about determining the key bits? $\endgroup$ – Pkr96 Mar 12 '18 at 9:03
  • $\begingroup$ I've obtained the key bits to be [0,1,0,1,0,1,1,0,1,1,0,0,1,0,0] $\endgroup$ – Pkr96 Mar 13 '18 at 13:57

Determine the key bits first.

Then write down the equations on $a, \ldots h$. Solve.


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