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How do I know where my XOR gates go? What does the F2 stand for here? Also the next task is to generate the sequence (with initialisation vector $s_0 = 1, s_1 = s_2 = s_3 = 0$) until it becomes periodic which I'm fairly certain I can do however even a few rows would be helpful as I won't have any other answers to these (not official homework assignment).

enter image description here

edit: my guess is now the xor port goes on top $s_3$, because of unknown reason. How will this affect the sequence? When generating it I shift and do I xor the last $s_3$ and first $s_1$ in order to receive the new bit?

edit2: my solution with sequence enter image description here

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  • $\begingroup$ I have tried looking at this among others, but I am still unsure. My guess is that si-1 = s0 and si-4 = s3, but I am still unsure how to draw it and why it becomes as such? $\endgroup$
    – cryptoquestion
    Oct 18, 2021 at 13:51
  • $\begingroup$ Also checked that before. This is in different form. I believe I can draw from polynomial form but not from this. Also what F2 stands for is still unknown to me and it isn't mentioned anywhere in your replies. $\endgroup$
    – cryptoquestion
    Oct 18, 2021 at 13:56
  • $\begingroup$ The sequence definition already gives you the hint. the next feedback is the sum( xor?) of previous and 4th previous? $\endgroup$
    – kelalaka
    Oct 18, 2021 at 13:59
  • $\begingroup$ So si-4 = s3 and the xor goes on top of s3? $\endgroup$
    – cryptoquestion
    Oct 18, 2021 at 14:00
  • $\begingroup$ Run you solution? $\endgroup$
    – kelalaka
    Oct 18, 2021 at 14:06

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