2.9. Given is a stream cipher which uses a single LFSR as key stream generator. The LFSR has a degree of 256. 1. How many plaintext/ciphertext bit pairs are needed to launch a successful attack? 2. Describe all steps of the attack in detail and develop the formulae that need to be solved. 3. What is the key in this system? Why doesn’t it make sense to use the initial contents of the LFSR as the key or as part of the key

Write a new lc-3 trap subroutine (i.e. a subroutine that will be invoked via the trap instruction) that will receive a numeric digit entered at the keyboard (i.e. an ascii character), echo it to the screen, and return in r0 the corresponding numeric value: so if the user types the digit '7', the character '7' will appear on the screen, but the value returned in r0 will be b0000 0000 0000 0111 (#7) you may not use any trap calls in your code - you must implement the "polling" code that interrogates the keyboard status and data registers. ; getnum_tsr ; a subroutine for obtaining a numeric value ; given ascii numeric digit input to keyboard. ; the numeric digit is echoed to the console (e.g. '7' = b0000 0000 0011 0111), ; but the value returned in r0 is the actual numeric value ; corresponding to the digit (e.g. b0000 0000 0000 0111 =