What is the degree of a LFSR?

a) What is the maximum length of random output bits you can obtain with an LFSR with a degree of 9?

b) What does the attacker need to obtain in order to recreate the random bit generation of an LFSR?

c) How many plain-text/cipher-text bit pairs are needed to launch a successful attack on the LFSR mentioned in (a)?

d) What is the mathematical technique an attacker can use to carry out the attack mentioned in (c)?

e) Explain how A5/1 (GSM Cipher) prevents the above attack?

f) Briefly describe what constitute the key of a stream cipher? Why is initial vector(IV) not part of the key?