# Dan Boneh's Cryptography lecture - problem with 802.11b

I am going through Dan Boneh's Cyprography lectures on Coursera.

In Lecture 6 https://class.coursera.org/crypto-010/lecture/6

At 7:30 minutes, he discusses the problems with 802.11b design. I understand his critique. However, he then moves on to what would be better design at 12:55 minutes.

He says that they could use a PRG to generate a very long key from the key and then use segments of the PRG(K) to encrypt each frame.

Even if you generate a very long PRG(K), considering the amount of traffic exchanged, wouldn't key still get repeated every few hours or so - i.e. you come to the end of the PRG(K), you have to start reusing first segment of PRG(K) again - which will lead to the key reuse problem. So what am I missing here?

• That's a great course. Just took it. Enjoy! – Linuxios Jun 25 '15 at 15:46

• Note that the problem with WEP was that they reused the input (i.e. the seed) to the PRG, it was not because the output cycled around! - yes I did understand that. However, I didn't know that PRGs didn't cycle. Thank you – user93353 Jun 25 '15 at 12:46