# OFB mode vs LFSR

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about OFB (Output Feedback) mode the authors say that:

The OFB mode produces a bit stream and it encrypts similarly to the LFSR(Linear-feedback shift register) method. The differences are that LFSR is faster, but OFB is more secure.

I don't understand why OFB operates as a LFSR. The author does not mention it. Can you explain to me ?

Presumably they mean that in both cases, the output has the form $$f(\mathit{iv}) \mathbin\| f(f(\mathit{iv})) \mathbin\| f(f(f(\mathit{iv}))) \mathbin\| \dotsb,$$ where $$f$$ is a secret function—the LFSR update function or a block cipher $$E_k$$ with secret key $$k$$.
• What does $iv$ represent ? – AleWolf Oct 17 '19 at 17:12
• And why $f$doesn't take also the plaintext ? – AleWolf Oct 17 '19 at 17:41