Re: Any pitfals of my stream cipher?

Captain Data wrote:
[snip]
I think that so long as the hash and the PRNG are not rubbish, then the
only way is to brute force the master key, and that a malicous guy
"Martin" cannot get anything out of sending bogus transmissions to Bob,
or by recording or altering the transmissions between Alice and Bob.

Question: If the master key can't be brute forced (with respect to
opponent's capability), why don't you simply use that as such?

M. K. Shen
.