Stream cipher -- Are all random bit generators suitable for stream cipher?

Question

I learned the stream cipher using LFSR in the book. I wonder whether all random bit generators (i.e. BBS, Rabin generator) are suitable for stream cipher. I search using keywords "stream cipher" and "BBS", and there are few results.

Answer 1

The requirements for cryptographically secure pseudo random number generator and those for a stream cipher are essentially the same. Obvious not all PRNG are secure, LFSR and mersenne-twister to name a few aren't suitable for any cryptographic task.

In some cases a PRNG will be not practical for use as a cipher. If you look at it in the pure form of a seed generating a stream of random bits than we are OK, random bits are random and knowing some won't help me know the others. But if you look at the full system, PRNGs require some entropy collection and this can make it unpractical when you want to make it a keyed cipher, some PRNGs may for instance have a huge seed which you will not want to use as a key.