Secure CSPRNG's for cryptographic keys
LFSR as such isn't a CSPRNG. There are diverse CSPRNGs, see crypto textbooks, also A. Menezes et al., Handbook of Applied Cryptography (freely available online). I have a code for a CSPRNG based on RSA, see Ex. 5 in s13.zetaboards.com/Crypto/topic/7234475/1/