I have a couple of related questions:
I read about an estimate, ascribed to Turing, of the entropy of English text to be between 0.6 and 1.3 bits per letter. The modern day corpus, including the huge and exponentially ever expanding volume of materials accessible via the Internet, is different from the one available a century back. Is there a revised estimate?
If one simply takes two books from one's small private library (that contains e.g. only very common novels) and arbitrarily select two starting points to combine with xor the letters, then the resulting pseudo-random sequence presumably could be argued to have a non-negligible risk of being attacked through brute-force by a knowledgeable opponent. But the actual choice of materials (including especially those via the Internet) to be combined is nowadays virtually unlimited. If one could thus appropriately choose a sufficiently large number of text sources to be combined, wouldn't the result be practically secure for crypto usages in view of the combinatorial explosion of the complexity that the attacker has to deal with? One could certainly also employ some more complex operations than xor and even a couple of different operations either simultaneously or in variations. Are some good schemes in this direction already being used in non-trivial practical applications?