On Mar 22, 2006, at 2:05 PM, Perry E. Metzger wrote:
Victor Duchovni <[EMAIL PROTECTED]> writes:
Actually calculating the entropy for real-world functions and
generators
may be intractable...
It is, in fact, generally intractable.
1) Kolmogorov-Chaitin entropy is just plain intractable -- finding the
smallest possible Turing machine to generate a sequence is not
computable.
2) Shannon entropy requires a precise knowledge of the probability of
all symbols, and in any real world situation that, too, is
impossible.
I'm not a cryptographer nor a mathematician, so I stand duly
corrected/chastised ;-)
So, if you folks care to educate me, I have several questions related
to entropy and information security (apologies to any physicists):
* How do you measure entropy? I was under the (false) impression that
Shannon gave a formula that measured the entropy of a message (or
information stream).
* Can you measure the entropy of a random oracle? Or is that what
both Victor and Perry are saying is intractable?
* Are there "units of entropy"?
* What is the relationship between randomness and entropy?
* (Apologies to the original poster) When the original poster
requested "passphrases with more than 160 bits of entropy", what was
he requesting?
* Does processing an 8 character password with a process similar to
PKCS#5 increase the entropy of the password?
* Can you add or increase entropy?
Thanks in advance,
Aram Perez
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