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In general, collisions in a hash function are a bad thing: if you have different $M_1$ and $M_2$ for which $hash(M_1)=hash(M_2)$, the situation will require special handling. In cryptography, hash functions can be seen as "summary" functions, that reduce a message of arbitrary length to messages of fixed length. Since the message space (all the possible ...


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By using the definition of $n$ bits of full entropy, NIST is abstracting away from the definition of a NRBG (or TRNG). They are basically trying to establish a minimum requirement for the quality of the random number generator, without going into the specifics on how this can be achieved. Basically this is NIST's way of saying: if we specify $n$ bits of full ...


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"Entropy" is more accurately defined, in cryptography, as "that which the attacker does not know". For instance, suppose that every day you take all rates at the closure of the New York stock exchange, and hash them with SHA-256. The resulting value is very unpredictable (otherwise you could become very rich), so, from a "physics" point of view, there is a ...


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First, take note of my answer to the question Estimating bits of entropy. A key phrase therein: You'll never be able to look at a bitstream without knowing the distribution and say "there are X bits of entropy here." The ent program doesn't know the distribution of the data it's looking at; instead it performs some statistical tests that any ...



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