Messages in this thread | | | From | (David Wagner) | Subject | Re: [RFC][PATCH] Make cryptoapi non-optional? | Date | Sat, 16 Aug 2003 06:27:44 +0000 (UTC) |
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Val Henson wrote: >If entropy(x) == entropy(y), then: > >entropy(x) >= entropy(x xor y) >entropy(y) >= entropy(x xor y)
No, that's still wrong. Please see my earlier email with a counterexample. That counterexample disproves not only the earlier claim, but also this more recent revised claim.
Let x and y be two 80-bit strings. Assume that x is either 0 or 1 (equal probability for both possibilities). Assume y is either 0 or 2 (equal probability for both possibilities), and is independent of x. Then entropy(x) = 1 bit entropy(y) = 1 bit entropy(x xor y) = 2 bits
Again, I believe there is little basis to distinguish between taking the first half of SHA vs. xor-ing both the halves of SHA. One can come up with scenarios where one or the other is better, but there is little basis for believing that one of those scenarios is especially more likely than the other.
In short, we're arguing about how many angels can fit on a pinhead. There are far better things to be worrying about. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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