[Cryptography] GHCQ Penetration of Belgacom
John Levine
johnl at iecc.com
Wed Dec 24 01:32:08 EST 2014
>I still remain astonished, that, since Babbage/Lovelace/Turing/etc, that
>many alleged programmers still do not know that 0.0 != 0.
To pile on a little, on every reasonably modern* architecture I know,
0.0 == 0, both semantically and the bit representation.
On the other hand, floating point numbers are an approximation to
reals, and due to accumulated quantization and rounding errors, a
calculation for which the real result would be zero will often produce
something else in floating point. It's been about 40 years since I've
had a numerical analysis course, but I recall that a lot of it was
about estimating error bounds so I could decide how different from
zero an answer could be and still be close enough to be semantic zero
for the problem under discussion.
It seems to me there are a lot of places in crypto that have similar
issues, the code we have is only an approximation to the Platonic
ideal, e.g., a Platonic CA would reliably check that alleged identity
exactly equals the real identity, but actual CAs tell us that alleged
identity equals real identity +/- 0.0004715 and we don't have a
very good understanding of how to deal with that.
R's,
John
* - no older than the PDP-6 or IBM S/360, which were designed 50 years ago
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