It seems to me that recording intermediate residues for
comparison during double checking is not going to save 
much time; although you'll save on average 50% of the 
doublechecking time for exponents that are mistested
(assuming even and uncorrelated distribution of the
point in checking that the error occurs), mistested
exponents are only a small fraction of the double 
checking work.. I forget the numbers being tossed around, 
but you'd only save 50% of (the error rate) of the 
checking time.

HOWEVER, there is a potential use for the intermediate
residues anyway... as larger and larger exponenets start
getting tested, and algorithms start having to be modified
to support the testing of those big exponents, we may
run into a situation where a widespread subset of 
machines with some obscure hardware bug test a range
of exponents wrongly... using intermediate residues during
double checking would halve the time that would
pass before the widespread error became obvious, and
would reduce the amount of wasted work performed.

-Ethan O'Connor
 [EMAIL PROTECTED]
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