NIST has updated their guidelines in appendix D of SP 800-56B rev2 (draft)
providing a formula for the number of security bits it terms of the length
of the RSA key.
This is an implementation of this formula using fixed point arithmetic.
For integers 1 .. 100,000 it rounds down to the next smaller 8 bit strength
270 times. It never errs to the high side. None of the rounded values occur
near any of the commonly selected lengths.
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7352)
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