why does RAND_add() take "randomness" as a "double"?
jb-openssl at wisemo.com
Wed May 22 23:10:00 UTC 2019
On 22/05/2019 19:32, Dennis Clarke wrote:
>> Good options inspired by other cryptographic libraries include:
>> - Number of bits of entropy passed in call (For example, a
>> perfectly balanced coin flipper could provide the 4 byte
>> values "head" or "tail" with an entropy of 1 bit).
> Let's drop the coin flipper. It was an off hand remark and by now we
> all know there ain't no such thing as a good coin flip for rng.
> See Professor Persi Diaconis at Stanford for that :
> Bell's theorem and kolmogorov aside get a radiation decay source as
> that is really the *only* real rng that we know of.
> Or that I know of. http://www.fourmilab.ch/hotbits/hardware.html
The coin flipper, even if theoretically problematic, is the standard
statistical example used to describe a 1-bit-at-a-time hardware RNG.
It includes a nice conceptual model to discuss hardware bias (using
Shannon's entropy formula etc.). Actual 1-bit sources include the
classic semiconductor shot noise fed to a comparator and some primitive
implementations of radioactive RNGs.
Also, radioactive sources are an unacceptable danger in many of the
embedded and portable applications most likely to lack floating point
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