G'Day Bodo,
A descent solution here is just to update to the documentation,
since the man page says it generates a num bit prime but in certain
cases, it does not :-) (num < 15?)
Some mention to the randomness of the prime at low num might
also be worthy (if indeed there is some issue around num=15 to 20)
(yes, my code requested safe primes, but the same problem happens if you
don't ask for safe primes!)
thanks,
Cameron
Bodo Moeller via RT wrote:
>On Fri, Jan 31, 2003 at 08:12:41AM +0100, Cameron Gregory via RT wrote:
>
>
>
>>for num < 15 .. always get the same result.. and it's larger than
>>expected...
>>
>>
>
>Reason: The internal OpenSSL function 'probable_prime' (in
>crypto/bn/bn_prime.c) uses a built-in list of small primes for sieving
>out candidate random numbers that cannot be prime. But the test does
>not correctly the handle the special case that the candidate *is* one
>of small primes in the list -- they will be falsely rejected.
>
>Generally the design cannot handle generation of *short* primes well,
>the desired bit-length is actually treated as a lower limit: if a
>candidate is rejected, some delta will be added to obtain a new
>candidate. For very short numbers, this addition is likely to
>increase the bit-length of the candidate.
>
>(Your code requests safe primes, so it is in general impossible to
>exactly meet the requested bit-length -- there is a two-bit prime,
>namely 3, but it is not a safe prime.)
>
>
>
>
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