100218: BigInteger staticRandom field

[Joe Darcy]

Hello,

Catching up on email after the holidays...

On 01/05/2012 09:58 AM, Doug Lea wrote:
> On 01/05/12 01:02, Bill Pugh wrote:
>
>> So I think the right thing to do is to abandon the original patch, 
>> and instead
>> make the following changes:
>>
>>     * add the following method to BigInteger public boolean
>>       *isProbablePrime*(int certainty, Random end) , which allows 
>> primality
>>       testing with arbitrary Random objects. In many cases, using a 
>> well seeded
>>       normal Random object will work just fine, and this will give 
>> users the
>>       ability to provide their own Random objects
>>     * Document SecureRandom to note that all instances of 
>> SecureRandom depend on
>>       a common shared source of randomness, and thus it can be a 
>> concurrency
>>       bottlenck.
>>     * Document that BigInteger.*isProbablePrime*(int certainty) is a 
>> concurrency
>>       bottleneck.
>
> This all sounds perfect to me.
> Joe Darcy - do you have any thoughts?

Hmmm.  While the API changes appear fine at first, I'm a bit concerned 
about how to make isProbablePrime*(int certainty, Random end) suitably 
robust against possibly adversarial sources of randomness (all zeros, 
all ones, etc.)  The number-theoretic primarily tests used by the 
existing isProbablePrime(int) rely on a good source of random bits; I'd 
have to research what the weakest assumptions on the source of 
randomness are for the existing checks to still be valid.

I think informative (not normative) notes in the javadoc on the latter 
two points would be fine.

Cheers,

-Joe