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Re: [PATCH 4/6] Do not use HP_TIMING_NOW for random bits
On 13/02/2019 16:06, Wilco Dijkstra wrote:
> Hi Adhemerval,
>
>> Currently __gen_tempname still requires at least 48 bits to generate the random
>> number, so I think returning 64 bits is still preferable. I think we can add
>> a comment that the 32 upper bits will show less entropy, what I am not sure is if
>> we should add some shuffling to upper bits as well or just document the shuffling
>> in lower bits.
>
> It uses just over 35 bits (62^6). Limiting to 32 bits loses 3 bits which don't encode
> much entropy to start with (given they only change every 4 seconds). Shifting the
> random number before adding the pid would add sufficient extra random bits.
>
> Note for comparison, the generic code has far less entropy, just 20+2 bits from
> gettimeofday in every 4 second period. So you'd get collisions when creating
> many temporary files in a short time.
>
> Wilco
>
Right, I think we live with 32 bits. I will update the patch.