Random number generation

Décio Luiz Gazzoni Filho decio at decpp.net
Thu Nov 3 15:07:53 CET 2005

On Nov 3, 2005, at 11:52 AM, Torbjorn Granlund wrote:

> Décio Luiz Gazzoni Filho <decio at decpp.net> writes:
>   I know I shouldn't try to help, but I will anyway.
> Naughty you!
>   ..., or perhaps read your CPU's cycle counter ...
> I'd like to mildy warn against that particular seeding source.
> The cycle counter typically is reset when a process is initiated,
> and while it might yield slightly different values for subsequent
> runs, it will typically only give a handful different values.

Really? I never noticed that -- to me this just counted the number of  
cycles since the machine booted. You're talking about e.g. the RDTSC  
instruction in IA-32, right?

> The current time is a better entropy source, except that it is
> not useful for cryptographic purposes.

Typically I'd use something like the time with microsecond  
granularity and the cycle counter. A bit more entropy than just the  

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