Re: new coreutil? shuffle - randomize file contents

[Paul Eggert]

Frederik Eaton <address@hidden> writes:

> On Thu, Jun 02, 2005 at 11:31:26PM -0700, Paul Eggert wrote:
>> Suppose you're randomizing an input file of 10 million lines.  And
>> suppose you want to approximate a "truly random" key by using a
>> 128-bit random key for each input line.
>> 
>> Then you'll need about 1.3 billion random bits. 
>
> No! Please see my penultimate email. This is what random seeds are
> for.

Sorry, I didn't follow your penultimate email.  But my admittedly
limited understanding of it suggested that you're thinking mostly of
collaborative applications (e.g., shuffling a CD play list) where I am
thinking also of adversarial applications (e.g., shuffling a card deck
for high-stakes poker).  To a first approximation, a pseudorandom
generator is fine for the first application, but questionable for the
second one.

As a practical matter I'm sure the 1.3 billion random bits is overkill
for sorting 10 million records.  But it's not at all clear to me how
many bits are adequate for all real-world applications.  Apparently
even the experts in this field don't always agree on that point; see,
e.g. <http://www.maa.org/mathland/mathtrek_10_16_00.html>.