Re: [patch #6797] shred option to use internal RNG

[Pádraig Brady]

James Youngman wrote:
> Follow-up Comment #5, patch #6797 (project coreutils):
> 
> IMO both /dev/urandom and /dev/random should be used as sources of data for
> seeding PRNGs, as opposed to being used as sources of random data directly.  
> My rationale for this is that even using /dev/urandom for large quantities of
> data will exhaust the system's entropy pool.  

Well that what I said previously though in an unclear manner,
though I've changed my opinion a little.

I now think the "random" data doesn't have to that random,
just random enough to make recovery of existing disk data difficult.
Therefore using the internal PRNG which is currently seeded with
getpid() & time() etc. is fine IMHO (and much faster as we've seen).
We already have the --random-source option, so
people can use that if they want an external "random" source.

So in summary I would do:

1. by default always use internal PRNG seeded with getpid()
2. if --random-source specified read all random data from there

Note 2 will allow one to specify /dev/zero if desired.
We could seed our PRNG with /dev/urandom if available, but
that complication is not necessary I think for this problem.

cheers,
Pádraig.