Messages in this thread | | | Date | Tue, 30 Oct 2012 20:56:56 +0000 | From | Pádraig Brady <> | Subject | Re: urandom is too slow |
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On 10/30/2012 06:54 PM, Theodore Ts'o wrote: > On Tue, Oct 30, 2012 at 04:55:22PM +0200, Lasse Kärkkäinen wrote: >> Apparently there has been little or no development on urandom even >> though the device is in widespread use for disk shredding and such >> use. The device emits data at rather slow rate of 19 MB/s even on >> modern hardware where other software-based PRNGs could do far >> better. An even better option seems to be utilizing AES for >> encrypting zeroes, using a random key, allowing for rates up to 500 >> MB/s with hardware that has AES-NI instructions. >> >> Why is urandom so slow and why isn't AES hardware acceleration utilized? > > If you can use a software-based PRNG, you should use one in userspace. > The intended use of urandom is for cryptographic purposes (i.e., > generating random session keys, long-term public keys, etc.). If you > just want to wipe a disk, you shouldn't be using /dev/urandom for that > purpose.
For the record, shred uses a user space PRNG for speed for the last 3 years or so, rather than using /dev/urandom: http://git.sv.gnu.org/gitweb/?p=coreutils.git;a=commit;h=af5723c7
$ shred-old -v -n3 t shred-old: t: pass 1/3 (random)... shred-old: t: pass 1/3 (random)...8.3MiB/1000MiB 0% shred-old: t: pass 1/3 (random)...17MiB/1000MiB 1% shred-old: t: pass 1/3 (random)...32MiB/1000MiB 3% ...
$ time shred-new -v t shred-new: t: pass 1/3 (random)... shred-new: t: pass 1/3 (random)...116MiB/1000MiB 11% shred-new: t: pass 1/3 (random)...216MiB/1000MiB 21% shred-new: t: pass 1/3 (random)...340MiB/1000MiB 34% ...
cheers, Pádraig. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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