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SubjectRe: /dev/urandom uses uninit bytes, leaks user data
Theodore Tso wrote:
> On Tue, Dec 18, 2007 at 01:43:28PM +1030, David Newall wrote:
>> On a server, keyboard and mouse are rarely used. As you've described it,
>> that leaves only the disk, and during the boot process, disk accesses and
>> timing are somewhat predictable. Whether this is sufficient to break the
>> RNG is (clearly) a matter of debate.
> In normal operaiton, entropy is accumlated on the system, extracted
> via /dev/urandom at shutdown, and then loaded back into the system
> when it boots up.

Thus, the entropy saved at shutdown can be known at boot-time. (You can
examine the saved entropy on disk.)

> If you have a server, the best thing you can do is use a hardware
> random number generator, if it exists. Fortunately a number of
> hardware platforms, such as IBM blades and Thinkpads, come with TPM
> modules that include hardware RNG's. That's ultimately the best way
> to solve these issues.

Just how random are they? Do they turn out to be quite predictable if
you're IBM?

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