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    SubjectRe: /dev/random in 2.4.6


    On Mon, 20 Aug 2001, Chris Friesen wrote:

    > Alex Bligh - linux-kernel wrote:
    >
    > > An alternative approach to all of this, perhaps, would be to use extremely
    > > finely grained timers (if they exist), in which case more bits of entropy
    > > could perhaps be derived per sample, and perhaps sample them on
    > > more operations. I don't know what the finest resolution timer we have
    > > is, but I'd have thought people would be happier using ANY existing
    > > mechanism (including network IRQs) if the timer resolution was (say)
    > > 1 nanosecond.
    >
    > Why don't we also switch to a cryptographically secure algorithm for
    > /dev/urandom? Then we could seed it with a value from /dev/random and we would
    > have a known number of cryptographically secure pseudorandom values. Once we
    > reach the end of the png cycle, we could re-seed it with another value from
    > /dev/random.
    >
    > Would this be a valid solution, or am I totally off my rocker?

    The latter, unless you only want to protect against lame attackers :-)

    Given the knowledge of the seed and the algorithm used, everything gets
    fully deterministic for an attacker -> enthropy _zero_.

    For example, let an attacker observe enough of your magic random data in
    order to guess the algorithm, and a whole prng cycle will only contain as
    many random bits as the number of bits of the seed value for this
    attacker.

    > Chris

    Gérard.


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