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    SubjectRe: /dev/random entropy calculations broken?
    On Mon, Oct 01, 2001 at 10:55:26PM +0100, Alex Bligh - linux-kernel wrote:
    > However, unless one is worried about someone having broken
    > SHA-1 OR one is worried about annoying blocking behavour
    > on read(), I'm not convinced the entropy calculation is
    > doing anything useful anyway.

    I think the /dev/random /dev/urandom solution is perfect
    from this point of view. Using /dev/random you can get
    random number that are secure _even_ if tomorrow SHA1 will
    be broken at the cost of a very slow generation.
    Or you may trust SHA1 (or some other crypto primitive) to
    avoid to collect too much entropy to generate the output.
    Probably real world applications should use
    /dev/urandom, assuming it's properly designed, i.e. the
    internal state is changed once there is enough entropy
    to create a new unguessable key, the entropy isn't
    overstimated, and so on.

    BTW I agree, instead to create a key being paranoid about
    the SHA1 security it's better to double check if the
    entropy source is ok. For example the linux PRNG used
    to collect a lot of entropy bits from the keyboard
    auto-repeat aaaaaaaaaaaaaa ...
    It's useless to try to collect enough entropy (and maybe
    overstimating it) to produce an output secure against
    SHA1 possible weakness (i.e. totally generated with
    entropy bits). It's probably better a more conservative
    approach in the entropy collection and to use a belived secure
    crypto primitive to produce the PRNG output.

    After all, unless you are using a one-time pad probably
    the key generated with /dev/random will be used with
    the crypto algorithms you refused to trust.

    Salvatore Sanfilippo <>
    finger for PGP key
    28 52 F5 4A 49 65 34 29 - 1D 1B F6 DA 24 C7 12 BF
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