Re: Tempfile vulnerabilities

From: Werner Koch (wkat_private)
Date: Wed Feb 02 2000 - 14:01:10 PST

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    On Wed, 2 Feb 2000, Theo de Raadt wrote:
    
    > I suppose then that anyone who attacks a machine which relies on
    > /dev/random -- a world readable device -- should do the following:
    >
    > 	cat /dev/random > /dev/null &
    
    Yep.
    
    > Crypto software which uses those devices should be doing some kind of
    > checking to make sure that they are getting at least good entropy.  I
    
    The good thing is that /dev/random blocks until there is enough entropy
    available.  /dev/urandom does not block but continues to return random
    bytes by using a PRNG.
    
    > suppose I could even argue that the random devices should make it easy
    > for customer software to determine that entropy is low.
    
    There is also an ioctl() to query some statistics.  OpenBSD has some
    more kinds of random devices but I don't know much about them.
    
    I have not checked the latest Linux kernels but rumors are that this
    device has been enhanced.
    
    
    --
    Werner Koch at guug.de           www.gnupg.org           keyid 621CC013
    



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