On Fri, Sep 28, 2012 at 5:14 AM, DG <dangets@xxxxxxxxx> wrote: > On Thu, Sep 27, 2012 at 5:09 PM, Mihir Pandya <mihir.m.pandya@xxxxxxxxx> wrote: >> Hey guys, >> >> I'm interested to know why generating cryptographically secure random >> numbers takes so long, particularly in my case. I have two Java classes that >> are generating a million random numbers. One is generating random numbers >> regularly while the other is using SecureRandom to generate the numbers. The >> SecureRandom method is taking almost double the time and I realised that >> it's because the method reads from /dev/urandom (not sure which) and obtains >> its random numbers from the entropy pool there. >> >> I wanted to know where I can read about the exact mechanism used to generate >> the cryptographically secure random numbers through SecureRandom and if >> there is any way to make it faster. >> >> -- >> Mihir Pandya >> > > From 'man urandom' > > When read, the /dev/random device will only return random bytes > within the estimated number of bits of noise in the entropy pool. > /dev/random should be suitable for uses > that need very high quality randomness such as one-time pad or > key generation. When the entropy pool is empty, reads from > /dev/random will block until additional envi‐ > ronmental noise is gathered. > > A read from the /dev/urandom device will not block waiting for > more entropy. As a result, if there is not sufficient entropy in the > entropy pool, the returned values are > theoretically vulnerable to a cryptographic attack on the > algorithms used by the driver. Knowledge of how to do this is not > available in the current unclassified litera‐ > ture, but it is theoretically possible that such an attack may > exist. If this is a concern in your application, use /dev/random > instead. > > Now I *believe* the entropy pool is filled by IO events - network > activity, disk access, keyboard pounding, etc... I'm sure there is > more documentation somewhere online as to the specifics. > > Hope that helps, > Danny G > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@xxxxxxxxxxxxxxxxx > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies The entropy pool is filled by IO events as mentioned previously. The random data is taken from various devices connected to the system. /dev/urandom uses the device's randomness. So urandom will take more time than /dev/random. Hope this helps, Prasanna Kumar T S M _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
