random(7)

NAME
     random, urandom - sources of random numbers

DESCRIPTION
     The special files /dev/random and /dev/urandom provide an access to the
     kernel implementation of a Pseudo Random Number Generator (PRNG).

     They are accessed like any ordinary file.
     Read calls return a buffer filled up with random bits.
     Write calls are reserved to the superuser. They perturb the state of the
     kernel PRNG.  A subsequent close call forces a reseed of the PRNG.

     The kernel PRNG implements the Yarrow algorithm.
     As opposed to some implementations of the random devices, where the
     characteristics of /dev/random and /dev/urandom differ, the Yarrow
     algorithm allows a similar behaviour of both special files.
     On IRIX, /dev/random and /dev/urandom do behave identically.
     /dev/urandom is shipped for compatibility purposes.

FILES
     /dev/random
     /dev/urandom

NOTES
     The design of the Yarrow algorithm was published in this document:

          "Yarrow-160: Notes on the design and analysis of the
           yarrow cryptographic pseudo random number generator"
          KESLEY, J. SCHNEIDER, B., and FERGUSON, N.
          6th Annual Workshop on Selected Areas in Cryptography,
          Springer-Verlag, 1999

     At the date this man page is written, the original information about the
     Yarrow algorithm can be retrieved at this URL:
          http://www.counterpane.com/yarrow.html


HISTORY
     The devices /dev/random and /dev/urandom were added in 6.5.19.