6. Really random sources
  
  This  section  describes so called "real random sources". It is an extension
  to  the  library  mechanism  of  random source objects that uses the devices
  /dev/random  and /dev/urandom available on Linux systems (and maybe on other
  operating  systems) providing random numbers that are impossible to predict.
  The  idea  is  that  such  sources  of  random numbers are useful to produce
  unpredictable secret keys for cryptographic applications.
  
  
  6.1 The functions
  
  6.1-1 RandomSource
  
  > RandomSource( rdev ) _______________________________________________method
  Returns:  a real random source object or fail
  
  The  first  argument  r  must  be  the GAP filter IsRealRandomSource and the
  second  either the string random or the string urandom. A real random source
  object  is  created  that  draws  its random numbers from the kernel devices
  /dev/random   and  /dev/urandom  respectively.  Whereas  /dev/random  always
  provides random numbers of not guaranteed "quality", the device /dev/urandom
  measures its entropy and produces guaranteed unpredictable numbers. However,
  it might block until enough "random" events (like mouse movements) have been
  accumulated.