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random(7D)			     Devices			      random(7D)

NAME
     random, urandom - Strong random number generator device

SYNOPSIS
     /dev/random

     /dev/urandom

DESCRIPTION
     The  /dev/random and /dev/urandom files are special files that are a source
     for random bytes generated by the kernel random  number  generator  device.
     The  /dev/random  and  /dev/urandom files are suitable for applications re-
     quiring high quality random numbers for cryptographic purposes.

     The generator device produces random numbers from data and  devices  avail-
     able  to  the kernel and estimates  the amount of randomness (or "entropy")
     collected from these sources. The entropy level determines  the  amount  of
     high quality random numbers that are produced at a given time.

     Applications  retrieve random bytes by reading /dev/random or /dev/urandom.
     The /dev/random interface returns random bytes only when sufficient  amount
     of  entropy  has  been collected. If there is no entropy to produce the re-
     quested number of bytes, /dev/random blocks until more entropy can  be  ob-
     tained. Non-blocking I/O mode can be used to disable the blocking behavior.
     The  /dev/random  interface  also supports poll(2). Note that using poll(2)
     will not increase the speed at which random numbers can be read.

     Bytes retrieved from /dev/random provide the highest quality random numbers
     produced by the generator, and can be used to generate long term  keys  and
     other high value keying material.

     The   /dev/urandom  interface returns bytes regardless of the amount of en-
     tropy available. It does not block on a read request due  to  lack  of  en-
     tropy.  While  bytes  produced  by  the /dev/urandom interface are of lower
     quality than bytes produced by /dev/random, they are  nonetheless	suitable
     for  less	demanding and shorter term cryptographic uses such as short term
     session keys, paddings, and challenge strings.

     Data can be written to /dev/random and /dev/urandom. Data written to either
     special file is added to the generator's internal state. Data that is  dif-
     ficult to predict by other users may contribute randomness to the generator
     state and help improve the quality of future generated random numbers.

     By  default, write access is restricted to the super-user. An administrator
     may change the default read/write restriction by changing	the  permissions
     on the appropriate special files.

     /dev/random  collects  entropy  from providers that are registered with the
     kernel-level cryptographic framework and implement random number generation
     routines. The cryptoadm(1M) utility allows an  administrator  to  configure
     which providers will be used with /dev/random.

ERRORS
     EAGAIN	     O_NDELAY  or  O_NONBLOCK  was  set  and no random bytes are
		     available for reading from /dev/random.

     EINTR	     A	signal	was  caught  while  reading  and  no  data   was
		     transferred.

     ENOXIO	     open(2)  request  failed  on /dev/random because no entropy
		     provider is available.

FILES
     /dev/random

     /dev/urandom

ATTRIBUTES
     See attributes(5) for descriptions of the following attributes:

     +------------------------------+-----------------------------+
     |	     ATTRIBUTE TYPE	    |	   ATTRIBUTE VALUE	  |
     +------------------------------+-----------------------------+
     | Availability		    | SUNWcsr			  |
     +------------------------------+-----------------------------+
     | Interface Stability	    |Evolving			  |
     +------------------------------+-----------------------------+

SEE ALSO
     cryptoadm(1M), open(2), poll(2), attributes(5)

NOTES
     /dev/random can be configured to use only the hardware-based providers reg-
     istered with the kernel-level  cryptographic  framework  by  disabling  the
     software-based provider using cryptoadm(1M). You can also use cryptoadm(1M)
     to obtain the name of the software-based provider.

     Because  no entropy is available, disabling all randomness providers causes
     read(2) and poll(2) on /dev/random to block indefinitely and results  in  a
     warning  message being logged and displayed on the system console. However,
     read(2) and poll(2) on /dev/random continue to work in this case.

     An implementation of the /dev/random and /dev/urandom  kernel-based  random
     number generator first appeared in Linux 1.3.30.

     A	/dev/random  interface	for  Solaris first appeared as part of the Cryp-
     toRand implementation.

SunOS 5.10			  21 June 2004			      random(7D)
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