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 requiring high quality random numbers for  cryptographic  pur-
       poses.

       The  generator  device  produces  random  numbers from data and devices available 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 suffi-
       cient amount of entropy has been collected. If there is no entropy to produce the requested number of bytes, /dev/random blocks until  more
       entropy	can  be  obtained.  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 entropy available. It does not block on a read request due to lack of
       entropy. 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 difficult to predict by other users may contribute randomness to the generator state and help improve the quality of future  gener-
       ated random numbers.

       /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 registered with the kernel-level	cryptographic  framework  by  dis-
       abling 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/urandom  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 CryptoRand implementation.

SunOS 5.11							    1 Sep 2008								random(7D)