rnd(9) - NetBSD Manual Pages

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RND(9)                       NetBSD Kernel Manual                       RND(9)


NAME

     RND, rnd_attach_source, rnd_detach_source, rnd_add_data, rnd_add_uint32 -
     functions to make a device available for entropy collection


SYNOPSIS

     #include <sys/rnd.h>

     void
     rnd_attach_source(rndsource_element_t *rnd_source, char *devname,
             u_int32_t source_type, u_int32_t flags);

     void
     rnd_detach_source(rndsource_element_t *rnd_source);

     void
     rnd_add_data(rndsource_element_t *rnd_source, void *data, u_int32_t len,
             u_int32_t entropy);

     void
     rnd_add_uint32(rndsource_element_t *rnd_source, u_int32_t datum);



DESCRIPTION

     These RND functions make a device available for entropy collection for
     /dev/random.

     Ideally the first argument rnd_source of these functions gets included in
     the devices' entity struct, but any means to permanently (static) attach
     one such argument to one incarnation of the device is ok.  Do not share
     rnd_source structures between two devices.



     rnd_attach_source(rndsource_element_t *rnd_source, char *devname,
              u_int32_t source_type, u_int32_t flags)

              This function announces the availability of a device for entropy
              collection.  It must be called before the source struct pointed
              to by rnd_source is used in any of the following functions.

              devname is the name of the device.  It is used to print a mes-
              sage (if the kernel is compiled with ``options RND_VERBOSE'')
              and also for status information printed with rndctl(8).

              source_type is RND_TYPE_NET for network devices, RND_TYPE_DISK
              for physical disks, RND_TYPE_TAPE for a tape drive, and
              RND_TYPE_TTY for a tty.  RND_TYPE_UNKNOWN is not to be used as a
              type.  It is used internally to the rnd system.

              flags are the logical OR of RND_FLAGS_NO_COLLECT (don't collect
              or estimate) RND_FLAGS_NO_ESTIMATE (don't estimate) to control
              the default setting for collection and estimation.  Note that
              devices of type RND_TYPE_NET default to RND_FLAGS_NO_ESTIMATE.


     rnd_detach_source(rndsource_element_t *rnd_source)
              This function disconnects the device from entropy collection.


     rnd_add_uint32(rndsource_element_t *rnd_source, u_int32_t datum)
              This function adds the value of datum to the entropy pool.  No
              entropy is assumed to be collected from this value, it merely
              helps stir the entropy pool.  All entropy is gathered from jit-
              ter between the timing of events.

              Note that using a constant for datum does not weaken security,
              but it does not help.  Try to use something that can change,
              such as an interrupt status register which might have a bit set
              for receive ready or transmit ready, or other device status in-
              formation.

              To allow the system to gather the timing information accurately,
              this call should be placed within the actual hardware interrupt
              service routine.  Care must be taken to ensure that the inter-
              rupt was actually serviced by the interrupt handler, since on
              some systems interrupts can be shared.

              This function loses nearly all usefulness if it is called from a
              scheduled software interrupt.  If that is the only way to add
              the device as an entropy source, don't.

              If it is desired to mix in the datum and to add in a timestamp,
              but not to actually estimate entropy from a source of random-
              ness, passing NULL for rnd_source is permitted, and the device
              does not need to be attached.


     rnd_add_data(rndsource_element_t *rnd_source, void *data, u_int32_t len,
              u_int32_t entropy)
              adds (hopefully) random data to the entropy pool.  len is the
              number of bytes in data and entropy is an "entropy quality" mea-
              surement.  If every bit of data is known to be random, entropy
              is the number of bits in data.

              Timing information is also used to add entropy into the system,
              using inter-event timings.

              If it is desired to mix in the data and to add in a timestamp,
              but not to actually estimate entropy from a source of random-
              ness, passing NULL for rnd_source is permitted, and the device
              does not need to be attached.


HISTORY

     The random device was introduced in NetBSD 1.3.


AUTHOR

     This implementation was written by Michael Graff <explorer@flame.org> us-
     ing ideas and algorithms gathered from many sources, including the driver
     written by Ted Ts'o.


BUGS

     The only good sources of randomness are quantum mechanical, and most com-
     puters avidly avoid having true sources of randomness included.  Don't
     expect to surpass "pretty good".


FILES

     These functions are declared in src/sys/sys/rnd.h and defined in
     src/sys/dev/rnd.c.


SEE ALSO

     rndctl(8), rnd(4)

NetBSD 1.4                     October 20, 1997                              2