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, uint32_t source_type, uint32_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 message (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,
RND_TYPE_TTY for a tty, and
RND_TYPE_RNG for a random number generator.
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_FLAG_NO_COLLECT (don't collect or estimate)
RND_FLAG_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_FLAG_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, uint32_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 jitter 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 information.
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 interrupt 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 randomness, 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, uint32_t len, uint32_t entropy)
adds (hopefully) random
data to the entropy pool.
len is the number of bytes in
data and
entropy is an "entropy quality" measurement. 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 randomness, passing
NULL for
rnd_source is permitted, and the device does not need to be attached.