haveged(8) SYSTEM ADMINISTRATION COMMANDS haveged(8)
NAME
haveged - Generate random numbers and feed Linux's random device.
SYNOPSIS
haveged [options]
DESCRIPTION
haveged generates an unpredictable stream of random numbers harvested
from the indirect effects of hardware events on hidden processor state
(caches, branch predictors, memory translation tables, etc) using the
HAVEGE (HArdware Volatile Entropy Gathering and Expansion) algorithm.
The algorithm operates in user space, no special privilege is required
for file system access to the output stream.
Linux pools randomness for distribution by the /dev/random and
/dev/urandom device interfaces. The standard mechanisms of filling the
/dev/random pool may not be sufficient to meet demand on systems with
high needs or limited user interaction. In those circumstances, haveged
may be run as a privileged daemon to fill the /dev/random pool whenever
the supply of random bits in /dev/random falls below the low water mark
of the device.
haveged tunes itself to its environment and provides the same built-in
test suite for the output stream as used on certified hardware security
devices. See NOTES below for further information.
OPTIONS
-b nnn, --buffer=nnn
Set collection buffer size to nnn KW. Default is 128KW (or
512KB).
-c cmd, --command=cmd
Switch to command mode and send a command to an already running
haveged process or daemon. Currently the only known commands are
close to close the current communication socket of the running
haveged process as well as root=<new_root> where <new_root> is a
place holder for the path of the real new root directory which
should provide a haveged installation. The haveged process or
daemon will perform a chroot(2) system call followed by a ex-
ecv(3) to become rebased within the new root directory.
-d nnn, --data=nnn
Set data cache size to nnn KB. Default is 16 or as determined dy-
namically.
-f file, --file=file
Set output file path for non-daemon use. Default is "sample", use
"-" for stdout.
-F , --Foreground
Run daemon in foreground. Do not fork and detach.
-e , --once
Provide entropy to the kernel once and quit immediatelly.
-i nnn, --inst=nnn
Set instruction cache size to nnn KB. Default is 16 or as deter-
mined dynamically.
-n nnn, --number=nnn
Set number of bytes written to the output file. The value may be
specified using one of the suffixes k, m, g, or t. The upper
bound of this value is "16t" (2^44 Bytes = 16TB). A value of 0
indicates unbounded output and forces output to stdout. This ar-
gument is required if the daemon interface is not present. If the
daemon interface is present, this setting takes precedence over
any --run value.
-o <spec>, --onlinetest=<spec>
Specify online tests to run. The <spec> consists of optional
"t"ot and "c"ontinuous groups, each group indicates the proce-
dures to be run, using "a<n>" to indicate a AIS-31 procedure A
variant, and "b" to indicate AIS procedure B. The specifications
are order independent (procedure B always runs first in each
group) and case insensitive. The a<n> variations exist to miti-
gate the a slow autocorrelation test (test5). Normally all proce-
dure A tests, except the first are iterated 257 times. An a<n>
option indicates test5 should only be executed every modulo <n>
times during the procedure's 257 repetitions. The effect is so
noticeable that A8 is the usual choice.
The "tot" tests run only at initialization - there are no nega-
tive performance consequences except for a slight increase in the
time required to initialize. The "tot" tests guarantee haveged
has initialized properly. The use of both test procedures in the
"tot" test is highly recommended because the two test emphasize
different aspects of RNG quality.
In continuous testing, the test sequence is cycled repeatedly.
For example, the string "tbca8b" (suitable for an AIS NTG.1 de-
vice) would run procedure B for the "tot" test, then cycle be-
tween procedure A8 and procedure B continuously for all further
output. Continuous testing does not come for free, impacting both
throughput and resource consumption. Continual testing also opens
up the possibility of a test failure. A strict retry procedure
recovers from spurious failure in all but the most extreme cir-
cumstances. When the retry fails, operation will terminate unless
a "w" has been appended to the test token to make the test advi-
sory only. In our example above, the string "tbca8wbw" would make
all continuous tests advisory. For more detailed information on
AIS retries see NOTES below.
Complete control over the test configuration is provided for
flexibility. The defaults (ta8bcb" if run as a daemon and "ta8b"
otherwise) are suitable for most circumstances.
-p file, --pidfile=file
Set file path for the daemon pid file. Default is
"/var/run/haveged.pid",
-r n, --run=n
Set run level for daemon interface:
n = 0 Run as daemon - must be root. Fills /dev/random when the
supply of random bits
falls below the low water mark of the device.
n = 1 Display configuration info and terminate.
n > 1 Write <n> kb of output. Deprecated (use --number instead),
only provided for backward compatibility.
If --number is specified, values other than 0,1 are ignored. De-
fault is 0.
-v n, --verbose=n
Set diagnostic bitmap as sum of following options:
1=Show build/tuning summary on termination, summary for online
test retries.
2=Show online test retry details
4=Show timing for collections
8=Show collection loop layout
16=Show collection loop code offsets
32=Show all online test completion detail
64=Show info on RNDADDENTROPY operation
Default is 0. Use -1 for all diagnostics.
-w nnn, --write=nnn
Set write_wakeup_threshold of daemon interface to nnn bits. Ap-
plies only to run level 0.
-V, --version
Print version information and exit
-?, --help
This summary of program options.
NOTES
haveged tunes the HAVEGE algorithm for maximum effectiveness using a hi-
erarchy of defaults, command line options, virtual file system informa-
tion, and cpuid information where available. Under most circumstances,
user input is not required for excellent results.
Run-time testing provides assurance of correct haveged operation. The
run-time test suite is modeled upon the AIS-31 specification of the Ger-
man Common Criteria body, BIS. This specification is typically applied
to hardware devices, requiring formal certification and mandated start-
up and continuous operational testing. Because haveged runs on many dif-
ferent hardware platforms, certification cannot be a goal, but the
AIS-31 test suite provides the means to assess haveged output with the
same operational tests applied to certified hardware devices.
AIS test procedure A performs 6 tests to check for statistically incon-
spicuous behavior. AIS test procedure B performs more theoretical tests
such as checking multi-step transition probabilities and making an em-
pirical entropy estimate. Procedure A is the much more resource and
compute intensive of the two but is still recommended for the haveged
start-up tests. Procedure B is well suited to use of haveged as a daemon
because the test entropy estimate confirms the entropy estimate haveged
uses when adding entropy to the /dev/random device.
No test is perfect. There is a 10e-4 probability that a perfect genera-
tor will fail either of the test procedures. AIS-31 mandates a strict
retry policy to filter out false alarms and haveged always logs test
procedure failures. Retries are expected but rarely observed except when
large data sets are generated with continuous testing. See the lib-
havege(3) notes for more detailed information.
FILES
If running as a daemon, access to the following files is required
/dev/random
/proc/sys/kernel/osrelease
/proc/sys/kernel/random/poolsize
/proc/sys/kernel/random/write_wakeup_threshold
DIAGNOSTICS
Haveged returns 0 for success and non-zero for failure. The failure re-
turn code is 1 "general failure" unless execution is terminated by sig-
nal <n>, in which case the return code will be 128 + <n>. The following
diagnostics are issued to stderr upon non-zero termination:
Cannot fork into the background
Call to daemon(3) failed.
Cannot open file <s> for writing.
Could not open sample file <s> for writing.
Cannot write data in file:
Could not write data to the sample file.
Couldn't get pool size.
Unable to read /proc/sys/kernel/random/poolsize
Couldn't initialize HAVEGE rng
Invalid data or instruction cache size.
Couldn't open PID file <s> for writing
Unable to write daemon PID
Couldn't open random device
Could not open /dev/random for read-write.
Couldn't query entropy-level from kernel: error
Call to ioctl(2) failed.
Couldn't open PID file <path> for writing
Error writing /var/run/haveged.pid
Fail:set_watermark()
Unable to write to /proc/sys/kernel/random/write_wakeup_threshold
RNDADDENTROPY failed!
Call to ioctl(2) to add entropy failed
RNG failed
The random number generator failed self-test or encountered a fa-
tal error.
Select error
Call to select(2) failed.
Stopping due to signal <n>
Signal <n> caught.
Unable to setup online tests
Memory unavailable for online test resources.
EXAMPLES
Write 1.5MB of random data to the file /tmp/random
haveged -n 1.5M -f /tmp/random
Generate a /tmp/keyfile for disk encryption with LUKS
haveged -n 2048 -f /tmp/keyfile
Overwrite partition /dev/sda1 with random data. Be careful, all data on
the partition will be lost!
haveged -n 0 | dd of=/dev/sda1
Generate random ASCII passwords of the length 16 characters
(haveged -n 1000 -f - 2>/dev/null | tr -cd '[:graph:]' | fold -w
16 && echo ) | head
Write endless stream of random bytes to the pipe. Utility pv measures
the speed by which data are written to the pipe.
haveged -n 0 | pv > /dev/null
Evaluate speed of haveged to generate 1GB of random data
haveged -n 1g -f - | dd of=/dev/null
Create a random key file containing 65 random keys for the encryption
program aespipe.
haveged -n 3705 -f - 2>/dev/null | uuencode -m - | head -n 66 |
tail -n 65
Test the randomness of the generated data with dieharder test suite
haveged -n 0 | dieharder -g 200 -a
Generate 16k of data, testing with procedure A and B with detailed test
results. No c result seen because a single buffer fill did not contain
enough data to complete the test.
haveged -n 16k -o tba8ca8 -v 33
Generate 16k of data as above with larger buffer. The c test now com-
pletes - enough data now generated to complete the test.
haveged -n 16k -o tba8ca8 -v 33 -b 512
Generate 16m of data as above, observe many c test completions with de-
fault buffer size.
haveged -n 16m -o tba8ca8 -v 33
Generate large amounts of data - in this case 16TB. Enable initializa-
tion test but made continuous tests advisory only to avoid a possible
situation that program will terminate because of procedureB failing two
times in a row. The probability of procedureB to fail two times in a row
can be estimated as <TB to generate>/3000 which yields 0.5% for 16TB.
haveged -n 16T -o tba8cbw -f - | pv > /dev/null
Generate large amounts of data (16TB). Disable continuous tests for the
maximum throughput but run the online tests at the startup to make sure
that generator for properly initialized:
haveged -n 16T -o tba8c -f - | pv > /dev/null
Create a password equivalent to a key strength of 256 bit
haveged -f - -n 32 2>/dev/null | base64 | tr -d =
SEE ALSO
libhavege(3),
cryptsetup(8), aespipe(1), pv(1), openssl(1), uuencode(1)
REFERENCES
HArdware Volatile Entropy Gathering and Expansion: generating unpre-
dictable random numbers at user level by A. Seznec, N. Sendrier, INRIA
Research Report, RR-4592, October 2002
A proposal for: Functionality classes for random number generators by W.
Killmann and W. Schindler, version 2.0, Bundesamt fur Sicherheit in der
Informationstechnik (BSI), September, 2011
A Statistical Test Suite for the Validation of Random NUmber Generators
and Pseudorandom Number Generators for Cryptographic Applications, spe-
cial publication SP800-22, National Institute of Standards and Technol-
ogy, revised April, 2010
Additional information can also be found at http://www.issi-
hosts.com/haveged/
AUTHORS
Gary Wuertz <gary@issiweb.com> and Jirka Hladky <hladky jiri AT gmail
DOT com>
version 1.9 February 10, 2014 haveged(8)
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