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 run-
ning 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
execv(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
dynamically.
-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.
-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
argument 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 specifica-
tions are order independent (procedure B always runs first in
each group) and case insensitive. The a<n> variations exist to
mitigate the a slow autocorrelation test (test5). Normally all
procedure 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 proce-
dures 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
device) would run procedure B for the "tot" test, then cycle
between procedure A8 and procedure B continuously for all fur-
ther output. Continuous testing does not come for free, impact-
ing 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 circumstances. When the retry fails, operation will ter-
minate unless a "w" has been appended to the test token to make
the test advisory 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.
Default 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
Default is 0. Use -1 for all diagnostics.
-w nnn, --write=nnn
Set write_wakeup_threshold of daemon interface to nnn bits.
Applies only to run level 0.
-?, --help
This summary of program options.
NOTES
haveged tunes the HAVEGE algorithm for maximum effectiveness using a
hierarchy of defaults, command line options, virtual file system infor-
mation, and cpuid information where available. Under most circum-
stances, 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
German Common Criteria body, BIS. This specification is typically
applied to hardware devices, requiring formal certification and man-
dated start-up and continuous operational testing. Because haveged runs
on many different 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
empirical 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 dae-
mon 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
libhavege(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
return code is 1 "general failure" unless execution is terminated by
signal <n>, in which case the return code will be 128 + <n>. The fol-
lowing 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_thresh-
old
RNDADDENTROPY failed!
Call to ioctl(2) to add entropy failed
RNG failed
The random number generator failed self-test or encountered a
fatal 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
default 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
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 AT issiweb.com> and Jirka Hladky <hladky jiri AT gmail
DOT com>
version 1.9 February 10, 2014 haveged(8)
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Huschi als Linux-Admin