NAME¶
libhavege, havege_create, havege_run, havege_rng, havege_destroy, havege_status,
havege_status_dump, havege_version - haveged RNG
SYNOPSIS¶
#include <haveged/havege.h>
H_PARAMS params = {0};
h_status status;
char status_buf[512];
if (NULL==havege_version(HAVEGE_PREP_VERSION)) exit(1);
H_PTR handle = havege_create(¶ms);
havege_status(handle, &status);
havege_run(handle);
rc = havege_rng(handle, handle->io_buf, handle->i_readSz/sizeof(H_UINT));
havege_status_dump(handle, H_SD_TOPIC_BUILD, status_buf, sizeof(status_buf));
havege_destroy(handle);
DESCRIPTION¶
The libhavege library provides the haveged random number generator and it's
associated tuning and testing facilities in a development sub-package. All
haveged conditional build features are preserved and all haveged options not
directly related to it's daemon or file system interfaces are available. This
means that the same haveged tuning and testing components are present in the
library with the equivalent controls provided by the haveged command line.
API METHODS¶
The libhavege library uses the opaque handle technique to manage it's required
resources. Errors are returned in the "error" member of the handle.
The havege_destroy() method should be called to dispose of any resources
claimed by havege_create().
H_PTR havege_create(H_PARAMS *params);
Create an anchor. Most members of the H_PARAMS input to this call correspond
closely to haveged command line options (see
haveged(8) for details).
The caller should check for a non-null return value with a error value of
H_NOERR. Any non-null return should be disposed of by a call to
havege_destroy() to free any resources. Possible error values: H_NOERR,
H_NOTESTSPEC, H_NOBUF, H_NOTESTMEM, H_NOINIT
void havege_destroy(H_PTR hptr);
Free all allocated anchor resources. If the multi-core option is used, this
method should be called from a signal handler to prevent zombie processes. If
called by the process that called haveged_create(), hptr will be freed when
all child processes (if any) have terminated. If called by a child process,
H_EXIT will be set and all children awakened to exit.
int havege_rng(H_PTR hptr, H_UINT *buf, H_UINT
sz);
Read random bytes from an active anchor. The RNG must have been previously
readied by a call to havege_run(). The read must take place within the
allocated buffer, hptr->io_buf. The range specified is the number of H_UINT
to read. If the multi-core option is used, this buffer is memory mapped
between collectors. Possible error values: H_NOERR, H_NOTESRUN, H_NOPOST,
H_NODONE, H_NORQST, H_NOCOMP, H_EXIT
int havege_run(H_PTR hptr);
Warm up the RNG and run the start-up tests. The operation succeeded if the error
member of the handle is H_NOERR. A failed handle should be disposed of by a
call to havege_destroy(). Possible error values: H_NOERR, H_NOCOLLECT,
H_NOWALK, H_NOTESTMEM, H_NOTASK, H_NOTESTTOT, H_NOWAIT, H_NOTIMER, and any
havege_rng() error.
void havege_status(H_PTR hptr, H_STATUS
hsts);
Fills in the h_status structure with read-only information collected from the
package build, run-time tuning, and test components.
int havege_status_dump(H_PTR hptr, H_SD_TOPIC
topic, char *buf, size_t len);
Calls havege_status() and formats standard presentations of havege status in the
supplied buffer. The standard formats are:
H_SD_TOPIC_BUILD
ver: %s; arch: %s; vend: %s; build: (%s); collect: %dK
H_SD_TOPIC_TUNE
cpu: (%s); data: %dK (%s); inst: %dK (%s); idx: %d/%d; sz: %d/%d
H_SD_TOPIC_TEST
[tot tests(%s): A:%d/%d B: %d/%d;][continuous tests(%s): A:%d/%d B: %d/%d;][last
entropy estimate %g]
H_SD_TOPIC_SUM
fills: %d, generated: %.4g %c bytes
const char *havege_version(const char *version);
Return/check library prep version. The prep version is the package version used
to build the library. A null argument returns the prep version
unconditionally. Using the definition of the prep string in havege.h as input
returns the prep version if the header file is compatible with the library, or
NULL if it is not. Intended to be called before attempting any initialization.
NOTES¶
The sizes of the processor level 1 instruction and data caches are used to tune
the HAVEGE algorithm for maximum sensitivity. If these sizes not specified,
haveged will attempt to determine the sizes dynamically from the Linux sysfs
and/or cpuid instruction with a fallback to a compiled default if no better
information is not available.
The haveged RNG includes a run time test facility based upon the test suite
defined in the AIS-31 specification from the The German Federal Office for
Information Security (Bundesamt für Sicherheit in der
Informationstechnik). The test suite consists of 11 statistical tests packaged
into two test suites ("A" and "B"). The tests can be run
at initialization (a.k.a. a "tot" test), or continuously to monitor
all output. Failure of a suite will abort operation unless the behavior is
explicitly waived in the test setup options.
Procedure A contains 6 test procedures designed to ensure statistically
inconspicuous behavior. The first test, "test0", checks the
disjointedness of 65k six-bit strings. The remainder of the procedure consists
of 257 repetitions of the FIPS140-1 tests, "test1" through
"test4", and an auto-correlation test, "test5". The fixed
size of the Procedure A input makes it ideal for continuous use, but the
procedure is slow and resource intensive. In particular, test5 is several
orders of magnitude slower than any other individual AIS test. As an
alternative for those who cannot tolerate this load, procedure A variants
A<n> are provided that execute all included tests but execute test5 only
every 2^n repetitions. Even with this accommodation, procedure A is much
slower than procedure B.
Procedure B contains 5 tests, "test6a", "test6b',
"test7a", "test7b", and "test8". The first 4
tests verify the expected frequencies for samples 100,000 one-step, two-step,
three-step, and four-step bit transitions. The last test provides an empirical
entropy estimate of the input. The input required to complete these tests is
variable, resulting in an ever-shifting bit alignment that guards against
buffering artifacts.
Each test procedure requires more than 1MB of data. Test input is managed by a
bit index into the collection buffer. An independent index manages where
integer output is taken from the same buffer. A buffer fill is triggered when
the output index indicates all data has been extracted from the buffer. Online
testing takes place after the buffer has been refilled but before the output
index update allows output to resume. If any online test fails while
processing the buffer, the buffer will be refilled and reprocessed until any
retry is complete and the buffer contains no failed online tests or the online
test procedure has failed and the RNG is considered broken.
It is recommend to run both AIS test procedures at start-up to ensure the RNG is
properly initialized. If resources are in short supply, omitting procedure A
will save memory and time, with little risk in circumstances where output is
mixed with other sources in /dev/random or other csprng. Continuous testing is
also recommended where the throughput penalty is acceptable. One recent
assessment of testing throughput costs is shown below.
- haveged -n0 -oc | pv > /dev/null
- 400MiB/s
- haveged -n0 -ocb | pv > /dev/null
- 70MiB/s
- haveged -n0 -oca8b | pv > /dev/null
- 13MiB/s
- haveged -n0 -oca8 | pv > /dev/null
- 8MiB/s
- haveged -n0 -oca | pv > /dev/null
- 100kiB/s
Continuous testing also exposes another possible pitfall. Even an ideal RNG has
a 10e-4 chance of failing either test procedure. The strict retry policy of
AIS-31 is designed to guarantee an ideal RNG will "almost never"
fail a test procedure. A single retry is mandated only to recover from a
previous attempt that experienced a single individual test failure. The
haveged implementation logs all retries and terminates on test procedure
failures unless the procedure has been flagged as advisory by the
"w" argument (see --onlinetest in
haveged(8) ). Little
evidence of the retry mechanism is seen unless large data sets are processed.
Procedure A is too slow to be practical in these situations, so procedure B
has been the best studied. Retries are observed at the approximate rate of
0.7-0.8 failures/GB, mostly in the test7 multi-step transition checks.
The probability that procedureB will fail two times in a row (in which case the
program will be terminated unless w option was specified) is 4e-7 which is
expected to happen at an approximate rate of once per 3,000 TB. When producing
large amounts of data in order of TBs it's recommended to use -w option to
make sure that program will not prematurely terminate because of a failed
retry and carefully examine the stderr output for any problems.
FILES¶
Tuning information may be extracted from the following virtual file paths if
tuning is required and the path exists.
/proc/cpuinfo
/proc/self/status
/sys/devices/system/cpu/online
/sys/devices/system/cpu/cpu%d/cache/index%d/level
DIAGNOSTICS¶
To enable diagnostic output, supply a msg_out callback when creating the handle.
All possible errors are enumerated in havege.h and reproduced here for
reference.
01 H_NOHANDLE
No memory for handle
02 H_NOBUF
Output buffer allocation failed
03 H_NOINIT
Semaphore init failed
04 H_NOCOLLECT
Collector allocation failed
05 H_NOWALK
Walk buffer allocation failed
06 H_NOTESTSPEC
Invalid test specification
07 H_NOTESTINIT
Test setup failed
08 H_NOTESTMEM
Unable to allocate test memory
09 H_NOTESTTOT
Power on (i.e. 'tot') test failed
10 H_NOTESTRUN
Continuous test failed
11 H_NOCORES
Too many cores specified
12 H_NOTASK
Unable to create child task
13 H_NOWAIT
sem_wait failed
14 H_NOPOST
sem_post failed
15 H_NODONE
sem_post done failed
16 H_NORQST
sem_post request failed
17 H_NOCOMP
wait for completion failed
18 H_EXIT
Exit signal
19 H_NOTIMER
Timer failed
EXAMPLE¶
The following minimal program writes the contents of 16 collection buffers of
random data to stdout with continuous testing.
#include <stdio.h>
#include <haveged/havege.h>
int main(void)
{
H_PTR havege_state;
H_PARAMS havege_parameters = {0};
int i, rc;
if (NULL==havege_version(HAVEGE_PREP_VERSION)) {
fprintf(stderr, "Incompatible library %s\n", havege_version(NULL));
return 1;
}
havege_parameters.testSpec="ta8bcb";
havege_state = havege_create(&havege_parameters);
rc = havege_state==NULL? H_NOHANDLE : havege_state->error;
if (H_NOERR==rc) {
if (0==havege_run(havege_state)) {
H_UINT *buf = havege_state->io_buf;
int size = havege_state->i_readSz /sizeof(H_UINT);
char info[256];
for(i=0;i<16;i++) {
rc = havege_rng(havege_state, buf, size);
if (rc != size) {
fprintf(stderr, "RNG read failed %d\n", havege_state->error);
break;
}
rc = fwrite(buf, 1, size*sizeof(H_UINT), stdout);
if ( rc < size ) {
fprintf(stderr, "Write failed\n");
break;
}
}
i = havege_status_dump(havege_state, H_SD_TOPIC_TEST, info, sizeof(info));
info[i++] = '\n';
havege_status_dump(havege_state, H_SD_TOPIC_SUM, info+i, sizeof(info)-i);
fprintf(stderr, "%s\n", info);
}
else fprintf(stderr, "Initialize failed %d\n", havege_state->error);
havege_destroy(havege_state);
}
else fprintf(stderr, "Create failed %d\n", rc);
return rc;
}
Defaults are provided for all inputs to havege_create() as documented in
havege.h. In this case for example, (16*4kb=65kb) will be written to stdout
because the default size for i_readsz in 4kb.
SEE ALSO¶
- haveged(8)
-
REFERENCES¶
haveged(8) references provides a basic reading list. The following links
are suggested as sources for further exploration.
- The origins of the HAVEGE concept can be found at:
- http://www.irisa.fr/caps/projects/hipsor/
- Tuning concepts inspired by (the complexity) at:
- http://www.open-mpi.org/projects/hwloc/
- Reference documentation for the AIS-31 test suite can be
found at:
- https://www.bsi.bund.de/SharedDocs/Downloads/DE/BSI/Zertifizierung/Interpretationen/AIS_31_Functionality_classes_for_random_number_generators_e.pdf?__blob=publicationFile
- Implementation and design information available at:
- http://www.issihosts.com/haveged/
AUTHORS¶
Gary Wuertz <gary@issiweb.com> and Jirka Hladky <hladky jiri AT gmail
DOT com>