libhavege (3) - Linux Manuals
libhavege: haveged RNG
NAME
libhavege, havege_create, havege_run, havege_rng, havege_destroy, havege_status, havege_status_dump, havege_version - haveged RNGSYNOPSIS
#include <haveged/havege.h>
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);
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:
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);
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.
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.
Tuning information may be extracted from the following virtual file paths if
tuning is required and the path exists.
/proc/self/status
/sys/devices/system/cpu/online
/sys/devices/system/cpu/cpu%d/cache/index%d/level
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
The following minimal program writes the contents of 16 collection buffers
of random data to stdout with continuous testing.
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.
haveged(8)
references provides a basic reading list. The following links are suggested as sources for
further exploration.
NOTES
FILES
DIAGNOSTICS
02 H_NOBUF
03 H_NOINIT
04 H_NOCOLLECT
05 H_NOWALK
06 H_NOTESTSPEC
07 H_NOTESTINIT
08 H_NOTESTMEM
09 H_NOTESTTOT
10 H_NOTESTRUN
11 H_NOCORES
12 H_NOTASK
13 H_NOWAIT
14 H_NOPOST
15 H_NODONE
16 H_NORQST
17 H_NOCOMP
18 H_EXIT
19 H_NOTIMER
EXAMPLE
#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;
}
REFERENCES
AUTHORS
Gary Wuertz <gary [at] issiweb.com> and Jirka Hladky <hladky jiri AT gmail DOT com>