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/*
* stats.c
*
* statistical tests
*
* David A. McGrew
* Cisco Systems, Inc.
*/
/*
*
* Copyright (c) 2001-2006, Cisco Systems, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* Neither the name of the Cisco Systems, Inc. nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "stat.h"
srtp_debug_module_t mod_stat = {
0, /* debugging is off by default */
(char *)"stat test" /* printable module name */
};
/*
* each test assumes that 20,000 bits (2500 octets) of data is
* provided as input
*/
#define STAT_TEST_DATA_LEN 2500
srtp_err_status_t
stat_test_monobit(uint8_t *data) {
uint8_t *data_end = data + STAT_TEST_DATA_LEN;
uint16_t ones_count;
ones_count = 0;
while (data < data_end) {
ones_count += octet_get_weight(*data);
data++;
}
debug_print(mod_stat, "bit count: %d", ones_count);
if ((ones_count < 9725) || (ones_count > 10275))
return srtp_err_status_algo_fail;
return srtp_err_status_ok;
}
srtp_err_status_t
stat_test_poker(uint8_t *data) {
int i;
uint8_t *data_end = data + STAT_TEST_DATA_LEN;
double poker;
uint16_t f[16] = {
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0
};
while (data < data_end) {
f[*data & 0x0f]++; /* increment freq. count for low nibble */
f[(*data) >> 4]++; /* increment freq. count for high nibble */
data++;
}
poker = 0.0;
for (i=0; i < 16; i++)
poker += (double) f[i] * f[i];
poker *= (16.0 / 5000.0);
poker -= 5000.0;
debug_print(mod_stat, "poker test: %f\n", poker);
if ((poker < 2.16) || (poker > 46.17))
return srtp_err_status_algo_fail;
return srtp_err_status_ok;
}
/*
* runs[i] holds the number of runs of size (i-1)
*/
srtp_err_status_t
stat_test_runs(uint8_t *data) {
uint8_t *data_end = data + STAT_TEST_DATA_LEN;
uint16_t runs[6] = { 0, 0, 0, 0, 0, 0 };
uint16_t gaps[6] = { 0, 0, 0, 0, 0, 0 };
uint16_t lo_value[6] = { 2315, 1114, 527, 240, 103, 103 };
uint16_t hi_value[6] = { 2685, 1386, 723, 384, 209, 209 };
int state = 0;
uint16_t mask;
int i;
/*
* the state variable holds the number of bits in the
* current run (or gap, if negative)
*/
while (data < data_end) {
/* loop over the bits of this byte */
for (mask = 1; mask < 256; mask <<= 1) {
if (*data & mask) {
/* next bit is a one */
if (state > 0) {
/* prefix is a run, so increment the run-count */
state++;
/* check for long runs */
if (state > 25) {
debug_print(mod_stat, ">25 runs: %d", state);
return srtp_err_status_algo_fail;
}
} else if (state < 0) {
/* prefix is a gap */
if (state < -25) {
debug_print(mod_stat, ">25 gaps: %d", state);
return srtp_err_status_algo_fail; /* long-runs test failed */
}
if (state < -6) {
state = -6; /* group together gaps > 5 */
}
gaps[-1-state]++; /* increment gap count */
state = 1; /* set state at one set bit */
} else {
/* state is zero; this happens only at initialization */
state = 1;
}
} else {
/* next bit is a zero */
if (state > 0) {
/* prefix is a run */
if (state > 25) {
debug_print(mod_stat, ">25 runs (2): %d", state);
return srtp_err_status_algo_fail; /* long-runs test failed */
}
if (state > 6) {
state = 6; /* group together runs > 5 */
}
runs[state-1]++; /* increment run count */
state = -1; /* set state at one zero bit */
} else if (state < 0) {
/* prefix is a gap, so increment gap-count (decrement state) */
state--;
/* check for long gaps */
if (state < -25) {
debug_print(mod_stat, ">25 gaps (2): %d", state);
return srtp_err_status_algo_fail;
}
} else {
/* state is zero; this happens only at initialization */
state = -1;
}
}
}
/* move along to next octet */
data++;
}
if (mod_stat.on) {
debug_print(mod_stat, "runs test", NULL);
for (i=0; i < 6; i++)
debug_print(mod_stat, " runs[]: %d", runs[i]);
for (i=0; i < 6; i++)
debug_print(mod_stat, " gaps[]: %d", gaps[i]);
}
/* check run and gap counts against the fixed limits */
for (i=0; i < 6; i++)
if ( (runs[i] < lo_value[i] ) || (runs[i] > hi_value[i])
|| (gaps[i] < lo_value[i] ) || (gaps[i] > hi_value[i]))
return srtp_err_status_algo_fail;
return srtp_err_status_ok;
}
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