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Diffstat (limited to 'crypto/jitterentropy.c')
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diff --git a/crypto/jitterentropy.c b/crypto/jitterentropy.c new file mode 100644 index 0000000000..fe9c233ec7 --- /dev/null +++ b/crypto/jitterentropy.c @@ -0,0 +1,782 @@ +/* + * Non-physical true random number generator based on timing jitter -- + * Jitter RNG standalone code. + * + * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 2023 + * + * Design + * ====== + * + * See https://www.chronox.de/jent.html + * + * License + * ======= + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, and the entire permission notice in its entirety, + * including the disclaimer of warranties. + * 2. 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. + * 3. The name of the author may not be used to endorse or promote + * products derived from this software without specific prior + * written permission. + * + * ALTERNATIVELY, this product may be distributed under the terms of + * the GNU General Public License, in which case the provisions of the GPL2 are + * required INSTEAD OF the above restrictions. (This clause is + * necessary due to a potential bad interaction between the GPL and + * the restrictions contained in a BSD-style copyright.) + * + * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED + * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF + * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR 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 NOT ADVISED OF THE POSSIBILITY OF SUCH + * DAMAGE. + */ + +/* + * This Jitterentropy RNG is based on the jitterentropy library + * version 3.4.0 provided at https://www.chronox.de/jent.html + */ + +#ifdef __OPTIMIZE__ + #error "The CPU Jitter random number generator must not be compiled with optimizations. See documentation. Use the compiler switch -O0 for compiling jitterentropy.c." +#endif + +typedef unsigned long long __u64; +typedef long long __s64; +typedef unsigned int __u32; +typedef unsigned char u8; +#define NULL ((void *) 0) + +/* The entropy pool */ +struct rand_data { + /* SHA3-256 is used as conditioner */ +#define DATA_SIZE_BITS 256 + /* all data values that are vital to maintain the security + * of the RNG are marked as SENSITIVE. A user must not + * access that information while the RNG executes its loops to + * calculate the next random value. */ + void *hash_state; /* SENSITIVE hash state entropy pool */ + __u64 prev_time; /* SENSITIVE Previous time stamp */ + __u64 last_delta; /* SENSITIVE stuck test */ + __s64 last_delta2; /* SENSITIVE stuck test */ + unsigned int osr; /* Oversample rate */ +#define JENT_MEMORY_BLOCKS 64 +#define JENT_MEMORY_BLOCKSIZE 32 +#define JENT_MEMORY_ACCESSLOOPS 128 +#define JENT_MEMORY_SIZE (JENT_MEMORY_BLOCKS*JENT_MEMORY_BLOCKSIZE) + unsigned char *mem; /* Memory access location with size of + * memblocks * memblocksize */ + unsigned int memlocation; /* Pointer to byte in *mem */ + unsigned int memblocks; /* Number of memory blocks in *mem */ + unsigned int memblocksize; /* Size of one memory block in bytes */ + unsigned int memaccessloops; /* Number of memory accesses per random + * bit generation */ + + /* Repetition Count Test */ + unsigned int rct_count; /* Number of stuck values */ + + /* Intermittent health test failure threshold of 2^-30 */ + /* From an SP800-90B perspective, this RCT cutoff value is equal to 31. */ + /* However, our RCT implementation starts at 1, so we subtract 1 here. */ +#define JENT_RCT_CUTOFF (31 - 1) /* Taken from SP800-90B sec 4.4.1 */ +#define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */ + /* Permanent health test failure threshold of 2^-60 */ + /* From an SP800-90B perspective, this RCT cutoff value is equal to 61. */ + /* However, our RCT implementation starts at 1, so we subtract 1 here. */ +#define JENT_RCT_CUTOFF_PERMANENT (61 - 1) +#define JENT_APT_CUTOFF_PERMANENT 355 +#define JENT_APT_WINDOW_SIZE 512 /* Data window size */ + /* LSB of time stamp to process */ +#define JENT_APT_LSB 16 +#define JENT_APT_WORD_MASK (JENT_APT_LSB - 1) + unsigned int apt_observations; /* Number of collected observations */ + unsigned int apt_count; /* APT counter */ + unsigned int apt_base; /* APT base reference */ + unsigned int apt_base_set:1; /* APT base reference set? */ +}; + +/* Flags that can be used to initialize the RNG */ +#define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more + * entropy, saves MEMORY_SIZE RAM for + * entropy collector */ + +/* -- error codes for init function -- */ +#define JENT_ENOTIME 1 /* Timer service not available */ +#define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */ +#define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */ +#define JENT_EVARVAR 5 /* Timer does not produce variations of + * variations (2nd derivation of time is + * zero). */ +#define JENT_ESTUCK 8 /* Too many stuck results during init. */ +#define JENT_EHEALTH 9 /* Health test failed during initialization */ + +/* + * The output n bits can receive more than n bits of min entropy, of course, + * but the fixed output of the conditioning function can only asymptotically + * approach the output size bits of min entropy, not attain that bound. Random + * maps will tend to have output collisions, which reduces the creditable + * output entropy (that is what SP 800-90B Section 3.1.5.1.2 attempts to bound). + * + * The value "64" is justified in Appendix A.4 of the current 90C draft, + * and aligns with NIST's in "epsilon" definition in this document, which is + * that a string can be considered "full entropy" if you can bound the min + * entropy in each bit of output to at least 1-epsilon, where epsilon is + * required to be <= 2^(-32). + */ +#define JENT_ENTROPY_SAFETY_FACTOR 64 + +#include <linux/fips.h> +#include "jitterentropy.h" + +/*************************************************************************** + * Adaptive Proportion Test + * + * This test complies with SP800-90B section 4.4.2. + ***************************************************************************/ + +/* + * Reset the APT counter + * + * @ec [in] Reference to entropy collector + */ +static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked) +{ + /* Reset APT counter */ + ec->apt_count = 0; + ec->apt_base = delta_masked; + ec->apt_observations = 0; +} + +/* + * Insert a new entropy event into APT + * + * @ec [in] Reference to entropy collector + * @delta_masked [in] Masked time delta to process + */ +static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked) +{ + /* Initialize the base reference */ + if (!ec->apt_base_set) { + ec->apt_base = delta_masked; + ec->apt_base_set = 1; + return; + } + + if (delta_masked == ec->apt_base) + ec->apt_count++; + + ec->apt_observations++; + + if (ec->apt_observations >= JENT_APT_WINDOW_SIZE) + jent_apt_reset(ec, delta_masked); +} + +/* APT health test failure detection */ +static int jent_apt_permanent_failure(struct rand_data *ec) +{ + return (ec->apt_count >= JENT_APT_CUTOFF_PERMANENT) ? 1 : 0; +} + +static int jent_apt_failure(struct rand_data *ec) +{ + return (ec->apt_count >= JENT_APT_CUTOFF) ? 1 : 0; +} + +/*************************************************************************** + * Stuck Test and its use as Repetition Count Test + * + * The Jitter RNG uses an enhanced version of the Repetition Count Test + * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical + * back-to-back values, the input to the RCT is the counting of the stuck + * values during the generation of one Jitter RNG output block. + * + * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8. + * + * During the counting operation, the Jitter RNG always calculates the RCT + * cut-off value of C. If that value exceeds the allowed cut-off value, + * the Jitter RNG output block will be calculated completely but discarded at + * the end. The caller of the Jitter RNG is informed with an error code. + ***************************************************************************/ + +/* + * Repetition Count Test as defined in SP800-90B section 4.4.1 + * + * @ec [in] Reference to entropy collector + * @stuck [in] Indicator whether the value is stuck + */ +static void jent_rct_insert(struct rand_data *ec, int stuck) +{ + if (stuck) { + ec->rct_count++; + } else { + /* Reset RCT */ + ec->rct_count = 0; + } +} + +static inline __u64 jent_delta(__u64 prev, __u64 next) +{ +#define JENT_UINT64_MAX (__u64)(~((__u64) 0)) + return (prev < next) ? (next - prev) : + (JENT_UINT64_MAX - prev + 1 + next); +} + +/* + * Stuck test by checking the: + * 1st derivative of the jitter measurement (time delta) + * 2nd derivative of the jitter measurement (delta of time deltas) + * 3rd derivative of the jitter measurement (delta of delta of time deltas) + * + * All values must always be non-zero. + * + * @ec [in] Reference to entropy collector + * @current_delta [in] Jitter time delta + * + * @return + * 0 jitter measurement not stuck (good bit) + * 1 jitter measurement stuck (reject bit) + */ +static int jent_stuck(struct rand_data *ec, __u64 current_delta) +{ + __u64 delta2 = jent_delta(ec->last_delta, current_delta); + __u64 delta3 = jent_delta(ec->last_delta2, delta2); + + ec->last_delta = current_delta; + ec->last_delta2 = delta2; + + /* + * Insert the result of the comparison of two back-to-back time + * deltas. + */ + jent_apt_insert(ec, current_delta); + + if (!current_delta || !delta2 || !delta3) { + /* RCT with a stuck bit */ + jent_rct_insert(ec, 1); + return 1; + } + + /* RCT with a non-stuck bit */ + jent_rct_insert(ec, 0); + + return 0; +} + +/* RCT health test failure detection */ +static int jent_rct_permanent_failure(struct rand_data *ec) +{ + return (ec->rct_count >= JENT_RCT_CUTOFF_PERMANENT) ? 1 : 0; +} + +static int jent_rct_failure(struct rand_data *ec) +{ + return (ec->rct_count >= JENT_RCT_CUTOFF) ? 1 : 0; +} + +/* Report of health test failures */ +static int jent_health_failure(struct rand_data *ec) +{ + return jent_rct_failure(ec) | jent_apt_failure(ec); +} + +static int jent_permanent_health_failure(struct rand_data *ec) +{ + return jent_rct_permanent_failure(ec) | jent_apt_permanent_failure(ec); +} + +/*************************************************************************** + * Noise sources + ***************************************************************************/ + +/* + * Update of the loop count used for the next round of + * an entropy collection. + * + * Input: + * @bits is the number of low bits of the timer to consider + * @min is the number of bits we shift the timer value to the right at + * the end to make sure we have a guaranteed minimum value + * + * @return Newly calculated loop counter + */ +static __u64 jent_loop_shuffle(unsigned int bits, unsigned int min) +{ + __u64 time = 0; + __u64 shuffle = 0; + unsigned int i = 0; + unsigned int mask = (1<<bits) - 1; + + jent_get_nstime(&time); + + /* + * We fold the time value as much as possible to ensure that as many + * bits of the time stamp are included as possible. + */ + for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) { + shuffle ^= time & mask; + time = time >> bits; + } + + /* + * We add a lower boundary value to ensure we have a minimum + * RNG loop count. + */ + return (shuffle + (1<<min)); +} + +/* + * CPU Jitter noise source -- this is the noise source based on the CPU + * execution time jitter + * + * This function injects the individual bits of the time value into the + * entropy pool using a hash. + * + * ec [in] entropy collector + * time [in] time stamp to be injected + * stuck [in] Is the time stamp identified as stuck? + * + * Output: + * updated hash context in the entropy collector or error code + */ +static int jent_condition_data(struct rand_data *ec, __u64 time, int stuck) +{ +#define SHA3_HASH_LOOP (1<<3) + struct { + int rct_count; + unsigned int apt_observations; + unsigned int apt_count; + unsigned int apt_base; + } addtl = { + ec->rct_count, + ec->apt_observations, + ec->apt_count, + ec->apt_base + }; + + return jent_hash_time(ec->hash_state, time, (u8 *)&addtl, sizeof(addtl), + SHA3_HASH_LOOP, stuck); +} + +/* + * Memory Access noise source -- this is a noise source based on variations in + * memory access times + * + * This function performs memory accesses which will add to the timing + * variations due to an unknown amount of CPU wait states that need to be + * added when accessing memory. The memory size should be larger than the L1 + * caches as outlined in the documentation and the associated testing. + * + * The L1 cache has a very high bandwidth, albeit its access rate is usually + * slower than accessing CPU registers. Therefore, L1 accesses only add minimal + * variations as the CPU has hardly to wait. Starting with L2, significant + * variations are added because L2 typically does not belong to the CPU any more + * and therefore a wider range of CPU wait states is necessary for accesses. + * L3 and real memory accesses have even a wider range of wait states. However, + * to reliably access either L3 or memory, the ec->mem memory must be quite + * large which is usually not desirable. + * + * @ec [in] Reference to the entropy collector with the memory access data -- if + * the reference to the memory block to be accessed is NULL, this noise + * source is disabled + * @loop_cnt [in] if a value not equal to 0 is set, use the given value + * number of loops to perform the LFSR + */ +static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt) +{ + unsigned int wrap = 0; + __u64 i = 0; +#define MAX_ACC_LOOP_BIT 7 +#define MIN_ACC_LOOP_BIT 0 + __u64 acc_loop_cnt = + jent_loop_shuffle(MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); + + if (NULL == ec || NULL == ec->mem) + return; + wrap = ec->memblocksize * ec->memblocks; + + /* + * testing purposes -- allow test app to set the counter, not + * needed during runtime + */ + if (loop_cnt) + acc_loop_cnt = loop_cnt; + + for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) { + unsigned char *tmpval = ec->mem + ec->memlocation; + /* + * memory access: just add 1 to one byte, + * wrap at 255 -- memory access implies read + * from and write to memory location + */ + *tmpval = (*tmpval + 1) & 0xff; + /* + * Addition of memblocksize - 1 to pointer + * with wrap around logic to ensure that every + * memory location is hit evenly + */ + ec->memlocation = ec->memlocation + ec->memblocksize - 1; + ec->memlocation = ec->memlocation % wrap; + } +} + +/*************************************************************************** + * Start of entropy processing logic + ***************************************************************************/ +/* + * This is the heart of the entropy generation: calculate time deltas and + * use the CPU jitter in the time deltas. The jitter is injected into the + * entropy pool. + * + * WARNING: ensure that ->prev_time is primed before using the output + * of this function! This can be done by calling this function + * and not using its result. + * + * @ec [in] Reference to entropy collector + * + * @return result of stuck test + */ +static int jent_measure_jitter(struct rand_data *ec) +{ + __u64 time = 0; + __u64 current_delta = 0; + int stuck; + + /* Invoke one noise source before time measurement to add variations */ + jent_memaccess(ec, 0); + + /* + * Get time stamp and calculate time delta to previous + * invocation to measure the timing variations + */ + jent_get_nstime(&time); + current_delta = jent_delta(ec->prev_time, time); + ec->prev_time = time; + + /* Check whether we have a stuck measurement. */ + stuck = jent_stuck(ec, current_delta); + + /* Now call the next noise sources which also injects the data */ + if (jent_condition_data(ec, current_delta, stuck)) + stuck = 1; + + return stuck; +} + +/* + * Generator of one 64 bit random number + * Function fills rand_data->hash_state + * + * @ec [in] Reference to entropy collector + */ +static void jent_gen_entropy(struct rand_data *ec) +{ + unsigned int k = 0, safety_factor = 0; + + if (fips_enabled) + safety_factor = JENT_ENTROPY_SAFETY_FACTOR; + + /* priming of the ->prev_time value */ + jent_measure_jitter(ec); + + while (!jent_health_failure(ec)) { + /* If a stuck measurement is received, repeat measurement */ + if (jent_measure_jitter(ec)) + continue; + + /* + * We multiply the loop value with ->osr to obtain the + * oversampling rate requested by the caller + */ + if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr)) + break; + } +} + +/* + * Entry function: Obtain entropy for the caller. + * + * This function invokes the entropy gathering logic as often to generate + * as many bytes as requested by the caller. The entropy gathering logic + * creates 64 bit per invocation. + * + * This function truncates the last 64 bit entropy value output to the exact + * size specified by the caller. + * + * @ec [in] Reference to entropy collector + * @data [in] pointer to buffer for storing random data -- buffer must already + * exist + * @len [in] size of the buffer, specifying also the requested number of random + * in bytes + * + * @return 0 when request is fulfilled or an error + * + * The following error codes can occur: + * -1 entropy_collector is NULL or the generation failed + * -2 Intermittent health failure + * -3 Permanent health failure + */ +int jent_read_entropy(struct rand_data *ec, unsigned char *data, + unsigned int len) +{ + unsigned char *p = data; + + if (!ec) + return -1; + + while (len > 0) { + unsigned int tocopy; + + jent_gen_entropy(ec); + + if (jent_permanent_health_failure(ec)) { + /* + * At this point, the Jitter RNG instance is considered + * as a failed instance. There is no rerun of the + * startup test any more, because the caller + * is assumed to not further use this instance. + */ + return -3; + } else if (jent_health_failure(ec)) { + /* + * Perform startup health tests and return permanent + * error if it fails. + */ + if (jent_entropy_init(ec->hash_state)) + return -3; + + return -2; + } + + if ((DATA_SIZE_BITS / 8) < len) + tocopy = (DATA_SIZE_BITS / 8); + else + tocopy = len; + if (jent_read_random_block(ec->hash_state, p, tocopy)) + return -1; + + len -= tocopy; + p += tocopy; + } + + return 0; +} + +/*************************************************************************** + * Initialization logic + ***************************************************************************/ + +struct rand_data *jent_entropy_collector_alloc(unsigned int osr, + unsigned int flags, + void *hash_state) +{ + struct rand_data *entropy_collector; + + entropy_collector = jent_zalloc(sizeof(struct rand_data)); + if (!entropy_collector) + return NULL; + + if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { + /* Allocate memory for adding variations based on memory + * access + */ + entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE); + if (!entropy_collector->mem) { + jent_zfree(entropy_collector); + return NULL; + } + entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE; + entropy_collector->memblocks = JENT_MEMORY_BLOCKS; + entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS; + } + + /* verify and set the oversampling rate */ + if (osr == 0) + osr = 1; /* minimum sampling rate is 1 */ + entropy_collector->osr = osr; + + entropy_collector->hash_state = hash_state; + + /* fill the data pad with non-zero values */ + jent_gen_entropy(entropy_collector); + + return entropy_collector; +} + +void jent_entropy_collector_free(struct rand_data *entropy_collector) +{ + jent_zfree(entropy_collector->mem); + entropy_collector->mem = NULL; + jent_zfree(entropy_collector); +} + +int jent_entropy_init(void *hash_state) +{ + int i; + __u64 delta_sum = 0; + __u64 old_delta = 0; + unsigned int nonstuck = 0; + int time_backwards = 0; + int count_mod = 0; + int count_stuck = 0; + struct rand_data ec = { 0 }; + + /* Required for RCT */ + ec.osr = 1; + ec.hash_state = hash_state; + + /* We could perform statistical tests here, but the problem is + * that we only have a few loop counts to do testing. These + * loop counts may show some slight skew and we produce + * false positives. + * + * Moreover, only old systems show potentially problematic + * jitter entropy that could potentially be caught here. But + * the RNG is intended for hardware that is available or widely + * used, but not old systems that are long out of favor. Thus, + * no statistical tests. + */ + + /* + * We could add a check for system capabilities such as clock_getres or + * check for CONFIG_X86_TSC, but it does not make much sense as the + * following sanity checks verify that we have a high-resolution + * timer. + */ + /* + * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is + * definitely too little. + * + * SP800-90B requires at least 1024 initial test cycles. + */ +#define TESTLOOPCOUNT 1024 +#define CLEARCACHE 100 + for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) { + __u64 time = 0; + __u64 time2 = 0; + __u64 delta = 0; + unsigned int lowdelta = 0; + int stuck; + + /* Invoke core entropy collection logic */ + jent_get_nstime(&time); + ec.prev_time = time; + jent_condition_data(&ec, time, 0); + jent_get_nstime(&time2); + + /* test whether timer works */ + if (!time || !time2) + return JENT_ENOTIME; + delta = jent_delta(time, time2); + /* + * test whether timer is fine grained enough to provide + * delta even when called shortly after each other -- this + * implies that we also have a high resolution timer + */ + if (!delta) + return JENT_ECOARSETIME; + + stuck = jent_stuck(&ec, delta); + + /* + * up to here we did not modify any variable that will be + * evaluated later, but we already performed some work. Thus we + * already have had an impact on the caches, branch prediction, + * etc. with the goal to clear it to get the worst case + * measurements. + */ + if (i < CLEARCACHE) + continue; + + if (stuck) + count_stuck++; + else { + nonstuck++; + + /* + * Ensure that the APT succeeded. + * + * With the check below that count_stuck must be less + * than 10% of the overall generated raw entropy values + * it is guaranteed that the APT is invoked at + * floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times. + */ + if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) { + jent_apt_reset(&ec, + delta & JENT_APT_WORD_MASK); + } + } + + /* Validate health test result */ + if (jent_health_failure(&ec)) + return JENT_EHEALTH; + + /* test whether we have an increasing timer */ + if (!(time2 > time)) + time_backwards++; + + /* use 32 bit value to ensure compilation on 32 bit arches */ + lowdelta = time2 - time; + if (!(lowdelta % 100)) + count_mod++; + + /* + * ensure that we have a varying delta timer which is necessary + * for the calculation of entropy -- perform this check + * only after the first loop is executed as we need to prime + * the old_data value + */ + if (delta > old_delta) + delta_sum += (delta - old_delta); + else + delta_sum += (old_delta - delta); + old_delta = delta; + } + + /* + * we allow up to three times the time running backwards. + * CLOCK_REALTIME is affected by adjtime and NTP operations. Thus, + * if such an operation just happens to interfere with our test, it + * should not fail. The value of 3 should cover the NTP case being + * performed during our test run. + */ + if (time_backwards > 3) + return JENT_ENOMONOTONIC; + + /* + * Variations of deltas of time must on average be larger + * than 1 to ensure the entropy estimation + * implied with 1 is preserved + */ + if ((delta_sum) <= 1) + return JENT_EVARVAR; + + /* + * Ensure that we have variations in the time stamp below 10 for at + * least 10% of all checks -- on some platforms, the counter increments + * in multiples of 100, but not always + */ + if ((TESTLOOPCOUNT/10 * 9) < count_mod) + return JENT_ECOARSETIME; + + /* + * If we have more than 90% stuck results, then this Jitter RNG is + * likely to not work well. + */ + if ((TESTLOOPCOUNT/10 * 9) < count_stuck) + return JENT_ESTUCK; + + return 0; +} |