summaryrefslogtreecommitdiffstats
path: root/crypto/jitterentropy.c
diff options
context:
space:
mode:
Diffstat (limited to 'crypto/jitterentropy.c')
-rw-r--r--crypto/jitterentropy.c782
1 files changed, 782 insertions, 0 deletions
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;
+}