* Non-physical true random number generator based on timing jitter --
* Jitter RNG standalone code.
*
- * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 2019
+ * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 2020
*
* Design
* ======
/*
* This Jitterentropy RNG is based on the jitterentropy library
- * version 2.1.2 provided at http://www.chronox.de/jent.html
+ * version 2.2.0 provided at http://www.chronox.de/jent.html
*/
#ifdef __OPTIMIZE__
unsigned int memblocksize; /* Size of one memory block in bytes */
unsigned int memaccessloops; /* Number of memory accesses per random
* bit generation */
+
+ /* Repetition Count Test */
+ int rct_count; /* Number of stuck values */
+
+ /* Adaptive Proportion Test for a significance level of 2^-30 */
+#define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */
+#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? */
+
+ unsigned int health_failure:1; /* Permanent health failure */
};
/* Flags that can be used to initialize the RNG */
* 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 */
+#define JENT_ERCT 10 /* RCT failed during initialization */
+
+#include "jitterentropy.h"
/***************************************************************************
- * Helper functions
+ * Adaptive Proportion Test
+ *
+ * This test complies with SP800-90B section 4.4.2.
***************************************************************************/
-#include "jitterentropy.h"
+/**
+ * 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++;
+
+ if (ec->apt_count >= JENT_APT_CUTOFF)
+ ec->health_failure = 1;
+ }
+
+ ec->apt_observations++;
+
+ if (ec->apt_observations >= JENT_APT_WINDOW_SIZE)
+ jent_apt_reset(ec, delta_masked);
+}
+
+/***************************************************************************
+ * 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 we have a count less than zero, a previous RCT round identified
+ * a failure. We will not overwrite it.
+ */
+ if (ec->rct_count < 0)
+ return;
+
+ if (stuck) {
+ ec->rct_count++;
+
+ /*
+ * The cutoff value is based on the following consideration:
+ * alpha = 2^-30 as recommended in FIPS 140-2 IG 9.8.
+ * In addition, we require an entropy value H of 1/OSR as this
+ * is the minimum entropy required to provide full entropy.
+ * Note, we collect 64 * OSR deltas for inserting them into
+ * the entropy pool which should then have (close to) 64 bits
+ * of entropy.
+ *
+ * Note, ec->rct_count (which equals to value B in the pseudo
+ * code of SP800-90B section 4.4.1) starts with zero. Hence
+ * we need to subtract one from the cutoff value as calculated
+ * following SP800-90B.
+ */
+ if ((unsigned int)ec->rct_count >= (31 * ec->osr)) {
+ ec->rct_count = -1;
+ ec->health_failure = 1;
+ }
+ } else {
+ ec->rct_count = 0;
+ }
+}
+
+/**
+ * Is there an RCT health test failure?
+ *
+ * @ec [in] Reference to entropy collector
+ *
+ * @return
+ * 0 No health test failure
+ * 1 Permanent health test failure
+ */
+static int jent_rct_failure(struct rand_data *ec)
+{
+ if (ec->rct_count < 0)
+ return 1;
+ return 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);
+ unsigned int delta_masked = current_delta & JENT_APT_WORD_MASK;
+
+ 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, delta_masked);
+
+ 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;
+}
+
+/**
+ * Report any health test failures
+ *
+ * @ec [in] Reference to entropy collector
+ *
+ * @return
+ * 0 No health test failure
+ * 1 Permanent health test failure
+ */
+static int jent_health_failure(struct rand_data *ec)
+{
+ /* Test is only enabled in FIPS mode */
+ if (!jent_fips_enabled())
+ return 0;
+
+ return ec->health_failure;
+}
+
+/***************************************************************************
+ * Noise sources
+ ***************************************************************************/
/**
* Update of the loop count used for the next round of
return (shuffle + (1<<min));
}
-/***************************************************************************
- * Noise sources
- ***************************************************************************/
-
/**
* CPU Jitter noise source -- this is the noise source based on the CPU
* execution time jitter
* the CPU execution time jitter. Any change to the loop in this function
* implies that careful retesting must be done.
*
- * Input:
- * @ec entropy collector struct
- * @time time stamp to be injected
- * @loop_cnt if a value not equal to 0 is set, use the given value as number of
- * loops to perform the folding
+ * @ec [in] entropy collector struct
+ * @time [in] time stamp to be injected
+ * @loop_cnt [in] if a value not equal to 0 is set, use the given value as
+ * number of loops to perform the folding
+ * @stuck [in] Is the time stamp identified as stuck?
*
* Output:
* updated ec->data
*
* @return Number of loops the folding operation is performed
*/
-static __u64 jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt)
+static void jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt,
+ int stuck)
{
unsigned int i;
__u64 j = 0;
new ^= tmp;
}
}
- ec->data = new;
- return fold_loop_cnt;
+ /*
+ * If the time stamp is stuck, do not finally insert the value into
+ * the entropy pool. Although this operation should not do any harm
+ * even when the time stamp has no entropy, SP800-90B requires that
+ * any conditioning operation (SP800-90B considers the LFSR to be a
+ * conditioning operation) to have an identical amount of input
+ * data according to section 3.1.5.
+ */
+ if (!stuck)
+ ec->data = new;
}
/**
* to reliably access either L3 or memory, the ec->mem memory must be quite
* large which is usually not desirable.
*
- * Input:
- * @ec 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 if a value not equal to 0 is set, use the given value as number of
- * loops to perform the folding
- *
- * @return Number of memory access operations
+ * @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 unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
+static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
{
unsigned int wrap = 0;
__u64 i = 0;
jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT);
if (NULL == ec || NULL == ec->mem)
- return 0;
+ return;
wrap = ec->memblocksize * ec->memblocks;
/*
ec->memlocation = ec->memlocation + ec->memblocksize - 1;
ec->memlocation = ec->memlocation % wrap;
}
- return i;
}
/***************************************************************************
* Start of entropy processing logic
***************************************************************************/
-
-/**
- * Stuck test by checking the:
- * 1st derivation of the jitter measurement (time delta)
- * 2nd derivation of the jitter measurement (delta of time deltas)
- * 3rd derivation of the jitter measurement (delta of delta of time deltas)
- *
- * All values must always be non-zero.
- *
- * Input:
- * @ec Reference to entropy collector
- * @current_delta 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)
-{
- __s64 delta2 = ec->last_delta - current_delta;
- __s64 delta3 = delta2 - ec->last_delta2;
-
- ec->last_delta = current_delta;
- ec->last_delta2 = delta2;
-
- if (!current_delta || !delta2 || !delta3)
- return 1;
-
- return 0;
-}
-
/**
* 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
* of this function! This can be done by calling this function
* and not using its result.
*
- * Input:
- * @entropy_collector Reference to entropy collector
+ * @ec [in] Reference to entropy collector
*
* @return result of stuck test
*/
{
__u64 time = 0;
__u64 current_delta = 0;
+ int stuck;
/* Invoke one noise source before time measurement to add variations */
jent_memaccess(ec, 0);
* invocation to measure the timing variations
*/
jent_get_nstime(&time);
- current_delta = time - ec->prev_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 */
- jent_lfsr_time(ec, current_delta, 0);
+ jent_lfsr_time(ec, current_delta, 0, stuck);
- /* Check whether we have a stuck measurement. */
- return jent_stuck(ec, current_delta);
+ return stuck;
}
/**
* Generator of one 64 bit random number
* Function fills rand_data->data
*
- * Input:
- * @ec Reference to entropy collector
+ * @ec [in] Reference to entropy collector
*/
static void jent_gen_entropy(struct rand_data *ec)
{
}
}
-/**
- * The continuous test required by FIPS 140-2 -- the function automatically
- * primes the test if needed.
- *
- * Return:
- * returns normally if FIPS test passed
- * panics the kernel if FIPS test failed
- */
-static void jent_fips_test(struct rand_data *ec)
-{
- if (!jent_fips_enabled())
- return;
-
- /* prime the FIPS test */
- if (!ec->old_data) {
- ec->old_data = ec->data;
- jent_gen_entropy(ec);
- }
-
- if (ec->data == ec->old_data)
- jent_panic("jitterentropy: Duplicate output detected\n");
-
- ec->old_data = ec->data;
-}
-
/**
* Entry function: Obtain entropy for the caller.
*
* This function truncates the last 64 bit entropy value output to the exact
* size specified by the caller.
*
- * Input:
- * @ec Reference to entropy collector
- * @data pointer to buffer for storing random data -- buffer must already
- * exist
- * @len size of the buffer, specifying also the requested number of random
- * in bytes
+ * @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
+ * -2 RCT failed
+ * -3 APT test failed
*/
int jent_read_entropy(struct rand_data *ec, unsigned char *data,
unsigned int len)
unsigned int tocopy;
jent_gen_entropy(ec);
- jent_fips_test(ec);
+
+ if (jent_health_failure(ec)) {
+ int ret;
+
+ if (jent_rct_failure(ec))
+ ret = -2;
+ else
+ ret = -3;
+
+ /*
+ * Re-initialize the noise source
+ *
+ * If the health test fails, the Jitter RNG remains
+ * in failure state and will return a health failure
+ * during next invocation.
+ */
+ if (jent_entropy_init())
+ return ret;
+
+ /* Set APT to initial state */
+ jent_apt_reset(ec, 0);
+ ec->apt_base_set = 0;
+
+ /* Set RCT to initial state */
+ ec->rct_count = 0;
+
+ /* Re-enable Jitter RNG */
+ ec->health_failure = 0;
+
+ /*
+ * Return the health test failure status to the
+ * caller as the generated value is not appropriate.
+ */
+ return ret;
+ }
+
if ((DATA_SIZE_BITS / 8) < len)
tocopy = (DATA_SIZE_BITS / 8);
else
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;
+
/* 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
/*
* TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
* definitely too little.
+ *
+ * SP800-90B requires at least 1024 initial test cycles.
*/
-#define TESTLOOPCOUNT 300
+#define TESTLOOPCOUNT 1024
#define CLEARCACHE 100
for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
__u64 time = 0;
/* Invoke core entropy collection logic */
jent_get_nstime(&time);
ec.prev_time = time;
- jent_lfsr_time(&ec, time, 0);
+ jent_lfsr_time(&ec, time, 0, 0);
jent_get_nstime(&time2);
/* test whether timer works */
if (!time || !time2)
return JENT_ENOTIME;
- delta = time2 - time;
+ delta = jent_delta(time, time2);
/*
* test whether timer is fine grained enough to provide
* delta even when called shortly after each other -- this
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);
+ if (jent_health_failure(&ec))
+ return JENT_EHEALTH;
+ }
+ }
+
+ /* Validate RCT */
+ if (jent_rct_failure(&ec))
+ return JENT_ERCT;
/* test whether we have an increasing timer */
if (!(time2 > time))
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