The oversampling rate (OSR) value specifies the heuristically implied
entropy in the recorded data - H_submitter = 1/osr. A different entropy
estimate implies a different APT/RCT cutoff value. This change adds
support for OSRs 1 through 15. This OSR can be selected by the caller
of the Jitter RNG.
For this patch, the caller still uses one hard-coded OSR. A subsequent
patch allows this value to be configured.
In addition, the power-up self test is adjusted as follows:
* It allows the caller to provide an oversampling rate that should be
tested with - commonly it should be the same as used for the actual
runtime operation. This makes the power-up testing therefore consistent
with the runtime operation.
* It calls now jent_measure_jitter (i.e. collects the full entropy
that can possibly be harvested by the Jitter RNG) instead of only
jent_condition_data (which only returns the entropy harvested from
the conditioning component). This should now alleviate reports where
the Jitter RNG initialization thinks there is too little entropy.
* The power-up test now solely relies on the (enhanced) APT and RCT
test that is used as a health test at runtime.
The code allowing the different OSRs as well as the power-up test
changes are present in the user space version of the Jitter RNG 3.4.1
and thus was already in production use for some time.
Reported-by "Ospan, Abylay" <[email protected]>
Signed-off-by: Stephan Mueller <[email protected]>
---
crypto/jitterentropy-kcapi.c | 4 +-
crypto/jitterentropy.c | 233 ++++++++++++++++++-----------------
crypto/jitterentropy.h | 3 +-
3 files changed, 123 insertions(+), 117 deletions(-)
diff --git a/crypto/jitterentropy-kcapi.c b/crypto/jitterentropy-kcapi.c
index 7d1463a1562a..1de730f94683 100644
--- a/crypto/jitterentropy-kcapi.c
+++ b/crypto/jitterentropy-kcapi.c
@@ -245,7 +245,7 @@ static int jent_kcapi_init(struct crypto_tfm *tfm)
crypto_shash_init(sdesc);
rng->sdesc = sdesc;
- rng->entropy_collector = jent_entropy_collector_alloc(1, 0, sdesc);
+ rng->entropy_collector = jent_entropy_collector_alloc(0, 0, sdesc);
if (!rng->entropy_collector) {
ret = -ENOMEM;
goto err;
@@ -334,7 +334,7 @@ static int __init jent_mod_init(void)
desc->tfm = tfm;
crypto_shash_init(desc);
- ret = jent_entropy_init(desc);
+ ret = jent_entropy_init(0, 0, desc);
shash_desc_zero(desc);
crypto_free_shash(tfm);
if (ret) {
diff --git a/crypto/jitterentropy.c b/crypto/jitterentropy.c
index fe9c233ec769..c99734af82b8 100644
--- a/crypto/jitterentropy.c
+++ b/crypto/jitterentropy.c
@@ -72,6 +72,8 @@ struct rand_data {
__u64 prev_time; /* SENSITIVE Previous time stamp */
__u64 last_delta; /* SENSITIVE stuck test */
__s64 last_delta2; /* SENSITIVE stuck test */
+
+ unsigned int flags; /* Flags used to initialize */
unsigned int osr; /* Oversample rate */
#define JENT_MEMORY_BLOCKS 64
#define JENT_MEMORY_BLOCKSIZE 32
@@ -88,16 +90,9 @@ struct rand_data {
/* 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
+ /* Adaptive Proportion Test cutoff values */
+ unsigned int apt_cutoff; /* Intermittent health test failure */
+ unsigned int apt_cutoff_permanent; /* Permanent health test failure */
#define JENT_APT_WINDOW_SIZE 512 /* Data window size */
/* LSB of time stamp to process */
#define JENT_APT_LSB 16
@@ -122,6 +117,9 @@ struct rand_data {
* 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 */
+#define JENT_EHASH 11 /* Hash self test failed */
+#define JENT_EMEM 12 /* Can't allocate memory for initialization */
/*
* The output n bits can receive more than n bits of min entropy, of course,
@@ -147,6 +145,48 @@ struct rand_data {
* This test complies with SP800-90B section 4.4.2.
***************************************************************************/
+/*
+ * See the SP 800-90B comment #10b for the corrected cutoff for the SP 800-90B
+ * APT.
+ * http://www.untruth.org/~josh/sp80090b/UL%20SP800-90B-final%20comments%20v1.9%2020191212.pdf
+ * In in the syntax of R, this is C = 2 + qbinom(1 − 2^(−30), 511, 2^(-1/osr)).
+ * (The original formula wasn't correct because the first symbol must
+ * necessarily have been observed, so there is no chance of observing 0 of these
+ * symbols.)
+ *
+ * For the alpha < 2^-53, R cannot be used as it uses a float data type without
+ * arbitrary precision. A SageMath script is used to calculate those cutoff
+ * values.
+ *
+ * For any value above 14, this yields the maximal allowable value of 512
+ * (by FIPS 140-2 IG 7.19 Resolution # 16, we cannot choose a cutoff value that
+ * renders the test unable to fail).
+ */
+static const unsigned int jent_apt_cutoff_lookup[15] = {
+ 325, 422, 459, 477, 488, 494, 499, 502,
+ 505, 507, 508, 509, 510, 511, 512 };
+static const unsigned int jent_apt_cutoff_permanent_lookup[15] = {
+ 355, 447, 479, 494, 502, 507, 510, 512,
+ 512, 512, 512, 512, 512, 512, 512 };
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+static void jent_apt_init(struct rand_data *ec, unsigned int osr)
+{
+ /*
+ * Establish the apt_cutoff based on the presumed entropy rate of
+ * 1/osr.
+ */
+ if (osr >= ARRAY_SIZE(jent_apt_cutoff_lookup)) {
+ ec->apt_cutoff = jent_apt_cutoff_lookup[
+ ARRAY_SIZE(jent_apt_cutoff_lookup) - 1];
+ ec->apt_cutoff_permanent = jent_apt_cutoff_permanent_lookup[
+ ARRAY_SIZE(jent_apt_cutoff_permanent_lookup) - 1];
+ } else {
+ ec->apt_cutoff = jent_apt_cutoff_lookup[osr - 1];
+ ec->apt_cutoff_permanent =
+ jent_apt_cutoff_permanent_lookup[osr - 1];
+ }
+}
/*
* Reset the APT counter
*
@@ -187,12 +227,12 @@ static void jent_apt_insert(struct rand_data *ec, unsigned int 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;
+ return (ec->apt_count >= ec->apt_cutoff_permanent) ? 1 : 0;
}
static int jent_apt_failure(struct rand_data *ec)
{
- return (ec->apt_count >= JENT_APT_CUTOFF) ? 1 : 0;
+ return (ec->apt_count >= ec->apt_cutoff) ? 1 : 0;
}
/***************************************************************************
@@ -275,15 +315,28 @@ static int jent_stuck(struct rand_data *ec, __u64 current_delta)
return 0;
}
-/* RCT health test failure detection */
+/*
+ * The cutoff value is based on the following consideration:
+ * alpha = 2^-30 or 2^-60 as recommended in SP800-90B.
+ * 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 (DATA_SIZE_BITS + ENTROPY_SAFETY_FACTOR)*osr deltas for
+ * inserting them into the entropy pool which should then have (close to)
+ * DATA_SIZE_BITS bits of entropy in the conditioned output.
+ *
+ * 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. Thus
+ * C = ceil(-log_2(alpha)/H) = 30*osr or 60*osr.
+ */
static int jent_rct_permanent_failure(struct rand_data *ec)
{
- return (ec->rct_count >= JENT_RCT_CUTOFF_PERMANENT) ? 1 : 0;
+ return (ec->rct_count >= (60 * ec->osr)) ? 1 : 0;
}
static int jent_rct_failure(struct rand_data *ec)
{
- return (ec->rct_count >= JENT_RCT_CUTOFF) ? 1 : 0;
+ return (ec->rct_count >= (30 * ec->osr)) ? 1 : 0;
}
/* Report of health test failures */
@@ -448,7 +501,7 @@ static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
*
* @return result of stuck test
*/
-static int jent_measure_jitter(struct rand_data *ec)
+static int jent_measure_jitter(struct rand_data *ec, __u64 *ret_current_delta)
{
__u64 time = 0;
__u64 current_delta = 0;
@@ -472,6 +525,10 @@ static int jent_measure_jitter(struct rand_data *ec)
if (jent_condition_data(ec, current_delta, stuck))
stuck = 1;
+ /* return the raw entropy value */
+ if (ret_current_delta)
+ *ret_current_delta = current_delta;
+
return stuck;
}
@@ -489,11 +546,11 @@ static void jent_gen_entropy(struct rand_data *ec)
safety_factor = JENT_ENTROPY_SAFETY_FACTOR;
/* priming of the ->prev_time value */
- jent_measure_jitter(ec);
+ jent_measure_jitter(ec, NULL);
while (!jent_health_failure(ec)) {
/* If a stuck measurement is received, repeat measurement */
- if (jent_measure_jitter(ec))
+ if (jent_measure_jitter(ec, NULL))
continue;
/*
@@ -554,7 +611,8 @@ int jent_read_entropy(struct rand_data *ec, unsigned char *data,
* Perform startup health tests and return permanent
* error if it fails.
*/
- if (jent_entropy_init(ec->hash_state))
+ if (jent_entropy_init(ec->osr, ec->flags,
+ ec->hash_state))
return -3;
return -2;
@@ -604,11 +662,15 @@ struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
/* verify and set the oversampling rate */
if (osr == 0)
- osr = 1; /* minimum sampling rate is 1 */
+ osr = 1; /* H_submitter = 1 / osr */
entropy_collector->osr = osr;
+ entropy_collector->flags = flags;
entropy_collector->hash_state = hash_state;
+ /* Initialize the APT */
+ jent_apt_init(entropy_collector, osr);
+
/* fill the data pad with non-zero values */
jent_gen_entropy(entropy_collector);
@@ -622,20 +684,14 @@ void jent_entropy_collector_free(struct rand_data *entropy_collector)
jent_zfree(entropy_collector);
}
-int jent_entropy_init(void *hash_state)
+int jent_entropy_init(unsigned int osr, unsigned int flags, 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;
+ struct rand_data *ec;
+ int i, time_backwards = 0, ret = 0;
+
+ ec = jent_entropy_collector_alloc(osr, flags, hash_state);
+ if (!ec)
+ return JENT_EMEM;
/* We could perform statistical tests here, but the problem is
* that we only have a few loop counts to do testing. These
@@ -664,31 +720,28 @@ int jent_entropy_init(void *hash_state)
#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;
+ __u64 start_time = 0, end_time = 0, delta = 0;
/* Invoke core entropy collection logic */
- jent_get_nstime(&time);
- ec.prev_time = time;
- jent_condition_data(&ec, time, 0);
- jent_get_nstime(&time2);
+ jent_measure_jitter(ec, &delta);
+ end_time = ec->prev_time;
+ start_time = ec->prev_time - delta;
/* test whether timer works */
- if (!time || !time2)
- return JENT_ENOTIME;
- delta = jent_delta(time, time2);
+ if (!start_time || !end_time) {
+ ret = JENT_ENOTIME;
+ goto out;
+ }
+
/*
* 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);
+ if (!delta || (end_time == start_time)) {
+ ret = JENT_ECOARSETIME;
+ goto out;
+ }
/*
* up to here we did not modify any variable that will be
@@ -700,49 +753,9 @@ int jent_entropy_init(void *hash_state)
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))
+ if (!(end_time > start_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;
}
/*
@@ -752,31 +765,23 @@ int jent_entropy_init(void *hash_state)
* 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;
+ if (time_backwards > 3) {
+ ret = JENT_ENOMONOTONIC;
+ goto out;
+ }
- /*
- * 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;
+ /* Did we encounter a health test failure? */
+ if (jent_rct_failure(ec)) {
+ ret = JENT_ERCT;
+ goto out;
+ }
+ if (jent_apt_failure(ec)) {
+ ret = JENT_EHEALTH;
+ goto out;
+ }
- /*
- * 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;
+out:
+ jent_entropy_collector_free(ec);
- return 0;
+ return ret;
}
diff --git a/crypto/jitterentropy.h b/crypto/jitterentropy.h
index 4c92176ea2b1..626c6228b7e2 100644
--- a/crypto/jitterentropy.h
+++ b/crypto/jitterentropy.h
@@ -9,7 +9,8 @@ extern int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len);
struct rand_data;
-extern int jent_entropy_init(void *hash_state);
+extern int jent_entropy_init(unsigned int osr, unsigned int flags,
+ void *hash_state);
extern int jent_read_entropy(struct rand_data *ec, unsigned char *data,
unsigned int len);
--
2.42.0