The Jitter RNG implementation is updated to comply with upstream version
2.1.2. The change covers the following aspects:
* Time variation measurement is conducted over the LFSR operation
instead of the XOR folding
* Invcation of stuck test during initialization
* Removal of the stirring functionality and the Von-Neumann
unbiaser as the LFSR using a primitive and irreducible polynomial
generates an identical distribution of random bits
This implementation was successfully used in FIPS 140-2 validations
as well as in German BSI evaluations.
This kernel implementation was tested as follows:
* The unchanged kernel code file jitterentropy.c is compiled as part
of user space application to generate raw unconditioned noise
data. That data is processed with the NIST SP800-90B non-IID test
tool to verify that the kernel code exhibits an equal amount of noise
as the upstream Jitter RNG version 2.1.2.
* Using AF_ALG with the libkcapi tool of kcapi-rng the Jitter RNG was
output tested with dieharder to verify that the output does not
exhibit statistical weaknesses. The following command was used:
kcapi-rng -n "jitterentropy_rng" -b 100000000000 | dieharder -a -g 200
* The unchanged kernel code file jitterentropy.c is compiled as part
of user space application to test the LFSR implementation. The
LFSR is injected a monotonically increasing counter as input and
the output is fed into dieharder to verify that the LFSR operation
does not exhibit statistical weaknesses.
* The patch was tested on the Muen separation kernel which returns
a more coarse time stamp to verify that the Jitter RNG does not cause
regressions with its initialization test considering that the Jitter
RNG depends on a high-resolution timer.
Tested-by: Reto Buerki <reet@xxxxxxxxxxx>
Signed-off-by: Stephan Mueller <smueller@xxxxxxxxxx>
---
crypto/jitterentropy-kcapi.c | 5 -
crypto/jitterentropy.c | 305 ++++++++++-------------------------
2 files changed, 82 insertions(+), 228 deletions(-)
diff --git a/crypto/jitterentropy-kcapi.c b/crypto/jitterentropy-kcapi.c
index 6ea1a270b8dc..699db1726ead 100644
--- a/crypto/jitterentropy-kcapi.c
+++ b/crypto/jitterentropy-kcapi.c
@@ -56,11 +56,6 @@ void jent_entropy_collector_free(struct rand_data *entropy_collector);
* Helper function
***************************************************************************/
-__u64 jent_rol64(__u64 word, unsigned int shift)
-{
- return rol64(word, shift);
-}
-
void *jent_zalloc(unsigned int len)
{
return kzalloc(len, GFP_KERNEL);
diff --git a/crypto/jitterentropy.c b/crypto/jitterentropy.c
index acf44b2d2d1d..77fa2120fe0c 100644
--- a/crypto/jitterentropy.c
+++ b/crypto/jitterentropy.c
@@ -2,7 +2,7 @@
* Non-physical true random number generator based on timing jitter --
* Jitter RNG standalone code.
*
- * Copyright Stephan Mueller <smueller@xxxxxxxxxx>, 2015
+ * Copyright Stephan Mueller <smueller@xxxxxxxxxx>, 2015 - 2019
*
* Design
* ======
@@ -47,7 +47,7 @@
/*
* This Jitterentropy RNG is based on the jitterentropy library
- * version 1.1.0 provided at http://www.chronox.de/jent.html
+ * version 2.1.2 provided at http://www.chronox.de/jent.html
*/
#ifdef __OPTIMIZE__
@@ -71,10 +71,7 @@ struct rand_data {
#define DATA_SIZE_BITS ((sizeof(__u64)) * 8)
__u64 last_delta; /* SENSITIVE stuck test */
__s64 last_delta2; /* SENSITIVE stuck test */
- unsigned int stuck:1; /* Time measurement stuck */
unsigned int osr; /* Oversample rate */
- unsigned int stir:1; /* Post-processing stirring */
- unsigned int disable_unbias:1; /* Deactivate Von-Neuman unbias */
#define JENT_MEMORY_BLOCKS 64
#define JENT_MEMORY_BLOCKSIZE 32
#define JENT_MEMORY_ACCESSLOOPS 128
@@ -89,8 +86,6 @@ struct rand_data {
};
/* Flags that can be used to initialize the RNG */
-#define JENT_DISABLE_STIR (1<<0) /* Disable stirring the entropy pool */
-#define JENT_DISABLE_UNBIAS (1<<1) /* Disable the Von-Neuman Unbiaser */
#define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more
* entropy, saves MEMORY_SIZE RAM for
* entropy collector */
@@ -99,19 +94,16 @@ struct rand_data {
#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_EMINVARIATION 4 /* Timer variations too small for RNG */
#define JENT_EVARVAR 5 /* Timer does not produce variations of
* variations (2nd derivation of time is
* zero). */
-#define JENT_EMINVARVAR 6 /* Timer variations of variations is tooi
- * small. */
+#define JENT_ESTUCK 8 /* Too many stuck results during init. */
/***************************************************************************
* Helper functions
***************************************************************************/
void jent_get_nstime(__u64 *out);
-__u64 jent_rol64(__u64 word, unsigned int shift);
void *jent_zalloc(unsigned int len);
void jent_zfree(void *ptr);
int jent_fips_enabled(void);
@@ -140,16 +132,16 @@ static __u64 jent_loop_shuffle(struct rand_data *ec,
jent_get_nstime(&time);
/*
- * mix the current state of the random number into the shuffle
- * calculation to balance that shuffle a bit more
+ * Mix the current state of the random number into the shuffle
+ * calculation to balance that shuffle a bit more.
*/
if (ec)
time ^= ec->data;
/*
- * we fold the time value as much as possible to ensure that as many
- * bits of the time stamp are included as possible
+ * 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) > i; i++) {
+ for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) {
shuffle ^= time & mask;
time = time >> bits;
}
@@ -169,38 +161,28 @@ static __u64 jent_loop_shuffle(struct rand_data *ec,
* CPU Jitter noise source -- this is the noise source based on the CPU
* execution time jitter
*
- * This function folds the time into one bit units by iterating
- * through the DATA_SIZE_BITS bit time value as follows: assume our time value
- * is 0xabcd
- * 1st loop, 1st shift generates 0xd000
- * 1st loop, 2nd shift generates 0x000d
- * 2nd loop, 1st shift generates 0xcd00
- * 2nd loop, 2nd shift generates 0x000c
- * 3rd loop, 1st shift generates 0xbcd0
- * 3rd loop, 2nd shift generates 0x000b
- * 4th loop, 1st shift generates 0xabcd
- * 4th loop, 2nd shift generates 0x000a
- * Now, the values at the end of the 2nd shifts are XORed together.
+ * This function injects the individual bits of the time value into the
+ * entropy pool using an LFSR.
*
- * The code is deliberately inefficient and shall stay that way. This function
- * is the root cause why the code shall be compiled without optimization. This
- * function not only acts as folding operation, but this function's execution
- * is used to measure the CPU execution time jitter. Any change to the loop in
- * this function implies that careful retesting must be done.
+ * The code is deliberately inefficient with respect to the bit shifting
+ * and shall stay that way. This function is the root cause why the code
+ * shall be compiled without optimization. This function not only acts as
+ * folding operation, but this function's execution is used to measure
+ * 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 -- may be NULL
- * @time time stamp to be folded
+ * @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
*
* Output:
- * @folded result of folding operation
+ * updated ec->data
*
* @return Number of loops the folding operation is performed
*/
-static __u64 jent_fold_time(struct rand_data *ec, __u64 time,
- __u64 *folded, __u64 loop_cnt)
+static __u64 jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt)
{
unsigned int i;
__u64 j = 0;
@@ -217,15 +199,34 @@ static __u64 jent_fold_time(struct rand_data *ec, __u64 time,
if (loop_cnt)
fold_loop_cnt = loop_cnt;
for (j = 0; j < fold_loop_cnt; j++) {
- new = 0;
+ new = ec->data;
for (i = 1; (DATA_SIZE_BITS) >= i; i++) {
__u64 tmp = time << (DATA_SIZE_BITS - i);
tmp = tmp >> (DATA_SIZE_BITS - 1);
+
+ /*
+ * Fibonacci LSFR with polynomial of
+ * x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is
+ * primitive according to
+ * http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf
+ * (the shift values are the polynomial values minus one
+ * due to counting bits from 0 to 63). As the current
+ * position is always the LSB, the polynomial only needs
+ * to shift data in from the left without wrap.
+ */
+ tmp ^= ((new >> 63) & 1);
+ tmp ^= ((new >> 60) & 1);
+ tmp ^= ((new >> 55) & 1);
+ tmp ^= ((new >> 30) & 1);
+ tmp ^= ((new >> 27) & 1);
+ tmp ^= ((new >> 22) & 1);
+ new <<= 1;
new ^= tmp;
}
}
- *folded = new;
+ ec->data = new;
+
return fold_loop_cnt;
}
@@ -258,7 +259,6 @@ static __u64 jent_fold_time(struct rand_data *ec, __u64 time,
*/
static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
{
- unsigned char *tmpval = NULL;
unsigned int wrap = 0;
__u64 i = 0;
#define MAX_ACC_LOOP_BIT 7
@@ -278,7 +278,7 @@ static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
acc_loop_cnt = loop_cnt;
for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) {
- tmpval = ec->mem + ec->memlocation;
+ unsigned char *tmpval = ec->mem + ec->memlocation;
/*
* memory access: just add 1 to one byte,
* wrap at 255 -- memory access implies read
@@ -316,7 +316,7 @@ static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
* 0 jitter measurement not stuck (good bit)
* 1 jitter measurement stuck (reject bit)
*/
-static void jent_stuck(struct rand_data *ec, __u64 current_delta)
+static int jent_stuck(struct rand_data *ec, __u64 current_delta)
{
__s64 delta2 = ec->last_delta - current_delta;
__s64 delta3 = delta2 - ec->last_delta2;
@@ -325,14 +325,15 @@ static void jent_stuck(struct rand_data *ec, __u64 current_delta)
ec->last_delta2 = delta2;
if (!current_delta || !delta2 || !delta3)
- ec->stuck = 1;
+ 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 folded into one
- * bit. You can call this function the "random bit generator" as it
- * produces one random bit per invocation.
+ * 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
@@ -341,12 +342,11 @@ static void jent_stuck(struct rand_data *ec, __u64 current_delta)
* Input:
* @entropy_collector Reference to entropy collector
*
- * @return One random bit
+ * @return result of stuck test
*/
-static __u64 jent_measure_jitter(struct rand_data *ec)
+static int jent_measure_jitter(struct rand_data *ec)
{
__u64 time = 0;
- __u64 data = 0;
__u64 current_delta = 0;
/* Invoke one noise source before time measurement to add variations */
@@ -360,109 +360,11 @@ static __u64 jent_measure_jitter(struct rand_data *ec)
current_delta = time - ec->prev_time;
ec->prev_time = time;
- /* Now call the next noise sources which also folds the data */
- jent_fold_time(ec, current_delta, &data, 0);
-
- /*
- * Check whether we have a stuck measurement. The enforcement
- * is performed after the stuck value has been mixed into the
- * entropy pool.
- */
- jent_stuck(ec, current_delta);
-
- return data;
-}
-
-/**
- * Von Neuman unbias as explained in RFC 4086 section 4.2. As shown in the
- * documentation of that RNG, the bits from jent_measure_jitter are considered
- * independent which implies that the Von Neuman unbias operation is applicable.
- * A proof of the Von-Neumann unbias operation to remove skews is given in the
- * document "A proposal for: Functionality classes for random number
- * generators", version 2.0 by Werner Schindler, section 5.4.1.
- *
- * Input:
- * @entropy_collector Reference to entropy collector
- *
- * @return One random bit
- */
-static __u64 jent_unbiased_bit(struct rand_data *entropy_collector)
-{
- do {
- __u64 a = jent_measure_jitter(entropy_collector);
- __u64 b = jent_measure_jitter(entropy_collector);
-
- if (a == b)
- continue;
- if (1 == a)
- return 1;
- else
- return 0;
- } while (1);
-}
-
-/**
- * Shuffle the pool a bit by mixing some value with a bijective function (XOR)
- * into the pool.
- *
- * The function generates a mixer value that depends on the bits set and the
- * location of the set bits in the random number generated by the entropy
- * source. Therefore, based on the generated random number, this mixer value
- * can have 2**64 different values. That mixer value is initialized with the
- * first two SHA-1 constants. After obtaining the mixer value, it is XORed into
- * the random number.
- *
- * The mixer value is not assumed to contain any entropy. But due to the XOR
- * operation, it can also not destroy any entropy present in the entropy pool.
- *
- * Input:
- * @entropy_collector Reference to entropy collector
- */
-static void jent_stir_pool(struct rand_data *entropy_collector)
-{
- /*
- * to shut up GCC on 32 bit, we have to initialize the 64 variable
- * with two 32 bit variables
- */
- union c {
- __u64 u64;
- __u32 u32[2];
- };
- /*
- * This constant is derived from the first two 32 bit initialization
- * vectors of SHA-1 as defined in FIPS 180-4 section 5.3.1
- */
- union c constant;
- /*
- * The start value of the mixer variable is derived from the third
- * and fourth 32 bit initialization vector of SHA-1 as defined in
- * FIPS 180-4 section 5.3.1
- */
- union c mixer;
- unsigned int i = 0;
-
- /*
- * Store the SHA-1 constants in reverse order to make up the 64 bit
- * value -- this applies to a little endian system, on a big endian
- * system, it reverses as expected. But this really does not matter
- * as we do not rely on the specific numbers. We just pick the SHA-1
- * constants as they have a good mix of bit set and unset.
- */
- constant.u32[1] = 0x67452301;
- constant.u32[0] = 0xefcdab89;
- mixer.u32[1] = 0x98badcfe;
- mixer.u32[0] = 0x10325476;
+ /* Now call the next noise sources which also injects the data */
+ jent_lfsr_time(ec, current_delta, 0);
- for (i = 0; i < DATA_SIZE_BITS; i++) {
- /*
- * get the i-th bit of the input random number and only XOR
- * the constant into the mixer value when that bit is set
- */
- if ((entropy_collector->data >> i) & 1)
- mixer.u64 ^= constant.u64;
- mixer.u64 = jent_rol64(mixer.u64, 1);
- }
- entropy_collector->data ^= mixer.u64;
+ /* Check whether we have a stuck measurement. */
+ return jent_stuck(ec, current_delta);
}
/**
@@ -480,48 +382,9 @@ static void jent_gen_entropy(struct rand_data *ec)
jent_measure_jitter(ec);
while (1) {
- __u64 data = 0;
-
- if (ec->disable_unbias == 1)
- data = jent_measure_jitter(ec);
- else
- data = jent_unbiased_bit(ec);
-
- /* enforcement of the jent_stuck test */
- if (ec->stuck) {
- /*
- * We only mix in the bit considered not appropriate
- * without the LSFR. The reason is that if we apply
- * the LSFR and we do not rotate, the 2nd bit with LSFR
- * will cancel out the first LSFR application on the
- * bad bit.
- *
- * And we do not rotate as we apply the next bit to the
- * current bit location again.
- */
- ec->data ^= data;
- ec->stuck = 0;
+ /* If a stuck measurement is received, repeat measurement */
+ if (jent_measure_jitter(ec))
continue;
- }
-
- /*
- * Fibonacci LSFR with polynom of
- * x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is
- * primitive according to
- * http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf
- * (the shift values are the polynom values minus one
- * due to counting bits from 0 to 63). As the current
- * position is always the LSB, the polynom only needs
- * to shift data in from the left without wrap.
- */
- ec->data ^= data;
- ec->data ^= ((ec->data >> 63) & 1);
- ec->data ^= ((ec->data >> 60) & 1);
- ec->data ^= ((ec->data >> 55) & 1);
- ec->data ^= ((ec->data >> 30) & 1);
- ec->data ^= ((ec->data >> 27) & 1);
- ec->data ^= ((ec->data >> 22) & 1);
- ec->data = jent_rol64(ec->data, 1);
/*
* We multiply the loop value with ->osr to obtain the
@@ -530,8 +393,6 @@ static void jent_gen_entropy(struct rand_data *ec)
if (++k >= (DATA_SIZE_BITS * ec->osr))
break;
}
- if (ec->stir)
- jent_stir_pool(ec);
}
/**
@@ -639,12 +500,6 @@ struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
osr = 1; /* minimum sampling rate is 1 */
entropy_collector->osr = osr;
- entropy_collector->stir = 1;
- if (flags & JENT_DISABLE_STIR)
- entropy_collector->stir = 0;
- if (flags & JENT_DISABLE_UNBIAS)
- entropy_collector->disable_unbias = 1;
-
/* fill the data pad with non-zero values */
jent_gen_entropy(entropy_collector);
@@ -656,7 +511,6 @@ void jent_entropy_collector_free(struct rand_data *entropy_collector)
jent_zfree(entropy_collector->mem);
entropy_collector->mem = NULL;
jent_zfree(entropy_collector);
- entropy_collector = NULL;
}
int jent_entropy_init(void)
@@ -665,8 +519,9 @@ int jent_entropy_init(void)
__u64 delta_sum = 0;
__u64 old_delta = 0;
int time_backwards = 0;
- int count_var = 0;
int count_mod = 0;
+ int count_stuck = 0;
+ struct rand_data ec = { 0 };
/* We could perform statistical tests here, but the problem is
* that we only have a few loop counts to do testing. These
@@ -695,12 +550,14 @@ int jent_entropy_init(void)
for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
__u64 time = 0;
__u64 time2 = 0;
- __u64 folded = 0;
__u64 delta = 0;
unsigned int lowdelta = 0;
+ int stuck;
+ /* Invoke core entropy collection logic */
jent_get_nstime(&time);
- jent_fold_time(NULL, time, &folded, 1<<MIN_FOLD_LOOP_BIT);
+ ec.prev_time = time;
+ jent_lfsr_time(&ec, time, 0);
jent_get_nstime(&time2);
/* test whether timer works */
@@ -715,6 +572,8 @@ int jent_entropy_init(void)
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
@@ -725,14 +584,14 @@ int jent_entropy_init(void)
if (CLEARCACHE > i)
continue;
+ if (stuck)
+ count_stuck++;
+
/* test whether we have an increasing timer */
if (!(time2 > time))
time_backwards++;
- /*
- * Avoid modulo of 64 bit integer to allow code to compile
- * on 32 bit architectures.
- */
+ /* use 32 bit value to ensure compilation on 32 bit arches */
lowdelta = time2 - time;
if (!(lowdelta % 100))
count_mod++;
@@ -743,14 +602,10 @@ int jent_entropy_init(void)
* only after the first loop is executed as we need to prime
* the old_data value
*/
- if (i) {
- if (delta != old_delta)
- count_var++;
- if (delta > old_delta)
- delta_sum += (delta - old_delta);
- else
- delta_sum += (old_delta - delta);
- }
+ if (delta > old_delta)
+ delta_sum += (delta - old_delta);
+ else
+ delta_sum += (old_delta - delta);
old_delta = delta;
}
@@ -763,25 +618,29 @@ int jent_entropy_init(void)
*/
if (3 < time_backwards)
return JENT_ENOMONOTONIC;
- /* Error if the time variances are always identical */
- if (!delta_sum)
- return JENT_EVARVAR;
/*
* 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_EMINVARVAR;
+ 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
+ * 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;
}
--
2.21.0
