/* * Non-physical true random number generator based on timing jitter. * * Copyright Stephan Mueller , 2014 - 2017 * * Design * ====== * * See documentation in doc/ folder. * * Interface * ========= * * See documentation in doc/ folder. * * 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. */ #undef _FORTIFY_SOURCE #pragma GCC optimize ("O0") #include "jitterentropy.h" #ifndef CONFIG_CRYPTO_CPU_JITTERENTROPY_STAT /* only check optimization in a compilation for real work */ #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-base.c." #endif #endif #define MAJVERSION 2 /* API / ABI incompatible changes, functional changes that * require consumer to be updated (as long as this number * is zero, the API is not considered stable and can * change without a bump of the major version) */ #define MINVERSION 1 /* API compatible, ABI may change, functional * enhancements only, consumer can be left unchanged if * enhancements are not considered */ #define PATCHLEVEL 0 /* API / ABI compatible, no functional changes, no * enhancements, bug fixes only */ /** * jent_version() - Return machine-usable version number of jent library * * The function returns a version number that is monotonic increasing * for newer versions. The version numbers are multiples of 100. For example, * version 1.2.3 is converted to 1020300 -- the last two digits are reserved * for future use. * * The result of this function can be used in comparing the version number * in a calling program if version-specific calls need to be make. * * Return: Version number of kcapi library */ JENT_PRIVATE_STATIC unsigned int jent_version(void) { unsigned int version = 0; version = MAJVERSION * 1000000; version += MINVERSION * 10000; version += PATCHLEVEL * 100; return version; } /** * Update of the loop count used for the next round of * an entropy collection. * * Input: * @ec entropy collector struct -- may be NULL * @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 uint64_t jent_loop_shuffle(struct rand_data *ec, unsigned int bits, unsigned int min) { uint64_t time = 0; uint64_t shuffle = 0; unsigned int i = 0; unsigned int mask = (1<data; /* * 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++) { shuffle ^= time & mask; time = time >> bits; } /* * We add a lower boundary value to ensure we have a minimum * RNG loop count. */ return (shuffle + (1<data * * @return Number of loops the folding operation is performed */ static uint64_t jent_lfsr_time(struct rand_data *ec, uint64_t time, uint64_t loop_cnt) { unsigned int i; uint64_t j = 0; uint64_t new = 0; #define MAX_FOLD_LOOP_BIT 4 #define MIN_FOLD_LOOP_BIT 0 uint64_t fold_loop_cnt = jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT); /* * testing purposes -- allow test app to set the counter, not * needed during runtime */ if (loop_cnt) fold_loop_cnt = loop_cnt; for (j = 0; j < fold_loop_cnt; j++) { new = ec->data; for (i = 1; (DATA_SIZE_BITS) >= i; i++) { uint64_t 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. */ new ^= tmp; new ^= ((new >> 63) & 1); new ^= ((new >> 60) & 1); new ^= ((new >> 55) & 1); new ^= ((new >> 30) & 1); new ^= ((new >> 27) & 1); new ^= ((new >> 22) & 1); new = rol64(new, 1); } } ec->data = new; return fold_loop_cnt; } /** * 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. * * 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 */ static unsigned int jent_memaccess(struct rand_data *ec, uint64_t loop_cnt) { unsigned int wrap = 0; uint64_t i = 0; #define MAX_ACC_LOOP_BIT 7 #define MIN_ACC_LOOP_BIT 0 uint64_t acc_loop_cnt = jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); if (NULL == ec || NULL == ec->mem) return 0; 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; } 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, uint64_t current_delta) { int64_t delta2 = ec->last_delta - current_delta; int64_t 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 * 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. * * Input: * @entropy_collector Reference to entropy collector * * @return: result of stuck test */ static int jent_measure_jitter(struct rand_data *ec) { uint64_t time = 0; uint64_t 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 = time - ec->prev_time; ec->prev_time = time; /* Now call the next noise sources which also injects the data */ jent_lfsr_time(ec, current_delta, 0); /* Check whether we have a stuck measurement. */ stuck = jent_stuck(ec, current_delta); /* * Rotate the data buffer by a prime number (any odd number would * do) to ensure that every bit position of the input time stamp * has an even chance of being merged with a bit position in the * entropy pool. We do not use one here as the adjacent bits in * successive time deltas may have some form of dependency. The * chosen value of 7 implies that the low 7 bits of the next * time delta value is concatenated with the current time delta. */ if (!stuck) ec->data = rol64(ec->data, 7); return stuck; } /** * 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 { uint64_t uint64; uint32_t uint32[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; /* Ensure that the function implements a constant time operation. */ union c throw_away; /* * 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.uint32[1] = 0x67452301; constant.uint32[0] = 0xefcdab89; mixer.uint32[1] = 0x98badcfe; mixer.uint32[0] = 0x10325476; 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.uint64 ^= constant.uint64; else throw_away.uint64 ^= constant.uint64; mixer.uint64 = rol64(mixer.uint64, 1); } entropy_collector->data ^= mixer.uint64; } /** * Generator of one 64 bit random number * Function fills rand_data->data * * Input: * @ec Reference to entropy collector */ static void jent_gen_entropy(struct rand_data *ec) { unsigned int k = 0; /* priming of the ->prev_time value */ jent_measure_jitter(ec); while (1) { /* 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 * ec->osr)) break; } if (ec->stir) jent_stir_pool(ec); } /** * The continuous test required by FIPS 140-2 -- the function automatically * primes the test if needed. * * Return: * 0 if FIPS test passed * < 0 if FIPS test failed */ static int jent_fips_test(struct rand_data *ec) { if (ec->fips_enabled == -1) return 0; if (ec->fips_enabled == 0) { if (!jent_fips_enabled()) { ec->fips_enabled = -1; return 0; } else ec->fips_enabled = 1; } /* prime the FIPS test */ if (!ec->old_data) { ec->old_data = ec->data; jent_gen_entropy(ec); } if (ec->data == ec->old_data) return -1; ec->old_data = ec->data; return 0; } /** * 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. * * 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 * * @return number of bytes returned when request is fulfilled or an error * * The following error codes can occur: * -1 entropy_collector is NULL * -2 FIPS test failed */ JENT_PRIVATE_STATIC ssize_t jent_read_entropy(struct rand_data *ec, char *data, size_t len) { char *p = data; size_t orig_len = len; if (NULL == ec) return -1; while (0 < len) { size_t tocopy; jent_gen_entropy(ec); if (jent_fips_test(ec)) return -2; if ((DATA_SIZE_BITS / 8) < len) tocopy = (DATA_SIZE_BITS / 8); else tocopy = len; memcpy(p, &ec->data, tocopy); len -= tocopy; p += tocopy; } /* * To be on the safe side, we generate one more round of entropy * which we do not give out to the caller. That round shall ensure * that in case the calling application crashes, memory dumps, pages * out, or due to the CPU Jitter RNG lingering in memory for long * time without being moved and an attacker cracks the application, * all he reads in the entropy pool is a value that is NEVER EVER * being used for anything. Thus, he does NOT see the previous value * that was returned to the caller for cryptographic purposes. */ /* * If we use secured memory, do not use that precaution as the secure * memory protects the entropy pool. Moreover, note that using this * call reduces the speed of the RNG by up to half */ #ifndef CONFIG_CRYPTO_CPU_JITTERENTROPY_SECURE_MEMORY jent_gen_entropy(ec); #endif return orig_len; } /*************************************************************************** * Initialization logic ***************************************************************************/ JENT_PRIVATE_STATIC struct rand_data *jent_entropy_collector_alloc(unsigned int osr, unsigned int flags) { struct rand_data *entropy_collector; entropy_collector = jent_zalloc(sizeof(struct rand_data)); if (NULL == entropy_collector) return NULL; if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { /* Allocate memory for adding variations based on memory * access */ entropy_collector->mem = (unsigned char *)jent_zalloc(JENT_MEMORY_SIZE); if (NULL == entropy_collector->mem) { jent_zfree(entropy_collector, sizeof(struct rand_data)); 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 (0 == 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); return entropy_collector; } JENT_PRIVATE_STATIC void jent_entropy_collector_free(struct rand_data *entropy_collector) { if (NULL != entropy_collector) { if (NULL != entropy_collector->mem) { jent_zfree(entropy_collector->mem, JENT_MEMORY_SIZE); entropy_collector->mem = NULL; } jent_zfree(entropy_collector, sizeof(struct rand_data)); } } JENT_PRIVATE_STATIC int jent_entropy_init(void) { int i; uint64_t delta_sum = 0; uint64_t old_delta = 0; int time_backwards = 0; int count_mod = 0; int count_stuck = 0; struct rand_data ec; memset(&ec, 0, sizeof(ec)); /* 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. */ #define TESTLOOPCOUNT 300 #define CLEARCACHE 100 for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) { uint64_t time = 0; uint64_t time2 = 0; uint64_t delta = 0; unsigned int lowdelta = 0; int stuck; /* Invoke core entropy collection logic */ jent_get_nstime(&time); ec.prev_time = time; jent_lfsr_time(&ec, time, 0); jent_get_nstime(&time2); /* test whether timer works */ if (!time || !time2) return ENOTIME; delta = time2 - time; /* * 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 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 (CLEARCACHE > i) continue; if (stuck) count_stuck++; /* 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 (3 < time_backwards) return 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 EMINVARVAR; /* * 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 ECOARSETIME; /* * If we have more than 90% stuck results, then this Jitter RNG is * likely to not work well. */ if (JENT_STUCK_INIT_THRES(TESTLOOPCOUNT) < count_stuck) return ESTUCK; return 0; } /*************************************************************************** * Statistical test logic not compiled for regular operation ***************************************************************************/ #ifdef CONFIG_CRYPTO_CPU_JITTERENTROPY_STAT /* * Statistical test: return the time duration for the folding operation. If min * is set, perform the given number of LFSR ops. Otherwise, allow the * loop count shuffling to define the number of LFSR ops. */ JENT_PRIVATE_STATIC uint64_t jent_lfsr_var_stat(struct rand_data *ec, unsigned int min) { uint64_t time = 0; uint64_t time2 = 0; jent_get_nstime(&time); jent_memaccess(ec, min); jent_lfsr_time(ec, time, min); jent_get_nstime(&time2); return ((time2 - time)); } #endif /* CONFIG_CRYPTO_CPU_JITTERENTROPY_STAT */