/* * 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; }