/* $OpenBSD: rnd.c,v 1.115 2010/12/31 22:32:20 deraadt Exp $ */ /* * rnd.c -- A strong random number generator * * Copyright (c) 1996, 1997, 2000-2002 Michael Shalayeff. * Copyright (c) 2008 Damien Miller. * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. * All rights reserved. * * 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 Public License, in which case the provisions of the GPL 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 ARE * 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 ADVISED * OF THE POSSIBILITY OF SUCH DAMAGE. */ /* * (now, with legal B.S. out of the way.....) * * This routine gathers environmental noise from device drivers, etc., * and returns good random numbers, suitable for cryptographic or * other use. * * Theory of operation * =================== * * Computers are very predictable devices. Hence it is extremely hard * to produce truly random numbers on a computer --- as opposed to * pseudo-random numbers, which can be easily generated by using an * algorithm. Unfortunately, it is very easy for attackers to guess * the sequence of pseudo-random number generators, and for some * applications this is not acceptable. Instead, we must try to * gather "environmental noise" from the computer's environment, which * must be hard for outside attackers to observe and use to * generate random numbers. In a Unix environment, this is best done * from inside the kernel. * * Sources of randomness from the environment include inter-keyboard * timings, inter-interrupt timings from some interrupts, and other * events which are both (a) non-deterministic and (b) hard for an * outside observer to measure. Randomness from these sources is * added to the "entropy pool", which is mixed using a CRC-like function. * This is not cryptographically strong, but it is adequate assuming * the randomness is not chosen maliciously, and it is fast enough that * the overhead of doing it on every interrupt is very reasonable. * As random bytes are mixed into the entropy pool, the routines keep * an *estimate* of how many bits of randomness have been stored into * the random number generator's internal state. * * When random bytes are desired, they are obtained by taking the MD5 * hash of the content of the entropy pool. The MD5 hash avoids * exposing the internal state of the entropy pool. It is believed to * be computationally infeasible to derive any useful information * about the input of MD5 from its output. Even if it is possible to * analyze MD5 in some clever way, as long as the amount of data * returned from the generator is less than the inherent entropy in * the pool, the output data is totally unpredictable. For this * reason, the routine decreases its internal estimate of how many * bits of "true randomness" are contained in the entropy pool as it * outputs random numbers. * * If this estimate goes to zero, the routine can still generate * random numbers; however, an attacker may (at least in theory) be * able to infer the future output of the generator from prior * outputs. This requires successful cryptanalysis of MD5, which is * believed to be not feasible, but there is a remote possibility. * Nonetheless, these numbers should be useful for the vast majority * of purposes. * * However, this MD5 output is not exported outside the subsystem. It * is next used as input to seed a RC4 stream cipher. Attempts are * made to follow best practice regarding this stream cipher - the first * chunk of output is discarded and the cipher is re-seeded from time to * time. This design provides very high amounts of output data from a * potentially small entropy base, at high enough speeds to encourage * use of random numbers in nearly any situation. * * The output of this single RC4 engine is then shared amongst many * consumers in the kernel and userland via various interfaces: * arc4random_buf(), arc4random(), arc4random_uniform(), the set of * /dev/random nodes, and the sysctl kern.arandom. * * Exported interfaces ---- input * ============================== * * The current exported interfaces for gathering environmental noise * from the devices are: * * void add_true_randomness(int data); * void add_timer_randomness(int data); * void add_mouse_randomness(int mouse_data); * void add_net_randomness(int isr); * void add_tty_randomness(int c); * void add_disk_randomness(int n); * void add_audio_randomness(int n); * void add_video_randomness(int n); * * add_true_randomness() uses true random number generators present * on some cryptographic and system chipsets. Entropy accounting * is not quitable, no timing is done, supplied 32 bits of pure entropy * are hashed into the pool plain and blindly, increasing the counter. * * add_timer_randomness() uses the random driver itselves timing, * measuring extract_entropy() and rndioctl() execution times. * * add_mouse_randomness() uses the mouse interrupt timing, as well as * the reported position of the mouse from the hardware. * * add_net_randomness() times the finishing time of net input. * * add_tty_randomness() uses the inter-keypress timing, as well as the * character as random inputs into the entropy pool. * * add_disk_randomness() times the finishing time of disk requests as well * as feeding both xfer size & time into the entropy pool. * * add_audio_randomness() times the finishing of audio codec dma * requests for both recording and playback, apparently supplies quite * a lot of entropy. I'd blame it on low resolution audio clock generators. * * All of these routines (except for add_true_randomness() of course) * try to estimate how many bits of randomness are in a particular * randomness source. They do this by keeping track of the first and * second order deltas of the event timings. * * Acknowledgements: * ================= * * Ideas for constructing this random number generator were derived * from Pretty Good Privacy's random number generator, and from private * discussions with Phil Karn. Colin Plumb provided a faster random * number generator, which speeds up the mixing function of the entropy * pool, taken from PGPfone. Dale Worley has also contributed many * useful ideas and suggestions to improve this driver. * * Any flaws in the design are solely my responsibility, and should * not be attributed to the Phil, Colin, or any of the authors of PGP. * * Further background information on this topic may be obtained from * RFC 1750, "Randomness Recommendations for Security", by Donald * Eastlake, Steve Crocker, and Jeff Schiller. * * Using a RC4 stream cipher as 2nd stage after the MD5 output * is the result of work by David Mazieres. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* * Master random number pool functions * ----------------------------------- */ /* * For the purposes of better mixing, we use the CRC-32 polynomial as * well to make a twisted Generalized Feedback Shift Register * * (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR generators. ACM * Transactions on Modeling and Computer Simulation 2(3):179-194. * Also see M. Matsumoto & Y. Kurita, 1994. Twisted GFSR generators * II. ACM Transactions on Mdeling and Computer Simulation 4:254-266) * * Thanks to Colin Plumb for suggesting this. * * We have not analyzed the resultant polynomial to prove it primitive; * in fact it almost certainly isn't. Nonetheless, the irreducible factors * of a random large-degree polynomial over GF(2) are more than large enough * that periodicity is not a concern. * * The input hash is much less sensitive than the output hash. All * we want from it is to be a good non-cryptographic hash - * i.e. to not produce collisions when fed "random" data of the sort * we expect to see. As long as the pool state differs for different * inputs, we have preserved the input entropy and done a good job. * The fact that an intelligent attacker can construct inputs that * will produce controlled alterations to the pool's state is not * important because we don't consider such inputs to contribute any * randomness. The only property we need with respect to them is that * the attacker can't increase his/her knowledge of the pool's state. * Since all additions are reversible (knowing the final state and the * input, you can reconstruct the initial state), if an attacker has * any uncertainty about the initial state, he/she can only shuffle * that uncertainty about, but never cause any collisions (which would * decrease the uncertainty). * * The chosen system lets the state of the pool be (essentially) the input * modulo the generator polynomial. Now, for random primitive polynomials, * this is a universal class of hash functions, meaning that the chance * of a collision is limited by the attacker's knowledge of the generator * polynomial, so if it is chosen at random, an attacker can never force * a collision. Here, we use a fixed polynomial, but we *can* assume that * ###--> it is unknown to the processes generating the input entropy. <-### * Because of this important property, this is a good, collision-resistant * hash; hash collisions will occur no more often than chance. */ /* * Stirring polynomials over GF(2) for various pool sizes. Used in * add_entropy_words() below. * * The polynomial terms are chosen to be evenly spaced (minimum RMS * distance from evenly spaced; except for the last tap, which is 1 to * get the twisting happening as fast as possible. * * The reultant polynomial is: * 2^POOLWORDS + 2^POOL_TAP1 + 2^POOL_TAP2 + 2^POOL_TAP3 + 2^POOL_TAP4 + 1 */ #define POOLBITS (POOLWORDS*32) #define POOLBYTES (POOLWORDS*4) #define POOLMASK (POOLWORDS - 1) #if POOLWORDS == 2048 #define POOL_TAP1 1638 #define POOL_TAP2 1231 #define POOL_TAP3 819 #define POOL_TAP4 411 #elif POOLWORDS == 1024 /* also (819, 616, 410, 207, 2) */ #define POOL_TAP1 817 #define POOL_TAP2 615 #define POOL_TAP3 412 #define POOL_TAP4 204 #elif POOLWORDS == 512 /* also (409,307,206,102,2), (409,309,205,103,2) */ #define POOL_TAP1 411 #define POOL_TAP2 308 #define POOL_TAP3 208 #define POOL_TAP4 104 #elif POOLWORDS == 256 #define POOL_TAP1 205 #define POOL_TAP2 155 #define POOL_TAP3 101 #define POOL_TAP4 52 #elif POOLWORDS == 128 /* also (103, 78, 51, 27, 2) */ #define POOL_TAP1 103 #define POOL_TAP2 76 #define POOL_TAP3 51 #define POOL_TAP4 25 #elif POOLWORDS == 64 #define POOL_TAP1 52 #define POOL_TAP2 39 #define POOL_TAP3 26 #define POOL_TAP4 14 #elif POOLWORDS == 32 #define POOL_TAP1 26 #define POOL_TAP2 20 #define POOL_TAP3 14 #define POOL_TAP4 7 #else #error No primitive polynomial available for chosen POOLWORDS #endif static void dequeue_randomness(void *); /* Master kernel random number pool. */ struct random_bucket { u_int add_ptr; u_int entropy_count; u_char input_rotate; u_int32_t pool[POOLWORDS]; u_int tmo; }; struct random_bucket random_state; struct mutex rndlock; /* * This function adds a byte into the entropy pool. It does not * update the entropy estimate. The caller must do this if appropriate. * * The pool is stirred with a polynomial of degree POOLWORDS over GF(2); * see POOL_TAP[1-4] above * * Rotate the input word by a changing number of bits, to help assure * that all bits in the entropy get toggled. Otherwise, if the pool * is consistently feed small numbers (such as keyboard scan codes) * then the upper bits of the entropy pool will frequently remain * untouched. */ static void add_entropy_words(const u_int32_t *buf, u_int n) { /* derived from IEEE 802.3 CRC-32 */ static const u_int32_t twist_table[8] = { 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158, 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 }; for (; n--; buf++) { u_int32_t w = (*buf << random_state.input_rotate) | (*buf >> (32 - random_state.input_rotate)); u_int i = random_state.add_ptr = (random_state.add_ptr - 1) & POOLMASK; /* * Normally, we add 7 bits of rotation to the pool. * At the beginning of the pool, add an extra 7 bits * rotation, so that successive passes spread the * input bits across the pool evenly. */ random_state.input_rotate = (random_state.input_rotate + (i ? 7 : 14)) & 31; /* XOR pool contents corresponding to polynomial terms */ w ^= random_state.pool[(i + POOL_TAP1) & POOLMASK] ^ random_state.pool[(i + POOL_TAP2) & POOLMASK] ^ random_state.pool[(i + POOL_TAP3) & POOLMASK] ^ random_state.pool[(i + POOL_TAP4) & POOLMASK] ^ random_state.pool[(i + 1) & POOLMASK] ^ random_state.pool[i]; /* + 2^POOLWORDS */ random_state.pool[i] = (w >> 3) ^ twist_table[w & 7]; } } /* * This function extracts randomness from the entropy pool, and * returns it in a buffer. This function computes how many remaining * bits of entropy are left in the pool, but it does not restrict the * number of bytes that are actually obtained. */ static void extract_entropy(u_int8_t *buf, int nbytes) { u_char buffer[16]; MD5_CTX tmp; u_int i; add_timer_randomness(nbytes); while (nbytes) { if (nbytes < sizeof(buffer) / 2) i = nbytes; else i = sizeof(buffer) / 2; /* Hash the pool to get the output */ MD5Init(&tmp); mtx_enter(&rndlock); MD5Update(&tmp, (u_int8_t*)random_state.pool, sizeof(random_state.pool)); if (random_state.entropy_count / 8 > i) random_state.entropy_count -= i * 8; else random_state.entropy_count = 0; mtx_leave(&rndlock); MD5Final(buffer, &tmp); /* * In case the hash function has some recognizable * output pattern, we fold it in half. */ buffer[0] ^= buffer[15]; buffer[1] ^= buffer[14]; buffer[2] ^= buffer[13]; buffer[3] ^= buffer[12]; buffer[4] ^= buffer[11]; buffer[5] ^= buffer[10]; buffer[6] ^= buffer[ 9]; buffer[7] ^= buffer[ 8]; /* Copy data to destination buffer */ bcopy(buffer, buf, i); nbytes -= i; buf += i; /* Modify pool so next hash will produce different results */ add_timer_randomness(nbytes); dequeue_randomness(NULL); } /* Wipe data from memory */ bzero(&tmp, sizeof(tmp)); bzero(buffer, sizeof(buffer)); } /* * Kernel-side entropy crediting API and handling of entropy-bearing events * ------------------------------------------------------------------------ */ /* pIII/333 reported to have some drops w/ these numbers */ #define QEVLEN (1024 / sizeof(struct rand_event)) #define QEVSLOW (QEVLEN * 3 / 4) /* yet another 0.75 for 60-minutes hour /-; */ #define QEVSBITS 10 /* There is one of these per entropy source */ struct timer_rand_state { u_int last_time; u_int last_delta; u_int last_delta2; u_int dont_count_entropy : 1; u_int max_entropy : 1; }; struct rand_event { struct timer_rand_state *re_state; u_int re_nbits; u_int re_time; u_int re_val; }; struct timer_rand_state rnd_states[RND_SRC_NUM]; struct rand_event rnd_event_space[QEVLEN]; struct rand_event *rnd_event_head = rnd_event_space; struct rand_event *rnd_event_tail = rnd_event_space; struct timeout rnd_timeout; struct rndstats rndstats; int rnd_attached; /* must be called at a proper spl, returns ptr to the next event */ static __inline struct rand_event * rnd_get(void) { struct rand_event *p = rnd_event_tail; if (p == rnd_event_head) return NULL; if (p + 1 >= &rnd_event_space[QEVLEN]) rnd_event_tail = rnd_event_space; else rnd_event_tail++; return p; } /* must be called at a proper spl, returns next available item */ static __inline struct rand_event * rnd_put(void) { struct rand_event *p = rnd_event_head + 1; if (p >= &rnd_event_space[QEVLEN]) p = rnd_event_space; if (p == rnd_event_tail) return NULL; return rnd_event_head = p; } /* must be called at a proper spl, returns number of items in the queue */ static __inline int rnd_qlen(void) { int len = rnd_event_head - rnd_event_tail; return (len < 0)? -len : len; } /* * This function adds entropy to the entropy pool by using timing * delays. It uses the timer_rand_state structure to make an estimate * of how many bits of entropy this call has added to the pool. * * The number "val" is also added to the pool - it should somehow describe * the type of event which just happened. Currently the values of 0-255 * are for keyboard scan codes, 256 and upwards - for interrupts. * On the i386, this is assumed to be at most 16 bits, and the high bits * are used for a high-resolution timer. */ void enqueue_randomness(int state, int val) { struct timer_rand_state *p; struct rand_event *rep; struct timespec ts; u_int time, nbits; #ifdef DIAGNOSTIC if (state < 0 || state >= RND_SRC_NUM) return; #endif p = &rnd_states[state]; val += state << 13; if (!rnd_attached) { if ((rep = rnd_put()) == NULL) { rndstats.rnd_drops++; return; } rep->re_state = &rnd_states[RND_SRC_TIMER]; rep->re_nbits = 0; rep->re_time = 0; rep->re_time = val; return; } nanotime(&ts); time = (ts.tv_nsec >> 10) + (ts.tv_sec << 20); nbits = 0; /* * Calculate the number of bits of randomness that we probably * added. We take into account the first and second order * deltas in order to make our estimate. */ if (!p->dont_count_entropy) { int delta, delta2, delta3; delta = time - p->last_time; delta2 = delta - p->last_delta; delta3 = delta2 - p->last_delta2; if (delta < 0) delta = -delta; if (delta2 < 0) delta2 = -delta2; if (delta3 < 0) delta3 = -delta3; if (delta > delta2) delta = delta2; if (delta > delta3) delta = delta3; delta3 = delta >>= 1; /* * delta &= 0xfff; * we don't do it since our time sheet is different from linux */ if (delta & 0xffff0000) { nbits = 16; delta >>= 16; } if (delta & 0xff00) { nbits += 8; delta >>= 8; } if (delta & 0xf0) { nbits += 4; delta >>= 4; } if (delta & 0xc) { nbits += 2; delta >>= 2; } if (delta & 2) { nbits += 1; delta >>= 1; } if (delta & 1) nbits++; /* * the logic is to drop low-entropy entries, * in hope for dequeuing to be more randomfull */ if (rnd_qlen() > QEVSLOW && nbits < QEVSBITS) { rndstats.rnd_drople++; return; } p->last_time = time; p->last_delta = delta3; p->last_delta2 = delta2; } else if (p->max_entropy) nbits = 8 * sizeof(val) - 1; /* given the multi-order delta logic above, this should never happen */ if (nbits >= 32) return; mtx_enter(&rndlock); if ((rep = rnd_put()) == NULL) { rndstats.rnd_drops++; mtx_leave(&rndlock); return; } rep->re_state = p; rep->re_nbits = nbits; rep->re_time = ts.tv_nsec ^ (ts.tv_sec << 20); rep->re_val = val; rndstats.rnd_enqs++; rndstats.rnd_ed[nbits]++; rndstats.rnd_sc[state]++; rndstats.rnd_sb[state] += nbits; if (rnd_qlen() > QEVSLOW/2 && !random_state.tmo) { random_state.tmo++; timeout_add(&rnd_timeout, 1); } mtx_leave(&rndlock); } /* ARGSUSED */ static void dequeue_randomness(void *v) { struct rand_event *rep; u_int32_t buf[2]; u_int nbits; timeout_del(&rnd_timeout); rndstats.rnd_deqs++; mtx_enter(&rndlock); while ((rep = rnd_get())) { buf[0] = rep->re_time; buf[1] = rep->re_val; nbits = rep->re_nbits; mtx_leave(&rndlock); add_entropy_words(buf, 2); rndstats.rnd_total += nbits; random_state.entropy_count += nbits; if (random_state.entropy_count > POOLBITS) random_state.entropy_count = POOLBITS; mtx_enter(&rndlock); } random_state.tmo = 0; mtx_leave(&rndlock); } /* * Exported kernel CPRNG API: arc4random() and friends * --------------------------------------------------- */ /* * Maximum number of bytes to serve directly from the main arc4random * pool. Larger requests are served from discrete arc4 instances keyed * from the main pool. */ #define ARC4_MAIN_MAX_BYTES 2048 /* * Key size (in bytes) for arc4 instances setup to serve requests larger * than ARC4_MAIN_MAX_BYTES. */ #define ARC4_SUB_KEY_BYTES (256 / 8) struct timeout arc4_timeout; struct rc4_ctx arc4random_state; int arc4random_initialized; static void arc4_stir(void) { struct timespec ts; u_int8_t buf[256], *p; int i; /* * Use MD5 PRNG data and a system timespec; early in the boot * process this is the best we can do -- some architectures do * not collect entropy very well during this time, but may have * clock information which is better than nothing. */ extract_entropy((u_int8_t *)buf, sizeof buf); nanotime(&ts); for (p = (u_int8_t *)&ts, i = 0; i < sizeof(ts); i++) buf[i] ^= p[i]; mtx_enter(&rndlock); rndstats.rnd_used += sizeof(buf) * 8; if (rndstats.arc4_nstirs > 0) rc4_crypt(&arc4random_state, buf, buf, sizeof(buf)); rc4_keysetup(&arc4random_state, buf, sizeof(buf)); rndstats.arc4_stirs += sizeof(buf); rndstats.arc4_nstirs++; /* * Throw away the first N words of output, as suggested in the * paper "Weaknesses in the Key Scheduling Algorithm of RC4" * by Fluher, Mantin, and Shamir. (N = 256 in our case.) */ rc4_skip(&arc4random_state, 256 * 4); mtx_leave(&rndlock); } /* * called by timeout to mark arc4 for stirring, * actual stirring happens on any access attempt. */ static void arc4_reinit(void *v) { arc4random_initialized = 0; } static void arc4maybeinit(void) { if (!arc4random_initialized) { #ifdef DIAGNOSTIC if (!rnd_attached) panic("arc4maybeinit: premature"); #endif arc4random_initialized++; arc4_stir(); /* 10 minutes, per dm@'s suggestion */ timeout_add_sec(&arc4_timeout, 10 * 60); } } void randomattach(void) { if (rnd_attached) return; timeout_set(&rnd_timeout, dequeue_randomness, NULL); timeout_set(&arc4_timeout, arc4_reinit, NULL); random_state.add_ptr = 0; random_state.entropy_count = 0; rnd_states[RND_SRC_TIMER].dont_count_entropy = 1; rnd_states[RND_SRC_TRUE].dont_count_entropy = 1; rnd_states[RND_SRC_TRUE].max_entropy = 1; mtx_init(&rndlock, IPL_HIGH); arc4_reinit(NULL); if (msgbufp && msgbufp->msg_magic == MSG_MAGIC) add_entropy_words((u_int32_t *)msgbufp->msg_bufc, msgbufp->msg_bufs / sizeof(u_int32_t)); rnd_attached = 1; } /* Return one word of randomness from an RC4 generator */ u_int32_t arc4random(void) { u_int32_t ret; arc4maybeinit(); mtx_enter(&rndlock); rc4_getbytes(&arc4random_state, (u_char *)&ret, sizeof(ret)); rndstats.arc4_reads += sizeof(ret); mtx_leave(&rndlock); return ret; } /* * Return a "large" buffer of randomness using an independantly-keyed RC4 * generator. */ static void arc4random_buf_large(void *buf, size_t n) { u_char lbuf[ARC4_SUB_KEY_BYTES]; struct rc4_ctx lctx; mtx_enter(&rndlock); rc4_getbytes(&arc4random_state, lbuf, sizeof(lbuf)); rndstats.arc4_reads += n; mtx_leave(&rndlock); rc4_keysetup(&lctx, lbuf, sizeof(lbuf)); rc4_skip(&lctx, 256 * 4); rc4_getbytes(&lctx, (u_char *)buf, n); bzero(lbuf, sizeof(lbuf)); bzero(&lctx, sizeof(lctx)); } /* * Fill a buffer of arbitrary length with RC4-derived randomness. */ void arc4random_buf(void *buf, size_t n) { arc4maybeinit(); /* Satisfy large requests via an independent ARC4 instance */ if (n > ARC4_MAIN_MAX_BYTES) { arc4random_buf_large(buf, n); return; } mtx_enter(&rndlock); rc4_getbytes(&arc4random_state, (u_char *)buf, n); rndstats.arc4_reads += n; mtx_leave(&rndlock); } /* * Calculate a uniformly distributed random number less than upper_bound * avoiding "modulo bias". * * Uniformity is achieved by generating new random numbers until the one * returned is outside the range [0, 2**32 % upper_bound). This * guarantees the selected random number will be inside * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) * after reduction modulo upper_bound. */ u_int32_t arc4random_uniform(u_int32_t upper_bound) { u_int32_t r, min; if (upper_bound < 2) return 0; #if (ULONG_MAX > 0xffffffffUL) min = 0x100000000UL % upper_bound; #else /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ if (upper_bound > 0x80000000) min = 1 + ~upper_bound; /* 2**32 - upper_bound */ else { /* (2**32 - x) % x == 2**32 % x when x <= 2**31 */ min = ((0xffffffff - upper_bound) + 1) % upper_bound; } #endif /* * This could theoretically loop forever but each retry has * p > 0.5 (worst case, usually far better) of selecting a * number inside the range we need, so it should rarely need * to re-roll. */ for (;;) { r = arc4random(); if (r >= min) break; } return r % upper_bound; } /* * random, srandom, urandom, arandom char devices * ------------------------------------------------------- */ int randomopen(dev_t dev, int flag, int mode, struct proc *p) { return (minor(dev) < RND_NODEV ? 0 : ENXIO); } int randomclose(dev_t dev, int flag, int mode, struct proc *p) { return 0; } int randomread(dev_t dev, struct uio *uio, int ioflag) { int ret = 0; u_int32_t *buf; if (uio->uio_resid == 0) return 0; buf = malloc(POOLBYTES, M_TEMP, M_WAITOK); while (!ret && uio->uio_resid > 0) { int n = min(POOLBYTES, uio->uio_resid); switch (minor(dev)) { case RND_RND: ret = EIO; /* no chip -- error */ break; case RND_SRND: case RND_URND: case RND_ARND: arc4random_buf(buf, n); break; default: ret = ENXIO; } if (n != 0 && ret == 0) { ret = uiomove((caddr_t)buf, n, uio); if (!ret && uio->uio_resid > 0) yield(); } } free(buf, M_TEMP); return ret; } int randomwrite(dev_t dev, struct uio *uio, int flags) { int ret = 0, newdata = 0; u_int32_t *buf; if (minor(dev) == RND_RND) return ENXIO; if (uio->uio_resid == 0) return 0; buf = malloc(POOLBYTES, M_TEMP, M_WAITOK); while (!ret && uio->uio_resid > 0) { u_int n = min(POOLBYTES, uio->uio_resid); ret = uiomove(buf, n, uio); if (ret) break; while (n % sizeof(u_int32_t)) ((u_int8_t *)buf)[n++] = 0; add_entropy_words(buf, n / 4); newdata = 1; } if (newdata) { mtx_enter(&rndlock); arc4random_initialized = 0; mtx_leave(&rndlock); } free(buf, M_TEMP); return ret; } int randomioctl(dev_t dev, u_long cmd, caddr_t data, int flag, struct proc *p) { int ret = 0; switch (cmd) { case FIOASYNC: /* rnd has no async flag in softc so this is really a no-op. */ break; case FIONBIO: /* Handled in the upper FS layer. */ break; default: ret = ENOTTY; } return ret; }