/* $OpenBSD: rnd.c,v 1.11 1996/10/19 13:25:58 mickey Exp $ */ /* * random.c -- A strong random number generator * * Copyright (c) 1996 Michael Shalayeff. * * Version 1.00, last modified 26-May-96 * * Copyright Theodore Ts'o, 1994, 1995, 1996. 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 use. * Besides the obvious cryptographic uses, these numbers are also good * for seeding TCP sequence numbers, and other places where it is * desirable to have numbers which are not only random, but hard to * predict by an attacker. * * 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 easily generated by using a * 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. So instead, we must try to * gather "environmental noise" from the computer's environment, which * must be hard for outside attackers to observe, and use that 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 are * added to an "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 contents 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 * not believed to be feasible, but there is a remote possibility. * Nonetheless, these numbers should be useful for the vast majority * of purposes. * * Exported interfaces ---- output * =============================== * * There are three exported interfaces; the first is one designed to * be used from within the kernel: * * void get_random_bytes(void *buf, int nbytes); * * This interface will return the requested number of random bytes, * and place it in the requested buffer. * * The two other interfaces are two character devices /dev/random and * /dev/urandom. /dev/random is suitable for use when very high * quality randomness is desired (for example, for key generation or * one-time pads), as it will only return a maximum of the number of * bits of randomness (as estimated by the random number generator) * contained in the entropy pool. * * The /dev/urandom device does not have this limit, and will return * as many bytes as are requested. As more and more random bytes are * requested without giving time for the entropy pool to recharge, * this will result in random numbers that are merely cryptographically * strong. For many applications, however, this is acceptable. * * Exported interfaces ---- input * ============================== * * The current exported interfaces for gathering environmental noise * from the devices are: * * void add_mouse_randomness(u_int32_t mouse_data); * void add_net_randomness(int isr); * void add_tty_randomness(dev_t dev, int c); * void add_blkdev_randomness(int irq); * * add_keyboard_randomness() uses the inter-keypress timing, as well as the * scancode as random inputs into the "entropy pool". * * add_mouse_randomness() uses the mouse interrupt timing, as well as * the reported position of the mouse from the hardware. * * add_interrupt_randomness() uses the inter-interrupt timing as random * inputs to the entropy pool. Note that not all interrupts are good * sources of randomness! For example, the timer interrupts is not a * good choice, because the periodicity of the interrupts is to * regular, and hence predictable to an attacker. Disk interrupts are * a better measure, since the timing of the disk interrupts are more * unpredictable. * * add_blkdev_randomness() times the finishing time of block requests. * * All of these routines try to estimate how many bits of randomness a * particular randomness source. They do this by keeping track of the * first and second order deltas of the event timings. * * Ensuring unpredictability at system startup * ============================================ * * When any operating system starts up, it will go through a sequence * of actions that are fairly predictable by an adversary, especially * if the start-up does not involve interaction with a human operator. * This reduces the actual number of bits of unpredictability in the * entropy pool below the value in entropy_count. In order to * counteract this effect, it helps to carry information in the * entropy pool across shut-downs and start-ups. To do this, put the * following lines an appropriate script which is run during the boot * sequence: * * echo "Initializing random number generator..." * # Carry a random seed from start-up to start-up * # Load and then save 512 bytes, which is the size of the entropy pool * if [ -f /etc/random-seed ]; then * cat /etc/random-seed >/dev/urandom * fi * dd if=/dev/urandom of=/etc/random-seed count=1 * * and the following lines in an appropriate script which is run as * the system is shutdown: * * # Carry a random seed from shut-down to start-up * # Save 512 bytes, which is the size of the entropy pool * echo "Saving random seed..." * dd if=/dev/urandom of=/etc/random-seed count=1 * * For example, on many Linux systems, the appropriate scripts are * usually /etc/rc.d/rc.local and /etc/rc.d/rc.0, respectively. * * Effectively, these commands cause the contents of the entropy pool * to be saved at shut-down time and reloaded into the entropy pool at * start-up. (The 'dd' in the addition to the bootup script is to * make sure that /etc/random-seed is different for every start-up, * even if the system crashes without executing rc.0.) Even with * complete knowledge of the start-up activities, predicting the state * of the entropy pool requires knowledge of the previous history of * the system. * * Configuring the /dev/random driver under Linux * ============================================== * * The /dev/random driver under Linux uses minor numbers 8 and 9 of * the /dev/mem major number (#1). So if your system does not have * /dev/random and /dev/urandom created already, they can be created * by using the commands: * * mknod /dev/random c 1 8 * mknod /dev/urandom c 1 9 * * Acknowledgements: * ================= * * Ideas for constructing this random number generator were derived * from the Pretty Good Privacy's random number generator, and from * private discussions with Phil Karn. Colin Plumb provided a faster * random number generator, which speed up the mixing function of the * entropy pool, taken from PGP 3.0 (under development). It has since * been modified by myself to provide better mixing in the case where * the input values to add_entropy_word() are mostly small numbers. * 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 authors of PGP. * * The code for MD5 transform was taken from Colin Plumb's * implementation, which has been placed in the public domain. The * MD5 cryptographic checksum was devised by Ronald Rivest, and is * documented in RFC 1321, "The MD5 Message Digest Algorithm". * * Further background information on this topic may be obtained from * RFC 1750, "Randomness Recommendations for Security", by Donald * Eastlake, Steve Crocker, and Jeff Schiller. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef DEBUG int rnd_debug = 0x0000; #define RD_INPUT 0x000f /* input data */ #define RD_OUTPUT 0x00f0 /* output data */ #define RD_WAIT 0x0100 /* sleep/wakeup for good data */ #endif #ifdef RND_USE_SHA #define HASH_BUFFER_SIZE 5 #define HASH_TRANSFORM SHATransform #else /* RND_USE_MD5 */ #ifndef RND_USE_MD5 #define RND_USE_MD5 #endif #define HASH_BUFFER_SIZE 4 #define HASH_TRANSFORM MD5Transform #endif /* * The pool is stirred with a primitive polynomial of degree 128 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1. * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1. */ #define POOLBITS (POOLWORDS*32) #if POOLWORDS == 128 #define TAP1 99 /* The polynomial taps */ #define TAP2 59 #define TAP3 31 #define TAP4 9 #define TAP5 7 #elif POOLWORDS == 64 #define TAP1 62 /* The polynomial taps */ #define TAP2 38 #define TAP3 10 #define TAP4 6 #define TAP5 1 #else #error No primitive polynomial available for chosen POOLWORDS #endif /* There is actually only one of these, globally. */ struct random_bucket { u_int add_ptr; u_int entropy_count; int input_rotate; u_int32_t *pool; }; /* There is one of these per entropy source */ struct timer_rand_state { u_long last_time; int last_delta; int dont_count_entropy:1; }; struct arc4_stream { u_char i; u_char j; u_char s[256]; }; /* tags for different random sources */ #define ENT_NET 0x100 #define ENT_BLKDEV 0x200 #define ENT_TTY 0x300 static struct random_bucket random_state; struct arc4_stream arc4random_state; static u_int32_t random_pool[POOLWORDS]; static struct timer_rand_state mouse_timer_state; static struct timer_rand_state extract_timer_state; static struct timer_rand_state net_timer_state[32]; /* XXX */ static struct timer_rand_state *blkdev_timer_state; static struct timer_rand_state *tty_timer_state; static int rnd_sleep = 0; #ifndef MIN #define MIN(a,b) (((a) < (b)) ? (a) : (b)) #endif static inline void add_entropy_word __P((struct random_bucket *r, const u_int32_t input)); static void add_timer_randomness __P((struct random_bucket *r, struct timer_rand_state *state, u_int num)); static inline int extract_entropy __P((struct random_bucket *r, char *buf, int nbytes)); /* Arcfour random stream generator. This code is derived from section * 17.1 of Applied Cryptography, second edition, which describes a * stream cipher allegedly compatible with RSA Labs "RC4" cipher (the * actual description of which is a trade secret). The same algorithm * is used as a stream cipher called "arcfour" in Tatu Ylonen's ssh * package. * * The initialization function here has been modified not to discard * old state, and its input always includes the time of day in * microseconds. Moreover, bytes from the stream may at any point be * diverted to multiple processes or even kernel functions desiring * random numbers. This increases the strenght of the random stream, * but makes it impossible to use this code for encryption--There is * no way ever to reproduce the same stream of random bytes. * * RC4 is a registered trademark of RSA Laboratories. */ static void arc4_init (struct arc4_stream *as, u_char *data, int len) { int n; u_char si; as->i--; for (n = 0; n < 256; n++) { as->i = (as->i + 1) & 0xff; si = as->s[as->i]; as->j = (as->j + si + data[n % len]) & 0xff; as->s[as->i] = as->s[as->j]; as->s[as->j] = si; } } static inline u_char arc4_getbyte (struct arc4_stream *as) { u_char si, sj; as->i = (as->i + 1) & 0xff; si = as->s[as->i]; as->j = (as->j + si) & 0xff; sj = as->s[as->j]; as->s[as->i] = sj; as->s[as->j] = si; return (as->s[(si + sj) & 0xff]); } u_int32_t arc4random (void) { return ((arc4_getbyte (&arc4random_state) << 24) | (arc4_getbyte (&arc4random_state) << 16) | (arc4_getbyte (&arc4random_state) << 8) | arc4_getbyte (&arc4random_state)); } void randomattach(void) { int i; struct timeval tv; random_state.add_ptr = 0; random_state.entropy_count = 0; random_state.pool = random_pool; blkdev_timer_state = malloc(nblkdev*sizeof(*blkdev_timer_state), M_DEVBUF, M_WAITOK); bzero(blkdev_timer_state, nblkdev*sizeof(*blkdev_timer_state)); tty_timer_state = malloc(nchrdev*sizeof(*tty_timer_state), M_DEVBUF, M_WAITOK); bzero(tty_timer_state, nchrdev*sizeof(*tty_timer_state)); extract_timer_state.dont_count_entropy = 1; for (i = 0; i < 256; i++) arc4random_state.s[i] = i; microtime (&tv); arc4_init (&arc4random_state, (u_char *) &tv, sizeof (tv)); } int randomopen(dev, flag, mode, p) dev_t dev; int flag; int mode; struct proc *p; { return (minor (dev) < RND_NODEV) ? 0 : ENXIO; } int randomclose(dev, flag, mode, p) dev_t dev; int flag; int mode; struct proc *p; { return 0; } /* * 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 primitive polynomial of degree 128 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1. * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1. * * We rotate the input word by a changing number of bits, to help * assure that all bits in the entropy get toggled. Otherwise, if we * consistently feed the entropy pool small numbers (like jiffies and * scancodes, for example), the upper bits of the entropy pool don't * get affected. --- TYT, 10/11/95 */ static inline void add_entropy_word(r, input) struct random_bucket *r; const u_int32_t input; { u_int i; u_int32_t w; w = (input << r->input_rotate) | (input >> (32 - r->input_rotate)); i = r->add_ptr = (r->add_ptr - 1) & (POOLWORDS-1); if (i) r->input_rotate = (r->input_rotate + 7) & 31; else /* * At the beginning of the pool, add an extra 7 bits * rotation, so that successive passes spread the * input bits across the pool evenly. */ r->input_rotate = (r->input_rotate + 14) & 31; /* XOR in the various taps */ w ^= r->pool[(i+TAP1)&(POOLWORDS-1)]; w ^= r->pool[(i+TAP2)&(POOLWORDS-1)]; w ^= r->pool[(i+TAP3)&(POOLWORDS-1)]; w ^= r->pool[(i+TAP4)&(POOLWORDS-1)]; w ^= r->pool[(i+TAP5)&(POOLWORDS-1)]; w ^= r->pool[i]; /* Rotate w left 1 bit (stolen from SHA) and store */ r->pool[i] = (w << 1) | (w >> 31); } /* * 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 "num" is also added to the pool - it should somehow describe * the type of event which just happened. This is currently 0-255 for * keyboard scan codes, and 256 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. * */ static void add_timer_randomness(r, state, num) struct random_bucket *r; struct timer_rand_state *state; u_int num; { int delta, delta2; u_int nbits; u_long time; { struct timeval tv; microtime(&tv); time = tv.tv_usec ^ tv.tv_sec; } add_entropy_word(r, (u_int32_t) num); add_entropy_word(r, time); /* * Calculate number of bits of randomness we probably * added. We take into account the first and second order * deltas in order to make our estimate. */ if (!state->dont_count_entropy) { delta = time - state->last_time; state->last_time = time; delta2 = delta - state->last_delta; state->last_delta = delta; if (delta < 0) delta = -delta; if (delta2 < 0) delta2 = -delta2; delta = MIN(delta, delta2) >> 1; for (nbits = 0; delta; nbits++) delta >>= 1; r->entropy_count += nbits; /* Prevent overflow */ if (r->entropy_count > POOLBITS) r->entropy_count = POOLBITS; } if (r->entropy_count > 8 && rnd_sleep != 0) { rnd_sleep--; #ifdef DEBUG if (rnd_debug & RD_WAIT) printf("rnd: wakeup[%d]{%u}\n", rnd_sleep, r->entropy_count); #endif wakeup(&rnd_sleep); } } void add_mouse_randomness(mouse_data) u_int32_t mouse_data; { add_timer_randomness(&random_state, &mouse_timer_state, mouse_data); } void add_net_randomness(isr) int isr; { if (isr >= sizeof(net_timer_state)/sizeof(*net_timer_state)) return; add_timer_randomness(&random_state, &net_timer_state[isr], ENT_NET + isr); } void add_blkdev_randomness(dev) dev_t dev; { if (major(dev) <= nblkdev || blkdev_timer_state == NULL) return; add_timer_randomness(&random_state, &blkdev_timer_state[major(dev)], ENT_BLKDEV + major(dev)); } void add_tty_randomness(dev, c) dev_t dev; int c; { if (major(dev) <= nchrdev || tty_timer_state == NULL) return; add_timer_randomness(&random_state, &tty_timer_state[major(dev)], ENT_TTY + c); } #if POOLWORDS % 16 #error extract_entropy() assumes that POOLWORDS is a multiple of 16 words. #endif /* * 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 inline int extract_entropy(r, buf, nbytes) struct random_bucket *r; char *buf; int nbytes; { int ret, i; u_int32_t tmp[HASH_BUFFER_SIZE]; add_timer_randomness(r, &extract_timer_state, nbytes); /* Redundant, but just in case... */ if (r->entropy_count > POOLBITS) r->entropy_count = POOLBITS; ret = nbytes; if (r->entropy_count / 8 >= nbytes) r->entropy_count -= nbytes*8; else r->entropy_count = 0; while (nbytes) { /* Hash the pool to get the output */ #ifdef RND_USE_MD5 MD5Init(tmp); #endif for (i = 0; i < POOLWORDS; i += 16) HASH_TRANSFORM(tmp, r->pool+i); /* Modify pool so next hash will produce different results */ add_entropy_word(r, tmp[0]); add_entropy_word(r, tmp[1]); add_entropy_word(r, tmp[2]); add_entropy_word(r, tmp[3]); #ifdef RND_USE_SHA add_entropy_word(r, tmp[5]); #endif /* * Run the MD5 Transform one more time, since we want * to add at least minimal obscuring of the inputs to * add_entropy_word(). --- TYT */ HASH_TRANSFORM(tmp, r->pool); /* * In case the hash function has some recognizable * output pattern, we fold it in half. */ { register u_int8_t *cp, *dp; cp = (u_int8_t *) tmp; dp = cp + (HASH_BUFFER_SIZE*sizeof(tmp[0])) - 1; for (i=0; i < HASH_BUFFER_SIZE*sizeof(tmp[0])/2; i++) { *cp ^= *dp; cp++; dp--; } } /* Copy data to destination buffer */ i = MIN(nbytes, HASH_BUFFER_SIZE*sizeof(tmp[0])); bcopy((caddr_t)tmp, buf, i); nbytes -= i; buf += i; add_timer_randomness(r, &extract_timer_state, nbytes); } /* Wipe data from memory */ bzero(tmp, sizeof(tmp)); return ret; } /* * This function is the exported kernel interface. It returns some * number of good random numbers, suitable for seeding TCP sequence * numbers, etc. */ void get_random_bytes(buf, nbytes) void *buf; size_t nbytes; { extract_entropy(&random_state, (char *) buf, nbytes); } int randomread(dev, uio, ioflag) dev_t dev; struct uio *uio; int ioflag; { int ret = 0; int s, i; if (uio->uio_resid == 0) return 0; while (!ret && uio->uio_resid > 0) { u_int32_t buf[ POOLWORDS ]; int n = min(sizeof(buf), uio->uio_resid); s = splhigh(); switch(minor(dev)) { case RND_RND: ret = EIO; /* no chip -- error */ break; case RND_SRND: if (random_state.entropy_count < 8) { if (ioflag & IO_NDELAY) { ret = EWOULDBLOCK; break; } #ifdef DEBUG if (rnd_debug & RD_WAIT) printf("rnd: sleep[%d]\n", rnd_sleep); #endif rnd_sleep++; ret = tsleep(&rnd_sleep, PWAIT | PCATCH, "rndrd", 0); #ifdef DEBUG if (rnd_debug & RD_WAIT) printf("rnd: awakened(%d)\n", ret); #endif if (ret) break; } n = min(n, random_state.entropy_count / 8); #ifdef DEBUG if (rnd_debug & RD_OUTPUT) printf("rnd: %u possible output\n", n); #endif case RND_URND: n = extract_entropy(&random_state, (char *)buf, n); #ifdef DEBUG if (rnd_debug & RD_OUTPUT) printf("rnd: %u bytes for output\n", n); #endif break; case RND_PRND: i = (n + 3) / 4; while (i--) buf[i] = random(); break; case RND_ARND: { u_char *cp = (u_char *) buf; u_char *end = cp + n; while (cp < end) *cp++ = arc4_getbyte (&arc4random_state); break; } } splx(s); if (n != 0 && ret == 0) ret = uiomove((caddr_t)buf, n, uio); } return ret; } int randomselect(dev, rw, p) dev_t dev; int rw; struct proc *p; { switch (rw) { case FREAD: return random_state.entropy_count > 0; case FWRITE: return 1; } return 0; } static inline void arc4_stir (struct arc4_stream *as) { int rsec = random_state.entropy_count >> 3; u_int buf[2 + POOLWORDS]; int n = min (sizeof(buf) - 2 * sizeof (u_int), rsec); microtime ((struct timeval *) buf); get_random_bytes (buf + 2, n); arc4_init (&arc4random_state, (u_char *) buf, 2 * sizeof (u_int) + n); } int randomwrite(dev, uio, flags) dev_t dev; struct uio *uio; int flags; { int ret = 0; if (minor(dev) == RND_RND || minor(dev) == RND_PRND) return ENXIO; if (uio->uio_resid == 0) return 0; while (!ret && uio->uio_resid > 0) { u_int32_t buf[ POOLWORDS ]; u_short n = min(sizeof(buf),uio->uio_resid); ret = uiomove((caddr_t)buf, n, uio); if (!ret) { int i; while (n % sizeof(u_int32_t)) ((u_char *) buf)[n++] = 0; n >>= 2; for (i = 0; i < n; i++) add_entropy_word(&random_state, buf[i]); } } if (minor(dev) == RND_ARND && !ret) arc4_stir (&arc4random_state); return ret; } int randomioctl(dev, cmd, data, flag, p) dev_t dev; u_long cmd; caddr_t data; int flag; struct proc *p; { int ret; u_int cnt; switch (cmd) { case RNDGETENTCNT: ret = copyout(&random_state.entropy_count, data, sizeof(random_state.entropy_count)); break; case RNDADDTOENTCNT: if (suser(p->p_ucred, &p->p_acflag) != 0) return EPERM; copyin(&cnt, data, sizeof(cnt)); random_state.entropy_count += cnt; if (random_state.entropy_count > POOLBITS) random_state.entropy_count = POOLBITS; break; case RNDZAPENTCNT: if (suser(p->p_ucred, &p->p_acflag) != 0) return EPERM; random_state.entropy_count = 0; ret = 0; break; case RNDSTIRARC4: if (suser(p->p_ucred, &p->p_acflag) != 0) return EPERM; if (random_state.entropy_count < 64) return EAGAIN; arc4_stir (&arc4random_state); ret = 0; break; default: ret = EINVAL; } return ret; }