entropy.c - security/openssh-library - Rivoreo Source Code Repositories

 /*
  * Copyright (c) 2000 Damien Miller.  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, this list of conditions and the following disclaimer.
  * 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.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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.
  */

 #include "includes.h"

 #include "ssh.h"
 #include "xmalloc.h"

 #include <openssl/rand.h>
 #include <openssl/sha.h>

 /* SunOS 4.4.4 needs this */
 #ifdef HAVE_FLOATINGPOINT_H
 # include <floatingpoint.h>
 #endif /* HAVE_FLOATINGPOINT_H */

 RCSID("$Id: entropy.c,v 1.22 2000/11/24 23:09:32 djm Exp $");

 #ifndef offsetof
 # define offsetof(type, member) ((size_t) &((type *)0)->member)
 #endif

 /* Number of times to pass through command list gathering entropy */
 #define NUM_ENTROPY_RUNS	1

 /* Scale entropy estimates back by this amount on subsequent runs */
 #define SCALE_PER_RUN		10.0

 /* Minimum number of commands to be considered valid */
 #define MIN_ENTROPY_SOURCES 16

 #define WHITESPACE " \t\n"

 #ifndef RUSAGE_SELF
 # define RUSAGE_SELF 0
 #endif
 #ifndef RUSAGE_CHILDREN
 # define RUSAGE_CHILDREN 0
 #endif

 #if defined(EGD_SOCKET) || defined(RANDOM_POOL)

 #ifdef EGD_SOCKET
 /* Collect entropy from EGD */
 int get_random_bytes(unsigned char *buf, int len)
 {
 	int fd;
 	char msg[2];
 	struct sockaddr_un addr;
 	int addr_len;

 	/* Sanity checks */
 	if (sizeof(EGD_SOCKET) > sizeof(addr.sun_path))
 		fatal("Random pool path is too long");
 	if (len > 255)
 		fatal("Too many bytes to read from EGD");

 	memset(&addr, '\0', sizeof(addr));
 	addr.sun_family = AF_UNIX;
 	strlcpy(addr.sun_path, EGD_SOCKET, sizeof(addr.sun_path));
 	addr_len = offsetof(struct sockaddr_un, sun_path) + sizeof(EGD_SOCKET);

 	fd = socket(AF_UNIX, SOCK_STREAM, 0);
 	if (fd == -1) {
 		error("Couldn't create AF_UNIX socket: %s", strerror(errno));
 		return(0);
 	}

 	if (connect(fd, (struct sockaddr*)&addr, addr_len) == -1) {
 		error("Couldn't connect to EGD socket \"%s\": %s",
 			addr.sun_path, strerror(errno));
 		close(fd);
 		return(0);
 	}

 	/* Send blocking read request to EGD */
 	msg[0] = 0x02;
 	msg[1] = len;

 	if (atomicio(write, fd, msg, sizeof(msg)) != sizeof(msg)) {
 		error("Couldn't write to EGD socket \"%s\": %s",
 			EGD_SOCKET, strerror(errno));
 		close(fd);
 		return(0);
 	}

 	if (atomicio(read, fd, buf, len) != len) {
 		error("Couldn't read from EGD socket \"%s\": %s",
 			EGD_SOCKET, strerror(errno));
 		close(fd);
 		return(0);
 	}

 	close(fd);

 	return(1);
 }
 #else /* !EGD_SOCKET */
 #ifdef RANDOM_POOL
 /* Collect entropy from /dev/urandom or pipe */
 int get_random_bytes(unsigned char *buf, int len)
 {
 	int random_pool;

 	random_pool = open(RANDOM_POOL, O_RDONLY);
 	if (random_pool == -1) {
 		error("Couldn't open random pool \"%s\": %s",
 			RANDOM_POOL, strerror(errno));
 		return(0);
 	}

 	if (atomicio(read, random_pool, buf, len) != len) {
 		error("Couldn't read from random pool \"%s\": %s",
 			RANDOM_POOL, strerror(errno));
 		close(random_pool);
 		return(0);
 	}

 	close(random_pool);

 	return(1);
 }
 #endif /* RANDOM_POOL */
 #endif /* EGD_SOCKET */

 /*
  * Seed OpenSSL's random number pool from Kernel random number generator
  * or EGD
  */
 void
 seed_rng(void)
 {
 	char buf[32];

 	debug("Seeding random number generator");

 	if (!get_random_bytes(buf, sizeof(buf))) {
 		if (!RAND_status())
 			fatal("Entropy collection failed and entropy exhausted");
 	} else {
 		RAND_add(buf, sizeof(buf), sizeof(buf));
 	}

 	memset(buf, '\0', sizeof(buf));
 }

 /* No-op */
 void init_rng(void) {}

 #else /* defined(EGD_SOCKET) || defined(RANDOM_POOL) */

 /*
  * FIXME: proper entropy estimations. All current values are guesses
  * FIXME: (ATL) do estimates at compile time?
  * FIXME: More entropy sources
  */

 /* slow command timeouts (all in milliseconds) */
 /* static int entropy_timeout_default = ENTROPY_TIMEOUT_MSEC; */
 static int entropy_timeout_current = ENTROPY_TIMEOUT_MSEC;

 static int prng_seed_saved = 0;
 static int prng_initialised = 0;
 uid_t original_uid;

 typedef struct
 {
 	/* Proportion of data that is entropy */
 	double rate;
 	/* Counter goes positive if this command times out */
 	unsigned int badness;
 	/* Increases by factor of two each timeout */
 	unsigned int sticky_badness;
 	/* Path to executable */
 	char *path;
 	/* argv to pass to executable */
 	char *args[5];
 	/* full command string (debug) */
 	char *cmdstring;
 } entropy_source_t;

 double stir_from_system(void);
 double stir_from_programs(void);
 double stir_gettimeofday(double entropy_estimate);
 double stir_clock(double entropy_estimate);
 double stir_rusage(int who, double entropy_estimate);
 double hash_output_from_command(entropy_source_t *src, char *hash);

 /* this is initialised from a file, by prng_read_commands() */
 entropy_source_t *entropy_sources = NULL;

 double
 stir_from_system(void)
 {
 	double total_entropy_estimate;
 	long int i;

 	total_entropy_estimate = 0;

 	i = getpid();
 	RAND_add(&i, sizeof(i), 0.5);
 	total_entropy_estimate += 0.1;

 	i = getppid();
 	RAND_add(&i, sizeof(i), 0.5);
 	total_entropy_estimate += 0.1;

 	i = getuid();
 	RAND_add(&i, sizeof(i), 0.0);
 	i = getgid();
 	RAND_add(&i, sizeof(i), 0.0);

 	total_entropy_estimate += stir_gettimeofday(1.0);
 	total_entropy_estimate += stir_clock(0.5);
 	total_entropy_estimate += stir_rusage(RUSAGE_SELF, 2.0);

 	return(total_entropy_estimate);
 }

 double
 stir_from_programs(void)
 {
 	int i;
 	int c;
 	double entropy_estimate;
 	double total_entropy_estimate;
 	char hash[SHA_DIGEST_LENGTH];

 	total_entropy_estimate = 0;
 	for(i = 0; i < NUM_ENTROPY_RUNS; i++) {
 		c = 0;
 		while (entropy_sources[c].path != NULL) {

 			if (!entropy_sources[c].badness) {
 				/* Hash output from command */
 				entropy_estimate = hash_output_from_command(&entropy_sources[c], hash);

 				/* Scale back entropy estimate according to command's rate */
 				entropy_estimate *= entropy_sources[c].rate;

 				/* Upper bound of entropy estimate is SHA_DIGEST_LENGTH */
 				if (entropy_estimate > SHA_DIGEST_LENGTH)
 					entropy_estimate = SHA_DIGEST_LENGTH;

 	 			/* Scale back estimates for subsequent passes through list */
 				entropy_estimate /= SCALE_PER_RUN * (i + 1.0);

 				/* Stir it in */
 				RAND_add(hash, sizeof(hash), entropy_estimate);

 				debug3("Got %0.2f bytes of entropy from '%s'", entropy_estimate,
 					entropy_sources[c].cmdstring);

 				total_entropy_estimate += entropy_estimate;

 			/* Execution times should be a little unpredictable */
 				total_entropy_estimate += stir_gettimeofday(0.05);
 				total_entropy_estimate += stir_clock(0.05);
 				total_entropy_estimate += stir_rusage(RUSAGE_SELF, 0.1);
 				total_entropy_estimate += stir_rusage(RUSAGE_CHILDREN, 0.1);
 			} else {
 				debug2("Command '%s' disabled (badness %d)",
 					entropy_sources[c].cmdstring, entropy_sources[c].badness);

 				if (entropy_sources[c].badness > 0)
 					entropy_sources[c].badness--;
 			}

 			c++;
 		}
 	}

 	return(total_entropy_estimate);
 }

 double
 stir_gettimeofday(double entropy_estimate)
 {
 	struct timeval tv;

 	if (gettimeofday(&tv, NULL) == -1)
 		fatal("Couldn't gettimeofday: %s", strerror(errno));

 	RAND_add(&tv, sizeof(tv), entropy_estimate);

 	return(entropy_estimate);
 }

 double
 stir_clock(double entropy_estimate)
 {
 #ifdef HAVE_CLOCK
 	clock_t c;

 	c = clock();
 	RAND_add(&c, sizeof(c), entropy_estimate);

 	return(entropy_estimate);
 #else /* _HAVE_CLOCK */
 	return(0);
 #endif /* _HAVE_CLOCK */
 }

 double
 stir_rusage(int who, double entropy_estimate)
 {
 #ifdef HAVE_GETRUSAGE
 	struct rusage ru;

 	if (getrusage(who, &ru) == -1)
 		return(0);

 	RAND_add(&ru, sizeof(ru), entropy_estimate);

 	return(entropy_estimate);
 #else /* _HAVE_GETRUSAGE */
 	return(0);
 #endif /* _HAVE_GETRUSAGE */
 }


 static
 int
 _get_timeval_msec_difference(struct timeval *t1, struct timeval *t2) {
 	int secdiff, usecdiff;

 	secdiff = t2->tv_sec - t1->tv_sec;
 	usecdiff = (secdiff*1000000) + (t2->tv_usec - t1->tv_usec);
 	return (int)(usecdiff / 1000);
 }

 double
 hash_output_from_command(entropy_source_t *src, char *hash)
 {
 	static int devnull = -1;
 	int p[2];
 	fd_set rdset;
 	int cmd_eof = 0, error_abort = 0;
 	struct timeval tv_start, tv_current;
 	int msec_elapsed = 0;
 	pid_t pid;
 	int status;
 	char buf[16384];
 	int bytes_read;
 	int total_bytes_read;
 	SHA_CTX sha;

 	debug3("Reading output from \'%s\'", src->cmdstring);

 	if (devnull == -1) {
 		devnull = open("/dev/null", O_RDWR);
 		if (devnull == -1)
 			fatal("Couldn't open /dev/null: %s", strerror(errno));
 	}

 	if (pipe(p) == -1)
 		fatal("Couldn't open pipe: %s", strerror(errno));

 	(void)gettimeofday(&tv_start, NULL); /* record start time */

 	switch (pid = fork()) {
 		case -1: /* Error */
 			close(p[0]);
 			close(p[1]);
 			fatal("Couldn't fork: %s", strerror(errno));
 			/* NOTREACHED */
 		case 0: /* Child */
 			dup2(devnull, STDIN_FILENO);
 			dup2(p[1], STDOUT_FILENO);
 			dup2(p[1], STDERR_FILENO);
 			close(p[0]);
 			close(p[1]);
 			close(devnull);

 			setuid(original_uid);
 			execv(src->path, (char**)(src->args));
 			debug("(child) Couldn't exec '%s': %s", src->cmdstring,
 			      strerror(errno));
 			_exit(-1);
 		default: /* Parent */
 			break;
 	}

 	RAND_add(&pid, sizeof(&pid), 0.0);

 	close(p[1]);

 	/* Hash output from child */
 	SHA1_Init(&sha);
 	total_bytes_read = 0;

 	while (!error_abort && !cmd_eof) {
 		int ret;
 		struct timeval tv;
 		int msec_remaining;

 		(void) gettimeofday(&tv_current, 0);
 		msec_elapsed = _get_timeval_msec_difference(&tv_start, &tv_current);
 		if (msec_elapsed >= entropy_timeout_current) {
 			error_abort=1;
 			continue;
 		}
 		msec_remaining = entropy_timeout_current - msec_elapsed;

 		FD_ZERO(&rdset);
 		FD_SET(p[0], &rdset);
 		tv.tv_sec =  msec_remaining / 1000;
 		tv.tv_usec = (msec_remaining % 1000) * 1000;

 		ret = select(p[0]+1, &rdset, NULL, NULL, &tv);

 		RAND_add(&tv, sizeof(tv), 0.0);

 		switch (ret) {
 		case 0:
 			/* timer expired */
 			error_abort = 1;
 			break;
 		case 1:
 			/* command input */
 			bytes_read = read(p[0], buf, sizeof(buf));
 			RAND_add(&bytes_read, sizeof(&bytes_read), 0.0);
 			if (bytes_read == -1) {
 				error_abort = 1;
 				break;
 			} else if (bytes_read) {
 				SHA1_Update(&sha, buf, bytes_read);
 				total_bytes_read += bytes_read;
 			} else {
 				cmd_eof = 1;
 			}
 			break;
 		case -1:
 		default:
 			/* error */
 			debug("Command '%s': select() failed: %s", src->cmdstring,
 			      strerror(errno));
 			error_abort = 1;
 			break;
 		}
 	}

 	SHA1_Final(hash, &sha);

 	close(p[0]);

 	debug3("Time elapsed: %d msec", msec_elapsed);

 	if (waitpid(pid, &status, 0) == -1) {
 	       error("Couldn't wait for child '%s' completion: %s", src->cmdstring,
 		     strerror(errno));
 		return(0.0);
 	}

 	RAND_add(&status, sizeof(&status), 0.0);

 	if (error_abort) {
 		/* closing p[0] on timeout causes the entropy command to
 		 * SIGPIPE. Take whatever output we got, and mark this command
 		 * as slow */
 		debug2("Command '%s' timed out", src->cmdstring);
 		src->sticky_badness *= 2;
 		src->badness = src->sticky_badness;
 		return(total_bytes_read);
 	}

 	if (WIFEXITED(status)) {
 		if (WEXITSTATUS(status)==0) {
 			return(total_bytes_read);
 		} else {
 			debug2("Command '%s' exit status was %d", src->cmdstring,
 				WEXITSTATUS(status));
 			src->badness = src->sticky_badness = 128;
 			return (0.0);
 		}
 	} else if (WIFSIGNALED(status)) {
 		debug2("Command '%s' returned on uncaught signal %d !", src->cmdstring,
 			status);
 		src->badness = src->sticky_badness = 128;
 		return(0.0);
 	} else
 		return(0.0);
 }

 /*
  * prng seedfile functions
  */
 int
 prng_check_seedfile(char *filename) {

 	struct stat st;

 	/* FIXME raceable: eg replace seed between this stat and subsequent open */
 	/* Not such a problem because we don't trust the seed file anyway */
 	if (lstat(filename, &st) == -1) {
 		/* Give up on hard errors */
 		if (errno != ENOENT)
 			debug("WARNING: Couldn't stat random seed file \"%s\": %s",
 			   filename, strerror(errno));

 		return(0);
 	}

 	/* regular file? */
 	if (!S_ISREG(st.st_mode))
 		fatal("PRNG seedfile %.100s is not a regular file", filename);

 	/* mode 0600, owned by root or the current user? */
 	if (((st.st_mode & 0177) != 0) || !(st.st_uid == original_uid)) {
 		debug("WARNING: PRNG seedfile %.100s must be mode 0600, owned by uid %d",
 			 filename, getuid());
 		return(0);
 	}

 	return(1);
 }

 void
 prng_write_seedfile(void) {
 	int fd;
 	char seed[1024];
 	char filename[1024];
 	struct passwd *pw;

 	/* Don't bother if we have already saved a seed */
 	if (prng_seed_saved)
 		return;

 	setuid(original_uid);

 	prng_seed_saved = 1;

 	pw = getpwuid(original_uid);
 	if (pw == NULL)
 		fatal("Couldn't get password entry for current user (%i): %s",
 			original_uid, strerror(errno));

 	/* Try to ensure that the parent directory is there */
 	snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
 		SSH_USER_DIR);
 	mkdir(filename, 0700);

 	snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
 		SSH_PRNG_SEED_FILE);

 	debug("writing PRNG seed to file %.100s", filename);

 	RAND_bytes(seed, sizeof(seed));

 	/* Don't care if the seed doesn't exist */
 	prng_check_seedfile(filename);

 	if ((fd = open(filename, O_WRONLY|O_TRUNC|O_CREAT, 0600)) == -1) {
 		debug("WARNING: couldn't access PRNG seedfile %.100s (%.100s)",
 		   filename, strerror(errno));
 	} else {
 		if (atomicio(write, fd, &seed, sizeof(seed)) != sizeof(seed))
 			fatal("problem writing PRNG seedfile %.100s (%.100s)", filename,
 				 strerror(errno));

 		close(fd);
 	}
 }

 void
 prng_read_seedfile(void) {
 	int fd;
 	char seed[1024];
 	char filename[1024];
 	struct passwd *pw;

 	pw = getpwuid(original_uid);
 	if (pw == NULL)
 		fatal("Couldn't get password entry for current user (%i): %s",
 			original_uid, strerror(errno));

 	snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
 		SSH_PRNG_SEED_FILE);

 	debug("loading PRNG seed from file %.100s", filename);

 	if (!prng_check_seedfile(filename)) {
 		verbose("Random seed file not found, creating new");
 		prng_write_seedfile();

 		/* Reseed immediatly */
 		(void)stir_from_system();
 		(void)stir_from_programs();
 		return;
 	}

 	/* open the file and read in the seed */
 	fd = open(filename, O_RDONLY);
 	if (fd == -1)
 		fatal("could not open PRNG seedfile %.100s (%.100s)", filename,
 			strerror(errno));

 	if (atomicio(read, fd, &seed, sizeof(seed)) != sizeof(seed)) {
 		verbose("invalid or short read from PRNG seedfile %.100s - ignoring",
 			filename);
 		memset(seed, '\0', sizeof(seed));
 	}
 	close(fd);

 	/* stir in the seed, with estimated entropy zero */
 	RAND_add(&seed, sizeof(seed), 0.0);
 }


 /*
  * entropy command initialisation functions
  */
 int
 prng_read_commands(char *cmdfilename)
 {
 	FILE *f;
 	char *cp;
 	char line[1024];
 	char cmd[1024];
 	char path[256];
 	int linenum;
 	int num_cmds = 64;
 	int cur_cmd = 0;
 	double est;
 	entropy_source_t *entcmd;

 	f = fopen(cmdfilename, "r");
 	if (!f) {
 		fatal("couldn't read entropy commands file %.100s: %.100s",
 		    cmdfilename, strerror(errno));
 	}

 	entcmd = (entropy_source_t *)xmalloc(num_cmds * sizeof(entropy_source_t));
 	memset(entcmd, '\0', num_cmds * sizeof(entropy_source_t));

 	/* Read in file */
 	linenum = 0;
 	while (fgets(line, sizeof(line), f)) {
 		int arg;
 		char *argv;

 		linenum++;

 		/* skip leading whitespace, test for blank line or comment */
 		cp = line + strspn(line, WHITESPACE);
 		if ((*cp == 0) || (*cp == '#'))
 			continue; /* done with this line */

 		/* First non-whitespace char should be double quote delimiting */
 		/* commandline */
 		if (*cp != '"') {
 			error("bad entropy command, %.100s line %d", cmdfilename,
 			     linenum);
 			continue;
 		}

 		/* first token, command args (incl. argv[0]) in double quotes */
 		cp = strtok(cp, "\"");
 		if (cp == NULL) {
 			error("missing or bad command string, %.100s line %d -- ignored",
 			      cmdfilename, linenum);
 			continue;
 		}
 		strlcpy(cmd, cp, sizeof(cmd));

 		/* second token, full command path */
 		if ((cp = strtok(NULL, WHITESPACE)) == NULL) {
 			error("missing command path, %.100s line %d -- ignored",
 			      cmdfilename, linenum);
 			continue;
 		}

 		/* did configure mark this as dead? */
 		if (strncmp("undef", cp, 5) == 0)
 			continue;

 		strlcpy(path, cp, sizeof(path));

 		/* third token, entropy rate estimate for this command */
 		if ((cp = strtok(NULL, WHITESPACE)) == NULL) {
 			error("missing entropy estimate, %.100s line %d -- ignored",
 			      cmdfilename, linenum);
 			continue;
 		}
 		est = strtod(cp, &argv);

 		/* end of line */
 		if ((cp = strtok(NULL, WHITESPACE)) != NULL) {
 			error("garbage at end of line %d in %.100s -- ignored", linenum,
 				cmdfilename);
 			continue;
 		}

 		/* save the command for debug messages */
 		entcmd[cur_cmd].cmdstring = xstrdup(cmd);

 		/* split the command args */
 		cp = strtok(cmd, WHITESPACE);
 		arg = 0;
 		argv = NULL;
 		do {
 			char *s = (char*)xmalloc(strlen(cp) + 1);
 			strncpy(s, cp, strlen(cp) + 1);
 			entcmd[cur_cmd].args[arg] = s;
 			arg++;
 		} while ((arg < 5) && (cp = strtok(NULL, WHITESPACE)));

 		if (strtok(NULL, WHITESPACE))
 			error("ignored extra command elements (max 5), %.100s line %d",
 			      cmdfilename, linenum);

 		/* Copy the command path and rate estimate */
 		entcmd[cur_cmd].path = xstrdup(path);
 		entcmd[cur_cmd].rate = est;

 		/* Initialise other values */
 		entcmd[cur_cmd].sticky_badness = 1;

 		cur_cmd++;

 		/* If we've filled the array, reallocate it twice the size */
 		/* Do this now because even if this we're on the last command,
 		   we need another slot to mark the last entry */
 		if (cur_cmd == num_cmds) {
 			num_cmds *= 2;
 			entcmd = xrealloc(entcmd, num_cmds * sizeof(entropy_source_t));
 		}
 	}

 	/* zero the last entry */
 	memset(&entcmd[cur_cmd], '\0', sizeof(entropy_source_t));

 	/* trim to size */
 	entropy_sources = xrealloc(entcmd, (cur_cmd+1) * sizeof(entropy_source_t));

 	debug("Loaded %d entropy commands from %.100s", cur_cmd, cmdfilename);

 	return (cur_cmd >= MIN_ENTROPY_SOURCES);
 }

 /*
  * Write a keyfile at exit
  */
 void
 prng_seed_cleanup(void *junk)
 {
 	prng_write_seedfile();
 }

 /*
  * Conditionally Seed OpenSSL's random number pool from
  * syscalls and program output
  */
 void
 seed_rng(void)
 {
 	void *old_sigchld_handler;

 	if (!prng_initialised)
 		fatal("RNG not initialised");

 	/* Make sure some other sigchld handler doesn't reap our entropy */
 	/* commands */
 	old_sigchld_handler = signal(SIGCHLD, SIG_DFL);

 	debug("Seeded RNG with %i bytes from programs", (int)stir_from_programs());
 	debug("Seeded RNG with %i bytes from system calls", (int)stir_from_system());

 	if (!RAND_status())
 		fatal("Not enough entropy in RNG");

 	signal(SIGCHLD, old_sigchld_handler);

 	if (!RAND_status())
 		fatal("Couldn't initialise builtin random number generator -- exiting.");
 }

 void init_rng(void)
 {
 	int original_euid;

 	original_uid = getuid();
 	original_euid = geteuid();

 	/* Read in collection commands */
 	if (!prng_read_commands(SSH_PRNG_COMMAND_FILE))
 		fatal("PRNG initialisation failed -- exiting.");

 	/* Set ourselves up to save a seed upon exit */
 	prng_seed_saved = 0;

 	/* Give up privs while reading seed file */
 	if ((original_uid != original_euid) && (seteuid(original_uid) == -1))
 		fatal("Couldn't give up privileges");

 	prng_read_seedfile();

 	if ((original_uid != original_euid) && (seteuid(original_euid) == -1))
 		fatal("Couldn't restore privileges");

 	fatal_add_cleanup(prng_seed_cleanup, NULL);
 	atexit(prng_write_seedfile);

 	prng_initialised = 1;
 }

 #endif /* defined(EGD_SOCKET) || defined(RANDOM_POOL) */
	/*
	* Copyright (c) 2000 Damien Miller. 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, this list of conditions and the following disclaimer.
	* 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.
	*
	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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.
	*/

	#include "includes.h"

	#include "ssh.h"
	#include "xmalloc.h"

	#include <openssl/rand.h>
	#include <openssl/sha.h>

	/* SunOS 4.4.4 needs this */
	#ifdef HAVE_FLOATINGPOINT_H
	# include <floatingpoint.h>
	#endif /* HAVE_FLOATINGPOINT_H */

	RCSID("$Id: entropy.c,v 1.22 2000/11/24 23:09:32 djm Exp $");

	#ifndef offsetof
	# define offsetof(type, member) ((size_t) &((type *)0)->member)
	#endif

	/* Number of times to pass through command list gathering entropy */
	#define NUM_ENTROPY_RUNS 1

	/* Scale entropy estimates back by this amount on subsequent runs */
	#define SCALE_PER_RUN 10.0

	/* Minimum number of commands to be considered valid */
	#define MIN_ENTROPY_SOURCES 16

	#define WHITESPACE " \t\n"

	#ifndef RUSAGE_SELF
	# define RUSAGE_SELF 0
	#endif
	#ifndef RUSAGE_CHILDREN
	# define RUSAGE_CHILDREN 0
	#endif

	#if defined(EGD_SOCKET) \|\| defined(RANDOM_POOL)

	#ifdef EGD_SOCKET
	/* Collect entropy from EGD */
	int get_random_bytes(unsigned char *buf, int len)
	{
	int fd;
	char msg[2];
	struct sockaddr_un addr;
	int addr_len;

	/* Sanity checks */
	if (sizeof(EGD_SOCKET) > sizeof(addr.sun_path))
	fatal("Random pool path is too long");
	if (len > 255)
	fatal("Too many bytes to read from EGD");

	memset(&addr, '\0', sizeof(addr));
	addr.sun_family = AF_UNIX;
	strlcpy(addr.sun_path, EGD_SOCKET, sizeof(addr.sun_path));
	addr_len = offsetof(struct sockaddr_un, sun_path) + sizeof(EGD_SOCKET);

	fd = socket(AF_UNIX, SOCK_STREAM, 0);
	if (fd == -1) {
	error("Couldn't create AF_UNIX socket: %s", strerror(errno));
	return(0);
	}

	if (connect(fd, (struct sockaddr*)&addr, addr_len) == -1) {
	error("Couldn't connect to EGD socket \"%s\": %s",
	addr.sun_path, strerror(errno));
	close(fd);
	return(0);
	}

	/* Send blocking read request to EGD */
	msg[0] = 0x02;
	msg[1] = len;

	if (atomicio(write, fd, msg, sizeof(msg)) != sizeof(msg)) {
	error("Couldn't write to EGD socket \"%s\": %s",
	EGD_SOCKET, strerror(errno));
	close(fd);
	return(0);
	}

	if (atomicio(read, fd, buf, len) != len) {
	error("Couldn't read from EGD socket \"%s\": %s",
	EGD_SOCKET, strerror(errno));
	close(fd);
	return(0);
	}

	close(fd);

	return(1);
	}
	#else /* !EGD_SOCKET */
	#ifdef RANDOM_POOL
	/* Collect entropy from /dev/urandom or pipe */
	int get_random_bytes(unsigned char *buf, int len)
	{
	int random_pool;

	random_pool = open(RANDOM_POOL, O_RDONLY);
	if (random_pool == -1) {
	error("Couldn't open random pool \"%s\": %s",
	RANDOM_POOL, strerror(errno));
	return(0);
	}

	if (atomicio(read, random_pool, buf, len) != len) {
	error("Couldn't read from random pool \"%s\": %s",
	RANDOM_POOL, strerror(errno));
	close(random_pool);
	return(0);
	}

	close(random_pool);

	return(1);
	}
	#endif /* RANDOM_POOL */
	#endif /* EGD_SOCKET */

	/*
	* Seed OpenSSL's random number pool from Kernel random number generator
	* or EGD
	*/
	void
	seed_rng(void)
	{
	char buf[32];

	debug("Seeding random number generator");

	if (!get_random_bytes(buf, sizeof(buf))) {
	if (!RAND_status())
	fatal("Entropy collection failed and entropy exhausted");
	} else {
	RAND_add(buf, sizeof(buf), sizeof(buf));
	}

	memset(buf, '\0', sizeof(buf));
	}

	/* No-op */
	void init_rng(void) {}

	#else /* defined(EGD_SOCKET) \|\| defined(RANDOM_POOL) */

	/*
	* FIXME: proper entropy estimations. All current values are guesses
	* FIXME: (ATL) do estimates at compile time?
	* FIXME: More entropy sources
	*/

	/* slow command timeouts (all in milliseconds) */
	/* static int entropy_timeout_default = ENTROPY_TIMEOUT_MSEC; */
	static int entropy_timeout_current = ENTROPY_TIMEOUT_MSEC;

	static int prng_seed_saved = 0;
	static int prng_initialised = 0;
	uid_t original_uid;

	typedef struct
	{
	/* Proportion of data that is entropy */
	double rate;
	/* Counter goes positive if this command times out */
	unsigned int badness;
	/* Increases by factor of two each timeout */
	unsigned int sticky_badness;
	/* Path to executable */
	char *path;
	/* argv to pass to executable */
	char *args[5];
	/* full command string (debug) */
	char *cmdstring;
	} entropy_source_t;

	double stir_from_system(void);
	double stir_from_programs(void);
	double stir_gettimeofday(double entropy_estimate);
	double stir_clock(double entropy_estimate);
	double stir_rusage(int who, double entropy_estimate);
	double hash_output_from_command(entropy_source_t src, char hash);

	/* this is initialised from a file, by prng_read_commands() */
	entropy_source_t *entropy_sources = NULL;

	double
	stir_from_system(void)
	{
	double total_entropy_estimate;
	long int i;

	total_entropy_estimate = 0;

	i = getpid();
	RAND_add(&i, sizeof(i), 0.5);
	total_entropy_estimate += 0.1;

	i = getppid();
	RAND_add(&i, sizeof(i), 0.5);
	total_entropy_estimate += 0.1;

	i = getuid();
	RAND_add(&i, sizeof(i), 0.0);
	i = getgid();
	RAND_add(&i, sizeof(i), 0.0);

	total_entropy_estimate += stir_gettimeofday(1.0);
	total_entropy_estimate += stir_clock(0.5);
	total_entropy_estimate += stir_rusage(RUSAGE_SELF, 2.0);

	return(total_entropy_estimate);
	}

	double
	stir_from_programs(void)
	{
	int i;
	int c;
	double entropy_estimate;
	double total_entropy_estimate;
	char hash[SHA_DIGEST_LENGTH];

	total_entropy_estimate = 0;
	for(i = 0; i < NUM_ENTROPY_RUNS; i++) {
	c = 0;
	while (entropy_sources[c].path != NULL) {

	if (!entropy_sources[c].badness) {
	/* Hash output from command */
	entropy_estimate = hash_output_from_command(&entropy_sources[c], hash);

	/* Scale back entropy estimate according to command's rate */
	entropy_estimate *= entropy_sources[c].rate;

	/* Upper bound of entropy estimate is SHA_DIGEST_LENGTH */
	if (entropy_estimate > SHA_DIGEST_LENGTH)
	entropy_estimate = SHA_DIGEST_LENGTH;

	/* Scale back estimates for subsequent passes through list */
	entropy_estimate /= SCALE_PER_RUN * (i + 1.0);

	/* Stir it in */
	RAND_add(hash, sizeof(hash), entropy_estimate);

	debug3("Got %0.2f bytes of entropy from '%s'", entropy_estimate,
	entropy_sources[c].cmdstring);

	total_entropy_estimate += entropy_estimate;

	/* Execution times should be a little unpredictable */
	total_entropy_estimate += stir_gettimeofday(0.05);
	total_entropy_estimate += stir_clock(0.05);
	total_entropy_estimate += stir_rusage(RUSAGE_SELF, 0.1);
	total_entropy_estimate += stir_rusage(RUSAGE_CHILDREN, 0.1);
	} else {
	debug2("Command '%s' disabled (badness %d)",
	entropy_sources[c].cmdstring, entropy_sources[c].badness);

	if (entropy_sources[c].badness > 0)
	entropy_sources[c].badness--;
	}

	c++;
	}
	}

	return(total_entropy_estimate);
	}

	double
	stir_gettimeofday(double entropy_estimate)
	{
	struct timeval tv;

	if (gettimeofday(&tv, NULL) == -1)
	fatal("Couldn't gettimeofday: %s", strerror(errno));

	RAND_add(&tv, sizeof(tv), entropy_estimate);

	return(entropy_estimate);
	}

	double
	stir_clock(double entropy_estimate)
	{
	#ifdef HAVE_CLOCK
	clock_t c;

	c = clock();
	RAND_add(&c, sizeof(c), entropy_estimate);

	return(entropy_estimate);
	#else /* _HAVE_CLOCK */
	return(0);
	#endif /* _HAVE_CLOCK */
	}

	double
	stir_rusage(int who, double entropy_estimate)
	{
	#ifdef HAVE_GETRUSAGE
	struct rusage ru;

	if (getrusage(who, &ru) == -1)
	return(0);

	RAND_add(&ru, sizeof(ru), entropy_estimate);

	return(entropy_estimate);
	#else /* _HAVE_GETRUSAGE */
	return(0);
	#endif /* _HAVE_GETRUSAGE */
	}


	static
	int
	_get_timeval_msec_difference(struct timeval t1, struct timeval t2) {
	int secdiff, usecdiff;

	secdiff = t2->tv_sec - t1->tv_sec;
	usecdiff = (secdiff*1000000) + (t2->tv_usec - t1->tv_usec);
	return (int)(usecdiff / 1000);
	}

	double
	hash_output_from_command(entropy_source_t src, char hash)
	{
	static int devnull = -1;
	int p[2];
	fd_set rdset;
	int cmd_eof = 0, error_abort = 0;
	struct timeval tv_start, tv_current;
	int msec_elapsed = 0;
	pid_t pid;
	int status;
	char buf[16384];
	int bytes_read;
	int total_bytes_read;
	SHA_CTX sha;

	debug3("Reading output from \'%s\'", src->cmdstring);

	if (devnull == -1) {
	devnull = open("/dev/null", O_RDWR);
	if (devnull == -1)
	fatal("Couldn't open /dev/null: %s", strerror(errno));
	}

	if (pipe(p) == -1)
	fatal("Couldn't open pipe: %s", strerror(errno));

	(void)gettimeofday(&tv_start, NULL); /* record start time */

	switch (pid = fork()) {
	case -1: /* Error */
	close(p[0]);
	close(p[1]);
	fatal("Couldn't fork: %s", strerror(errno));
	/* NOTREACHED */
	case 0: /* Child */
	dup2(devnull, STDIN_FILENO);
	dup2(p[1], STDOUT_FILENO);
	dup2(p[1], STDERR_FILENO);
	close(p[0]);
	close(p[1]);
	close(devnull);

	setuid(original_uid);
	execv(src->path, (char**)(src->args));
	debug("(child) Couldn't exec '%s': %s", src->cmdstring,
	strerror(errno));
	_exit(-1);
	default: /* Parent */
	break;
	}

	RAND_add(&pid, sizeof(&pid), 0.0);

	close(p[1]);

	/* Hash output from child */
	SHA1_Init(&sha);
	total_bytes_read = 0;

	while (!error_abort && !cmd_eof) {
	int ret;
	struct timeval tv;
	int msec_remaining;

	(void) gettimeofday(&tv_current, 0);
	msec_elapsed = _get_timeval_msec_difference(&tv_start, &tv_current);
	if (msec_elapsed >= entropy_timeout_current) {
	error_abort=1;
	continue;
	}
	msec_remaining = entropy_timeout_current - msec_elapsed;

	FD_ZERO(&rdset);
	FD_SET(p[0], &rdset);
	tv.tv_sec = msec_remaining / 1000;
	tv.tv_usec = (msec_remaining % 1000) * 1000;

	ret = select(p[0]+1, &rdset, NULL, NULL, &tv);

	RAND_add(&tv, sizeof(tv), 0.0);

	switch (ret) {
	case 0:
	/* timer expired */
	error_abort = 1;
	break;
	case 1:
	/* command input */
	bytes_read = read(p[0], buf, sizeof(buf));
	RAND_add(&bytes_read, sizeof(&bytes_read), 0.0);
	if (bytes_read == -1) {
	error_abort = 1;
	break;
	} else if (bytes_read) {
	SHA1_Update(&sha, buf, bytes_read);
	total_bytes_read += bytes_read;
	} else {
	cmd_eof = 1;
	}
	break;
	case -1:
	default:
	/* error */
	debug("Command '%s': select() failed: %s", src->cmdstring,
	strerror(errno));
	error_abort = 1;
	break;
	}
	}

	SHA1_Final(hash, &sha);

	close(p[0]);

	debug3("Time elapsed: %d msec", msec_elapsed);

	if (waitpid(pid, &status, 0) == -1) {
	error("Couldn't wait for child '%s' completion: %s", src->cmdstring,
	strerror(errno));
	return(0.0);
	}

	RAND_add(&status, sizeof(&status), 0.0);

	if (error_abort) {
	/* closing p[0] on timeout causes the entropy command to
	* SIGPIPE. Take whatever output we got, and mark this command
	* as slow */
	debug2("Command '%s' timed out", src->cmdstring);
	src->sticky_badness *= 2;
	src->badness = src->sticky_badness;
	return(total_bytes_read);
	}

	if (WIFEXITED(status)) {
	if (WEXITSTATUS(status)==0) {
	return(total_bytes_read);
	} else {
	debug2("Command '%s' exit status was %d", src->cmdstring,
	WEXITSTATUS(status));
	src->badness = src->sticky_badness = 128;
	return (0.0);
	}
	} else if (WIFSIGNALED(status)) {
	debug2("Command '%s' returned on uncaught signal %d !", src->cmdstring,
	status);
	src->badness = src->sticky_badness = 128;
	return(0.0);
	} else
	return(0.0);
	}

	/*
	* prng seedfile functions
	*/
	int
	prng_check_seedfile(char *filename) {

	struct stat st;

	/* FIXME raceable: eg replace seed between this stat and subsequent open */
	/* Not such a problem because we don't trust the seed file anyway */
	if (lstat(filename, &st) == -1) {
	/* Give up on hard errors */
	if (errno != ENOENT)
	debug("WARNING: Couldn't stat random seed file \"%s\": %s",
	filename, strerror(errno));

	return(0);
	}

	/* regular file? */
	if (!S_ISREG(st.st_mode))
	fatal("PRNG seedfile %.100s is not a regular file", filename);

	/* mode 0600, owned by root or the current user? */
	if (((st.st_mode & 0177) != 0) \|\| !(st.st_uid == original_uid)) {
	debug("WARNING: PRNG seedfile %.100s must be mode 0600, owned by uid %d",
	filename, getuid());
	return(0);
	}

	return(1);
	}

	void
	prng_write_seedfile(void) {
	int fd;
	char seed[1024];
	char filename[1024];
	struct passwd *pw;

	/* Don't bother if we have already saved a seed */
	if (prng_seed_saved)
	return;

	setuid(original_uid);

	prng_seed_saved = 1;

	pw = getpwuid(original_uid);
	if (pw == NULL)
	fatal("Couldn't get password entry for current user (%i): %s",
	original_uid, strerror(errno));

	/* Try to ensure that the parent directory is there */
	snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
	SSH_USER_DIR);
	mkdir(filename, 0700);

	snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
	SSH_PRNG_SEED_FILE);

	debug("writing PRNG seed to file %.100s", filename);

	RAND_bytes(seed, sizeof(seed));

	/* Don't care if the seed doesn't exist */
	prng_check_seedfile(filename);

	if ((fd = open(filename, O_WRONLY\|O_TRUNC\|O_CREAT, 0600)) == -1) {
	debug("WARNING: couldn't access PRNG seedfile %.100s (%.100s)",
	filename, strerror(errno));
	} else {
	if (atomicio(write, fd, &seed, sizeof(seed)) != sizeof(seed))
	fatal("problem writing PRNG seedfile %.100s (%.100s)", filename,
	strerror(errno));

	close(fd);
	}
	}

	void
	prng_read_seedfile(void) {
	int fd;
	char seed[1024];
	char filename[1024];
	struct passwd *pw;

	pw = getpwuid(original_uid);
	if (pw == NULL)
	fatal("Couldn't get password entry for current user (%i): %s",
	original_uid, strerror(errno));

	snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
	SSH_PRNG_SEED_FILE);

	debug("loading PRNG seed from file %.100s", filename);

	if (!prng_check_seedfile(filename)) {
	verbose("Random seed file not found, creating new");
	prng_write_seedfile();

	/* Reseed immediatly */
	(void)stir_from_system();
	(void)stir_from_programs();
	return;
	}

	/* open the file and read in the seed */
	fd = open(filename, O_RDONLY);
	if (fd == -1)
	fatal("could not open PRNG seedfile %.100s (%.100s)", filename,
	strerror(errno));

	if (atomicio(read, fd, &seed, sizeof(seed)) != sizeof(seed)) {
	verbose("invalid or short read from PRNG seedfile %.100s - ignoring",
	filename);
	memset(seed, '\0', sizeof(seed));
	}
	close(fd);

	/* stir in the seed, with estimated entropy zero */
	RAND_add(&seed, sizeof(seed), 0.0);
	}


	/*
	* entropy command initialisation functions
	*/
	int
	prng_read_commands(char *cmdfilename)
	{
	FILE *f;
	char *cp;
	char line[1024];
	char cmd[1024];
	char path[256];
	int linenum;
	int num_cmds = 64;
	int cur_cmd = 0;
	double est;
	entropy_source_t *entcmd;

	f = fopen(cmdfilename, "r");
	if (!f) {
	fatal("couldn't read entropy commands file %.100s: %.100s",
	cmdfilename, strerror(errno));
	}

	entcmd = (entropy_source_t )xmalloc(num_cmds sizeof(entropy_source_t));
	memset(entcmd, '\0', num_cmds * sizeof(entropy_source_t));

	/* Read in file */
	linenum = 0;
	while (fgets(line, sizeof(line), f)) {
	int arg;
	char *argv;

	linenum++;

	/* skip leading whitespace, test for blank line or comment */
	cp = line + strspn(line, WHITESPACE);
	if ((cp == 0) \|\| (cp == '#'))
	continue; /* done with this line */

	/* First non-whitespace char should be double quote delimiting */
	/* commandline */
	if (*cp != '"') {
	error("bad entropy command, %.100s line %d", cmdfilename,
	linenum);
	continue;
	}

	/* first token, command args (incl. argv[0]) in double quotes */
	cp = strtok(cp, "\"");
	if (cp == NULL) {
	error("missing or bad command string, %.100s line %d -- ignored",
	cmdfilename, linenum);
	continue;
	}
	strlcpy(cmd, cp, sizeof(cmd));

	/* second token, full command path */
	if ((cp = strtok(NULL, WHITESPACE)) == NULL) {
	error("missing command path, %.100s line %d -- ignored",
	cmdfilename, linenum);
	continue;
	}

	/* did configure mark this as dead? */
	if (strncmp("undef", cp, 5) == 0)
	continue;

	strlcpy(path, cp, sizeof(path));

	/* third token, entropy rate estimate for this command */
	if ((cp = strtok(NULL, WHITESPACE)) == NULL) {
	error("missing entropy estimate, %.100s line %d -- ignored",
	cmdfilename, linenum);
	continue;
	}
	est = strtod(cp, &argv);

	/* end of line */
	if ((cp = strtok(NULL, WHITESPACE)) != NULL) {
	error("garbage at end of line %d in %.100s -- ignored", linenum,
	cmdfilename);
	continue;
	}

	/* save the command for debug messages */
	entcmd[cur_cmd].cmdstring = xstrdup(cmd);

	/* split the command args */
	cp = strtok(cmd, WHITESPACE);
	arg = 0;
	argv = NULL;
	do {
	char s = (char)xmalloc(strlen(cp) + 1);
	strncpy(s, cp, strlen(cp) + 1);
	entcmd[cur_cmd].args[arg] = s;
	arg++;
	} while ((arg < 5) && (cp = strtok(NULL, WHITESPACE)));

	if (strtok(NULL, WHITESPACE))
	error("ignored extra command elements (max 5), %.100s line %d",
	cmdfilename, linenum);

	/* Copy the command path and rate estimate */
	entcmd[cur_cmd].path = xstrdup(path);
	entcmd[cur_cmd].rate = est;

	/* Initialise other values */
	entcmd[cur_cmd].sticky_badness = 1;

	cur_cmd++;

	/* If we've filled the array, reallocate it twice the size */
	/* Do this now because even if this we're on the last command,
	we need another slot to mark the last entry */
	if (cur_cmd == num_cmds) {
	num_cmds *= 2;
	entcmd = xrealloc(entcmd, num_cmds * sizeof(entropy_source_t));
	}
	}

	/* zero the last entry */
	memset(&entcmd[cur_cmd], '\0', sizeof(entropy_source_t));

	/* trim to size */
	entropy_sources = xrealloc(entcmd, (cur_cmd+1) * sizeof(entropy_source_t));

	debug("Loaded %d entropy commands from %.100s", cur_cmd, cmdfilename);

	return (cur_cmd >= MIN_ENTROPY_SOURCES);
	}

	/*
	* Write a keyfile at exit
	*/
	void
	prng_seed_cleanup(void *junk)
	{
	prng_write_seedfile();
	}

	/*
	* Conditionally Seed OpenSSL's random number pool from
	* syscalls and program output
	*/
	void
	seed_rng(void)
	{
	void *old_sigchld_handler;

	if (!prng_initialised)
	fatal("RNG not initialised");

	/* Make sure some other sigchld handler doesn't reap our entropy */
	/* commands */
	old_sigchld_handler = signal(SIGCHLD, SIG_DFL);

	debug("Seeded RNG with %i bytes from programs", (int)stir_from_programs());
	debug("Seeded RNG with %i bytes from system calls", (int)stir_from_system());

	if (!RAND_status())
	fatal("Not enough entropy in RNG");

	signal(SIGCHLD, old_sigchld_handler);

	if (!RAND_status())
	fatal("Couldn't initialise builtin random number generator -- exiting.");
	}

	void init_rng(void)
	{
	int original_euid;

	original_uid = getuid();
	original_euid = geteuid();

	/* Read in collection commands */
	if (!prng_read_commands(SSH_PRNG_COMMAND_FILE))
	fatal("PRNG initialisation failed -- exiting.");

	/* Set ourselves up to save a seed upon exit */
	prng_seed_saved = 0;

	/* Give up privs while reading seed file */
	if ((original_uid != original_euid) && (seteuid(original_uid) == -1))
	fatal("Couldn't give up privileges");

	prng_read_seedfile();

	if ((original_uid != original_euid) && (seteuid(original_euid) == -1))
	fatal("Couldn't restore privileges");

	fatal_add_cleanup(prng_seed_cleanup, NULL);
	atexit(prng_write_seedfile);

	prng_initialised = 1;
	}

	#endif /* defined(EGD_SOCKET) \|\| defined(RANDOM_POOL) */