source: trunk/third/openssh/ssh-rand-helper.c @ 18759

/*
 * Copyright (c) 2001-2002 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 <openssl/rand.h>
#include <openssl/sha.h>
#include <openssl/crypto.h>

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

#include "misc.h"
#include "xmalloc.h"
#include "atomicio.h"
#include "pathnames.h"
#include "log.h"

RCSID("$Id: ssh-rand-helper.c,v 1.1.1.1 2003-02-05 19:03:52 zacheiss Exp $");

/* Number of bytes we write out */
#define OUTPUT_SEED_SIZE        48

/* Length of on-disk seedfiles */
#define SEED_FILE_SIZE          1024

/* Maximum number of command-line arguments to read from file */
#define NUM_ARGS                10

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

/* Path to on-disk seed file (relative to user's home directory */
#ifndef SSH_PRNG_SEED_FILE
# define SSH_PRNG_SEED_FILE      _PATH_SSH_USER_DIR"/prng_seed"
#endif

/* Path to PRNG commands list */
#ifndef SSH_PRNG_COMMAND_FILE
# define SSH_PRNG_COMMAND_FILE   SSHDIR "/ssh_prng_cmds"
#endif

#ifdef HAVE___PROGNAME
extern char *__progname;
#else
char *__progname;
#endif

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

#define WHITESPACE " \t\n"

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

#if !defined(PRNGD_SOCKET) && !defined(PRNGD_PORT)
# define USE_SEED_FILES
#endif

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[NUM_ARGS]; /* XXX: arbitrary limit */
        /* full command string (debug) */
        char *cmdstring;
} entropy_cmd_t;

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

/* this is initialised from a file, by prng_read_commands() */
static entropy_cmd_t *entropy_cmds = NULL;

/* Prototypes */
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_command_output(entropy_cmd_t *src, unsigned char *hash);
int get_random_bytes_prngd(unsigned char *buf, int len, 
    unsigned short tcp_port, char *socket_path);

/*
 * Collect 'len' bytes of entropy into 'buf' from PRNGD/EGD daemon
 * listening either on 'tcp_port', or via Unix domain socket at *
 * 'socket_path'.
 * Either a non-zero tcp_port or a non-null socket_path must be 
 * supplied.
 * Returns 0 on success, -1 on error
 */
int
get_random_bytes_prngd(unsigned char *buf, int len, 
    unsigned short tcp_port, char *socket_path)
{
        int fd, addr_len, rval, errors;
        char msg[2];
        struct sockaddr_storage addr;
        struct sockaddr_in *addr_in = (struct sockaddr_in *)&addr;
        struct sockaddr_un *addr_un = (struct sockaddr_un *)&addr;
        mysig_t old_sigpipe;

        /* Sanity checks */
        if (socket_path == NULL && tcp_port == 0)
                fatal("You must specify a port or a socket");
        if (socket_path != NULL &&
            strlen(socket_path) >= sizeof(addr_un->sun_path))
                fatal("Random pool path is too long");
        if (len > 255)
                fatal("Too many bytes to read from PRNGD");

        memset(&addr, '\0', sizeof(addr));

        if (tcp_port != 0) {
                addr_in->sin_family = AF_INET;
                addr_in->sin_addr.s_addr = htonl(INADDR_LOOPBACK);
                addr_in->sin_port = htons(tcp_port);
                addr_len = sizeof(*addr_in);
        } else {
                addr_un->sun_family = AF_UNIX;
                strlcpy(addr_un->sun_path, socket_path,
                    sizeof(addr_un->sun_path));
                addr_len = offsetof(struct sockaddr_un, sun_path) +
                    strlen(socket_path) + 1;
        }

        old_sigpipe = mysignal(SIGPIPE, SIG_IGN);

        errors = 0;
        rval = -1;
reopen:
        fd = socket(addr.ss_family, SOCK_STREAM, 0);
        if (fd == -1) {
                error("Couldn't create socket: %s", strerror(errno));
                goto done;
        }

        if (connect(fd, (struct sockaddr*)&addr, addr_len) == -1) {
                if (tcp_port != 0) {
                        error("Couldn't connect to PRNGD port %d: %s",
                            tcp_port, strerror(errno));
                } else {
                        error("Couldn't connect to PRNGD socket \"%s\": %s",
                            addr_un->sun_path, strerror(errno));
                }
                goto done;
        }

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

        if (atomicio(write, fd, msg, sizeof(msg)) != sizeof(msg)) {
                if (errno == EPIPE && errors < 10) {
                        close(fd);
                        errors++;
                        goto reopen;
                }
                error("Couldn't write to PRNGD socket: %s",
                    strerror(errno));
                goto done;
        }

        if (atomicio(read, fd, buf, len) != len) {
                if (errno == EPIPE && errors < 10) {
                        close(fd);
                        errors++;
                        goto reopen;
                }
                error("Couldn't read from PRNGD socket: %s",
                    strerror(errno));
                goto done;
        }

        rval = 0;
done:
        mysignal(SIGPIPE, old_sigpipe);
        if (fd != -1)
                close(fd);
        return rval;
}

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
timeval_diff(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_command_output(entropy_cmd_t *src, unsigned char *hash)
{
        char buf[8192];
        fd_set rdset;
        int bytes_read, cmd_eof, error_abort, msec_elapsed, p[2];
        int status, total_bytes_read;
        static int devnull = -1;
        pid_t pid;
        SHA_CTX sha;
        struct timeval tv_start, tv_current;

        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);

                        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);

        cmd_eof = error_abort = msec_elapsed = total_bytes_read = 0;
        while (!error_abort && !cmd_eof) {
                int ret;
                struct timeval tv;
                int msec_remaining;

                (void) gettimeofday(&tv_current, 0);
                msec_elapsed = timeval_diff(&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 */
                        do {
                                bytes_read = read(p[0], buf, sizeof(buf));
                        } while (bytes_read == -1 && errno == EINTR);
                        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;
}

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 c;
        double entropy, total_entropy;
        unsigned char hash[SHA_DIGEST_LENGTH];

        total_entropy = 0;
        for(c = 0; entropy_cmds[c].path != NULL; c++) {
                if (!entropy_cmds[c].badness) {
                        /* Hash output from command */
                        entropy = hash_command_output(&entropy_cmds[c],
                            hash);

                        /* Scale back estimate by command's rate */
                        entropy *= entropy_cmds[c].rate;

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

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

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

                        total_entropy += entropy;

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

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

        return total_entropy;
}

/*
 * prng seedfile functions
 */
int
prng_check_seedfile(char *filename)
{
        struct stat st;

        /*
         * XXX raceable: eg replace seed between this stat and subsequent 
         * open. Not such a problem because we don't really trust the 
         * seed file anyway.
         * XXX: use secure path checking as elsewhere in OpenSSH
         */
        if (lstat(filename, &st) == -1) {
                /* Give up on hard errors */
                if (errno != ENOENT)
                        debug("WARNING: Couldn't stat random seed file "
                            "\"%.100s\": %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 == getuid())) {
                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;
        unsigned char seed[SEED_FILE_SIZE];
        char filename[MAXPATHLEN];
        struct passwd *pw;

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

        /* Try to ensure that the parent directory is there */
        snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
            _PATH_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[SEED_FILE_SIZE], filename[MAXPATHLEN];
        struct passwd *pw;

        pw = getpwuid(getuid());
        if (pw == NULL)
                fatal("Couldn't get password entry for current user "
                    "(%i): %s", getuid(), 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 or invalid, ignoring.");
                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)
{
        char cmd[SEED_FILE_SIZE], *cp, line[1024], path[SEED_FILE_SIZE];
        double est;
        entropy_cmd_t *entcmd;
        FILE *f;
        int cur_cmd, linenum, num_cmds, arg;

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

        num_cmds = 64;
        entcmd = xmalloc(num_cmds * sizeof(entropy_cmd_t));
        memset(entcmd, '\0', num_cmds * sizeof(entropy_cmd_t));

        /* Read in file */
        cur_cmd = linenum = 0;
        while (fgets(line, sizeof(line), f)) {
                linenum++;

                /* Skip leading whitespace, blank lines and comments */
                cp = line + strspn(line, WHITESPACE);
                if ((*cp == 0) || (*cp == '#'))
                        continue; /* done with this line */

                /*
                 * The first non-whitespace char should be a double quote 
                 * delimiting the 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, NULL);

                /* 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;
                do {
                        entcmd[cur_cmd].args[arg] = xstrdup(cp);
                        arg++;
                } while(arg < NUM_ARGS && (cp = strtok(NULL, WHITESPACE)));

                if (strtok(NULL, WHITESPACE))
                        error("ignored extra commands (max %d), %.100s "
                            "line %d", NUM_ARGS, 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_cmd_t));
                }
        }

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

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

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

        return cur_cmd < MIN_ENTROPY_SOURCES ? -1 : 0;
}

void
usage(void)
{
        fprintf(stderr, "Usage: %s [options]\n", __progname);
        fprintf(stderr, "  -v          Verbose; display verbose debugging messages.\n");
        fprintf(stderr, "              Multiple -v increases verbosity.\n");
        fprintf(stderr, "  -x          Force output in hexidecimal (for debugging)\n");
        fprintf(stderr, "  -X          Force output in binary\n");
        fprintf(stderr, "  -b bytes    Number of bytes to output (default %d)\n",
            OUTPUT_SEED_SIZE);
}

int 
main(int argc, char **argv)
{
        unsigned char *buf;
        int ret, ch, debug_level, output_hex, bytes;
        extern char *optarg;
        LogLevel ll;

        __progname = get_progname(argv[0]);
        log_init(argv[0], SYSLOG_LEVEL_INFO, SYSLOG_FACILITY_USER, 1);

        ll = SYSLOG_LEVEL_INFO;
        debug_level = output_hex = 0;
        bytes = OUTPUT_SEED_SIZE;

        /* Don't write binary data to a tty, unless we are forced to */
        if (isatty(STDOUT_FILENO))
                output_hex = 1;
        
        while ((ch = getopt(argc, argv, "vxXhb:")) != -1) {
                switch (ch) {
                case 'v':
                        if (debug_level < 3)
                                ll = SYSLOG_LEVEL_DEBUG1 + debug_level++;
                        break;
                case 'x':
                        output_hex = 1;
                        break;
                case 'X':
                        output_hex = 0;
                        break;
                case 'b':
                        if ((bytes = atoi(optarg)) <= 0)
                                fatal("Invalid number of output bytes");
                        break;
                case 'h':
                        usage();
                        exit(0);
                default:
                        error("Invalid commandline option");
                        usage();
                }
        }

        log_init(argv[0], ll, SYSLOG_FACILITY_USER, 1);
        
#ifdef USE_SEED_FILES
        prng_read_seedfile();
#endif

        buf = xmalloc(bytes);

        /*
         * Seed the RNG from wherever we can
         */
         
        /* Take whatever is on the stack, but don't credit it */
        RAND_add(buf, bytes, 0);

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

#ifdef PRNGD_PORT
        if (get_random_bytes_prngd(buf, bytes, PRNGD_PORT, NULL) == -1)
                fatal("Entropy collection failed");
        RAND_add(buf, bytes, bytes);
#elif defined(PRNGD_SOCKET)
        if (get_random_bytes_prngd(buf, bytes, 0, PRNGD_SOCKET) == -1)
                fatal("Entropy collection failed");
        RAND_add(buf, bytes, bytes);
#else
        /* Read in collection commands */
        if (prng_read_commands(SSH_PRNG_COMMAND_FILE) == -1)
                fatal("PRNG initialisation failed -- exiting.");
        debug("Seeded RNG with %i bytes from programs", 
            (int)stir_from_programs());
#endif

#ifdef USE_SEED_FILES
        prng_write_seedfile();
#endif

        /*
         * Write the seed to stdout
         */

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

        RAND_bytes(buf, bytes);

        if (output_hex) {
                for(ret = 0; ret < bytes; ret++)
                        printf("%02x", (unsigned char)(buf[ret]));
                printf("\n");
        } else
                ret = atomicio(write, STDOUT_FILENO, buf, bytes);
                
        memset(buf, '\0', bytes);
        xfree(buf);
        
        return ret == bytes ? 0 : 1;
}