- (djm) Ignore fix & patchlevel in OpenSSL version check. Patch from

   solar@openwall.com
 - (djm) Rework entropy code. If the OpenSSL PRNG is has not been
   internally seeded, execute a subprogram "ssh-rand-helper" to obtain
   some entropy for us. Rewrite the old in-process entropy collecter as
   an example ssh-rand-helper.
 - (djm) Always perform ssh_prng_cmds path lookups in configure, even if
   we don't end up using ssh_prng_cmds (so we always get a valid file)

1 files changed, 75 insertions, 851 deletions

diff --git a/entropy.c b/entropy.c
index d9760cc1d..86ea81aa2 100644
--- a/entropy.c
+++ b/entropy.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000 Damien Miller.  All rights reserved.
+ * Copyright (c) 2001 Damien Miller.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -25,14 +25,8 @@
 #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 "ssh.h"
 #include "misc.h"
 #include "xmalloc.h"
@@ -40,878 +34,108 @@
 #include "pathnames.h"
 #include "log.h"
 
-RCSID("$Id: entropy.c,v 1.38 2001/08/06 06:51:49 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(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
-# define SAVED_IDS_WORK_WITH_SETEUID
-#endif
-
-static void
-check_openssl_version(void) 
-{
-        if (SSLeay() != OPENSSL_VERSION_NUMBER)
-                fatal("OpenSSL version mismatch. Built against %lx, you "
-                    "have %lx", OPENSSL_VERSION_NUMBER, SSLeay());
-}
-
-#if defined(PRNGD_SOCKET) || defined(PRNGD_PORT)
-# define USE_PRNGD
-#endif
-
-#if defined(USE_PRNGD) || defined(RANDOM_POOL)
-
-#ifdef USE_PRNGD
-/* Collect entropy from PRNGD/EGD */
-int
-get_random_bytes(unsigned char *buf, int len)
-{
-        int fd;
-        char msg[2];
-#ifdef PRNGD_PORT
-        struct sockaddr_in addr;
-#else
-        struct sockaddr_un addr;
-#endif
-        int addr_len, rval, errors;
-        mysig_t old_sigpipe;
-
-        memset(&addr, '\0', sizeof(addr));
-
-#ifdef PRNGD_PORT
-        addr.sin_family = AF_INET;
-        addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
-        addr.sin_port = htons(PRNGD_PORT);
-        addr_len = sizeof(struct sockaddr_in);
-#else /* use IP socket PRNGD_SOCKET instead */
-        /* Sanity checks */
-        if (sizeof(PRNGD_SOCKET) > sizeof(addr.sun_path))
-                fatal("Random pool path is too long");
-        if (len > 255)
-                fatal("Too many bytes to read from PRNGD");
-
-        addr.sun_family = AF_UNIX;
-        strlcpy(addr.sun_path, PRNGD_SOCKET, sizeof(addr.sun_path));
-        addr_len = offsetof(struct sockaddr_un, sun_path) +
-            sizeof(PRNGD_SOCKET);
-#endif
-
-        old_sigpipe = mysignal(SIGPIPE, SIG_IGN);
-
-        errors = rval = 0;
-reopen:
-#ifdef PRNGD_PORT
-        fd = socket(addr.sin_family, SOCK_STREAM, 0);
-        if (fd == -1) {
-                error("Couldn't create AF_INET socket: %s", strerror(errno));
-                goto done;
-        }
-#else
-        fd = socket(addr.sun_family, SOCK_STREAM, 0);
-        if (fd == -1) {
-                error("Couldn't create AF_UNIX socket: %s", strerror(errno));
-                goto done;
-        }
-#endif
-
-        if (connect(fd, (struct sockaddr*)&addr, addr_len) == -1) {
-#ifdef PRNGD_PORT
-                error("Couldn't connect to PRNGD port %d: %s",
-                    PRNGD_PORT, strerror(errno));
-#else
-                error("Couldn't connect to PRNGD socket \"%s\": %s",
-                    addr.sun_path, strerror(errno));
-#endif
-                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 = 1;
-done:
-        mysignal(SIGPIPE, old_sigpipe);
-        if (fd != -1)
-                close(fd);
-        return(rval);
-}
-#else /* !USE_PRNGD */
-#ifdef RANDOM_POOL
-/* Collect entropy from /dev/urandom or pipe */
-static 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 /* USE_PRNGD */
-
 /*
- * Seed OpenSSL's random number pool from Kernel random number generator
- * or PRNGD/EGD
+ * Portable OpenSSH PRNG seeding:
+ * If OpenSSL has not "internally seeded" itself (e.g. pulled data from 
+ * /dev/random), then we execute a "ssh-rand-helper" program which 
+ * collects entropy and writes it to stdout. The child program must 
+ * write at least RANDOM_SEED_SIZE bytes. The child is run with stderr
+ * attached, so error/debugging output should be visible.
+ *
+ * XXX: we should tell the child how many bytes we need.
  */
-void
-seed_rng(void)
-{
-        unsigned char buf[32];
 
-        debug("Seeding random number generator");
+#define RANDOM_SEED_SIZE 48
 
-        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));
-        }
+RCSID("$Id: entropy.c,v 1.39 2001/12/23 14:41:48 djm Exp $");
 
-        memset(buf, '\0', sizeof(buf));
-}
+static uid_t original_uid, original_euid;
 
 void
-init_rng(void) 
-{
-        check_openssl_version();
-}
-
-#else /* defined(USE_PRNGD) || 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)
+seed_rng(void)
 {
-        static int devnull = -1;
+        int devnull;
         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 */
-                        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);
-}
-
-/*
- * 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));
+        int ret;
+        unsigned char buf[RANDOM_SEED_SIZE];
 
-                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)
+        if (RAND_status() == 1) {
+                debug3("RNG is ready, skipping seeding");
                 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,
-                _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[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 or not valid, 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)
-{
-        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));
+        debug3("Seeing PRNG from %s", SSH_RAND_HELPER);
 
-                /* 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));
+        if ((devnull = open("/dev/null", O_RDWR)) == -1)
+                fatal("Couldn't open /dev/null: %s", strerror(errno));
+        if (pipe(p) == -1)
+                fatal("pipe: %s", strerror(errno));
+
+        if ((pid = fork()) == -1)
+                fatal("Couldn't fork: %s", strerror(errno));
+        if (pid == 0) {
+                dup2(devnull, STDIN_FILENO);
+                dup2(p[1], STDOUT_FILENO);
+                /* Keep stderr open for errors */
+                close(p[0]);
+                close(p[1]);
+                close(devnull);
+
+                if (original_uid != original_euid && 
+                    setuid(original_uid) == -1) {
+                        fprintf(stderr, "(rand child) setuid: %s\n", 
+                            strerror(errno));
+                        _exit(1);
                 }
+                
+                execl(SSH_RAND_HELPER, "ssh-rand-helper", NULL);
+                fprintf(stderr, "(rand child) Couldn't exec '%s': %s\n", 
+                    SSH_RAND_HELPER, strerror(errno));
+                _exit(1);
         }
 
-        /* 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)
-{
-        mysig_t old_sigchld_handler;
-
-        if (!prng_initialised)
-                fatal("RNG not initialised");
+        close(devnull);
+        close(p[1]);
 
-        /* Make sure some other sigchld handler doesn't reap our entropy */
-        /* commands */
-        old_sigchld_handler = mysignal(SIGCHLD, SIG_DFL);
+        memset(buf, '\0', sizeof(buf));
+        ret = atomicio(read, p[0], buf, sizeof(buf));
+        if (ret == -1)
+                fatal("Couldn't read from ssh-rand-helper: %s",
+                    strerror(errno));
+        if (ret != sizeof(buf))
+                fatal("ssh-rand-helper child produced insufficient data");
 
-        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());
+        close(p[0]);
 
-        if (!RAND_status())
-                fatal("Not enough entropy in RNG");
+        if (waitpid(pid, &ret, 0) == -1)
+               fatal("Couldn't wait for ssh-rand-helper completion: %s", 
+                   strerror(errno));
 
-        mysignal(SIGCHLD, old_sigchld_handler);
+        /* We don't mind if the child exits upon a SIGPIPE */
+        if (!WIFEXITED(ret) && 
+            (!WIFSIGNALED(ret) || WTERMSIG(ret) != SIGPIPE))
+                fatal("ssh-rand-helper terminated abnormally");
+        if (WEXITSTATUS(ret) != 0)
+                fatal("ssh-rand-helper exit with exit status %d", ret);
 
-        if (!RAND_status())
-                fatal("Couldn't initialise builtin random number generator -- exiting.");
+        RAND_add(buf, sizeof(buf), sizeof(buf));
+        memset(buf, '\0', sizeof(buf));
 }
 
 void
-init_rng(void)
+init_rng(void) 
 {
-        int original_euid;
-
-        check_openssl_version();
-
-        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 */
-#ifdef SAVED_IDS_WORK_WITH_SETEUID
-        if ((original_uid != original_euid) && (seteuid(original_uid) == -1))
-                fatal("Couldn't give up privileges");
-#else /* SAVED_IDS_WORK_WITH_SETEUID */
         /*
-         * Propagate the privileged uid to all of our uids.
-         * Set the effective uid to the given (unprivileged) uid. 
+         * OpenSSL version numbers: MNNFFPPS: major minor fix patch status
+         * We match major, minor, fix and status (not patch)
          */
-        if (original_uid != original_euid && (setuid(original_euid) == -1 || 
-            seteuid(original_uid) == -1))
-                fatal("Couldn't give up privileges");
-#endif /* SAVED_IDS_WORK_WITH_SETEUID */
-
-        prng_read_seedfile();
-
-#ifdef SAVED_IDS_WORK_WITH_SETEUID
-        if ((original_uid != original_euid) && (seteuid(original_euid) == -1))
-                fatal("Couldn't restore privileges");
-#else /* SAVED_IDS_WORK_WITH_SETEUID */
-        /*
-         * We are unable to restore the real uid to its unprivileged value.
-         * Propagate the real uid (usually more privileged) to effective uid
-         * as well.
-         */
-        if (original_uid != original_euid && (seteuid(original_euid) == -1 || 
-            setuid(original_uid) == -1))
-                fatal("Couldn't restore privileges");
-#endif /* SAVED_IDS_WORK_WITH_SETEUID */
-
-        fatal_add_cleanup(prng_seed_cleanup, NULL);
-        atexit(prng_write_seedfile);
+        if ((SSLeay() ^ OPENSSL_VERSION_NUMBER) & ~0xff0L)
+                fatal("OpenSSL version mismatch. Built against %lx, you "
+                    "have %lx", OPENSSL_VERSION_NUMBER, SSLeay());
 
-        prng_initialised = 1;
+        if ((original_uid = getuid()) == -1)
+                fatal("getuid: %s", strerror(errno));
+        if ((original_euid = geteuid()) == -1)
+                fatal("geteuid: %s", strerror(errno));
 }
-
-#endif /* defined(USE_PRNGD) || defined(RANDOM_POOL) */