Casey Marshall wrote:

I've been hacking together a way to use rsync with OpenSSL, and have
attached my current patch against a recent CVS tree. The details of
this implementation are:

  1. The SSL code is added as a "layer" that is forked into its own
     process.

  2. An SSL connection is established by the client issuing the
     command:

       #starttls

     And, if the daemon allows SSL, it replies with

       @RSYNCD: starttls

     At which point both sides begin negotiating the SSL connection.
     Servers that can't or don't want to use SSL just treat it as a
     normal unknown command.

  3. The SSL code is meant to be unobtrusive, and when this patch is
     applied the program may still be built with no SSL code.

  4. There are a number of details not implemented.

All warnings apply; I don't do C programming all that often, so I
can't say if I've left any cleanup/compatibility errors in the code.

To use this patch, run these commands for a successful build:

    patch -p1 <patches/openssl-support.diff
    ./prepare-source
    ./configure
    make

--- old/Makefile.in
+++ new/Makefile.in
@@ -39,7 +39,7 @@ OBJS3=progress.o pipe.o
 DAEMON_OBJ = params.o loadparm.o clientserver.o access.o connection.o authenticate.o
 popt_OBJS=popt/findme.o  popt/popt.o  popt/poptconfig.o \
 	popt/popthelp.o popt/poptparse.o
-OBJS=$(OBJS1) $(OBJS2) $(OBJS3) $(DAEMON_OBJ) $(LIBOBJ) $(ZLIBOBJ) @BUILD_POPT@
+OBJS=$(OBJS1) $(OBJS2) $(OBJS3) $(DAEMON_OBJ) $(LIBOBJ) $(ZLIBOBJ) @BUILD_POPT@ @SSL_OBJS@
 
 TLS_OBJ = tls.o syscall.o lib/compat.o lib/snprintf.o lib/permstring.o
 
--- old/cleanup.c
+++ new/cleanup.c
@@ -26,6 +26,9 @@
 extern int am_server;
 extern int am_daemon;
 extern int io_error;
+#ifdef HAVE_OPENSSL
+extern int use_ssl;
+#endif
 extern int keep_partial;
 extern int log_got_error;
 extern char *partial_dir;
@@ -117,6 +120,14 @@ NORETURN void _exit_cleanup(int code, co
 				code, file, line);
 		}
 
+#ifdef HAVE_OPENSSL
+		/* FALLTHROUGH */
+#include "case_N.h"
+
+		if (use_ssl)
+			end_tls();
+#endif
+
 		/* FALLTHROUGH */
 #include "case_N.h"
 
--- old/clientserver.c
+++ new/clientserver.c
@@ -30,6 +30,9 @@ extern int am_sender;
 extern int am_server;
 extern int am_daemon;
 extern int am_root;
+#ifdef HAVE_OPENSSL
+extern int use_ssl;
+#endif
 extern int rsync_port;
 extern int kluge_around_eof;
 extern int daemon_over_rsh;
@@ -106,8 +109,18 @@ int start_socket_client(char *host, char
 	set_socket_options(fd, sockopts);
 
 	ret = start_inband_exchange(user, path, fd, fd, argc);
+	if (ret)
+		return ret;
 
-	return ret ? ret : client_run(fd, fd, -1, argc, argv);
+#ifdef HAVE_OPENSSL
+	if (use_ssl) {
+		int f_in = get_tls_rfd();
+		int f_out = get_tls_wfd();
+		return client_run(f_in, f_out, -1, argc, argv);
+	}
+#endif
+
+	return client_run(fd, fd, -1, argc, argv);
 }
 
 int start_inband_exchange(char *user, char *path, int f_in, int f_out,
@@ -168,6 +181,33 @@ int start_inband_exchange(char *user, ch
 	if (verbose > 1)
 		print_child_argv(sargs);
 
+#ifdef HAVE_OPENSSL
+	if (use_ssl) {
+		io_printf(f_out, "#starttls\n");
+		while (1) {
+			if (!read_line(f_in, line, sizeof(line)-1)) {
+				rprintf(FERROR, "rsync: did not receive reply to #starttls\n");
+				return -1;
+			}
+			if (strncmp(line, "@ERROR", 6) == 0) {
+				rprintf(FERROR, "%s\n", line);
+				return -1;
+			}
+			if (strcmp(line, "@RSYNCD: starttls") == 0) {
+				break;
+			}
+			rprintf(FINFO, "%s\n", line);
+		}
+		if (start_tls(f_in, f_out)) {
+			rprintf(FERROR, "rsync: error during SSL handshake: %s\n",
+				get_ssl_error());
+			return -1;
+		}
+		f_in = get_tls_rfd();
+		f_out = get_tls_wfd();
+	}
+#endif
+
 	p = strchr(path,'/');
 	if (p) *p = 0;
 	io_printf(f_out, "%s\n", path);
@@ -196,6 +236,10 @@ int start_inband_exchange(char *user, ch
 			 * server to terminate the listing of modules.
 			 * We don't want to go on and transfer
 			 * anything; just exit. */
+#ifdef HAVE_OPENSSL
+			if (use_ssl)
+				end_tls();
+#endif
 			exit(0);
 		}
 
@@ -203,6 +247,10 @@ int start_inband_exchange(char *user, ch
 			rprintf(FERROR, "%s\n", line);
 			/* This is always fatal; the server will now
 			 * close the socket. */
+#ifdef HAVE_OPENSSL
+			if (use_ssl)
+				end_tls();
+#endif
 			return -1;
 		}
 
@@ -780,6 +828,9 @@ int start_daemon(int f_in, int f_out)
 	if (protocol_version > remote_protocol)
 		protocol_version = remote_protocol;
 
+#ifdef HAVE_OPENSSL
+retry:
+#endif
 	line[0] = 0;
 	if (!read_line(f_in, line, sizeof line - 1))
 		return -1;
@@ -791,6 +842,20 @@ int start_daemon(int f_in, int f_out)
 		return -1;
 	}
 
+#ifdef HAVE_OPENSSL
+	if (use_ssl && strcmp(line, "#starttls") == 0) {
+		io_printf(f_out, "@RSYNCD: starttls\n");
+		if (start_tls(f_in, f_out)) {
+			rprintf(FLOG, "SSL connection failed: %s\n",
+				get_ssl_error());
+			return -1;
+		}
+		f_in = get_tls_rfd();
+		f_out = get_tls_wfd();
+		goto retry;
+	}
+#endif
+
 	if (*line == '#') {
 		/* it's some sort of command that I don't understand */
 		io_printf(f_out, "@ERROR: Unknown command '%s'\n", line);
--- old/configure.in
+++ new/configure.in
@@ -290,6 +290,21 @@ if test x"$enable_locale" != x"no"; then
 	AC_DEFINE(CONFIG_LOCALE)
 fi
 
+AC_ARG_ENABLE(openssl,
+              AC_HELP_STRING([--enable-openssl], [compile SSL support with OpenSSL.]))
+
+if test "x$enable_openssl" != xno
+then
+	have_ssl=yes
+	AC_CHECK_LIB(ssl, SSL_library_init, , [have_ssl=no])
+	if test "x$have_ssl" = xyes
+	then
+		AC_DEFINE(HAVE_OPENSSL, 1, [true if you want to use SSL.])
+		SSL_OBJS=ssl.o
+		AC_SUBST(SSL_OBJS)
+	fi
+fi
+
 AC_MSG_CHECKING([whether to call shutdown on all sockets])
 case $host_os in
 	*cygwin* ) AC_MSG_RESULT(yes)
--- old/options.c
+++ new/options.c
@@ -173,6 +173,14 @@ int logfile_format_has_o_or_i = 0;
 int always_checksum = 0;
 int list_only = 0;
 
+#ifdef HAVE_OPENSSL
+int use_ssl = 0;
+char *ssl_cert_path = NULL;
+char *ssl_key_path = NULL;
+char *ssl_key_passwd = NULL;
+char *ssl_ca_path = NULL;
+#endif
+
 #define MAX_BATCH_NAME_LEN 256	/* Must be less than MAXPATHLEN-13 */
 char *batch_name = NULL;
 
@@ -201,6 +209,7 @@ static void print_rsync_version(enum log
 	char const *hardlinks = "no ";
 	char const *links = "no ";
 	char const *ipv6 = "no ";
+	char const *ssl = "no ";
 	STRUCT_STAT *dumstat;
 
 #ifdef HAVE_SOCKETPAIR
@@ -223,6 +232,10 @@ static void print_rsync_version(enum log
 	ipv6 = "";
 #endif
 
+#ifdef HAVE_OPENSSL
+	ssl = "";
+#endif
+
 	rprintf(f, "%s  version %s  protocol version %d\n",
 		RSYNC_NAME, RSYNC_VERSION, PROTOCOL_VERSION);
 	rprintf(f, "Copyright (C) 1996-2006 by Andrew Tridgell, Wayne Davison, and others.\n");
@@ -235,9 +248,9 @@ static void print_rsync_version(enum log
 	/* Note that this field may not have type ino_t.  It depends
 	 * on the complicated interaction between largefile feature
 	 * macros. */
-	rprintf(f, "              %sinplace, %sIPv6, "
+	rprintf(f, "              %sinplace, %sIPv6, %sSSL, "
 		"%d-bit system inums, %d-bit internal inums\n",
-		have_inplace, ipv6,
+		have_inplace, ipv6, ssl,
 		(int) (sizeof dumstat->st_ino * 8),
 		(int) (sizeof (int64) * 8));
 #ifdef MAINTAINER_MODE
@@ -385,6 +398,13 @@ void usage(enum logcode F)
   rprintf(F," -4, --ipv4                  prefer IPv4\n");
   rprintf(F," -6, --ipv6                  prefer IPv6\n");
 #endif
+#ifdef HAVE_OPENSSL
+  rprintf(F,"     --ssl                   allow socket connections to use SSL\n");
+  rprintf(F,"     --ssl-cert=FILE         path to daemon's SSL certificate\n");
+  rprintf(F,"     --ssl-key=FILE          path to daemon's SSL private key\n");
+  rprintf(F,"     --ssl-key-passwd=PASS   password for PEM-encoded private key\n");
+  rprintf(F,"     --ssl-ca-certs=FILE     path to trusted CA certificates\n");
+#endif
   rprintf(F,"     --version               print version number\n");
   rprintf(F,"(-h) --help                  show this help (-h works with no other options)\n");
 
@@ -398,7 +418,7 @@ enum {OPT_VERSION = 1000, OPT_DAEMON, OP
       OPT_FILTER, OPT_COMPARE_DEST, OPT_COPY_DEST, OPT_LINK_DEST, OPT_HELP,
       OPT_INCLUDE, OPT_INCLUDE_FROM, OPT_MODIFY_WINDOW, OPT_MIN_SIZE, OPT_CHMOD,
       OPT_READ_BATCH, OPT_WRITE_BATCH, OPT_ONLY_WRITE_BATCH, OPT_MAX_SIZE,
-      OPT_NO_D,
+      OPT_NO_D, OPT_USE_SSL,
       OPT_SERVER, OPT_REFUSED_BASE = 9000};
 
 static struct poptOption long_options[] = {
@@ -545,6 +565,13 @@ static struct poptOption long_options[] 
   {"checksum-seed",    0,  POPT_ARG_INT,    &checksum_seed, 0, 0, 0 },
   {"server",           0,  POPT_ARG_NONE,   0, OPT_SERVER, 0, 0 },
   {"sender",           0,  POPT_ARG_NONE,   0, OPT_SENDER, 0, 0 },
+#ifdef HAVE_OPENSSL
+  {"ssl",              0,  POPT_ARG_NONE,   0, OPT_USE_SSL, 0, 0},
+  {"ssl-cert",         0,  POPT_ARG_STRING, &ssl_cert_path, OPT_USE_SSL, 0, 0},
+  {"ssl-key",          0,  POPT_ARG_STRING, &ssl_key_path, OPT_USE_SSL, 0, 0},
+  {"ssl-key-passwd",   0,  POPT_ARG_STRING, &ssl_key_passwd, OPT_USE_SSL, 0, 0},
+  {"ssl-ca-certs",     0,  POPT_ARG_STRING, &ssl_ca_path, OPT_USE_SSL, 0, 0},
+#endif
   /* All the following options switch us into daemon-mode option-parsing. */
   {"config",           0,  POPT_ARG_STRING, 0, OPT_DAEMON, 0, 0 },
   {"daemon",           0,  POPT_ARG_NONE,   0, OPT_DAEMON, 0, 0 },
@@ -572,6 +599,13 @@ static void daemon_usage(enum logcode F)
   rprintf(F," -4, --ipv4                  prefer IPv4\n");
   rprintf(F," -6, --ipv6                  prefer IPv6\n");
 #endif
+#ifdef HAVE_OPENSSL
+  rprintf(F,"     --ssl                   allow socket connections to use SSL\n");
+  rprintf(F,"     --ssl-cert=FILE         path to daemon's SSL certificate\n");
+  rprintf(F,"     --ssl-key=FILE          path to daemon's SSL private key\n");
+  rprintf(F,"     --ssl-key-passwd=PASS   password for PEM-encoded private key\n");
+  rprintf(F,"     --ssl-ca-certs=FILE     path to trusted CA certificates\n");
+#endif
   rprintf(F,"     --help                  show this help screen\n");
 
   rprintf(F,"\n");
@@ -598,6 +632,13 @@ static struct poptOption long_daemon_opt
   {"protocol",         0,  POPT_ARG_INT,    &protocol_version, 0, 0, 0 },
   {"server",           0,  POPT_ARG_NONE,   &am_server, 0, 0, 0 },
   {"temp-dir",        'T', POPT_ARG_STRING, &tmpdir, 0, 0, 0 },
+#ifdef HAVE_OPENSSL
+  {"ssl",              0,  POPT_ARG_NONE,   0, OPT_USE_SSL, 0, 0},
+  {"ssl-cert",         0,  POPT_ARG_STRING, &ssl_cert_path, OPT_USE_SSL, 0, 0},
+  {"ssl-key",          0,  POPT_ARG_STRING, &ssl_key_path, OPT_USE_SSL, 0, 0},
+  {"ssl-key-passwd",   0,  POPT_ARG_STRING, &ssl_key_passwd, OPT_USE_SSL, 0, 0},
+  {"ssl-ca-certs",     0,  POPT_ARG_STRING, &ssl_ca_path, OPT_USE_SSL, 0, 0},
+#endif
   {"verbose",         'v', POPT_ARG_NONE,   0, 'v', 0, 0 },
   {"no-verbose",       0,  POPT_ARG_VAL,    &verbose, 0, 0, 0 },
   {"no-v",             0,  POPT_ARG_VAL,    &verbose, 0, 0, 0 },
@@ -855,6 +896,12 @@ int parse_arguments(int *argc, const cha
 					verbose++;
 					break;
 
+#ifdef HAVE_OPENSSL
+				case OPT_USE_SSL:
+					use_ssl = 1;
+					break;
+#endif
+
 				default:
 					rprintf(FERROR,
 					    "rsync: %s: %s (in daemon mode)\n",
@@ -878,6 +925,17 @@ int parse_arguments(int *argc, const cha
 				exit_cleanup(RERR_SYNTAX);
 			}
 
+#ifdef HAVE_OPENSSL
+			if (use_ssl) {
+				if (init_tls()) {
+					snprintf(err_buf, sizeof(err_buf),
+						 "Openssl error: %s\n",
+						 get_ssl_error());
+					return 0;
+				}
+			}
+#endif
+
 			*argv = poptGetArgs(pc);
 			*argc = count_args(*argv);
 			am_starting_up = 0;
@@ -1089,6 +1147,12 @@ int parse_arguments(int *argc, const cha
 			usage(FINFO);
 			exit_cleanup(0);
 
+#ifdef HAVE_OPENSSL
+		case OPT_USE_SSL:
+			use_ssl = 1;
+			break;
+#endif
+
 		default:
 			/* A large opt value means that set_refuse_options()
 			 * turned this option off. */
@@ -1365,6 +1429,17 @@ int parse_arguments(int *argc, const cha
 	if (delay_updates && !partial_dir)
 		partial_dir = tmp_partialdir;
 
+#ifdef HAVE_OPENSSL
+	if (use_ssl) {
+		if (init_tls()) {
+			snprintf(err_buf, sizeof(err_buf),
+				 "Openssl error: %s\n",
+				 get_ssl_error());
+			return 0;
+		}
+	}
+#endif
+
 	if (inplace) {
 #ifdef HAVE_FTRUNCATE
 		if (partial_dir) {
@@ -1782,10 +1857,27 @@ char *check_for_hostspec(char *s, char *
 	char *p;
 	int not_host;
 	int hostlen;
+	int url_prefix_len = sizeof URL_PREFIX - 1;
 
-	if (port_ptr && strncasecmp(URL_PREFIX, s, strlen(URL_PREFIX)) == 0) {
+	if (!port_ptr)
+		url_prefix_len = 0;
+	else if (strncasecmp(URL_PREFIX, s, url_prefix_len) != 0) {
+#ifdef HAVE_OPENSSL
+		url_prefix_len = sizeof SSL_URL_PREFIX - 1;
+		if (strncasecmp(SSL_URL_PREFIX, s, url_prefix_len) != 0)
+			url_prefix_len = 0;
+		else {
+			if (!use_ssl)
+				init_tls();
+			use_ssl = 1;
+		}
+#else
+		url_prefix_len = 0;
+#endif
+	}
+	if (url_prefix_len) {
 		char *path;
-		s += strlen(URL_PREFIX);
+		s += url_prefix_len;
 		if ((p = strchr(s, '/')) != NULL) {
 			hostlen = p - s;
 			path = p + 1;
--- old/rsync.h
+++ new/rsync.h
@@ -32,6 +32,7 @@
 
 #define DEFAULT_LOCK_FILE "/var/run/rsyncd.lock"
 #define URL_PREFIX "rsync://"
+#define SSL_URL_PREFIX "rsyncs://"
 
 #define BACKUP_SUFFIX "~"
 
@@ -419,6 +420,11 @@ enum msgcode {
 # define SIZEOF_INT64 SIZEOF_OFF_T
 #endif
 
+#ifdef HAVE_OPENSSL
+#include <openssl/ssl.h>
+#include <openssl/err.h>
+#endif
+
 /* Starting from protocol version 26, we always use 64-bit
  * ino_t and dev_t internally, even if this platform does not
  * allow files to have 64-bit inums.  That's because the
--- old/ssl.c
+++ new/ssl.c
@@ -0,0 +1,370 @@
+/* -*- c-file-style: "linux" -*-
+ * ssl.c: operations for negotiating SSL rsync connections. 
+ *
+ * Copyright (C) 2003  Casey Marshall <rsdio@metastatic.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include "rsync.h"
+
+#ifdef HAVE_SYS_SELECT_H
+#include <sys/select.h>
+#else
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+#endif
+#include <string.h>
+
+#define BUF_SIZE 1024
+
+extern int verbose;
+extern int am_daemon;
+extern int am_server;
+
+extern char *ssl_cert_path;
+extern char *ssl_key_path;
+extern char *ssl_key_passwd;
+extern char *ssl_ca_path;
+
+static SSL_CTX *ssl_ctx;
+static SSL *ssl;
+static int tls_read[2] = { -1, -1 };
+static int tls_write[2] = { -1, -1 };
+static int ssl_running;
+static int ssl_pid = -1;
+
+#ifdef HAVE_SIGACTION
+static struct sigaction sigact;
+#endif
+
+/**
+ * A non-interactive callback to be passed to SSL_CTX_set_default_password_cb,
+ * which merely copies the value of ssl_key_passwd into buf. This is
+ * used for when the private key password is supplied via an option.
+ */
+static int default_password_cb(char *buf, int n, UNUSED(int f), UNUSED(void *u))
+{
+	if (ssl_key_passwd == NULL || n < (int)strlen(ssl_key_passwd))
+		return 0;
+	strncpy(buf, ssl_key_passwd, n-1);
+	return strlen(ssl_key_passwd);
+}
+
+/**
+ * If verbose, this method traces the status of the SSL handshake.
+ */
+static void info_callback(const SSL *ssl, int cb, int val)
+{
+	char buf[128];
+	char *cbs;
+
+	switch (cb) {
+	case SSL_CB_LOOP:
+		cbs = "SSL_CB_LOOP";
+		break;
+	case SSL_CB_EXIT:
+		cbs = "SSL_CB_EXIT";
+		break;
+	case SSL_CB_READ:
+		cbs = "SSL_CB_READ";
+		break;
+	case SSL_CB_WRITE:
+		cbs = "SSL_CB_WRITE";
+		break;
+	case SSL_CB_ALERT:
+		cbs = "SSL_CB_ALERT";
+		break;
+	case SSL_CB_READ_ALERT:
+		cbs = "SSL_CB_READ_ALERT";
+		break;
+	case SSL_CB_WRITE_ALERT:
+		cbs = "SSL_CB_WRITE_ALERT";
+		break;
+	case SSL_CB_ACCEPT_LOOP:
+		cbs = "SSL_CB_ACCEPT_LOOP";
+		break;
+	case SSL_CB_ACCEPT_EXIT:
+		cbs = "SSL_CB_ACCEPT_EXIT";
+		break;
+	case SSL_CB_CONNECT_LOOP:
+		cbs = "SSL_CB_CONNECT_LOOP";
+		break;
+	case SSL_CB_CONNECT_EXIT:
+		cbs = "SSL_CB_CONNECT_EXIT";
+		break;
+	case SSL_CB_HANDSHAKE_START:
+		cbs = "SSL_CB_HANDSHAKE_START";
+		break;
+	case SSL_CB_HANDSHAKE_DONE:
+		cbs = "SSL_CB_HANDSHAKE_DONE";
+		break;
+	default:
+		snprintf(buf, sizeof buf, "??? (%d)", cb);
+		cbs = buf;
+		break;
+	}
+	if (verbose > 2) {
+		rprintf(FLOG, "SSL: info_callback(%p,%s,%d)\n", ssl, cbs, val);
+		if (cb == SSL_CB_HANDSHAKE_DONE) {
+			SSL_CIPHER_description(SSL_get_current_cipher((SSL*)ssl),
+					       buf, sizeof buf);
+			rprintf(FLOG, "SSL: cipher: %s", buf);
+		}
+	}
+}
+
+/**
+ * Initializes the SSL context for TLSv1 connections; returns zero on
+ * success.
+ */
+int init_tls(void)
+{
+	if (ssl_ctx)
+		return 0;
+	SSL_library_init();
+	SSL_load_error_strings();
+	ssl_ctx = SSL_CTX_new(TLSv1_method());
+	if (!ssl_ctx)
+		return 1;
+	SSL_CTX_set_info_callback(ssl_ctx, info_callback);
+
+	/* Sets the certificate sent to the other party. */
+	if (ssl_cert_path != NULL
+	    && SSL_CTX_use_certificate_file(ssl_ctx, ssl_cert_path,
+					    SSL_FILETYPE_PEM) != 1)
+		return 1;
+	/* Set up the simple non-interactive callback if the password
+	 * was supplied on the command line. */
+	if (ssl_key_passwd != NULL)
+		SSL_CTX_set_default_passwd_cb(ssl_ctx, default_password_cb);
+	/* Sets the private key that matches the public certificate. */
+	if (ssl_key_path != NULL) {
+		if (SSL_CTX_use_PrivateKey_file(ssl_ctx, ssl_key_path,
+						SSL_FILETYPE_PEM) != 1)
+			return 1;
+		if (SSL_CTX_check_private_key(ssl_ctx) != 1)
+			return 1;
+	}
+	if (ssl_ca_path != NULL
+	    && !SSL_CTX_load_verify_locations(ssl_ctx, ssl_ca_path, NULL))
+		return 1;
+
+	return 0;
+}
+
+/**
+ * Returns the error string for the current SSL error, if any.
+ */
+char *get_ssl_error(void)
+{
+	return ERR_error_string(ERR_get_error(), NULL);
+}
+
+/**
+ * Returns the input file descriptor for the SSL connection.
+ */
+int get_tls_rfd(void)
+{
+	return tls_read[0];
+}
+
+/**
+ * Returns the output file descriptor for the SSL connection.
+ */
+int get_tls_wfd(void)
+{
+	return tls_write[1];
+}
+
+/**
+ * Signal handler that ends the SSL connection.
+ */
+static RETSIGTYPE tls_sigusr1(int UNUSED(val))
+{
+	if (ssl) {
+		SSL_shutdown(ssl);
+		SSL_free(ssl);
+		ssl = NULL;
+	}
+	ssl_running = 0;
+}
+
+/**
+ * Negotiates the TLS connection, creates a socket pair for communicating
+ * with the rsync process, then forks into a new process that will handle
+ * the communication.
+ *
+ * 0 is returned on success.
+ */
+int start_tls(int f_in, int f_out)
+{
+	int tls_fd;
+	int n = 0, r;
+	unsigned char buf1[BUF_SIZE], buf2[BUF_SIZE];
+	int avail1 = 0, avail2 = 0, write1 = 0, write2 = 0;
+	fd_set rd, wd;
+
+	if (fd_pair(tls_read))
+		return 1;
+	if (fd_pair(tls_write))
+		return 1;
+
+	set_blocking(tls_read[0]);
+	set_blocking(tls_read[1]);
+	set_blocking(tls_write[0]);
+	set_blocking(tls_write[1]);
+	set_blocking(f_in);
+	set_blocking(f_out);
+
+	ssl_pid = do_fork();
+	if (ssl_pid < 0)
+		return -1;
+	if (ssl_pid != 0) {
+		close(tls_write[0]);
+		close(tls_read[1]);
+		return 0;
+	}
+
+	SIGACTION(SIGUSR1, tls_sigusr1);
+	ssl = SSL_new(ssl_ctx);
+	if (!ssl)
+		goto closed;
+	if (am_daemon || am_server)
+		SSL_set_accept_state(ssl);
+	else
+		SSL_set_connect_state(ssl);
+	SSL_set_rfd(ssl, f_in);
+	SSL_set_wfd(ssl, f_out);
+
+	tls_fd = SSL_get_fd(ssl);
+	n = tls_write[0];
+	n = MAX(tls_read[1], n);
+	n = MAX(tls_fd, n) + 1;
+
+	ssl_running = 1;
+	while (ssl_running) {
+		FD_ZERO(&rd);
+		FD_ZERO(&wd);
+		FD_SET(tls_write[0], &rd);
+		FD_SET(tls_read[1], &wd);
+		FD_SET(tls_fd, &rd);
+		FD_SET(tls_fd, &wd);
+
+		r = select(n, &rd, &wd, NULL, NULL);
+
+		if (r == -1 && errno == EINTR)
+			continue;
+		if (FD_ISSET(tls_write[0], &rd)) {
+			r = read(tls_write[0], buf1+avail1, BUF_SIZE-avail1);
+			if (r >= 0)
+				avail1 += r;
+			else {
+				rprintf(FERROR, "pipe read error: %s\n",
+					strerror(errno));
+				break;
+			}
+		}
+		if (FD_ISSET(tls_fd, &rd)) {
+			r = SSL_read(ssl, buf2+avail2, BUF_SIZE-avail2);
+			if (r > 0)
+				avail2 += r;
+			else {
+				switch (SSL_get_error(ssl, r)) {
+				case SSL_ERROR_ZERO_RETURN:
+					goto closed;
+				case SSL_ERROR_WANT_READ:
+				case SSL_ERROR_WANT_WRITE:
+					break;
+				case SSL_ERROR_SYSCALL:
+					if (r == 0)
+						rprintf(FERROR, "SSL spurious EOF\n");
+					else
+						rprintf(FERROR, "SSL I/O error: %s\n",
+							strerror(errno));
+					goto closed;
+				case SSL_ERROR_SSL:
+					rprintf(FERROR, "SSL: %s\n",
+						ERR_error_string(ERR_get_error(), NULL));
+					goto closed;
+				default:
+					rprintf(FERROR, "unexpected ssl error %d\n", r);
+					goto closed;
+				}
+			}
+		}
+		if (FD_ISSET(tls_read[1], &wd) && write2 < avail2) {
+			r = write(tls_read[1], buf2+write2, avail2-write2);
+			if (r >= 0)
+				write2 += r;
+			else {
+				rprintf(FERROR, "pipe write error: %s\n",
+					strerror(errno));
+				break;
+			}
+		}
+		if (FD_ISSET(tls_fd, &wd) && write1 < avail1) {
+			r = SSL_write(ssl, buf1+write1, avail1-write1);
+			if (r > 0)
+				write1 += r;
+			else {
+				switch (SSL_get_error(ssl, r)) {
+				case SSL_ERROR_ZERO_RETURN:
+					goto closed;
+				case SSL_ERROR_WANT_READ:
+				case SSL_ERROR_WANT_WRITE:
+					break;
+				case SSL_ERROR_SYSCALL:
+					if (r == 0)
+						rprintf(FERROR, "SSL: spurious EOF\n");
+					else
+						rprintf(FERROR, "SSL: I/O error: %s\n",
+							strerror(errno));
+					goto closed;
+				case SSL_ERROR_SSL:
+					rprintf(FERROR, "SSL: %s\n",
+						ERR_error_string(ERR_get_error(), NULL));
+					goto closed;
+				default:
+					rprintf(FERROR, "unexpected ssl error %d\n", r);
+					goto closed;
+				}
+			}
+		}
+		if (avail1 == write1)
+			avail1 = write1 = 0;
+		if (avail2 == write2)
+			avail2 = write2 = 0;
+	}
+
+	/* XXX I'm pretty sure that there is a lot that I am not considering
+	   here. Bugs? Yes, probably. */
+
+	/* We're finished. */
+    closed:
+	close(tls_read[1]);
+	close(tls_write[0]);
+	exit(0);
+}
+
+/**
+ * Ends the TLS connection.
+ */
+void end_tls(void)
+{
+	if (ssl_pid > 0)
+		kill(ssl_pid, SIGUSR1);
+}
--- old/proto.h
+++ new/proto.h
@@ -246,6 +246,12 @@ void start_accept_loop(int port, int (*f
 void set_socket_options(int fd, char *options);
 void become_daemon(void);
 int sock_exec(const char *prog);
+int init_tls(void);
+char *get_ssl_error(void);
+int get_tls_rfd(void);
+int get_tls_wfd(void);
+int start_tls(int f_in, int f_out);
+void end_tls(void);
 int do_unlink(const char *fname);
 int do_symlink(const char *fname1, const char *fname2);
 int do_link(const char *fname1, const char *fname2);
--- old/configure
+++ new/configure
@@ -662,6 +662,7 @@ INSTALL_PROGRAM
 INSTALL_SCRIPT
 INSTALL_DATA
 HAVE_REMSH
+SSL_OBJS
 LIBOBJS
 ALLOCA
 OBJ_SAVE
@@ -1258,6 +1259,7 @@ Optional Features:
   --disable-largefile     omit support for large files
   --disable-ipv6          don't even try to use IPv6
   --disable-locale        turn off locale features
+  --enable-openssl        compile SSL support with OpenSSL.
 
 Optional Packages:
   --with-PACKAGE[=ARG]    use PACKAGE [ARG=yes]
@@ -4827,6 +4829,116 @@ _ACEOF
 
 fi
 
+# Check whether --enable-openssl was given.
+if test "${enable_openssl+set}" = set; then
+  enableval=$enable_openssl;
+fi
+
+
+if test "x$enable_openssl" != xno
+then
+	have_ssl=yes
+
+{ echo "$as_me:$LINENO: checking for SSL_library_init in -lssl" >&5
+echo $ECHO_N "checking for SSL_library_init in -lssl... $ECHO_C" >&6; }
+if test "${ac_cv_lib_ssl_SSL_library_init+set}" = set; then
+  echo $ECHO_N "(cached) $ECHO_C" >&6
+else
+  ac_check_lib_save_LIBS=$LIBS
+LIBS="-lssl  $LIBS"
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char SSL_library_init ();
+int
+main ()
+{
+return SSL_library_init ();
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext conftest$ac_exeext
+if { (ac_try="$ac_link"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_link") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } &&
+	 { ac_try='test -z "$ac_c_werror_flag" || test ! -s conftest.err'
+  { (case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_try") 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; } &&
+	 { ac_try='test -s conftest$ac_exeext'
+  { (case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
+  (eval "$ac_try") 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+  ac_cv_lib_ssl_SSL_library_init=yes
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	ac_cv_lib_ssl_SSL_library_init=no
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
+      conftest$ac_exeext conftest.$ac_ext
+LIBS=$ac_check_lib_save_LIBS
+fi
+{ echo "$as_me:$LINENO: result: $ac_cv_lib_ssl_SSL_library_init" >&5
+echo "${ECHO_T}$ac_cv_lib_ssl_SSL_library_init" >&6; }
+if test $ac_cv_lib_ssl_SSL_library_init = yes; then
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_LIBSSL 1
+_ACEOF
+
+  LIBS="-lssl $LIBS"
+
+else
+  have_ssl=no
+fi
+
+	if test "x$have_ssl" = xyes
+	then
+
+cat >>confdefs.h <<\_ACEOF
+#define HAVE_OPENSSL 1
+_ACEOF
+
+		SSL_OBJS=ssl.o
+
+	fi
+fi
+
 { echo "$as_me:$LINENO: checking whether to call shutdown on all sockets" >&5
 echo $ECHO_N "checking whether to call shutdown on all sockets... $ECHO_C" >&6; }
 case $host_os in
@@ -15481,6 +15593,7 @@ INSTALL_PROGRAM!$INSTALL_PROGRAM$ac_deli
 INSTALL_SCRIPT!$INSTALL_SCRIPT$ac_delim
 INSTALL_DATA!$INSTALL_DATA$ac_delim
 HAVE_REMSH!$HAVE_REMSH$ac_delim
+SSL_OBJS!$SSL_OBJS$ac_delim
 LIBOBJS!$LIBOBJS$ac_delim
 ALLOCA!$ALLOCA$ac_delim
 OBJ_SAVE!$OBJ_SAVE$ac_delim
@@ -15490,7 +15603,7 @@ BUILD_POPT!$BUILD_POPT$ac_delim
 LTLIBOBJS!$LTLIBOBJS$ac_delim
 _ACEOF
 
-  if test `sed -n "s/.*$ac_delim\$/X/p" conf$$subs.sed | grep -c X` = 71; then
+  if test `sed -n "s/.*$ac_delim\$/X/p" conf$$subs.sed | grep -c X` = 72; then
     break
   elif $ac_last_try; then
     { { echo "$as_me:$LINENO: error: could not make $CONFIG_STATUS" >&5
--- old/config.h.in
+++ new/config.h.in
@@ -164,6 +164,9 @@
 /* Define to 1 if you have the `socket' library (-lsocket). */
 #undef HAVE_LIBSOCKET
 
+/* Define to 1 if you have the `ssl' library (-lssl). */
+#undef HAVE_LIBSSL
+
 /* Define to 1 if you have the <limits.h> header file. */
 #undef HAVE_LIMITS_H
 
@@ -229,6 +232,9 @@
 /* Define to 1 if you have the `open64' function. */
 #undef HAVE_OPEN64
 
+/* true if you want to use SSL. */
+#undef HAVE_OPENSSL
+
 /* Define to 1 if you have the `putenv' function. */
 #undef HAVE_PUTENV