diff --git a/common/os/CMakeLists.txt b/common/os/CMakeLists.txt
index 77ff363..82f1165 100644
--- a/common/os/CMakeLists.txt
+++ b/common/os/CMakeLists.txt
@@ -3,4 +3,5 @@
 add_library(os STATIC
   print.c
   net.c
-  os.cxx)
+  os.cxx
+  tls.cxx)
diff --git a/common/os/Makefile.am b/common/os/Makefile.am
index d87a0da..ab4f2d7 100644
--- a/common/os/Makefile.am
+++ b/common/os/Makefile.am
@@ -1,8 +1,8 @@
 noinst_LTLIBRARIES = libos.la
 
-HDRS = net.h print.h os.h
+HDRS = net.h print.h os.h tls.h
 
-libos_la_SOURCES = $(HDRS) print.c net.c os.cxx
+libos_la_SOURCES = $(HDRS) print.c net.c os.cxx tls.cxx
 
 libos_la_CPPFLAGS = -I$(top_srcdir)/common
 
diff --git a/common/os/tls.cxx b/common/os/tls.cxx
new file mode 100644
index 0000000..5ef8898
--- /dev/null
+++ b/common/os/tls.cxx
@@ -0,0 +1,193 @@
+/* Copyright (C) 2011 TightVNC Team.  All Rights Reserved.
+ *
+ * This 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 software 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 software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <os/tls.h>
+
+#include <iomanip>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sstream>
+#include <sys/types.h>
+#include <time.h>
+
+using namespace std;
+
+#ifdef HAVE_GNUTLS
+#include <gnutls/gnutls.h>
+#include <gnutls/x509.h>
+
+#ifndef HAVE_GNUTLS_X509_CRT_PRINT
+
+#define UNKNOWN_SUBJECT(err) \
+	do { \
+		ss << "unknown subject (" << gnutls_strerror(err) << "), "; \
+	} while (0)
+
+#define UNKNOWN_ISSUER(err) \
+	do { \
+		ss << "unknown issuer (" << gnutls_strerror(err) << "), "; \
+	} while (0)
+
+
+static void
+hexprint(ostringstream &ss, const char *data, size_t len)
+{
+	size_t j;
+	char tmp[3];
+
+	if (len == 0)
+		ss << "00";
+	else {
+		for (j = 0; j < len; j++) {
+			snprintf(tmp, sizeof(tmp), "%.2x", (unsigned char) data[j]);
+			ss << tmp;
+		}
+	}
+}
+
+/* Implementation based on gnutls_x509_crt_print from GNUTLS */
+int
+gnutls_x509_crt_print(gnutls_x509_crt_t cert,
+		      gnutls_certificate_print_formats_t format,
+		      gnutls_datum_t * out)
+{
+	ostringstream ss;
+	
+	int err;
+
+	char *dn;
+	size_t dn_size = 0;
+
+	/* Subject */
+	err = gnutls_x509_crt_get_dn(cert, NULL, &dn_size);
+	if (err != GNUTLS_E_SHORT_MEMORY_BUFFER)
+		UNKNOWN_SUBJECT(err);
+	else {
+		dn = (char *)malloc(dn_size);
+		if (dn == NULL) {
+			UNKNOWN_SUBJECT(GNUTLS_E_MEMORY_ERROR);
+		} else {
+			err = gnutls_x509_crt_get_dn(cert, dn, &dn_size);
+			if (err < 0) {
+				UNKNOWN_SUBJECT(err);
+			} else
+				ss << "subject `" << dn << "', ";
+			free(dn);
+		}
+	}
+
+	/* Issuer */
+	dn = NULL;
+	dn_size = 0;
+	err = gnutls_x509_crt_get_issuer_dn(cert, NULL, &dn_size);
+	if (err != GNUTLS_E_SHORT_MEMORY_BUFFER)
+		UNKNOWN_ISSUER(err);
+	else {
+		dn = (char *)malloc(dn_size);
+		if (dn == NULL) {
+			UNKNOWN_ISSUER(GNUTLS_E_MEMORY_ERROR);
+		} else {
+			err = gnutls_x509_crt_get_issuer_dn(cert, dn, &dn_size);
+			if (err < 0)
+				UNKNOWN_ISSUER(err);
+			else
+				ss << "issuer `" << dn << "', ";
+			free(dn);
+		}
+	}
+
+	/* Key algorithm and size */
+	unsigned int bits;
+	const char *name;
+	name = gnutls_pk_algorithm_get_name( (gnutls_pk_algorithm_t)
+		gnutls_x509_crt_get_pk_algorithm(cert, &bits));
+	if (name == NULL)
+		name = "Unknown";
+	ss << name << " key " << bits << " bits, ";
+
+	/* Signature algorithm */
+	err = gnutls_x509_crt_get_signature_algorithm(cert);
+	if (err < 0) {
+		ss << "unknown signature algorithm (" << gnutls_strerror(err)
+		   << "), ";
+	} else {
+		const char *name;
+		name = gnutls_sign_algorithm_get_name((gnutls_sign_algorithm_t)err);
+		if (name == NULL)
+			name = "Unknown";
+
+		ss << "signed using " << name;
+		if (err == GNUTLS_SIGN_RSA_MD5 || err == GNUTLS_SIGN_RSA_MD2)
+			ss << " (broken!)";
+		ss << ", ";
+	}
+
+	/* Validity */
+	time_t tim;
+	char s[42];
+	size_t max = sizeof(s);
+	struct tm t;
+
+	tim = gnutls_x509_crt_get_activation_time(cert);
+	if (gmtime_r(&tim, &t) == NULL)
+		ss << "unknown activation (" << (unsigned long) tim << ")";
+	else if (strftime(s, max, "%Y-%m-%d %H:%M:%S UTC", &t) == 0)
+		ss << "failed activation (" << (unsigned long) tim << ")";
+	else
+		ss << "activated `" << s << "'";
+	ss << ", ";
+
+	tim = gnutls_x509_crt_get_expiration_time(cert);
+	if (gmtime_r(&tim, &t) == NULL)
+		ss << "unknown expiry (" << (unsigned long) tim << ")";
+	else if (strftime(s, max, "%Y-%m-%d %H:%M:%S UTC", &t) == 0)
+		ss << "failed expiry (" << (unsigned long) tim << ")";
+	else
+		ss << "expires `" << s << "'";
+	ss << ", ";
+
+	/* Fingerprint */
+	char buffer[20];
+	size_t size = sizeof(buffer);
+
+	err = gnutls_x509_crt_get_fingerprint(cert, GNUTLS_DIG_SHA1, buffer, &size);
+	if (err < 0)
+		ss << "unknown fingerprint (" << gnutls_strerror(err) << ")";
+	else {
+		ss << "SHA-1 fingerprint `";
+		hexprint(ss, buffer, size);
+		ss << "'";
+	}
+
+	out->data = (unsigned char *) strdup(ss.str().c_str());
+	if (out->data == NULL)
+		return GNUTLS_E_MEMORY_ERROR;
+	out->size = strlen((char *)out->data);
+
+	return 0;
+}
+
+#endif /* HAVE_GNUTLS_X509_CRT_PRINT */
+
+#endif /* HAVE_GNUTLS */
+
diff --git a/common/os/tls.h b/common/os/tls.h
new file mode 100644
index 0000000..a6d09da
--- /dev/null
+++ b/common/os/tls.h
@@ -0,0 +1,49 @@
+/* Copyright (C) 2011 TightVNC Team.  All Rights Reserved.
+ *
+ * This 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 software 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 software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+
+#ifndef OS_TLS_H
+#define OS_TLS_H
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#ifdef HAVE_GNUTLS
+#include <gnutls/gnutls.h>
+
+#ifndef HAVE_GNUTLS_X509_CRT_PRINT
+#ifdef WIN32
+#error "Please install more recent GNUTLS with gnutls_x509_crt_print() function"
+#endif
+
+typedef enum {
+	GNUTLS_CRT_PRINT_ONELINE = 1
+} gnutls_certificate_print_formats_t;
+
+/*
+ * Prints certificate in human-readable form.
+ */
+int
+gnutls_x509_crt_print(gnutls_x509_crt_t cert,
+		      gnutls_certificate_print_formats_t format,
+		      gnutls_datum_t * out);
+#endif /* HAVE_GNUTLS_X509_CRT_PRINT */
+#endif /* HAVE_GNUTLS */
+
+#endif /* OS_TLS_H */
+