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Add the nmap.get_ssl_certificate NSE function, which returns the peer

Browse Source 
certificate of an SSL socket.
This commit is contained in:
david
2009-08-13 23:32:33 +00:00
parent 0df6272cf9
commit 6c766c58cd
6 changed files with 630 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
Makefile.in
View File

@@ -71,9 +71,9 @@ NSE_SRC=nse_main.cc nse_nsock.cc nse_fs.cc nse_nmaplib.cc nse_debug.cc nse_pcrel
NSE_HDRS=nse_main.h nse_nsock.h nse_fs.h nse_nmaplib.h nse_debug.h nse_pcrelib.h nse_binlib.h nse_bit.h
NSE_OBJS=nse_main.o nse_nsock.o nse_fs.o nse_nmaplib.o nse_debug.o nse_pcrelib.o nse_binlib.o nse_bit.o
ifneq (@OPENSSL_LIBS@,)
NSE_SRC+=nse_openssl.cc
NSE_HDRS+=nse_openssl.h
NSE_OBJS+=nse_openssl.o
NSE_SRC+=nse_openssl.cc nse_ssl_cert.cc
NSE_HDRS+=nse_openssl.h nse_ssl_cert.h
NSE_OBJS+=nse_openssl.o nse_ssl_cert.o
endif
endif

28
nse_nsock.cc
View File

@@ -13,6 +13,7 @@ extern "C"
#include "nse_nsock.h"
#include "nse_main.h"
#include "nse_ssl_cert.h"
#include "nsock.h"
#include "nmap_error.h"
@@ -395,6 +396,7 @@ int luaopen_nsock(lua_State * L)
{"pcap_close", l_nsock_ncap_close},
{"pcap_register", l_nsock_ncap_register},
{"pcap_receive", l_nsock_pcap_receive},
{"get_ssl_certificate", l_get_ssl_certificate},
// {"callback_test", l_nsock_pcap_callback_test},
{NULL, NULL}
};
@@ -441,6 +443,11 @@ int luaopen_nsock(lua_State * L)
luaL_newmetatable(L, "nsock_proxy");
#if HAVE_OPENSSL
/* Set up the SSL certificate userdata code in nse_ssl_cert.cc. */
nse_nsock_init_ssl_cert(L);
#endif
nsp = nsp_new(NULL);
if (o.scriptTrace())
nsp_settrace(nsp, NSOCK_TRACE_LEVEL, o.getStartTime());
@@ -1736,6 +1743,27 @@ int ncap_restore_lua(ncap_request * nr)
return 0;
}
#if HAVE_OPENSSL
const SSL *nse_nsock_get_ssl(lua_State *L)
{
const l_nsock_udata *udata;
udata = (l_nsock_udata *) luaL_checkudata(L, 1, "nsock");
if (!nsi_checkssl(udata->nsiod))
error("Socket is not an SSL socket");
return (SSL *) nsi_getssl(udata->nsiod);
}
#else
/* If HAVE_OPENSSL is defined, this comes from nse_ssl_cert.cc. */
int l_get_ssl_certificate(lua_State *L)
{
error("Socket is not an SSL socket");
return 0;
}
#endif
/****************** DNET ******************************************************/
static int l_dnet_open_ethernet(lua_State * L);

7
nse_nsock.h
View File

@@ -1,6 +1,8 @@
#ifndef NMAP_LUA_NSOCK_H
#define NMAP_LUA_NSOCK_H
#include "nmap_config.h"
int luaopen_nsock(lua_State *);
int l_nsock_new(lua_State *);
int l_nsock_sleep(lua_State *L);
@@ -10,5 +12,10 @@ int l_dnet_get_interface_link(lua_State *);
#define NSE_NSOCK_LOOP "NSOCK_LOOP"
#if HAVE_OPENSSL
#include <openssl/ssl.h>
const SSL *nse_nsock_get_ssl(lua_State *L);
#endif
#endif

456
nse_ssl_cert.cc Normal file
View File

@@ -0,0 +1,456 @@
/***************************************************************************
* nse_ssl_cert.cc -- NSE userdatum representing an SSL certificate. *
* *
***********************IMPORTANT NMAP LICENSE TERMS************************
* *
* The Nmap Security Scanner is (C) 1996-2009 Insecure.Com LLC. Nmap is *
* also a registered trademark of Insecure.Com LLC. This program is free *
* software; you may redistribute and/or modify it under the terms of the *
* GNU General Public License as published by the Free Software *
* Foundation; Version 2 with the clarifications and exceptions described *
* below. This guarantees your right to use, modify, and redistribute *
* this software under certain conditions. If you wish to embed Nmap *
* technology into proprietary software, we sell alternative licenses *
* (contact sales@insecure.com). Dozens of software vendors already *
* license Nmap technology such as host discovery, port scanning, OS *
* detection, and version detection. *
* *
* Note that the GPL places important restrictions on "derived works", yet *
* it does not provide a detailed definition of that term. To avoid *
* misunderstandings, we consider an application to constitute a *
* "derivative work" for the purpose of this license if it does any of the *
* following: *
* o Integrates source code from Nmap *
* o Reads or includes Nmap copyrighted data files, such as *
* nmap-os-db or nmap-service-probes. *
* o Executes Nmap and parses the results (as opposed to typical shell or *
* execution-menu apps, which simply display raw Nmap output and so are *
* not derivative works.) *
* o Integrates/includes/aggregates Nmap into a proprietary executable *
* installer, such as those produced by InstallShield. *
* o Links to a library or executes a program that does any of the above *
* *
* The term "Nmap" should be taken to also include any portions or derived *
* works of Nmap. This list is not exclusive, but is meant to clarify our *
* interpretation of derived works with some common examples. Our *
* interpretation applies only to Nmap--we don't speak for other people's *
* GPL works. *
* *
* If you have any questions about the GPL licensing restrictions on using *
* Nmap in non-GPL works, we would be happy to help. As mentioned above, *
* we also offer alternative license to integrate Nmap into proprietary *
* applications and appliances. These contracts have been sold to dozens *
* of software vendors, and generally include a perpetual license as well *
* as providing for priority support and updates as well as helping to *
* fund the continued development of Nmap technology. Please email *
* sales@insecure.com for further information. *
* *
* As a special exception to the GPL terms, Insecure.Com LLC grants *
* permission to link the code of this program with any version of the *
* OpenSSL library which is distributed under a license identical to that *
* listed in the included COPYING.OpenSSL file, and distribute linked *
* combinations including the two. You must obey the GNU GPL in all *
* respects for all of the code used other than OpenSSL. If you modify *
* this file, you may extend this exception to your version of the file, *
* but you are not obligated to do so. *
* *
* If you received these files with a written license agreement or *
* contract stating terms other than the terms above, then that *
* alternative license agreement takes precedence over these comments. *
* *
* Source is provided to this software because we believe users have a *
* right to know exactly what a program is going to do before they run it. *
* This also allows you to audit the software for security holes (none *
* have been found so far). *
* *
* Source code also allows you to port Nmap to new platforms, fix bugs, *
* and add new features. You are highly encouraged to send your changes *
* to nmap-dev@insecure.org for possible incorporation into the main *
* distribution. By sending these changes to Fyodor or one of the *
* Insecure.Org development mailing lists, it is assumed that you are *
* offering the Nmap Project (Insecure.Com LLC) the unlimited, *
* non-exclusive right to reuse, modify, and relicense the code. Nmap *
* will always be available Open Source, but this is important because the *
* inability to relicense code has caused devastating problems for other *
* Free Software projects (such as KDE and NASM). We also occasionally *
* relicense the code to third parties as discussed above. If you wish to *
* specify special license conditions of your contributions, just say so *
* when you send them. *
* *
* 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 v2.0 for more details at *
* http://www.gnu.org/licenses/gpl-2.0.html , or in the COPYING file *
* included with Nmap. *
* *
***************************************************************************/
/* $Id:$ */
#include <assert.h>
#include <errno.h>
#include <openssl/bio.h>
#include <openssl/pem.h>
#include <openssl/ssl.h>
#include <openssl/x509.h>
extern "C"
{
#include "lua.h"
#include "lauxlib.h"
}
#include "nse_nsock.h"
#include "nbase.h"
struct cert_userdata {
X509 *cert;
int attributes_table;
};
/* This is a reference to a table that will be used as the metatable for
certificate attribute tables. It has an __index entry that points to the
global table of certificate functions like digest. */
static int ssl_cert_methods_index_ref = LUA_NOREF;
/* Calculate the digest of the certificate using the given algorithm. */
static int ssl_cert_digest(lua_State *L)
{
struct cert_userdata *udata;
const char *algorithm;
unsigned char buf[256];
size_t n;
const EVP_MD *md;
udata = (struct cert_userdata *) luaL_checkudata(L, 1, "SSL_CERT");
algorithm = luaL_checkstring(L, 2);
md = EVP_get_digestbyname(algorithm);
if (md == NULL)
return 0;
n = sizeof(buf);
if (X509_digest(udata->cert, md, buf, &n) != 1)
return 0;
lua_pushlstring(L, (char *) buf, n);
return 1;
}
/* These are the contents of the table that is pointed to by the table that has
ssl_cert_methods_index_ref as a reference. */
static struct luaL_reg ssl_cert_methods[] = {
{ "digest", ssl_cert_digest },
{ NULL, NULL },
};
/* This is a helper function for x509_name_to_table. It takes the ASN1_OBJECT
passed as an argument, turns it into a table key, and pushes it on the stack.
The key is a string (like "commonName") if the object has an NID known by
OBJ_obj2nid; otherwise it is an array containing the OID components as
strings: { "2", "5", "4", "3" }. */
static void obj_to_key(lua_State *L, const ASN1_OBJECT *obj)
{
int nid;
nid = OBJ_obj2nid(obj);
if (nid == NID_undef) {
size_t size = 0;
char *buf = NULL;
const char *p, *q;
int i, n;
while ((n = OBJ_obj2txt(buf, size, obj, 1)) < 0 || (unsigned) n >= size) {
size = size * 2 + 1;
buf = (char *) safe_realloc(buf, size);
}
lua_newtable(L);
i = 1;
p = buf;
q = p;
while (*q != '\0') {
q = strchr(p, '.');
if (q == NULL)
q = strchr(p, '\0');
lua_pushlstring(L, p, q - p);
lua_rawseti(L, -2, i++);
p = q + 1;
}
free(buf);
} else {
lua_pushstring(L, OBJ_nid2ln(nid));
}
}
/* This is a helper function for l_get_ssl_certificate. It builds a table from
the given X509_NAME, using keys returned from obj_to_key as keys. The result
is pushed on the stack. */
static void x509_name_to_table(lua_State *L, X509_NAME *name)
{
int i;
lua_newtable(L);
for (i = 0; i < X509_NAME_entry_count(name); i++) {
X509_NAME_ENTRY *entry;
const ASN1_OBJECT *obj;
const ASN1_STRING *value;
entry = X509_NAME_get_entry(name, i);
obj = X509_NAME_ENTRY_get_object(entry);
value = X509_NAME_ENTRY_get_data(entry);
obj_to_key(L, obj);
lua_pushlstring(L, (const char *) value->data, value->length);
lua_settable(L, -3);
}
}
/* Parse as a decimal integer the len characters starting at s. This function
can only process positive numbers; if the return value is negative then a
parsing error occurred. */
static int parse_int(const unsigned char *s, size_t len)
{
char buf[32];
char *tail;
long v;
if (len == 0)
return -1;
if (!isdigit((int) (unsigned char) s[0]))
return -1;
if (len > sizeof(buf) - 1)
return -1;
memcpy(buf, s, len);
buf[len] = '\0';
errno = 0;
v = strtol(buf, &tail, 10);
if (errno != 0 || *tail != '\0')
return -1;
if ((int) v != v || v < 0)
return -1;
return (int) v;
}
/* This is a helper function for asn1_time_to_obj. It parses a tectual ASN1_TIME
value and stores the time in the given struct tm. It returns 0 on success and
-1 on a parse error. */
static int time_to_tm(const ASN1_TIME *t, struct tm *result)
{
const unsigned char *p;
p = t->data;
if (t->length == 13 && t->data[t->length - 1] == 'Z') {
/* yymmddhhmmssZ */
int year;
year = parse_int(t->data, 2);
if (year < 0)
return -1;
/* "In coming up with the worlds least efficient machine-readable time
encoding format, the ISO nevertheless decided to forgo the encoding of
centuries, a problem which has been kludged around by redefining the time
as UTCTime if the date is 2049 or ealier, and GeneralizedTime if the date
is 2050 or later."
http://www.cs.auckland.ac.nz/~pgut001/pubs/x509guide.txt */
if (year < 50)
result->tm_year = 2000 + year;
else
result->tm_year = 1900 + year;
p = t->data + 2;
} else if (t->length == 14) {
/* yyyymmddhhmmss */
result->tm_year = parse_int(t->data, 4);
if (result->tm_year < 0)
return -1;
p = t->data + 4;
} else {
return -1;
}
result->tm_mon = parse_int(p, 2);
result->tm_mday = parse_int(p + 2, 2);
result->tm_hour = parse_int(p + 4, 2);
result->tm_min = parse_int(p + 6, 2);
result->tm_sec = parse_int(p + 8, 2);
if (result->tm_mon < 0 || result->tm_mday < 0 || result->tm_hour < 0
|| result->tm_min < 0 || result->tm_sec < 0) {
return -1;
}
return 0;
}
/* This is a helper function for asn1_time_to_obj. It converts a struct tm into
a date table as returned by the Lua date os.date("!*t"), with the exception
that the wday and yday fields are not present. */
static void tm_to_table(lua_State *L, const struct tm *tm)
{
lua_newtable(L);
lua_pushnumber(L, tm->tm_year);
lua_setfield(L, -2, "year");
lua_pushnumber(L, tm->tm_mon + 1);
lua_setfield(L, -2, "month");
lua_pushnumber(L, tm->tm_mday);
lua_setfield(L, -2, "day");
lua_pushnumber(L, tm->tm_hour);
lua_setfield(L, -2, "hour");
lua_pushnumber(L, tm->tm_min);
lua_setfield(L, -2, "min");
lua_pushnumber(L, tm->tm_sec);
lua_setfield(L, -2, "sec");
/* Omit tm_wday and tm_yday. */
}
/* This is a helper functino for x509_validity_to_table. It takes teh given
ASN1_TIME and covnerts it to a value on the stack, which is one of
nil, if the time is NULL;
a date table, if the date can be parsed; and
a string of the raw bytes, if the date cannot be parsed. */
static void asn1_time_to_obj(lua_State *L, const ASN1_TIME *s)
{
struct tm tm;
if (s == NULL) {
lua_pushnil(L);
} else if (time_to_tm(s, &tm) == 0) {
tm_to_table(L, &tm);
} else {
lua_pushlstring(L, (const char *) s->data, s->length);
}
}
/* This is a helper functino for x509_validity_to_table. It builds a table with
the two members "notBefore" and "notAfter", whose values are what is returned
from asn1_time_to_obj. */
static void x509_validity_to_table(lua_State *L, const X509 *cert)
{
lua_newtable(L);
asn1_time_to_obj(L, X509_get_notBefore(cert));
lua_setfield(L, -2, "notBefore");
asn1_time_to_obj(L, X509_get_notAfter(cert));
lua_setfield(L, -2, "notAfter");
}
/* This is a helper function for l_get_ssl_certificate. It converts the
certificate into a PEM-encoded string on the stack. */
static void cert_pem_to_string(lua_State *L, X509 *cert)
{
BIO *bio;
char *buf;
long size;
bio = BIO_new(BIO_s_mem());
assert(bio != NULL);
assert(PEM_write_bio_X509(bio, cert));
size = BIO_get_mem_data(bio, &buf);
lua_pushlstring(L, buf, size);
BIO_vfree(bio);
}
int l_get_ssl_certificate(lua_State *L)
{
const SSL *ssl;
struct cert_userdata *udata;
X509 *cert;
X509_NAME *subject, *issuer;
ssl = nse_nsock_get_ssl(L);
cert = SSL_get_peer_certificate(ssl);
if (cert == NULL) {
lua_pushnil(L);
return 1;
}
udata = (struct cert_userdata *) lua_newuserdata(L, sizeof(*udata));
udata->cert = cert;
lua_newtable(L);
subject = X509_get_subject_name(cert);
if (subject != NULL) {
x509_name_to_table(L, subject);
lua_setfield(L, -2, "subject");
}
issuer = X509_get_issuer_name(cert);
if (issuer != NULL) {
x509_name_to_table(L, issuer);
lua_setfield(L, -2, "issuer");
}
x509_validity_to_table(L, cert);
lua_setfield(L, -2, "validity");
cert_pem_to_string(L, cert);
lua_setfield(L, -2, "pem");
/* At this point the certificate-specific table of attributes is at the top of
the stack. We give it a metatable with an __index entry that points into
the global shared table of certificate functions. */
lua_rawgeti(L, LUA_REGISTRYINDEX, ssl_cert_methods_index_ref);
lua_setmetatable(L, -2);
udata->attributes_table = luaL_ref(L, LUA_REGISTRYINDEX);
luaL_getmetatable(L, "SSL_CERT");
lua_setmetatable(L, -2);
return 1;
}
static int l_ssl_cert_index(lua_State *L)
{
struct cert_userdata *udata;
udata = (struct cert_userdata *) luaL_checkudata(L, 1, "SSL_CERT");
lua_rawgeti(L, LUA_REGISTRYINDEX, udata->attributes_table);
/* The key. */
lua_pushvalue(L, 2);
/* Look it up in the table of attributes. */
lua_gettable(L, -2);
return 1;
}
static int l_ssl_cert_gc(lua_State *L)
{
struct cert_userdata *udata;
udata = (struct cert_userdata *) luaL_checkudata(L, 1, "SSL_CERT");
X509_free(udata->cert);
luaL_unref(L, LUA_REGISTRYINDEX, udata->attributes_table);
return 0;
}
void nse_nsock_init_ssl_cert(lua_State *L)
{
luaL_newmetatable(L, "SSL_CERT");
lua_pushcclosure(L, l_ssl_cert_index, 0);
lua_setfield(L, -2, "__index");
lua_pushcclosure(L, l_ssl_cert_gc, 0);
lua_setfield(L, -2, "__gc");
/* Create a table with an __index entry that will be used as a metatable for
per-certificate attribute tables. This gives the tables access to the
global shared table of certificate functions. */
lua_newtable(L);
lua_newtable(L);
luaL_register(L, NULL, ssl_cert_methods);
lua_setfield(L, -2, "__index");
ssl_cert_methods_index_ref = luaL_ref(L, LUA_REGISTRYINDEX);
}

93
nse_ssl_cert.h Normal file
View File

@@ -0,0 +1,93 @@
/***************************************************************************
* nse_ssl_cert.h -- NSE userdatum representing an SSL certificate. *
* *
***********************IMPORTANT NMAP LICENSE TERMS************************
* *
* The Nmap Security Scanner is (C) 1996-2009 Insecure.Com LLC. Nmap is *
* also a registered trademark of Insecure.Com LLC. This program is free *
* software; you may redistribute and/or modify it under the terms of the *
* GNU General Public License as published by the Free Software *
* Foundation; Version 2 with the clarifications and exceptions described *
* below. This guarantees your right to use, modify, and redistribute *
* this software under certain conditions. If you wish to embed Nmap *
* technology into proprietary software, we sell alternative licenses *
* (contact sales@insecure.com). Dozens of software vendors already *
* license Nmap technology such as host discovery, port scanning, OS *
* detection, and version detection. *
* *
* Note that the GPL places important restrictions on "derived works", yet *
* it does not provide a detailed definition of that term. To avoid *
* misunderstandings, we consider an application to constitute a *
* "derivative work" for the purpose of this license if it does any of the *
* following: *
* o Integrates source code from Nmap *
* o Reads or includes Nmap copyrighted data files, such as *
* nmap-os-db or nmap-service-probes. *
* o Executes Nmap and parses the results (as opposed to typical shell or *
* execution-menu apps, which simply display raw Nmap output and so are *
* not derivative works.) *
* o Integrates/includes/aggregates Nmap into a proprietary executable *
* installer, such as those produced by InstallShield. *
* o Links to a library or executes a program that does any of the above *
* *
* The term "Nmap" should be taken to also include any portions or derived *
* works of Nmap. This list is not exclusive, but is meant to clarify our *
* interpretation of derived works with some common examples. Our *
* interpretation applies only to Nmap--we don't speak for other people's *
* GPL works. *
* *
* If you have any questions about the GPL licensing restrictions on using *
* Nmap in non-GPL works, we would be happy to help. As mentioned above, *
* we also offer alternative license to integrate Nmap into proprietary *
* applications and appliances. These contracts have been sold to dozens *
* of software vendors, and generally include a perpetual license as well *
* as providing for priority support and updates as well as helping to *
* fund the continued development of Nmap technology. Please email *
* sales@insecure.com for further information. *
* *
* As a special exception to the GPL terms, Insecure.Com LLC grants *
* permission to link the code of this program with any version of the *
* OpenSSL library which is distributed under a license identical to that *
* listed in the included COPYING.OpenSSL file, and distribute linked *
* combinations including the two. You must obey the GNU GPL in all *
* respects for all of the code used other than OpenSSL. If you modify *
* this file, you may extend this exception to your version of the file, *
* but you are not obligated to do so. *
* *
* If you received these files with a written license agreement or *
* contract stating terms other than the terms above, then that *
* alternative license agreement takes precedence over these comments. *
* *
* Source is provided to this software because we believe users have a *
* right to know exactly what a program is going to do before they run it. *
* This also allows you to audit the software for security holes (none *
* have been found so far). *
* *
* Source code also allows you to port Nmap to new platforms, fix bugs, *
* and add new features. You are highly encouraged to send your changes *
* to nmap-dev@insecure.org for possible incorporation into the main *
* distribution. By sending these changes to Fyodor or one of the *
* Insecure.Org development mailing lists, it is assumed that you are *
* offering the Nmap Project (Insecure.Com LLC) the unlimited, *
* non-exclusive right to reuse, modify, and relicense the code. Nmap *
* will always be available Open Source, but this is important because the *
* inability to relicense code has caused devastating problems for other *
* Free Software projects (such as KDE and NASM). We also occasionally *
* relicense the code to third parties as discussed above. If you wish to *
* specify special license conditions of your contributions, just say so *
* when you send them. *
* *
* 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 v2.0 for more details at *
* http://www.gnu.org/licenses/gpl-2.0.html , or in the COPYING file *
* included with Nmap. *
* *
***************************************************************************/
/* $Id:$ */
int l_get_ssl_certificate(lua_State *L);
void nse_nsock_init_ssl_cert(lua_State *L);

43
nselib/nmap.luadoc
View File

@@ -467,6 +467,49 @@ function pcap_receive()
-- @usage socket:pcap_close()
function pcap_close()
---
-- Retrieves the SSL certificate of the peer. The returned value can be accessed
-- like a table and has the following members:
--
-- <code>
-- subject = { commonName = "...", countryName = "...",
-- { "2", "5", "4", "15" } = "...", ... },
-- issuer = { commonName = "...", ... },
-- validity = { notBefore = { year = 2020, month = 5, day = 5,
-- hour = 0, min = 0, sec = 0 },
-- notAfter = { year = 2021, month = 5, day = 5,
-- hour = 0, min = 0, sec = 0 } },
-- pem = "-----BEGIN CERTIFICATE-----\nMIIFxzCCBK+gAwIBAgIQX02QuADDB7CVj..."
-- </code>
--
-- It also has the following member functions:
--
-- * <code>digest(algorithm)</code> returns the digest of the certificate using the given digest algorithm, which is any of the strings returned by <code>openssl.supported_digests</code>, typicaly something like <code>"md5"</code> or <code>"sha1"</code>.
--
-- The <code>"subject"</code> and <code>"issuer"</code> fields hold each
-- distinguished name. Fields with an unknown OID are represented as an array
-- whose elements are the numeric components of the OID, encoded as strings.
--
-- The <code>"validity"</code> table has the members <code>"notBefore"</code>
-- and <code>"notAfter"</code>. Each of these is a table as returned by
-- <code>os.date("!*t")</code> if the date in the certificate could be parsed,
-- except that they lack the <code>"wday"</code> and <code>"yday"</code>
-- members. If the date could not be parsed, the value will be a string
-- containing the raw byte values of the field. If absent, the value will be
-- <code>nil</code>.
--
-- The <code>"pem"</code> field contains a PEM-encoded string of the entire
-- contents of the certificate.
-- @return A table as described above.
-- @usage
-- local s = nmap.new_socket()
-- local status, error = s:connect(host.ip, port.number, "ssl")
-- if status then
-- local cert = s:get_ssl_certificate()
-- local digest = s:digest("md5")
-- end
function get_ssl_certificate()
--- Creates a new dnet object, used to send raw packets.
-- @usage local dnet = nmap.new_dnet()
function new_dnet()