New function, sslcert.parse_ssl_certificate

For reasons, the function is exported from nse_ssl_cert.cc into
nmap.socket, then included and documented in sslcert.lua because it fits
better there.

nse_nsock.cc

@@ -1048,6 +1048,7 @@ LUALIB_API int luaopen_nsock (lua_State *L)
     {"loop", l_loop},
     {"new", l_new},
     {"sleep", l_sleep},
+    {"parse_ssl_certificate", l_parse_ssl_certificate},
     {NULL, NULL}
   };
 

nse_ssl_cert.cc

@@ -426,13 +426,32 @@ static const char *pkey_type_to_string(int type)
   }
 }
 
+static int parse_ssl_cert(lua_State *L, X509 *cert);
+
+int l_parse_ssl_certificate(lua_State *L)
+{
+  X509 *cert;
+  size_t l;
+  const char *der;
+
+  der = luaL_checklstring(L, 1, &l);
+  if (der == NULL) {
+    lua_pushnil(L);
+    return 1;
+  }
+
+  cert = d2i_X509(NULL, (const unsigned char **) &der, l);
+  if (cert == NULL) {
+    lua_pushnil(L);
+    return 1;
+  }
+  return parse_ssl_cert(L, cert);
+}
+
 int l_get_ssl_certificate(lua_State *L)
 {
   SSL *ssl;
-  struct cert_userdata *udata;
   X509 *cert;
-  X509_NAME *subject, *issuer;
-  EVP_PKEY *pubkey;
 
   ssl = nse_nsock_get_ssl(L);
   cert = SSL_get_peer_certificate(ssl);
@@ -440,6 +459,14 @@ int l_get_ssl_certificate(lua_State *L)
     lua_pushnil(L);
     return 1;
   }
+  return parse_ssl_cert(L, cert);
+}
+
+static int parse_ssl_cert(lua_State *L, X509 *cert)
+{
+  struct cert_userdata *udata;
+  X509_NAME *subject, *issuer;
+  EVP_PKEY *pubkey;
 
   udata = (struct cert_userdata *) lua_newuserdata(L, sizeof(*udata));
   udata->cert = cert;

nse_ssl_cert.h

@@ -123,5 +123,6 @@
 /* $Id:$ */
 
 int l_get_ssl_certificate(lua_State *L);
+int l_parse_ssl_certificate(lua_State *L);
 void nse_nsock_init_ssl_cert(lua_State *L);
 

nselib/sslcert.lua

@@ -29,6 +29,14 @@ local string = require "string"
 local xmpp = require "xmpp"
 _ENV = stdnse.module("sslcert", stdnse.seeall)
 
+--- Parse an X.509 certificate from DER-encoded string
+--@name parse_ssl_certificate
+--@class function
+--@param der DER-encoded certificate
+--@return table containing decoded certificate
+--@see nmap.get_ssl_certificate
+_ENV.parse_ssl_certificate = nmap.socket.parse_ssl_certificate
+
 StartTLS = {
 
   -- TODO: Implement STARTTLS for NNTP