Parse Contents in signature dictionary without encryption

Various PDF digital signing tools do not encrypt /Contents value in signature dictionary. Adobe Acrobat Reader DC can handle a PDF with the /Contents value not encrypted. Write Contents in signature dictionary without encryption Tests ensure that string /Contents are not handled specially when not found in sig dicts.

Parse Contents in signature dictionary without encryption
Various PDF digital signing tools do not encrypt /Contents value in signature dictionary. Adobe Acrobat Reader DC can handle a PDF with the /Contents value not encrypted. Write Contents in signature dictionary without encryption Tests ensure that string /Contents are not handled specially when not found in sig dicts.
Masamichi Hosoda · Jay Berkenbilt
1 parent cdc46d78
Showing 4 changed files with 128 additions and 3 deletions
include/qpdf/QPDFWriter.hh
libqpdf/QPDFObjectHandle.cc
libqpdf/QPDFWriter.cc
qpdf/qtest/qpdf.test
@@ -481,6 +481,7 @@ class QPDFWriter
     static int const f_filtered =	1 << 1;
     static int const f_in_ostream =     1 << 2;
     static int const f_hex_string =     1 << 3;
+    static int const f_no_encryption =  1 << 4;
     enum trailer_e { t_normal, t_lin_first, t_lin_second };
@@ -1779,12 +1779,19 @@ QPDFObjectHandle::parseInternal(PointerHolder&lt;InputSource&gt; input,
     bool done = false;
     int bad_count = 0;
     int good_count = 0;
+    bool b_contents = false;
+    std::vector<std::string> contents_string_stack;
+    contents_string_stack.push_back("");
+    std::vector<qpdf_offset_t> contents_offset_stack;
+    contents_offset_stack.push_back(-1);
     while (! done)
     {
         bool bad = false;
         SparseOHArray& olist = olist_stack.back();
         parser_state_e state = state_stack.back();
         offset = offset_stack.back();
+        std::string& contents_string = contents_string_stack.back();
+        qpdf_offset_t& contents_offset = contents_offset_stack.back();
 	object = QPDFObjectHandle();
 	set_offset = false;
@@ -1894,6 +1901,9 @@ QPDFObjectHandle::parseInternal(PointerHolder&lt;InputSource&gt; input,
                 state_stack.push_back(
                     (token.getType() == QPDFTokenizer::tt_array_open) ?
                     st_array : st_dictionary);
+                b_contents = false;
+                contents_string_stack.push_back("");
+                contents_offset_stack.push_back(-1);
             }
 	    break;
@@ -1914,7 +1924,19 @@ QPDFObjectHandle::parseInternal(PointerHolder&lt;InputSource&gt; input,
 	    break;
 	  case QPDFTokenizer::tt_name:
-	    object = newName(token.getValue());
+	    {
+		std::string name = token.getValue();
+		object = newName(name);
+
+		if (name == "/Contents")
+		{
+		    b_contents = true;
+		}
+		else
+		{
+		    b_contents = false;
+		}
+	    }
 	    break;
 	  case QPDFTokenizer::tt_word:
@@ -1975,6 +1997,12 @@ QPDFObjectHandle::parseInternal(PointerHolder&lt;InputSource&gt; input,
 		std::string val = token.getValue();
                 if (decrypter)
                 {
+                    if (b_contents)
+                    {
+                        contents_string = val;
+                        contents_offset = input->getLastOffset();
+                        b_contents = false;
+                    }
                     decrypter->decryptString(val);
                 }
 		object = QPDFObjectHandle::newString(val);
@@ -2168,6 +2196,18 @@ QPDFObjectHandle::parseInternal(PointerHolder&lt;InputSource&gt; input,
                     }
                     dict[key] = val;
                 }
+		if (!contents_string.empty() &&
+		    dict.count("/Type") &&
+		    dict["/Type"].isName() &&
+		    dict["/Type"].getName() == "/Sig" &&
+		    dict.count("/ByteRange") &&
+		    dict.count("/Contents") &&
+		    dict["/Contents"].isString())
+		{
+		    dict["/Contents"]
+		      = QPDFObjectHandle::newString(contents_string);
+		    dict["/Contents"].setParsedOffset(contents_offset);
+		}
                 object = newDictionary(dict);
                 setObjectDescriptionFromInput(
                     object, context, object_description, input, offset);
@@ -2190,6 +2230,8 @@ QPDFObjectHandle::parseInternal(PointerHolder&lt;InputSource&gt; input,
             {
                 olist_stack.back().append(object);
             }
+            contents_string_stack.pop_back();
+            contents_offset_stack.pop_back();
         }
     }
@@ -1695,7 +1695,7 @@ QPDFWriter::unparseObject(QPDFObjectHandle object, int level,
 	    {
                 QTC::TC("qpdf", "QPDFWriter no encryption sig contents");
 		unparseChild(object.getKey(key), level + 1,
-			     child_flags | f_hex_string);
+			     child_flags | f_hex_string | f_no_encryption);
 	    }
 	    else
 	    {
@@ -1866,6 +1866,7 @@ QPDFWriter::unparseObject(QPDFObjectHandle object, int level,
 	std::string val;
 	if (this->m->encrypted &&
 	    (! (flags & f_in_ostream)) &&
+	    (! (flags & f_no_encryption)) &&
 	    (! this->m->cur_data_key.empty()))
 	{
 	    val = object.getStringValue();
@@ -3999,7 +3999,6 @@ show_ntests();
 # ----------
 $td->notify("--- Signature Dictionary ---");
 $n_tests += 6;
-
 foreach my $i (qw(preserve disable generate))
 {
     $td->runtest("sig dict contents hex (object-streams=$i)",
@@ -4017,6 +4016,88 @@ foreach my $i (qw(preserve disable generate))
                       $td->EXIT_STATUS => 0});
 }
+$n_tests += 4;
+foreach my $i (qw(preserve disable))
+{
+    $td->runtest("non sig dict contents text string (object-streams=$i)",
+                 {$td->COMMAND =>
+                      "qpdf --object-streams=$i comment-annotation.pdf a.pdf"},
+                 {$td->STRING => "",
+                      $td->EXIT_STATUS => 0});
+    $td->runtest("find desired contents as non hex (object-streams=$i)",
+                 {$td->COMMAND =>
+                      "grep \"/Contents (Salad)\" a.pdf"},
+                 {$td->REGEXP => ".*",
+                      $td->EXIT_STATUS => 0});
+}
+
+$n_tests += 2;
+    $td->runtest("non sig dict contents text string (object-streams=generate)",
+                 {$td->COMMAND =>
+                      "qpdf --object-streams=generate comment-annotation.pdf a.pdf"},
+                 {$td->STRING => "",
+                      $td->EXIT_STATUS => 0});
+    $td->runtest("plain text not found due to compression (object-streams=generate)",
+                 {$td->COMMAND =>
+                      "grep \"/Contents (Salad)\" a.pdf"},
+                 {$td->REGEXP => ".*",
+                      $td->EXIT_STATUS => 1});
+
+$n_tests += 12;
+foreach my $i (qw(40 128 256))
+{
+    $td->runtest("encrypt $i",
+                 {$td->COMMAND =>
+                      "qpdf --encrypt '' o $i -- digitally-signed.pdf a.pdf"},
+                 {$td->STRING => "",
+                      $td->EXIT_STATUS => 0});
+    $td->runtest("find desired contents (encrypt $i)",
+                 {$td->COMMAND =>
+                      "grep -f digitally-signed-sig-dict-contents.out a.pdf"},
+                 {$td->REGEXP => ".*",
+                      $td->EXIT_STATUS => 0});
+    $td->runtest("decrypt",
+                 {$td->COMMAND =>
+                      "qpdf --decrypt a.pdf b.pdf"},
+                 {$td->REGEXP => ".*",
+                      $td->EXIT_STATUS => 0});
+    $td->runtest("find desired contents (decrypt $i)",
+                 {$td->COMMAND =>
+                      "grep -f digitally-signed-sig-dict-contents.out b.pdf"},
+                 {$td->REGEXP => ".*",
+                      $td->EXIT_STATUS => 0});
+}
+
+$n_tests += 15;
+foreach my $i (qw(40 128 256))
+{
+    $td->runtest("non sig dict encrypt $i",
+                 {$td->COMMAND =>
+                      "qpdf --encrypt '' o $i -- comment-annotation.pdf a.pdf"},
+                 {$td->STRING => "",
+                      $td->EXIT_STATUS => 0});
+    $td->runtest("plain text not found due to encryption (non sig dict encrypt $i)",
+                 {$td->COMMAND =>
+                      "grep \"/Contents (Salad)\" a.pdf"},
+                 {$td->REGEXP => ".*",
+                      $td->EXIT_STATUS => 1});
+    $td->runtest("find encrypted contents (non sig dict encrypt $i)",
+                 {$td->COMMAND =>
+                      "grep \"/Contents <.*>\" a.pdf"},
+                 {$td->REGEXP => ".*",
+                      $td->EXIT_STATUS => 0});
+    $td->runtest("non sig dict decrypt",
+                 {$td->COMMAND =>
+                      "qpdf --decrypt a.pdf b.pdf"},
+                 {$td->REGEXP => ".*",
+                      $td->EXIT_STATUS => 0});
+    $td->runtest("find desired contents (non sig dict decrypt $i)",
+                 {$td->COMMAND =>
+                      "grep \"/Contents (Salad)\" b.pdf"},
+                 {$td->REGEXP => ".*",
+                      $td->EXIT_STATUS => 0});
+}
+
 show_ntests();
 # ----------
 $td->notify("--- Get XRef Table ---");