From 012c5b16cd1c98c9d8211186f14c230d40470855 Mon Sep 17 00:00:00 2001
From: Your Name <you@example.com>
Date: Tue, 13 Jul 2021 00:22:06 +0200
Subject: [PATCH] m25400.pm take the user-password into account

---
 tools/test_modules/m25400.pm | 96 +++++++++++++++++++++++-------------
 1 file changed, 61 insertions(+), 35 deletions(-)

diff --git a/tools/test_modules/m25400.pm b/tools/test_modules/m25400.pm
index 0f0d15e85..7b4b03363 100644
--- a/tools/test_modules/m25400.pm
+++ b/tools/test_modules/m25400.pm
@@ -86,7 +86,6 @@ sub pdf_compute_encryption_key_owner
   my $R         = shift;
   my $enc       = shift;
 
-  # TODO use user password as input for md5 of o_digest if no owner password is set
   my $data;
   $data .= $word;
   $data .= substr ($padding, 0, 32 - length $word);
@@ -110,7 +109,7 @@ sub pdf_compute_encryption_key_owner
   }
   else
   {
-  $o_key = substr($o_digest, 0, 16); #length is always 128 bits or 16 bytes
+    $o_key = substr($o_digest, 0, 16); #length is always 128 bits or 16 bytes
   }
   #printf("\$o_key = %s\n", unpack ("H*", $o_key));
 
@@ -127,6 +126,7 @@ sub module_generate_hash
   my $V    = shift;
   my $R    = shift;
   my $enc  = shift;
+  my $u_pass  = shift;
 
   if (defined $u == 0)
   {
@@ -173,45 +173,56 @@ sub module_generate_hash
   ################ USER PASSWORD #################
   # do not change $u if it exists, keep this the same, as we don't know the user password,
   #  we cannot calculate this part of the hash again
-  if("".$u eq "0000000000000000000000000000000000000000000000000000000000000000")
+  my $res;
+  if("".$u_pass eq "")
   {
-    my $res = pdf_compute_encryption_key_user($word, $padding, $id, $u, $o, $P, $V, $R, $enc);
-
-    my $digest = md5 ($padding . pack ("H*", $id));
-
-    my $m = Crypt::RC4->new ($res);
-    $u = $m->RC4 ($digest);
-
-    my @ress = split "", $res;
-
-    #do xor of rc4 19 times
-    for (my $x = 1; $x <= 19; $x++)
-    {
-      my @xor;
-
-      for (my $i = 0; $i < 16; $i++)
-      {
-        $xor[$i] = chr (ord ($ress[$i]) ^ $x);
-      }
-
-      my $s = join ("", @xor);
-
-      my $m2 = Crypt::RC4->new ($s);
-
-      $u = $m2->RC4 ($u);
-    }
-    $u .= substr (pack ("H*", $u_save), 16, 16);
+    $res = pdf_compute_encryption_key_user($word, $padding, $id, $u, $o, $P, $V, $R, $enc);
   }
   else
   {
-    $u = pack("H*", $u)
+    #$u = pack("H*", $u)
+    #now that we know the user-password we can generate it
+    $res = pdf_compute_encryption_key_user($u_pass, $padding, $id, $u, $o, $P, $V, $R, $enc);
   }
 
+  my $digest = md5 ($padding . pack ("H*", $id));
+
+  my $m = Crypt::RC4->new ($res);
+  $u = $m->RC4 ($digest);
+
+  my @ress = split "", $res;
+
+  #do xor of rc4 19 times
+  for (my $x = 1; $x <= 19; $x++)
+  {
+    my @xor;
+
+    for (my $i = 0; $i < 16; $i++)
+    {
+      $xor[$i] = chr (ord ($ress[$i]) ^ $x);
+    }
+
+    my $s = join ("", @xor);
+
+    my $m2 = Crypt::RC4->new ($s);
+
+    $u = $m2->RC4 ($u);
+  }
+  $u .= substr (pack ("H*", $u_save), 16, 16);
+
   ################ OWNER PASSWORD #################
   my $o_key = pdf_compute_encryption_key_owner($word, $padding, $id, $u, $o, $P, $V, $R, $enc);
   my $n = Crypt::RC4->new ($o_key);
-  $o = $n->RC4(substr ($padding, 0, 32 - length "")); # TODO dynamically add user password including padding to the RC4 input for the computation of the pdf o-value
-
+  if("".$u_pass eq "")
+  {
+     $o = $n->RC4(substr ($padding, 0, 32 - length ""));
+  }
+  else
+  {
+    #dynamically add user password including padding to the RC4 input for the computation of the pdf o-value
+    $o = $n->RC4($u_pass.substr ($padding, 0, 32 - length $u_pass));
+  }
+ 
   #printf("padding_empty_str = %s\n", unpack ("H*", substr ($padding, 0, 32 - length "")));
 
   my @ress2 = split "", $o_key;
@@ -240,7 +251,15 @@ sub module_generate_hash
   #printf("\$o = %s\n", unpack ("H*", $o));
   #printf("\$u = %s\n", unpack ("H*", $u));
 
-  my $hash = sprintf ('$pdf$%d*%d*128*%d*%d*16*%s*32*%s*32*%s', $V, $R, $P, $enc, $id, unpack ("H*", $u), unpack ("H*", $o));
+  my $hash;
+  if("".$u_pass eq "")
+  {
+    $hash = sprintf ('$pdf$%d*%d*128*%d*%d*16*%s*32*%s*32*%s', $V, $R, $P, $enc, $id, unpack ("H*", $u), unpack ("H*", $o));
+  }
+  else
+  {
+    $hash = sprintf ('$pdf$%d*%d*128*%d*%d*16*%s*32*%s*32*%s*%s', $V, $R, $P, $enc, $id, unpack ("H*", $u), unpack ("H*", $o), $u_pass);
+  }
   #print("hash\n".$hash."\n");
   return $hash;
 }
@@ -256,7 +275,8 @@ sub module_verify_hash
 
   my @data = split /\*/, $hash_in;
 
-  return unless scalar @data == 11;
+  my $i_data = scalar @data;
+  return unless ($i_data == 11) || ($i_data == 12); #or 12 if user-password is included
 
   my $V        = shift @data; $V = substr ($V, 5, 1);
   my $R        = shift @data;
@@ -270,12 +290,18 @@ sub module_verify_hash
   return unless (shift @data eq '32');
   my $o        = shift @data;
 
+  my $u_pass = "";
+  if($i_data == 12) {
+    $u_pass = shift @data;
+    #printf("u_pass = %s\n", $u_pass);
+  }
+
   return unless defined $id;
   return unless defined $word;
 
   $word = pack_if_HEX_notation ($word);
 
-  my $new_hash = module_generate_hash ($word, $id, $u, $o, $P, $V, $R, $enc);
+  my $new_hash = module_generate_hash ($word, $id, $u, $o, $P, $V, $R, $enc, $u_pass);
 
   return ($new_hash, $word);
 }