plan9fox/sys/lib/ghostscript/pdf_sec.ps

%   Copyright (C) 1996-1998 Geoffrey Keating. 
%	Copyright (C) 2001 Artifex Software, Inc.
% This file may be freely distributed with or without modifications,
% so long as modified versions are marked as such and copyright notices are
% not removed.

% $Id: pdf_sec.ps,v 1.15 2004/03/12 01:55:58 dan Exp $
% Implementation of security hooks for PDF reader.

% This file contains the procedures that have to take encryption into
% account when reading a PDF file. It replaces the stub version of this
% file that is shipped with GhostScript. It requires GhostScript 7.01
% or later.

% Documentation for using this file is available at
% http://www.ozemail.com.au/%7Egeoffk/pdfencrypt/

% Modified by Alex Cherepanov to work with GS 6.60 and higher.
% New versions of GS require explicit checks for /true , /false, and /null
% in .decpdfrun . This fix is backward-compatible.

% Modified by Raph Levien and Ralph Giles to use the new C
% implementations of md5 and arcfour in ghostscript 7.01, and to
% be compatible with PDF 1.4 128-bit encryption.

/.setlanguagelevel where { pop 2 .setlanguagelevel } if
.currentglobal true .setglobal
/pdfdict where { pop } { /pdfdict 100 dict def } ifelse
pdfdict begin

% Older ghostscript versions do not have .pdftoken, so we use 'token' instead.
/.pdftoken where { pop } { /.pdftoken /token load def } ifelse

% take a stream and arc4 decrypt it.
% <stream> <key> arc4decodefilter <stream>
/arc4decodefilter {
  1 dict begin
  /Key exch def
  currentdict end /ArcfourDecode filter
} bind def

% <ciphertext> <key> arc4decode <plaintext>
/arc4decode {
  %(key: ) print dup == (ct: ) print 1 index ==
  1 index length 0 eq {
    pop
  } {
    1 index length string 3 1 roll arc4decodefilter exch readstring pop
  } ifelse
} bind def

/md5 {
  16 string dup /MD5Encode filter dup 4 3 roll writestring closefile
} bind def

/md5_trunk {
  md5 0 pdf_key_length getinterval
} bind def


/pdf_padding_string
   <28bf4e5e4e758a41 64004e56fffa0108
    2e2e00b6d0683e80 2f0ca9fe6453697a>
def

% Pad a key out to 32 bytes.
/pdf_pad_key {		% <key> pdf_pad_key <padded key>
  dup length 32 gt { 0 32 getinterval } if
  pdf_padding_string
  0 32 3 index length sub getinterval
  concatstrings
} bind def

/pdf_xorbytes {      % <iter-num> <key> pdf_xorbytes <xored-key>
  dup length dup string
  exch 1 sub 0 1 3 2 roll {
    % <iter-num> <key> <new-key> <byte-num>
    dup 3 index exch get 4 index xor
    % <iter-num> <key> <new-key> <byte-num> <byte>
    3 copy put pop pop
  } for
  3 1 roll pop pop
} bind def

% Get length of encryption key in bytes
/pdf_key_length {    % pdf_key_length <key_length>
  Trailer /Encrypt oget /Length knownoget { -3 bitshift } { 5 } ifelse
} bind def

% Algorithm 3.2
/pdf_compute_encryption_key {  % <password> pdf_compute_encryption_key <key>
  % Step 1.
  pdf_pad_key

  % Step 2, 3.
  Trailer /Encrypt oget dup /O oget
  % <padded-key> <encrypt> <O>

  % Step 4.
  exch /P oget 4 string exch
  2 copy 255 and 0 exch put
  2 copy -8 bitshift 255 and 1 exch put
  2 copy -16 bitshift 255 and 2 exch put
  2 copy -24 bitshift 255 and 3 exch put pop
  % <padded-key> <O> <P>

  % Step 5.
  Trailer /ID knownoget { 0 oget } {
    ()
    (   **** ID key in the trailer is required for encrypted files.\n) pdfformaterror
  } ifelse
  3 { concatstrings } repeat 
  % We will finish step 5 after possibly including step 6.

  % The following only executed for /R equal to 3 or more
  Trailer /Encrypt oget dup /R oget dup 3 ge {

     % Step 6.  If EncryptMetadata is false, pass 0xFFFFFFFF to md5 function
     % The PDF 1.5 Spec says that EncryptMetadata is an undocumented
     % feature of PDF 1.4.  That implies that this piece of logic should
     % be executed if R >= 3.  However testing with Acrobat 5.0 and 6.0 shows
     % that this step is not executed if R equal to 3.  Thus we have a test for
     % R being >= 4.
     4 ge {
       /EncryptMetadata knownoget	% Get EncryptMetadata (if present)
       not { true } if			% Default is true
       not {				% If EncryptMetadata is false
         <ff ff ff ff> concatstrings	% Add 0xFFFFFFFF to working string
       } if
     } {
       pop				% Remove Encrypt dict
     } ifelse
     md5_trunk				% Finish step 5 and 6.

     % Step 7.  Executed as part of step 6
     % Step 8.  (This step is defintely a part of PDF 1.4.)
     50 { md5_trunk } repeat
  } {
     pop pop md5_trunk			% Remove R, Encrypt dict, finish step 5
  } ifelse

  % Step 9 - Done in md5_trunk.
} bind def

% Algorithm 3.4
/pdf_gen_user_password_R2 { % <filekey> pdf_gen_user_password_R2 <U>

  % Step 2.
  pdf_padding_string exch arc4decode
} bind def

% Algorithm 3.5
/pdf_gen_user_password_R3 { % <filekey> pdf_gen_user_password_R3 <U>

  % Step 2.
  pdf_padding_string

  % Step 3.
  Trailer /ID knownoget { 0 oget } {
    ()
    (   **** ID key in the trailer is required for encrypted files.\n) pdfformaterror
  } ifelse
  concatstrings md5

  % Step 4.
  1 index arc4decode

  % Step 5.
  1 1 19 {
    2 index pdf_xorbytes arc4decode
  } for
  exch pop

} bind def

/pdf_gen_user_password { % <password> pdf_gen_user_password <filekey> <U>
  % common Step 1 of Algorithms 3.4 and 3.5.
  pdf_compute_encryption_key dup

  Trailer /Encrypt oget

  /R oget dup 2 eq {
    pop pdf_gen_user_password_R2
  } {
    dup 3 eq {
      pop pdf_gen_user_password_R3
    } {
      dup 4 eq {	% 4 uses the algorithm as 3
        pop pdf_gen_user_password_R3
      } {
        (   **** This file uses an unknown standard security handler revision: )
        exch =string cvs concatstrings pdfformaterror printProducer
        /pdf_check_user_password cvx /undefined signalerror
      } ifelse
    } ifelse
  } ifelse
} bind def

% Algorithm 3.6
/pdf_check_user_password { % <password> pdf_check_user_password <filekey> true
                           % <password> pdf_check_user_password false
  pdf_gen_user_password

  Trailer /Encrypt oget /U oget

  0 2 index length getinterval eq {
    true
  } {
    pop false
  } ifelse
} bind def

% Compute an owner key, ie the result of step 4 of Algorithm 3.3
/pdf_owner_key % <password> pdf_owner_key <owner-key>
{
  % Step 1.
  pdf_pad_key

  % Step 2.
  md5_trunk

  % 3.3 Step 3.  Only executed for /R equal to 3 or more
  Trailer /Encrypt oget /R oget 3 ge {
    50 { md5_trunk } repeat
  } if

  % Step 4 - Done in md5_trunk.
} bind def

% Algorithm 3.7
/pdf_check_owner_password { % <password> pdf_check_owner_password <filekey> true
                            % <password> pdf_check_owner_password false
  % Step 1.
  pdf_owner_key

  % Step 2.
  Trailer /Encrypt oget dup /O oget 2 index arc4decode
  % <encryption-key> <encrypt-dict> <decrypted-O>

  % Step 3.  Only executed for /R equal to 3 or more
  exch /R oget 3 ge {
    1 1 19 {
      2 index pdf_xorbytes arc4decode
    } for
  } if
  exch pop
  % <result-of-step-3>

  pdf_check_user_password
} bind def

% Process the encryption information in the Trailer.
/pdf_process_Encrypt {
  Trailer /Encrypt oget
  /Filter oget /Standard eq not {
    (   **** This file uses an unknown security handler.\n) pdfformaterror
    printProducer
    /pdf_process_Encrypt cvx /undefined signalerror
  } if
  () pdf_check_user_password
  {
    /FileKey exch def
  } {
    /PDFPassword where {
       pop PDFPassword pdf_check_user_password
       {
         /FileKey exch def
       } {
         PDFPassword pdf_check_owner_password
         {
           /FileKey exch def
         } {
           (   **** Password did not work.\n) pdfformaterror
	   printProducer
	   /pdf_process_Encrypt cvx /invalidfileaccess signalerror
         } ifelse
       } ifelse
    } {
      (   **** This file requires a password for access.\n) pdfformaterror
      printProducer
      /pdf_process_Encrypt cvx /invalidfileaccess signalerror
    } ifelse
  } ifelse

%   Trailer /Encrypt oget /P oget 4 and 0 eq #? and
%    { (   ****This owner of this file has requested you do not print it.\n)
%      pdfformaterror printProducer
%      /pdf_process_Encrypt cvx /invalidfileaccess signalerror
%    }
%   if
} bind def

% Calculate the key used to decrypt an object (to pass to .decpdfrun or
% put into a stream dictionary).
/computeobjkey	% <object#> <generation#> computeobjkey <keystring>
{
  exch
  FileKey length 5 add string
  dup 0 FileKey putinterval
  exch
		% stack:  gen# string obj#
    2 copy 255 and FileKey length exch put
    2 copy -8 bitshift 255 and FileKey length 1 add exch put
    2 copy -16 bitshift 255 and FileKey length 2 add exch put
  pop exch
    2 copy 255 and FileKey length 3 add exch put
    2 copy -8 bitshift 255 and FileKey length 4 add exch put
  pop md5 0 FileKey length 5 add 2 index length .min getinterval
} bind def

% As .pdfrun, but decrypt strings with key <key>.
/.decpdfrun			% <file> <keystring> <opdict> .decpdfrun -
 {	% Construct a procedure with the file, opdict and key bound into it.
   2 index cvlit mark mark 5 2 roll
    { .pdftoken not { (%%EOF) cvn cvx } if
      dup xcheck
       { PDFDEBUG { dup == flush } if
	 3 -1 roll pop
	 2 copy .knownget
	  { exch pop exch pop exec
          }
	  { exch pop
            dup /true eq
              { pop //true
              }
              { dup /false eq
                  { pop //false 
                  }
                  { dup /null eq
                      { pop //null
                      }
                      { (   **** Unknown operator: ) 
	                exch =string cvs concatstrings (\n) concatstrings
			pdfformaterror
                      }
                    ifelse
                  }
                ifelse
              }
            ifelse
	  }
	 ifelse
       }
       { exch pop PDFDEBUG { dup ==only ( ) print flush } if
	 dup type /stringtype eq
          {
	% Check if we have encrypted strings  R=4 allows for
	% selection of encryption on streams and strings
            Trailer /Encrypt oget	% Get encryption dictionary
            dup /R oget 4 lt		% only 4 has selectable
             {				% R < 4 --> encrypted strings
	       pop 1 index arc4decode	% Decrypt string
	       PDFDEBUG { (%Decrypted: ) print dup == flush } if
             } {			% Else R = 4
	       /StrF knownoget		% Get StrF (if present)
	        {			% If StrF is present ...
		  /Identity eq not	% Check if StrF != Identity
	  	   { 1 index arc4decode	% Decrypt string
		     PDFDEBUG { (%Decrypted: ) print dup == flush } if
		   }
		  if			% If StrF != identity
		}
	       if			% If StrF is known
      	     }
	    ifelse			% Ifelse R < 4
	  }
	 if				% If  = stringtype
	 exch pop
       }
      ifelse
    }
   aload pop .packtomark cvx
   /loop cvx 2 packedarray cvx
    { stopped /PDFsource } aload pop
   PDFsource
    { store { stop } if } aload pop .packtomark cvx 
   /PDFsource 3 -1 roll store exec
 } bind def

% Run the code to resolve an object reference.
/pdf_run_resolve
{ /FileKey where			% Check if the file is encrypted
  { pop					% File is encrypted
    2 copy computeobjkey dup 4 1 roll
    PDFfile exch resolveopdict .decpdfrun
    dup dup dup 5 2 roll
	% stack: object object key object object
    {	% Use loop to provide an exitable context.
      xcheck exch type /dicttype eq and % Check if executable dictionary
      not {				% If object is not ...
        pop pop				% ignore object
        exit				% Exit 'loop' context
      } if				% If not possible stream
	% Starting with PDF 1.4 (R = 3), there are some extra features
	% which control encryption of streams.  The EncryptMetadata entry
	% in the Encrypt dict controls the encryption of metadata streams.
      Trailer /Encrypt oget		% Get encryption dictionary
      dup /R oget dup 3 lt		% Only PDF 1.4 and higher has options
      {					% R < 3 --> all streams encrypted
        pop pop /StreamKey exch put	% Insert StreamKey in dictionary
	exit				% Exit 'loop' context
      } if
	% Check EncryptMeta.  stack:  object object key Encrypt R
      exch dup /EncryptMetadata knownoget % Get EncryptMetadata (if present)
      not { true } if			% If not present default = true
      not				% Check if EncryptMetadata = false
      { 				% if false we need to check the stream type
	3 index /Type knownoget		% Get stream type (if present)
	not { //null } if		% If type not present use fake name
	/Metadata eq			% Check if the type is Metadata
        { pop pop pop pop		% Type == Metadata --> no encryption
	  exit				% Exit 'loop' context
        } if
      } if
    	% PDF 1.5 encryption (R == 4) has selectable encryption handlers.  If
	% this is not PDF 1.5 encryption (R < 4) then we are done checking and
	% we need to decrypt the stream.  stack:  object object key R Encrypt
      exch 4 lt				% Check for less than PDF 1.5
      { pop /StreamKey exch put		% Insert StreamKey in dictionary
	exit				% Exit 'loop' context
      } if
	% Check if the stream encryption handler (StmF) == Identity.
      /StmF knownoget			% Get StmF (if present)
      not { /Identity } if		% If StmF not present default = Identity
      /Identity eq 			% Check if StmF == Identity
      { pop pop				% Identity --> no encryption
	exit				% Exit 'loop' context
      } if
      	% If we get here then we need to decrypt the stream.
      /StreamKey exch put		% Insert StreamKey into dictionary
      exit				% Exit 'loop' context, never loop
    } loop				% End of loop exitable context
  } {					% Else file is not encrypted
    PDFfile resolveopdict .pdfrun
  } ifelse				% Ifelse encrypted
} bind def

% Prefix a decryption filter to a stream if needed.
% Stack: readdata? dict parms file/string filternames
% (both before and after).
/pdf_decrypt_stream
 { 3 index /StreamKey known	% Check if the file is encrypted
   {
      exch 
	% Stack: readdata? dict parms filternames file/string
      3 index /Length oget
      dup 0 eq {
	% Handle Length=0 case specially to avoid SubFileDecode semantics
        pop pop ()
      } {
        () /SubFileDecode filter
      } ifelse
      3 index /StreamKey get arc4decodefilter
      exch
   } if
 } bind def

end			% pdfdict
.setglobal