MINI SHELL

%   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 1.11.2.2 2004/01/29 12:08:47 igor 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 pdf_key_length 0 exch 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 md5_trunk

  % Step 6.
  Trailer /Encrypt oget /R oget 3 eq {
     50 { md5_trunk } repeat
  } if

  % Step 7 - 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
    } {
      (   **** This file uses an unknown standard security handler revision: )
      exch =string cvs concatstrings pdfformaterror printProducer
      /pdf_check_user_password cvx /undefined signalerror
    } 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.
  Trailer /Encrypt oget /R oget 3 eq {
    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.
  exch /R oget 3 eq {
    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
	  { 1 index arc4decode
	    PDFDEBUG { (%Decrypted: ) print dup == flush } if
	  }
	 if
	 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
    { pop
      2 copy computeobjkey dup 4 1 roll
      PDFfile exch resolveopdict .decpdfrun
      dup dup dup 5 2 roll
	% stack: object object key object object
      xcheck exch type /dicttype eq and
       { /StreamKey exch put }
       { pop pop }
      ifelse
    }
    { PDFfile resolveopdict .pdfrun }
   ifelse
 } 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
   {
      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