path: root/kghostview/data/pdf_sec.ps

%    Copyright (C) 1996-1998 Geoffrey Keating. 
% 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.

% pdf_sec.ps (version 1.0.4)
% 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 version 4.02
% or later.

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

/.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

% An implementation of an algorithm compatible with the RSA Data Security 
% Inc. RC4 stream encryption algorithm.

% <string> rc4setkey <dict>
/rc4setkey
{
  6 dict begin
    /k exch def
    /a 256 string def
    0 1 255 { a exch dup put } for
    /l k length def
    /j 0 def
    0 1 255
    {
      /i exch def
      /j a i get k i l mod get add j add 255 and def
      a i a j get a j a i get put put
    } for
    3 dict dup begin
      /a a def
      /x 0 def
      /y 0 def
    end
  end
} bind def

% <rc4key> <string> rc4 <string> <rc4key>
/rc4
{
  1 index begin
    dup dup length 1 sub 0 exch 1 exch
    {
      /x x 1 add 255 and def
      /y a x get y add 255 and def
      a x a y get a y a x get put put
% stack: string string index
      2 copy get
      a dup x get a y get add 255 and get
      xor put dup
    } for
    pop
  end
} bind def

% take a stream and rc4 decrypt it.
% <stream> <key> rc4decodefilter <stream>
/rc4decodefilter {
  currentglobal exch true setglobal
  dup length string copy rc4setkey
  exch setglobal
  exch 512 string
   % stack: <key> <stream> <string>
  { readstring pop rc4 exch pop } aload pop
   8 array astore cvx 0 () /SubFileDecode filter 
} bind def

% MD5 derived from RFC 1321, "The MD5 Message-Digest Algorithm",
% R. Rivest, MIT, RSADSI; implemented in PostScript by Geoffrey Keating.

% We construct the MD5 transform by a sort of inline expansion.
% this takes up quite a bit of memory (around 17k), but gives a
% factor-of-two speed increase.
% This also allows us to take advantage of interpreters with 64-bit
% wide integers.
% This will not run on interpreters with 16-bit wide integers, if such
% things exist.
20 dict begin

/T [
16#d76aa478 16#e8c7b756 16#242070db 16#c1bdceee
16#f57c0faf 16#4787c62a 16#a8304613 16#fd469501
16#698098d8 16#8b44f7af 16#ffff5bb1 16#895cd7be
16#6b901122 16#fd987193 16#a679438e 16#49b40821
16#f61e2562 16#c040b340 16#265e5a51 16#e9b6c7aa
16#d62f105d 16#02441453 16#d8a1e681 16#e7d3fbc8
16#21e1cde6 16#c33707d6 16#f4d50d87 16#455a14ed
16#a9e3e905 16#fcefa3f8 16#676f02d9 16#8d2a4c8a
16#fffa3942 16#8771f681 16#6d9d6122 16#fde5380c
16#a4beea44 16#4bdecfa9 16#f6bb4b60 16#bebfbc70
16#289b7ec6 16#eaa127fa 16#d4ef3085 16#04881d05
16#d9d4d039 16#e6db99e5 16#1fa27cf8 16#c4ac5665
16#f4292244 16#432aff97 16#ab9423a7 16#fc93a039
16#655b59c3 16#8f0ccc92 16#ffeff47d 16#85845dd1
16#6fa87e4f 16#fe2ce6e0 16#a3014314 16#4e0811a1
16#f7537e82 16#bd3af235 16#2ad7d2bb 16#eb86d391
] def
/F [
{ c d /xor b /and d /xor } { b c /xor d /and c /xor }
{ b c /xor d /xor } { d /not b /or c /xor }
] def
/R [
16#0007 16#010c 16#0211 16#0316 16#0407 16#050c 16#0611 16#0716
16#0807 16#090c 16#0a11 16#0b16 16#0c07 16#0d0c 16#0e11 16#0f16
16#0105 16#0609 16#0b0e 16#0014 16#0505 16#0a09 16#0f0e 16#0414
16#0905 16#0e09 16#030e 16#0814 16#0d05 16#0209 16#070e 16#0c14
16#0504 16#080b 16#0b10 16#0e17 16#0104 16#040b 16#0710 16#0a17
16#0d04 16#000b 16#0310 16#0617 16#0904 16#0c0b 16#0f10 16#0217
16#0006 16#070a 16#0e0f 16#0515 16#0c06 16#030a 16#0a0f 16#0115
16#0806 16#0f0a 16#060f 16#0d15 16#0406 16#0b0a 16#020f 16#0915
] def

/W 1 31 bitshift 0 gt def
/A W { /add } { /md5add } ifelse def
/t W { 1744 } { 1616 } ifelse array def
/C 0 def

0 1 63 {
  /i exch def
  /r R i get def
  /a/b/c/d 4 i 3 and roll [ /d/c/b/a ] { exch def } forall

  t C [
    a F i -4 bitshift get exec 
    a A /x r -8 bitshift /get A T i get A
    W { 1 32 bitshift 1 sub /and } if
    /dup r 31 and /bitshift /exch r 31 and 32 sub /bitshift /or
    b A
    /def
  ] dup length C add /C exch def putinterval
} for

1 1 C 1 sub {
  dup 1 sub t exch get /def cvx eq
    {pop}
    {t exch 2 copy get cvx put}
  ifelse
} for

% If we could put t into a _packed_ array, its memory requirements
% would go from about 13k to about 4k. Unfortunately, we'd need around
% 1600 stack positions, around 3 times what we can expect to have 
% available---and if that kind of memory is available, we don't really
% need to pack t. Sigh.

% In fact, it's worse than that. You can't even determine what t will 
% be and write it in directly (something like
% { /a c d xor b and d xor a md5add x 0 get md5add -680876936 md5add dup 7 
%   bitshift exch -25 bitshift or b md5add def /d b c xor a ...
% ) because the scanner uses the operand stack to accumulate procedures.
% So the only way to have md5transform as a single procedure is the above 
% trick.

W /md5transform t end cvx bind def

% Unfortunately, PostScript & its imitators convert large
% integers to floating-point. Worse, the fp representation probably
% won't have 32 significant bits.
% This procedure accounts for about 35% of the total time on 32-bit 
% machines.
not {
  /md5add {
    2 copy xor 0 lt
      % if one is positive and one is negative, can't overflow
      { add }
      % if both are positive or negative
      { 16#80000000 xor add 16#80000000 xor }
      % same as subtracting (or adding) 2^31 and then subtracting (or 
      % adding) it back.
    ifelse
  } bind def
} {
  /md5add {
    add 16#0FFFFFFFF and
  } bind def
} ifelse

/md5 {
  20 dict begin

  % initialise a,b,c,d,x
  /a 16#67452301 def
  /b 16#efcdab89 def
  /c 16#98badcfe def
  /d 16#10325476 def
  /x 16 array def

  % parameters
  /origs exch def
  /oslen origs length def

  % pad string to multiple of 512 bits
  /s oslen 72 add 64 idiv 64 mul dup /slen exch def string def
  s 0 origs putinterval
  s oslen 16#80 put
  s slen 8 sub oslen 31 and 3 bitshift put
  s slen 7 sub oslen -5 bitshift 255 and put
  s slen 6 sub oslen -13 bitshift 255 and put

  0 64 slen 64 sub {
    dup 1 exch 63 add { s exch get } for
    15 -1 0 { x exch 6 2 roll 3 { 8 bitshift or } repeat put } for
    a b c d
    md5transform
    d md5add /d exch def
    c md5add /c exch def
    b md5add /b exch def
    a md5add /a exch def
  } for
  
  16 string
  [ [ a b c d ] { 3 { dup -8 bitshift } repeat } forall ]
  0 1 15 {
    3 copy dup 3 1 roll get 255 and put pop
  } for
  pop

  end
} bind 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
   <28bf4e5e4e758a41 64004e56fffa0108
    2e2e00b6d0683e80 2f0ca9fe6453697a>
   0 32 3 index length sub getinterval
   concatstrings
 } bind def

% Try a user key for a PDF file.
/pdf_try_key		% <key> pdf_try_key <filekey> true
			% <key> pdf_try_key false
 { Trailer /Encrypt oget
   dup /O oget 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
   Trailer /ID oget 0 oget
   3 { concatstrings } repeat
   md5 0 5 getinterval
   dup
   Trailer /Encrypt oget /U oget dup length string copy exch
   rc4setkey exch rc4 exch pop
   <28bf4e5e4e758a41 64004e56fffa0108
    2e2e00b6d0683e80 2f0ca9fe6453697a> eq
   dup not { exch pop } if
 } 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) print flush
	/pdf_process_Encrypt cvx /undefined signalerror
    }
   if
   () pdf_pad_key pdf_try_key
    { /FileKey exch def } 
    { /PDFPassword where
       { pop PDFPassword pdf_pad_key pdf_try_key 
	  { true }
	  { PDFPassword pdf_pad_key md5 0 5 getinterval rc4setkey
	    Trailer /Encrypt oget /O oget dup length string copy
	       rc4 exch pop
	    pdf_try_key
	  }
	 ifelse
	  { /FileKey exch def }
	  { (****Password did not work.\n) print flush
	    /pdf_process_Encrypt cvx /invalidfileaccess signalerror
	  }
	 ifelse 
       }
       { (****This file has a user password set.\n) print flush
	 /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)
	print flush
      /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
  10 string
  dup 0 FileKey putinterval
  exch
		% stack:  gen# string obj#
    2 copy 255 and 5 exch put
    2 copy -8 bitshift 255 and 6 exch put
    2 copy -16 bitshift 255 and 7 exch put
  pop exch
    2 copy 255 and 8 exch put
    2 copy -8 bitshift 255 and 9 exch put
  pop md5 0 10 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
       { DEBUG { dup == flush } if
	 3 -1 roll pop
	 2 copy .knownget
	  { exch pop exch pop exec }
	  { (%stderr) (w) file
	    dup (****************Unknown operator: ) writestring
	    dup 3 -1 roll .writecvs dup (\n) writestring flushfile
	    pop
	  }
	 ifelse
       }
       { exch pop DEBUG { dup ==only ( ) print flush } if
	 dup type /stringtype eq
	  { exch rc4setkey exch rc4 }
	 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 () /SubFileDecode filter
      3 index /StreamKey get rc4decodefilter
      exch
   } if
 } bind def

end			% pdfdict
.setglobal