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2003-01-03
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% 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.
% $RCSfile$ $Revision$
% 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
/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 oget 0 oget
3 { concatstrings } repeat md5
% Step 6.
Trailer /Encrypt oget /R oget 3 eq {
50 { md5 } repeat
} if
% Step 7.
0 pdf_key_length getinterval
} 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 oget 0 oget
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: )
print == flush
/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
% 3.3 Step 3.
Trailer /Encrypt oget /R oget 3 eq {
50 { md5 } repeat
} if
% Step 4.
0 pdf_key_length getinterval
} 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) print flush
/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) print flush
/pdf_process_Encrypt cvx /invalidfileaccess signalerror
} ifelse
} ifelse
} {
(****This file requires a password for access.\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
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
{ DEBUG { 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
}
{ (%stderr) (w) file
dup (****************Unknown operator: ) writestring
dup 3 -1 roll .writecvs dup (\n) writestring flushfile
}
ifelse
}
ifelse
}
ifelse
}
ifelse
}
{ exch pop DEBUG { dup ==only ( ) print flush } if
dup type /stringtype eq
{ 1 index arc4decode
DEBUG { (%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