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Editing: pdf_sec.ps
% Copyright (C) 2001-2020 Artifex Software, Inc. % All Rights Reserved. % % This software is provided AS-IS with no warranty, either express or % implied. % % This software is distributed under license and may not be copied, % modified or distributed except as expressly authorized under the terms % of the license contained in the file LICENSE in this distribution. % % Refer to licensing information at http://www.artifex.com or contact % Artifex Software, Inc., 1305 Grant Avenue - Suite 200, Novato, % CA 94945, U.S.A., +1(415)492-9861, for further information. % % Copyright (C) 1996-1998 Geoffrey Keating. % Copyright (C) 2001-2008 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. % 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 was originally distributed % separately by Geoffrey Keating as an add-on to version 6 and earlier. % 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. % Modified by Ralph Giles for PDF 1.6 AES encryption. % Modified by Michael Constant for PDF 1.7 ExtensionLevel 3 % AES-256 encryption. /.setlanguagelevel where { pop 2 .setlanguagelevel } if .currentglobal //true .setglobal 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 executeonly def % <ciphertext> <key> arc4decode <plaintext> /arc4decode { 1 index length 0 eq { pop } { 1 index length string 3 1 roll arc4decodefilter exch readstring pop } ifelse } bind executeonly def % take a stream and aes decrypt it. % <stream> <key> aesdecodefilter <stream> /aesdecodefilter { 1 dict begin /Key exch def currentdict end /AESDecode filter } bind executeonly def % AES decrypt a string, returning a string. The second argument can % be a dictionary of the form << /Key key /Padding false >>, which % specifies the key and any options for the AESDecode filter, or it % can just be a string (the key). % % <ciphertext> <dict> aesdecode <plaintext> % <ciphertext> <key> aesdecode <plaintext> /aesdecode { 1 index length 0 eq { pop } { 1 index length string 3 1 roll % If our second argument is a dictionary, it's the full set % of decoding options (including the key); pass it directly % to the AESDecode filter. Otherwise, it's just the key, so % call aesdecodefilter to construct the dictionary. dup type /dicttype eq { /AESDecode filter } { aesdecodefilter } ifelse exch readstring pop } ifelse } bind executeonly def /md5 { 16 string dup /MD5Encode filter dup 4 3 roll writestring closefile } bind executeonly def /md5_trunk { md5 0 pdf_key_length getinterval } bind executeonly def /sha256 { 32 string dup /SHA256Encode filter dup 4 3 roll writestring closefile } bind executeonly def % <string> contains_non_ascii <bool> /contains_non_ascii { //false exch { 128 ge { pop //true exit } if } forall } bind executeonly 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 executeonly 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 executeonly def % Get length of encryption key in bytes /pdf_key_length { % pdf_key_length <key_length> Trailer /Encrypt oget dup /V knownoget not { 0 } if 1 eq { pop 5 } % If V == 1 then always use 40 bits { /Length knownoget { -3 bitshift } { 5 } ifelse } ifelse } bind executeonly 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 } { () ( **** Error: ID key in the trailer is required for encrypted files.\n) pdfformaterror ( File may not be possible to decrypt.\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 executeonly def % Algorithm 3.4 /pdf_gen_user_password_R2 { % <filekey> pdf_gen_user_password_R2 <U> % Step 2. pdf_padding_string exch arc4decode } bind executeonly 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 } { () ( **** Error: ID key in the trailer is required for encrypted files.\n) pdfformaterror ( File may not be possible to decrypt.\n) pdfformaterror } ifelse concatstrings md5 % Step 4. 1 index arc4decode % Step 5. 1 1 19 { 2 index pdf_xorbytes arc4decode } for exch pop } bind executeonly 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 procedure is only used if R is between 2 and 4, % so we should never get here. /pdf_gen_user_password cvx /undefined signalerror } ifelse } ifelse } ifelse } bind executeonly def % Algorithm 3.6 % <password> pdf_check_pre_r5_user_password <filekey> true % <password> pdf_check_pre_r5_user_password false /pdf_check_pre_r5_user_password { pdf_gen_user_password Trailer /Encrypt oget /U oget 0 2 index length getinterval eq { //true } { pop //false } ifelse } bind executeonly 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 executeonly def % Algorithm 3.7 % <password> pdf_check_pre_r5_owner_password <filekey> true % <password> pdf_check_pre_r5_owner_password false /pdf_check_pre_r5_owner_password { % 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_pre_r5_user_password } bind executeonly def % Algorithm 3.2a % <password> pdf_check_r5_password <filekey> true % <password> pdf_check_r5_password false /pdf_check_r5_password { 10 dict begin % temporary dict for local variables % Step 1. % If the .saslprep operator isn't available (because ghostscript % wasn't built with libidn support), just skip this step. ASCII % passwords will still work fine, and even most non-ASCII passwords % will be okay; any non-ASCII passwords that fail will produce a % warning from pdf_process_Encrypt. /.saslprep where { pop .saslprep } if % Step 2. dup length 127 gt { 0 127 getinterval } if /Password exch def % Step 3. /O Trailer /Encrypt oget /O oget def /U Trailer /Encrypt oget /U oget def Password O 32 8 getinterval concatstrings U 0 48 getinterval concatstrings sha256 O 0 32 getinterval eq { % Step 3, second paragraph. Password O 40 8 getinterval concatstrings U 0 48 getinterval concatstrings sha256 16 string Trailer /Encrypt oget /OE oget concatstrings << /Key 4 -1 roll /Padding //false >> aesdecode //true } { % Step 4. Password U 32 8 getinterval concatstrings sha256 U 0 32 getinterval eq { % Step 4, second paragraph. Password U 40 8 getinterval concatstrings sha256 16 string Trailer /Encrypt oget /UE oget concatstrings << /Key 4 -1 roll /Padding //false >> aesdecode //true } { //false } ifelse } ifelse % Step 5. dup { % Adobe says to decrypt the Perms string using "ECB mode with % an initialization vector of zero", which must be a mistake -- % ECB mode doesn't use initialization vectors. It looks like % they meant "ECB mode, or CBC mode with an initialization % vector of zero", since the two are equivalent for a single- % block message. We use the latter. 16 string Trailer /Encrypt oget /Perms oget concatstrings << /Key 4 index /Padding //false >> aesdecode 9 3 getinterval (adb) eq not { ( **** Error: Failed to decrypt Perms string.\n) pdfformaterror ( Cannot decrypt PDF file.\n) pdfformaterror printProducer /pdf_check_r5_password cvx /rangecheck signalerror } if } if end } bind executeonly def % <password> pdf_check_password <filekey> true % <password> pdf_check_password false /pdf_check_password { % If R is 2, 3, or 4, use Algorithms 3.6 and 3.7 to see if this is % a valid user or owner password. Following historical practice, % we treat the password as an arbitrary string of bytes and don't % interpret it in any way. (If the password fails, it would be % nice to try some plausible character set conversions, but this % gets complicated. Even Adobe products don't seem to handle it % consistently.) % % If R is 5, use Algorithm 3.2a. The password should be text, in % either UTF-8 or the current locale's charset. Trailer /Encrypt oget /R oget dup dup 2 ge exch 4 le and { pop dup pdf_check_pre_r5_user_password { exch pop //true } { pdf_check_pre_r5_owner_password } ifelse } { dup 5 eq { pop % First, try the password as UTF-8. dup pdf_check_r5_password { exch pop //true } { % The password didn't work as UTF-8, so maybe it's in the % locale character set instead. If possible, convert it to % UTF-8 and try again. /.locale_to_utf8 where { pop .locale_to_utf8 pdf_check_r5_password } { pop //false } ifelse } ifelse } { dup 6 eq { pop % First, try the password as UTF-8. dup Trailer /Encrypt oget //check_r6_password exec { exch pop //true } { % The password didn't work as UTF-8, so maybe it's in the % locale character set instead. If possible, convert it to % UTF-8 and try again. /.locale_to_utf8 where { pop .locale_to_utf8 Trailer /Encrypt oget //check_r6_password exec } { pop //false } ifelse } ifelse } { ( **** Warning: This file uses an unknown standard security handler revision: ) exch =string cvs concatstrings (\n) concatstrings pdfformatwarning ( Cannot decrypt PDF file.\n) pdfformaterror printProducer /pdf_check_password cvx /undefined signalerror } ifelse } ifelse } ifelse } bind executeonly def systemdict /check_r6_password .forceundef % Process the encryption information in the Trailer. /pdf_process_Encrypt { Trailer /Encrypt oget /Filter oget /Standard eq not { ( **** Warning: This file uses an unknown security handler.\n) pdfformatwarning ( Cannot decrypt PDF file.\n) pdfformaterror printProducer /pdf_process_Encrypt cvx /undefined signalerror } if % Bug 702598: We can have a trailer dictionary with an /Encrypt entry, and if the % Encrypt dictionary is V 4 or greater we can (should ?) have StrF and stmF entries. % % The code below checks for the existence of StmF and StrF entries. Its possible % that both may be /Identity (which means no encryption) in which case we don't need to check % the password, as we won't need to decrypt any streams or strings. Note that the dict may still % have a non-Identity /EFF (embedded files) key, but Ghostscript doesn't process embedded % files so we don't have to worry about that. Trailer /Encrypt oget dup /V get 4 ge { % NB: Entries in the Encrypt dictionary cannot be indirect references dup /StmF .knownget { /Identity eq not } { false % default StmF is Identity }ifelse 1 index /StrF .knownget { /Identity eq not } { false % default StrF is Identity }ifelse or % ...still in the V4 or above checking... % Even if StmF and StrF are Identity, if the StdCF is missing AuthEvent % or it is DocOpen, we require the password. Check for that. 1 index /CF .knownget { /StdCF .knownget { /AuthEvent .knownget { /DocOpen eq or } { pop true % no AuthEvent, default is DocOpen, require password } ifelse } { pop true % no StdCF, require password } ifelse } { pop true % no CF, require password } ifelse exch pop % discard Encrypt dict }{ % Not V4 or later pop true % discard Encrypt dict, require password } ifelse % If we were given a PDFPassword, check it anyway, even if the % code above said we didn't need one. This will allow us to process % PDF files with an initial CryptFilter which has StrF=StmF=Identity, % but contains streams which themselves have non-Identity StmF or StrF. /PDFPassword where { pop true } { false } ifelse or { () pdf_check_password { /FileKey exch def } { /PDFPassword where { pop PDFPassword pdf_check_password { /FileKey exch def } { ( **** Error: Password did not work.\n) pdfformaterror ( Cannot decrypt PDF file.\n) pdfformaterror % If ghostscript was built without libidn, it's missing the % .saslprep operator and thus can't do proper Unicode password % normalization. Similarly, if the system provides neither % iconv nor the Windows MultiByteToWideChar function, then we % won't have the .locale_to_utf8 operator to convert passwords % from the locale character set to UTF-8. % % It's not a huge problem if you're missing either or both of % these. ASCII passwords will work fine regardless, and even % Unicode passwords will often be okay. % % However, if .saslprep or .locale_to_utf8 is missing, and the % user enters a non-ASCII password that doesn't work, we give % a warning message. PDFPassword contains_non_ascii { /.saslprep where not { ( **** WARNING: Ghostscript was configured without libidn,\n) ( **** so non-ASCII passwords aren't supported!\n) concatstrings pdfformaterror } { pop /.locale_to_utf8 where not { ( **** WARNING: Ghostscript was configured without iconv,\n) ( **** so non-ASCII passwords aren't supported!\n) concatstrings pdfformaterror } { pop } ifelse } ifelse } if /pdf_process_Encrypt cvx /invalidfileaccess signalerror } ifelse } { ( **** This file requires a password for access.\n) pdfformaterror /pdf_process_Encrypt cvx /invalidfileaccess signalerror } ifelse } ifelse } { ( **** This file has an Encryption dictionary, but both the StmF and StrF entries\n) pdfformatwarning ( **** are /Identity, and AuthEvent allows the document to be opened. It is possible\n) pdfformatwarning ( **** that embedded streams may still use encryption, if the file fails to process\n) pdfformatwarning ( **** you may need to supply a User or Owner password by setting -sPDFPassword=\n) pdfformatwarning } ifelse } bind executeonly def % Calculate the key used to decrypt an object (to pass to .decpdfrun or % put into a stream dictionary). /computeobjkey % <object#> <generation#> computeobjkey <keystring> { Trailer /Encrypt oget /V oget 5 eq { % Encrypt version 5 doesn't use object keys; everything is % encrypted with the file key. pop pop FileKey } { 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 % this step is for the AES cipher only Trailer /Encrypt oget dup /StmF knownoget { %% Treat StmF of 'Identity' the same as if it is missing. dup /Identity eq { pop pop } { exch /CF knownoget { exch oget /CFM oget /AESV2 eq { (sAlT) concatstrings } if } { pop } ifelse } ifelse } { pop } ifelse md5 0 FileKey length 5 add 2 index length .min getinterval } ifelse } bind executeonly def % As .pdfrun, but decrypt strings with key <key>. /PDFScanRules_true << /PDFScanRules //true >> def /PDFScanRules_null << /PDFScanRules //null >> def /.decpdfrun % <file> <keystring> <opdict> .decpdfrun - { % Construct a procedure with the file, opdict and key bound into it. 2 index cvlit mark /PDFScanRules .getuserparam //null eq { //PDFScanRules_true { setuserparams } 0 get % force PDF scanning mode mark 7 4 roll } { mark 5 2 roll } ifelse { .pdftoken not { (%%EOF) cvn cvx } if dup xcheck { PDFDEBUG { dup //== exec 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 } { ( **** Error: Unknown operator: ) exch =string cvs concatstrings (\n) concatstrings pdfformaterror ( Output may be incorrect.\n) 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 --> arc4 strings pop 1 index arc4decode % Decrypt string PDFDEBUG { (%Decrypted: ) print dup //== exec flush } if } { % Else R >= 4 /StrF knownoget % Get StrF (if present) { % If StrF is present ... dup /Identity eq not % Check if StrF != Identity { /StdCF eq { Trailer /Encrypt oget /CF knownoget { /StdCF oget /CFM oget dup /AESV2 eq exch /AESV3 eq or } { //false } ifelse { % Decrypt string 1 index aesdecode } { 1 index arc4decode } ifelse } { 1 index arc4decode } ifelse % If StrF != StdCF PDFDEBUG { (%Decrypted: ) print dup //== exec flush } if } { pop } ifelse % If StrF != identity } if % If StrF is known } ifelse % Ifelse R < 4 } { dup type /nametype eq { .pdffixname } if } ifelse exch pop } ifelse } aload pop //.packtomark exec cvx { loop } 0 get 2 packedarray cvx { stopped } 0 get /PDFScanRules .getuserparam //null eq { //PDFScanRules_null { setuserparams } 0 get % reset PDF scannig mode if it was off } if /PDFsource PDFsource { store { stop } if } aload pop //.packtomark exec cvx /PDFsource 3 -1 roll store exec } bind executeonly def currentdict /PDFScanRules_true undef currentdict /PDFScanRules_null undef % 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. PDFDEBUG { Trailer /Encrypt oget /CF knownoget { /StdCF oget /CFM oget (Encrypt StmF is StdCF with CFM ) print = } if } if /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 executeonly 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 /StreamKey get Trailer /Encrypt oget dup /StmF knownoget { % stack: key Encrypt StmF exch /CF knownoget { exch oget /CFM oget % stack: key StmF-CFM dup /AESV2 eq exch /AESV3 eq or } { pop //false } ifelse { aesdecodefilter } % install the requested filter { arc4decodefilter } ifelse } { pop arc4decodefilter } % fallback for no StmF ifelse exch } if } bind executeonly def end % pdfdict systemdict /pdfdict .forceundef % hide pdfdict .setglobal
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