Multibooter

Integrity Checker of Win9x/XP DLLs

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I am looking for a tool to easily and quickly check the integrity of Win9x/XP DLLs.

UltraISO and WinISO, for example, can quickly create a good-looking .iso from a bad CD (e.g. in UltraISO with -> Tools -> Make CD/DVD Image), without displaying a message that a bad sector was encountered on the CD during read-in. Bad sectors on the CD are usually stored in an .iso image as zeroes. As a result, files extracted from such an .iso may contain "holes" filled with zeroes, as displayed by Beyond Compare/Hex Viewer when compared against a good file.

Ideally the tool should be able to go quickly thru all the dll files in a mounted .iso and flag those which are corrupt. I have 100+ .iso images, which I would like to check whether they contain corrupt DLLs.

Ideally the tool should also identify corrupt CAB files (e.g. .DL_, .EX_ and .IN_) in a mounted .iso, and flag corrupt DLLs inside a CAB file in a .iso

Any suggestions?

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Well, uncorrupted exe and dll files usually contain rather big areas of themselves filled with zeros (which is a part of why exe compression is often so efficient) so I don't think you can do anything along the lines of what you're looking for as you'd yeld countless false positives IMO.

However what you may want to do in the future is use some synchronization utility that uses checksuming, crc32 or other, and compare the content of the CD and the ISO image with it immediately after creating the latter.

Edited by loblo
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However what you may want to do in the future is use some synchronization utility that uses checksuming, crc32 or other, and compare the content of the CD and the ISO image with it immediately after creating the latter.

Hi loblo,

ImgBurn, for examle, displays a message when it creates a .iso file and encounters a bad sector during read-in. So creating a good .iso file with ImgBurn in the future is no problem, but what should I do with the 100+ .iso files created over the years with UltraISO? Maybe only 5% of these .iso files contain zeroed-out bad sectors, but which .iso files are the bad ones, i.e. which of my CD/DVD backups are bad?

A safe way to verify that a .iso was created correctly is to mount the .iso and make a binary compare with Beyond Compare of the files on the CD vs the mounted .iso image, although this does not verify the content of the boot sector on the CD, if the CD is bootable. With old, nearly-bad CDs this compare might become a nightmare.

Also, how can one know that a downloaded .iso file doesn't contain corrupt .DLL files?

MiTeC EXE Explorer can somewhat analyse the integrity of a DLL, e.g. if I open a .DLL file with MiTeC EXE Explorer, and it

- indicates a good .exe type, and

- under the Resource tab -> BITMAP section, all entries greater 1x1 display good images in the bottom window of MiTeC

the .DLL may be Ok, but there is no guarantee.

Using MiTeC EXE Explorer would be feasible for checking a few individual DLL files, but not for checking 100+ .iso files. Another solution may be to re-create the 100+ iso files from the CDs with ImgBurn, but this is very time-consuming and some CDs may have gone bad since the time the previous .iso files were created with UltraISO. Any other suggestions?

Edited by Multibooter
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If a few bytes or even a single bit of code has been corrupted, Mitec or any other PE analyzer will show you what appears to be a valid file when in fact it is not.

There is no way you can be certain of the integrity of those files unless they've been checksumed, either individually or the ISO itself and you can then verify the integrity

But you knew all that already, didn't you?

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If a few bytes or even a single bit of code has been corrupted, Mitec or any other PE analyzer will show you what appears to be a valid file when in fact it is not.
Thanks loblo.

With a .really badly damaged DLL file MiTeC displayed "File is not in supported format". With another badly damaged file MiTeC only displayed the Hex View tab, not the other tabs like Header, Section, Directories etc.

Damaged files from CDs most likely don't differ from good files by just a few bytes, but rather contain zeroed-out sector-size "holes" [about 2k, http://en.wikipedia.org/wiki/CD-ROM , multiplied by the number of contiguous bad sectors], so damaged files from a bad CD have a quite distinct look in Beyond Compare/Hex Viewer when compared to the good file, and can be immediately recognized as damaged.

I am not interested in the authenticity of files (e.g. from MS), but in the integrity, there may be quite a few patched files in these 100+ .isos.

There is no way you can be certain of the integrity of those files unless they've been checksumed, either individually or the ISO itself and you can then verify the integrity
Sad to hear this. I had thought that there could be a reverse-engineering tool which de-compiles, de-links or whatever and then comes up with a message like "success" or "failure" of the process, and thereby identifies the corrupt files.

But let me re-phrase my question: Is there a tool which can identify a DLL as corrupt? This would help a lot, because it would tell me which isos of the 100+ would have to be re-created from the CDs. Even a tool which can identify some bad DLLs would be of help, because the flagging of just 1 bad DLL would be sufficient as a flag for a bad .iso/bad CD.

Well, as I am thinking about it, maybe it's easier to extract flat all cab files (DL_, EX_, IN_) from a .iso image, and then test extract these CAB files. A bad CAB file would flag a bad .iso just as well as a bad DLL. But there must be a more elegant solution, with 100+ .isos. Maybe a CAB repair tool could flag bad cab files in a mounted .iso, I'll be checking.

Edited by Multibooter
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@Multibooter,

There is no way you can be certain of the integrity of those files unless they've been checksumed, either individually or the ISO itself and you can then verify the integrity

This is the ONLY way to guarantee that ANY type of file has not been damaged, corrupted, changed, edited, modified, enhanced, or any other type of change you can possibly think of to ask about. PERIOD And that would of had to of been done before you ever copied the iso or files off the CD/DVD to begin with. But you are welcome to keep looking for an alternate solution.

Cheers and Regards

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This is the ONLY way to guarantee that ANY type of file has not been damaged, corrupted, changed, edited, modified, enhanced, or any other type of change you can possibly think of to ask about. PERIOD
Hi bphlpt,

I disagree with you for philosophical reasons. For me there are many roads which lead to Rome, so I haven't given up yet.

1. Test with Advanced CAB Repair v1.2:

- I extracted all files from the bad .iso into a folder. The bad .iso contains about 130 corrupt files with zeroed-out "holes" in them

- I renamed about 4500 files in this folder from*.??_ to *.CAB (e.g. .EX_, .DL_, .IN_). Advanced CAB Repair v1.2 only works on files with the .CAB extension

- I made a Batch Repair of these 4500 CAB files

- unfortunately, Advance CAB Repair repaired all except 2 .CAB files (the good ones and the corrupt ones), and did not display a message which CAB files were good, and which ones were bad.

The actually corrupt CAB files contained after the repair corrupt DLLs, severely truncated in size. I checked just 1 dll files in a "repaired" cab: the extracted .DLL was 64KB, compared to 1092KB of the DLL extracted from a corresponding good CAB file. Advanced CAB Repair could neither flag corrupt CAB files, nor repair corrupt CAB files in this test, although MiTeC Explorer did display several tabs for the truncated DLL extracted from the corrupt/repairedCAB.

2. Test with 7-Zip:

- I extracted again all files from the mounted bad .iso into a folder

- without renaming any files I selected everything in that folder and had 7-Zip extract everything to another folder. Files which were not archives (e.g. boot.bmp) were displayed in the message window as "Can not open file xxx as archive". And here the amazing result of this experiment:

- the corrupt CAB files were displayed in the message window like:

K:\junk\I386\TRACERT6.EX_

Data error in 'tracert6.exe'. File is broken

7-Zip can apparently identify all broken CAB files and many other broken archive files in a .iso (.CH_, .DL_, .EX_, .JP_, .. TS_, .TT_, ., .EN_, .FR, .IT_, .CAB, .EXE, .CHM, etc)

You simply have to:

1 - mount the .iso

2 - copy everything from the mounted .iso on the virtual drive to an empty folder

3 - select everything in this folder -> right-click and drag to another empty folder -> select 7-Zip -> select Extract Here

The extraction may take 2-3 minutes. If no msg "File is broken" is displayed in the 7-Zip message window, the .iso contains no broken archives and the .iso is most likely Ok

If there are broken archives in the .iso, 7-Zip will display them with the message "File is broken" Such isos have to be re-created, from the original bad CD.

I have just tested in the manner described above a reconstructed .iso, which I had created from a really badly damaged CD. 7-Zip did not detect any broken archives in the .iso, so the recovery of this bad CD seems to have been successful. :)

I am quite optimistic that there is a way to quickly identify corrupt DLLs, and hope that somebody else will pick up from here.

Edited by Multibooter
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I disagree with you for philosophical reasons. For me there are many roads which lead to Rome, so I haven't given up yet.

I admire your spirit, and do not in any way want to dampen your enthusiasm or discourage your search. Many wonderful discoveries have been made in all fields when people did not accept "It can't be done". But I stand by my statement. Your method does seem to pick up some files that have specific types of errors. But note that I said "changed, edited, modified, enhanced" as well. if you substitute an old version of a file for a newer one, or take any type of archived file and rename it as another, say take NOTEPAD.EX_ and rename it as TRACERT6.EX_, your method will not find that to be a problem at all. Also, not all files on an iso are stored as compressed files, and as you found out, 7-Zip will not be able to help with anything that is not an archive. Not to mention that in essentially all cases 7-Zip can only identify and not repair those errors it finds. And what about missing files? As a result, your assumption that -- 'If no msg "File is broken" is displayed in the 7-Zip message window, the .iso contains no broken archives and the .iso is most likely Ok' -- will not always be correct. But I admit that if you are only looking to identify if there is a particular type of error in certain files that your method could be of help. Continue your search! We might all learn something from your efforts.

Cheers and Regards

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Hmmm... this will not "fix" them but will (maybe) help identify them (?) - IsoBuster? (and NOT the "contents" Compressed files, just the BASIC filenames).

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Damaged files from CDs most likely don't differ from good files by just a few bytes, but rather contain zeroed-out sector-size "holes" [about 2k, http://en.wikipedia.org/wiki/CD-ROM , multiplied by the number of contiguous bad sectors], so damaged files from a bad CD have a quite distinct look in Beyond Compare/Hex Viewer when compared to the good file, and can be immediately recognized as damaged.

As I have already mentioned, most (all?) uncompressed (and uncorrupted) executable files have many such 2k+ "holes" in them so i am not sure how easily if at all your tools will let you see which of those "holes" are due to corruption and which are not.

Anyway, here is a nice little hex editor you may find interesting/useful, it's called BZ and it's got the rare feature of being able of displaying a bitmap image of the opened file (with zeros represented as white) and it is very easy to identify visually (and jump to) the location of various thing in executables with it, large areas consisting of zeros being the easiest to spot.

http://download.forest.impress.co.jp/pub/win/b/binaryeditbz/bz162.zip

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Anyway, here is a nice little hex editor you may find interesting/useful, it's called BZ and it's got the rare feature of being able of displaying a bitmap image of the opened file (with zeros represented as white) and it is very easy to identify visually (and jump to) the location of various thing in executables with it, large areas consisting of zeros being the easiest to spot.

http://download.forest.impress.co.jp/pub/win/b/binaryeditbz/bz162.zip

Good idea, definitely useful for inspecting individual files.

It could perhaps also be done in Beyond Compare/Hex Viewer by creating a blank file containing only zeroes, and then comparing various DLLs against this blank file. On the left side of the Beyond Compare/Hex Viewer window is a sliding bar window, with lines or rectangles, depending on the size of the file and the size of the matching/differing sections.

BTW, the mass-extraction with 7-zip of DLLs etc from the CAB files in .iso images or on CDs, indicated above, could perhaps be used to build a huge archive/repository of various versions of MS etc. DLLs. I still have among the stuff I got from a garage sale, for about $10, a binder filled with maybe 100 MS Technet Plus subscription CDs, Sept.1999 to July 2000, from a guy who was a MS certified something until the bust of the internet boom, and who then became a real estate agent, until the bust of the real estate boom. Would this be just a backup of stuff of an age gone by, or could such a pile of various DLL versions still be useful?

Edited by Multibooter
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Well... it's my understanding you'd like to be able to check the integrity of every file in a CD/DVD or a CD/DVD image.

I have no solution for that, sorry!

However, as your initial post mentions specifically DLLs, I do have a partial solution for that, that may be of interest. Let's see its limitations:

Not all files are executables, and for non-executables this won't work. Not all executables are PE files (i.e.: files in the Portable Executable format), and for non-PE files this won't work. Not all PE files are checksummed (i.e.: there are PE files with the header checksum set to zero, when the true checksum is not zero), and for non-checksummed PE files this won't work. But it works for all checksummed PE files! :w00t:

Now, the bad news is Win 9x/ME does not care about the checksum, so non-checksummed PE files are more common for those OSes than for those of the NT-family. In any case I've done some quick statistics using my C:\WINDOWS\SYSTEM folder as a reasonable enough sample to see how useful my method might be, and here're the results:

Of 2232 files, 1574 (70% of the total files) are PE files.

Of these: 1111 (70% of all PE files) have matching checksums, 451 (29% of all PE files) have zero checksum on the header and 12 (1% of all PE files) have wrong checksums (those are sloppily patched files, which checksum was not corrected, in this case).

So, all in all, I was able to confirm that 49% of the total files are not corrupt, and had to investigate just 12 files... Seems good enough for me! :D

The method consists in calculating de novo the true checksum of a PE file and comparing it to the checksum present in the Optional Header: when both match, the file can be assumed to be non-corrupted. The exceptions to this rule are some files that chip with a wrong checksum in the header... I found out that QuickTime.cpl is an example of such a file (three different versions of it straight from the distribution package came with wrong checksum set in the header). I've thrown a little console app together, which I call VRFYPE (attached to this post), to perform the checksum test on any number of files. It accepts "*.*" as a filespec and proceeds to check each of the files, ignoring the non-PE files, and providing three possible veredicts on the PE files it finds: checksums match, or do not match or the header checksum is zero, returning all info for any given file in a single line, together with the filename, so as to be convenient for filtering with FIND or related DOS filters.

Please do test VRFYPE, and let me know of any bugs you find.

VRFYPE.7z

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Thanks dencorso. I'll definitely find your tool very useful. I'm just wondering whether it would be possible to have a switch to list only files which have wrong checksum. What I mean is something like this:

vrfype.exe /x folder\*.*

and the output would be a list of files with wrong checksum (with no additional info).

It would be possible to do this:

FOR /F %%I IN ('vrfype.exe /x folder\*.*') DO modifype.exe "%%I" -c

Edited by tomasz86
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You may try:

vrfype folder\*.* | find /I "match"

if that does not solve it, let me know, and I'll implement the required switch.

Just a heads up: modifype.exe is not a good idea anymore, since it refuses to work right under Vista and 7. n7Epsilon's PEChecksum.exe should be used instead, in all cases.
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It works! I guess I need to learn more about using "|" in batch scripts.

This works to get a full path of the file:

FOR /F "tokens=1,2 delims=:" %%I IN ('vrfype.exe *.* ^| FIND /I "match"') DO ECHO %%I:%%J

I'll check PEChecksum.exe.

Edit: It seems to be a little bit tricky. The above script will work only if you use a full path, ex:

FOR /F "tokens=1,2 delims=:" %%I IN ('vrfype.exe %systemroot%\system32\*.* ^| FIND /I "match"') DO ECHO %%I:%%J

It doesn't work if you use it in a folder with *.* because the output looks like this:

1) when using a full path (%systemroot%\system32):

C:\WINNT\system32\file.dll: Header Chksum: 000136D1 Real Chksum: 0000D181 Chksums do not match! 

2) when using "*.*":

.\file.dll: Header Chksum: 000136D1 Real Chksum: 0000D181 Chksums do not match! 

so it must be this for "*.*":

FOR /F "tokens=2 delims=\:" %%I IN ('vrfype.exe *.* ^| FIND /I "match"') DO ECHO %%I

The output file be just the filename.extension, ex. file1.dll, file2.dll, etc.

Edited by tomasz86
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