| Title: | -={ H A C K E R S }=- |
| Notice: | Write locked - see NOTED::HACKERS |
| Moderator: | DIEHRD::MORRIS |
| Created: | Thu Feb 20 1986 |
| Last Modified: | Mon Aug 03 1992 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 680 |
| Total number of notes: | 5456 |
There has been quite a discussion about this in vmsnotes but most
of it centering around WHY and not an answer... someone suggested
posting it here ,so here goes...
<<< VAXWRK::WRKD$:[NOTES$LIBRARY]VMSNOTES.NOTE;1 >>>
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Note 936.0 is this file an image? 21 replies
USHS01::MALLORY "Cluster Killer" 20 lines 4-JUN-1986 19:43
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What is the correct way to find out if a file is an image?
I have a customer in a hostile environment who has users that hide
images in files like x.txt.
My approach is to:
1) see if the file has a 512 byte record if so if not next file
2) open the file
read block 1 as if it were an IHD
check ihd$w_imgidoff to see if it is gt 5 and lt 500
(got these values from IMAGEINFO tool on toolshed)
don't have a fiche reader handy, someone with source code on-line
handy look at ana/image and send me a code segment mabey?
adv<thanks>ance
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 252.1 | Your test will get you passed round one... | TLE::BRETT | Fri Jun 06 1986 23:07 | 16 | |
If the environment is that hostile, and all he does is look for 512
byte fixed length files, he has a shock coming.
All the people have to do is modify the record attributes from FIX
to VAR and your program won't find the hidden .exe's; furthermore
a trivial "encryption" (eg: xor'ing with a fixed key) will conceal
any other attributes of a file header.
A better approach would be to raise a flag about any file whose
contents aren't obviously text.
An even better question is "why" - but if that's being addressed
in VMSNOTES...
/Bevin
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| 252.2 | There's a command to do it. | DELNI::CANTOR | Dave Cantor | Sat Jun 07 1986 01:48 | 4 |
How about a simple ANAL/IMAGE filename.typ and check the $STATUS
for success?
Dave C.
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| 252.3 | takes too long | USHS01::MALLORY | Cluster Killer | Sat Jun 07 1986 09:55 | 5 |
RE .2 this too was discussed in vmsnotes... there are 48 ra81's
worth of data to look on (on a *regular* basis) ana/image would
take weeks!
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