For some time I am wondering and searching through Internet looking for answer about iso files that are written on DVD or CD discs (ISO 9660 standard as far as I know).
I have found this paper http://www.cs.cmu.edu/~varun/cs315p/iso9660.pdf about this standard. At page 45 there is tabel describing what is set on which bit. Two rows are quite interesting for me: Volume Creation Date and Time and Volume Experiation Date and Time. If I am getting it right there is a possibility that I can make CD that won't run after date that I will set at expiriation date, or is it other thing.
Also does any of you ever use those bits. I was looking for something different in this paper, but it is quite interesting and I would like to dig into this topic, so maybe you have got also any extra materials about it.
Thank you for answer in advance.
From what I can tell this MAY have something to do with backup media and backup solutions to know when the backed up data has expired. And the archive slot is now available for re-use or from when it MUST-NOT be used as the backup is past it's expiry date.
This is quite common for other backup media like tape backups. Various software solutions require the need to specify expiry dates to know when to re-use tapes and when to generate warnings and alerts based on the solution's own implementation.
I believe this is a compatibility field to allow large scale systems to be able to replace legacy systems with iso9660 images (CDs etc).
I don't think this is actually enforced by most of the software that consumers use at the moment.
Even in the olden days the software using the backup media will have an override parameter to ensure that expired volumes/archives can actually be used by a forced manual override.
Hope this helps.
Related
Do you know if there are unchangeable EXIF datas ?
In my case i want to know the real date of creation of a jpeg image. So I thought the EXIF's datas was the best way but I realized that with a software like XnView you can change it. So there is any way i can now the real date of the creation of an image ?
In another hand, is it possible to know if a EXIF datas has been modified ?
Thx fo all,
And sorry for my bad english
Have a good day !
:)
In principle, it is not possible to be sure the data hasn't been edited, although it may take a great deal of skill to do so indetectably. Some of the major camera makers (Canon and Nikon, possibly others) offer an "image authentication" feature in their pro model cameras which is designed to make it impossible to modify the image after it has been taken. They do this for the benefit of people doing legal work - evidence shots and the like. To use this, you have to switch it on (via the camera settings) before you take the picture. Even with these though, it is still possible to alter the data: both the Canon and Nikon authentication systems have been cracked (presumably with considerable difficulty).
As for normal pictures, yes, these are very easy to alter. However many (most?) programs which can edit EXIF data leave their own signs. For example, Adobe Photoshop always adds its own name somewhere in the EXIF, apparently whether you want it to or not. You can see this with many different EXIF viewers, especially with the more advanced ones like PhotoME. (Which, sadly, is no longer maintained.)
Short answer: yes, it is always possible to exit EXIF, and almost always possible to do it indetectably, but it may requite the right tools and quite a lot of skill. You can't ever be certain it has not been done.
Many sites and articles on getting widescreen monitors to work on notebooks in their native resolution mention something called the "Mode Removal Table" in the Video BIOS which specifically prevents certain video modes:
http://www.avsforum.com/avs-vb/showthread.php?t=947830
http://software.intel.com/en-us/forums/showthread.php?t=61326
http://forum.notebookreview.com/dell-xps-studio-xps/313573-xps-m1330-hdmi-hdmi-tv-issue-2.html
http://forums.entechtaiwan.com/index.php?action=printpage;topic=3363.0
Does such a thing really exist? The fix worked for me but I wanted to find out if I can read, modify, or work around this table. However I can't find any mention of it in the various VESA standards. Perhaps it actually goes by some other more cryptic name?
“Many sites and articles”? The first couple of dozen results are from you, and most of the rest are from that Intel article you mentioned or other people linking to that article.
You could always try asking someone who talks as though they know how to do it. There's another thread that discusses it—though it too has no information on the table, only a quick mention of it.
There does not seem to be any currently known way to read the GMA video BIOS. You would have to dump the BIOS and reverse-engineer it to figure out where the table is and how to interpret it. Unfortunately, even extracting it is difficult since nobody seems to have had enough interest in creating a tool to automate it. Looks, like you’ve got even more reversing to do. (Techincally, because the GMA is an integrated graphics-adapter, you'll need to extract the video BIOS from the system BIOS, then extract the table.)
For not-free iphone applications, can I use sound files from this websites?
Tintagel's Free Sound File Archive
Can I download the wav files and use/play them in my app, without getting into any problems? I just need several very short wav sounds(shorter than 1 second).
If you really want to be safe, record your own sounds - that way, you know that the copyright holder has given you permission to use them. Unless you have a blanket release of copyright on those (or other) files, or an explicit licence to use them for any purpose, you can still get into trouble.
And I don't mean something wishy-washy like:
To the best of our knowledge, blah blah blah ...
That's unlikely to hold up in a court of law :-)
The main problem with digital copies is that they're perfect reproductions, meaning the copyright holder can easily tell that you've ripped off their work.
Not that I would suggest this as an option, since it's still probably a derivative work, but if you really can't record your own sounds, you might want to think about editing the sounds somewhat to make that harder, ideally fed from the computer out through a speaker back into a microphone and into another file :-)
Or, look into sites on the web where they actually state that they own the copyright and license you to use the files as you see fit. That way, you at least have some protection if they (or someone else) comes back later to collect payment.
One example is Partners In Rhyme, which has a huge range of effects which they appear to own the copyright to, and with a generous royalty-free licence. This was found as the second entry when googling "public domain sound effects" (this first was a rather useless, content-free tutorial on how to find public domain sound effects). There are plenty of other links bought up that you may wish to check as well.
To be safe, I'd actually print out the licence and screen dump the pages where you're downloading from but that's because I'm inherently paranoid :-)
Well, the top of the website says that they are provided free of charge, so that would mean they've been release to the public domain and you're fine.
However, the second sentences says "to the best of our knowledge," which implies that whoever made the website did not create the sounds, and might not have the rights to give them away. Given the way it's worded, it sounds like someone just found those sounds and put them up online. I'd look somewhere else if you're worried about the legality; there are plenty of websites that offer media with real, proper free licenses.
The very top of the page says:
To the best of our knowledge, all wave, midi, and audio files presented here are in the public domain and are available for use without restriction.
So, yes, if you trust that.
How and why do 7- and 35-pass erases work?
Shouldn't a simple rewrite with all zeroes be enough?
A single pass with zeros doesn't completely erase magnetic artifacts from a disk. It's still possible to recover the data from the drive. A 7-pass erasure using random data will do a pretty complete job to prevent reconstruction of the data on the drive.
Wikipedia has a number of different articles relating to this topic.
http://en.wikipedia.org/wiki/Data_remanence
http://en.wikipedia.org/wiki/Computer_forensics
http://en.wikipedia.org/wiki/Data_erasure
I'd never heard of the 35-part erase: http://en.wikipedia.org/wiki/Gutmann_method
The Gutmann method is an algorithm for
securely erasing the contents of
computer hard drives, such as files.
Devised by Peter Gutmann and Colin
Plumb, it does so by writing a series
of 35 patterns over the region to be
erased. The selection of patterns
assumes that the user doesn't know the
encoding mechanism used by the drive,
and so includes patterns designed
specifically for three different types
of drives. A user who knows which type
of encoding the drive uses can choose
only those patterns intended for their
drive. A drive with a different
encoding mechanism would need
different patterns. Most of the
patterns in the Gutmann method were
designed for older MFM/RLL encoded
disks. Relatively modern drives no
longer use the older encoding
techniques, making many of the
patterns specified by Gutmann
superfluous.[1]
Also interesting:
One standard way to recover data that
has been overwritten on a hard drive
is to capture the analog signal which
is read by the drive head prior to
being decoded. This analog signal will
be close to an ideal digital signal,
but the differences are what is
important. By calculating the ideal
digital signal and then subtracting it
from the actual analog signal it is
possible to ignore that last
information written, amplify the
remaining signal and see what was
written before.
As mentioned before, magnetic artifacts are present from the previous data on the platter.
In a recent issue of MaximumPC they put this to the test. They took a drive, ran it through a pass of all zeros, and hired a data recovery firm to try and recover what they could. Answer: Not one bit was recovered. Their analysis was that unless you expect the NSA to try, a zero pass is probably enough.
Personally, I'd run an alternating pattern or two across it.
one random pass is enough for plausible deniability, as the lost data will have to be mostly "reconstructed" with a margin of error that grows with the length of the data trying to be recovered, as well as whether or not the data is contiguous (most cases, its not).
for the insanely paranoid, three passes is good. 0xAA (10101010), 0x55 (01010101), and then random. the first two will grey out residual bits, the last random pass will obliterate any "residual residual" bits.
never do passes with zeros. under magnetic microscopy the data is still there, its just "faded".
never trust "single file shredding", especially on solid state mediums like flash drives. if you need to "shred" a file, well, "delete" it and fill your drive with random data files until it runs out of space. then next time think twice about housing shred-worthy data on the same medium as "low-clearance" stuff.
the gutmann method is based on tin-foil hat speculation, it does various things to get drives to degauss themselves, which is admirable in an artistic sense, but pragmatically its overkill. no private organisation to-date has successfully recovered data from even a single random pass. and as for big brother, if the DoD considers it gone then you know its gone, the military industrial complex gets all the big bucks to try and do exactly what gutmann claims they can do, and believe you me if they had the tech to do so it would already have been leaked to the private sector since they're all in bed with each other. however if you want to use gutmann in spite of this, check out the secure-delete package for linux.
7 pass and 35 pass would take forever to finish. HIPAA only requires DOD 3-pass overwrite,
and I am not certain why DOD even has a 7 pass overwrite as it seems they just simply
shred the disks before disposing of machines anyway. Theoretically, you could recover
data off of the outer edges of each track (using a scanning electron microscope or
microscopic magnetic probe), but it practice you would need the resources of a disk
drive maker or one of the three letter government organizations to do this.
The reason to perform multipass writes is to take advantage of the slight errors in positioning to overwrite the edges of the track also, making recovery far less likely.
Most drive recovery companies can't recover a drive that has had its data overwritten
even once. They are typically taking advantage of the fact that Windows doesn't zero out the data blocks, just changes the directory to mark the space free. They simply 'undelete'
the file and make it visable again.
If you don't believe me, call them up and ask them if they can recover a disk
that has been dd'ed over... they will typically tell you no, and if they do agree to try, it will be serious $$$ to get it back...
DOD 3 pass followed by a zero overwrite should be more than sufficent for most (i.e.
non- TOP SECRET) folks.
DBAN (and its commercially supported decendent, EBAN) do this all cleanly... I would
recommed these.
See: Secure Deletion of Data from Magnetic and Solid-State Memory
Advanced recovery tools can recover single pass deleted files easily. And they are expensive too (e.g http://accessdata.com/).
A visual GUI for Gutmann passes from http://sourceforge.net/projects/gutmannmethod/ shows it has 8 semi random passes. I never seen a proof that files deleted by Gutmann been recovered.
An overkill, maybe, still far better that Windows soft delete.
Regarding the second part of the question, some of the answers here actually contradict real research on that exact atopic. According the the Number of overwrites needed of the Data erasure article on wikipedia, on modern drives, erasing with more than one pass is redundant:
"ATA disk drives manufactured after 2001 (over 15 GB) clearing by
overwriting the media once is adequate to protect the media from both
keyboard and laboratory attack." (citation)
Also, infosec did a nice article entitled "The Urban Legend of Multipass Hard Disk Overwrite", on the entire subject, talking about the old USA Government erasure standards, among others, of how the multi-pass myth established itself in the industry.
"Fortunately, several security researchers presented a paper [WRIG08]
at the Fourth International Conference on Information Systems Security
(ICISS 2008) that declares the “great wiping controversy” about how
many passes of overwriting with various data values to be settled:
their research demonstrates that a single overwrite using an arbitrary
data value will render the original data irretrievable even if MFM and
STM techniques are employed.
The researchers found that the probability of recovering a single bit
from a previously used HDD was only slightly better than a coin toss,
and that the probability of recovering more bits decreases
exponentially so that it quickly becomes close to zero.
Therefore, a single pass overwrite with any arbitrary value (randomly
chosen or not) is sufficient to render the original HDD data
effectively irretrievable."
There's a lot of misinformation around this, though most of the answers I see on this page are correct. I've worked in the data recovery industry for 25 years and have addressed this exact question an enormous number of times.
The "residual magnetism" hypothesis never worked in real life. And back then, tolerances were millions of times looser.
If you still doubt this, remember that a rotational hard drive uses the same storage principle as an audio tape - moving magnetic substrate storage - and the audio tape that was recorded over a single time in the Watergate case has still not been recovered.
A single zero-pass wipe renders all the data on a HDD unrecoverable unless some malfunction or mistake causes the overwrite to be incomplete. This was true even back in the days when Peter Gutmann released his paper (which was like a tsunami in the erasure industry.) Gutmann's paper was pure hypothesis, it never panned out in reality. Even in the days of MFM/RLL drives, nobody could recover from a single-pass overwrite. It should be noted that Gutmann patented the algorithm that his paper said would be required to ensure complete erasure. Presumably, every time erasure was sold with his algorithm, he got paid. I am not saying there was intentional deception on his part, just pointing out that his algorithm, though there was never any evidence it erased better than a single overwrite, was patented and sold.
Please note that SSDs are different. SSDs can (and often do) use a pool of sectors that are rotated in and out of use, so if data is written to an SSD and then "deleted" and the drive rotates the sectors on which the deleted file is on out of the pool, an erasure might not be able to reach those sectors because the firmware in the SSD has control that software can't override. One way around this is to continuously overwrite until all sectors have been rotated into use.
The reason multiple passes exist is because hardware can malfunction. If the drive somehow malfunctions during one pass, it's possible that not all sectors will be erased - however, most good erasure software offers a full verification, which basically reads every bit on the drive to make sure the erasure didn't malfunction. With that, multi-pass overwrites are overkill.
And sometimes, data is so sensitive, it makes sense to go overboard in making sure it's destroyed. For example, I heard about a drive that was erased by the military with a 7-pass zero-fill, then the drive was run over by a tank, and then the remains were buried in a secret location in a highly secured area. Practically, the recoverability is about the same as a single-pass overwrite, but if lives could be lost as a result of the data falling into the wrong hands, then why not go for the overkill?
I had the idea of a search engine that would index web items like other search engines do now but would only store the file's title, url and a hash of the contents.
This way it would be easy to find items on the web if you already had them and didn't know where they came from or wanted to know all the places that something appeared.
More useful for non textual items like images, executables and archives.
I was wondering if there is already something similar?
Check out the wikipedia page on locality sensitive hashing. There's also a good page hosted by a research on MIT.
In general, there are several flavors available: hashes for strings (such as simhash), sets or 0/1 features (such as min-wise hashes), and for real vectors.
The main trick for numerical hashes is basically dimension reduction, so far. For strings, the idea is to come up with a representation that's robust in the face of minor edits.
I'm also doing a little research in this field, although I guess stackoverflow might not be the right place for nascent work.
The question seems to focus on exact match hashes, which we understand better than nearest-neighbor approaches, and are indeed worthwhile, especially if people can share tags and other metadata that way.
As #rjmunro notes, hash-based searching is a popular idea in the P2P world, and Bitzi did pretty much this, though they have shut down and their Bitpedia (Digital Media Encyclopedia) isn't hosted there any more, though some of it at least is still available at Archive.org.
Bitzi also produced software like Bitcollider (SourceForge.net),
and the Magnet URI scheme, which allows for specifying a file by hash and is thus a content-based identifier. Various applications support searching at various databases via Magnet URIs as described at that Wikipedia page.
The same idea is popular in the password-cracking scene - see e.g. findmyhash - Python script to crack hashes using online services etc.
Going a step further, I think it would be great if there were databases and online repositories identifying content by hash and providing tags and other metadata about the content from various perspectives. Then I could leave my music collection in its pristine state (no wasted backup space and time), but still tag them myself and add other metadata, via external tag databases. If my applications knew how to grab the tags, it would seem much better than the current system where we modify and copy around big files just to move tags from e.g. my desktop to my phone.
See a related idea at Metadata Independent Hashing for Media Identification & P2P Transfer Optimisation (pdf).
Well, for images, there's http://tineye.com, which will one-up that, and find you similar images too.
It's not a bad idea. Sometimes I find myself stumbled upon some file trying to figure out where it comes from :) But how are you going to track item's sources? Content can be obtained by various means - web browser, download manager, simply by copying from network share.
If I understand your proposal right, http://bitzi.com/ has done this for a while.