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TinyDisk, A File System on Someone Else's Web App
Psy writes "I attended Phreaknic this weekend where Acidus released TinyDisk, a shared file system that runs on top of TinyURL or his own implementation NanoURL. TinyDisk compresses a file, encrypts it, and dices it into clusters. Each cluster is submitted to TinyURL as if it were a url. This clusters can be read back out of the database, making TinyDisk a global file system anyone can use. There are safeguards in the default config to prevent people from dumping gigs of MP3s into TinyURL. While file-system-on-web-applications are nothing new (GMail file system anyone?) this hack shows how easy it is to accidentally design a web application insecurely despite the default PHP protections. See his presentation for more info"
Nifty little program all the same and a nice hack ,
Having it running on his NanoURL implementation locally , could allow for a cool little service . Though there are better ways to offer web based file systems in the real world .
He does state in the FAQ that its not intended to pollute TinURL in any way
Perhaps it will give TinyURL a nudge to tighten up their security though .
The only things certain in war are Propaganda and Death. You can never be sure which is which though
TinyURL might become not so tiny anymore...
One that hath name thou can not otter
I saw this a few hours ago, and from what I understand the process goes as follows:
:)
1- Open a meta file
2- Retrieve and concatenate all the clusters from TinyURL in the order
specified in the meta file.
2- Base64 decode the file
3- Decrypt the file with the algorithm and key in the meta file
4- Decompress the file with the algorithm in the meta file.
5 - Verify the file size given in the meta file is correct for the
decoded/decrypted/decompressed file
6- Verify the checksum with the algorithm and value in the meta file matches
for the decoded/decrypted/decompressed file
7- Set the filename of the decoded/decrypted/decompressed file to the
filename specified in the meta file.
Hope that helps somebody
46487 466780 252994 376409 96920 39622 205366 244315 622115 512361 668040 63608 259203 955314 811176 652718 166330 23922
Insecure? Rancid tabloid hyperbole more like.
I like NanoURL but it scratches real easily.
Bwahahahahaha.
That's pretty much what I understood.
I adore the ingenuity (correct spelling?) of the hack but... I can't really find a problem this hack is a solution for.
As a way to distribute files, it's probably too slow. The pro's I see here: the file is not stored as one single file but it's stored as a distributed file (a set of Base-64 encoded clusters), making removal of the file hard. On the other hand, if one single segment drops out, the file will be destroyed (except if some redundancy exists, of which I did not find evidence).
If you want to send attachments in an e-mail, this is a very complicated way to do it. Every receiver must have the decoder program to re-assemble the file.
Moreover, if tinyURL builds in a check to see whether the submitted URL exists (not just some 404 page), the whole concept would probably break.
Anyways, very clever hack!
--Use ant to make
But overall 'WHY?' must be the question? Al Quaeda or The Real IRA? They still have their old working communication channels. Also who needs space like this? Space of this amount could be made redundant and available by using GoogleMail, Yahoo and Hotmail in synchrony. If none of those are available, presumably you'd have it on USB key as well.
[% slash_sig_val.text %]
I noticed that the whole of Alice in Wonderland is compressed to just 20 clusters and each cluster is represented by the five-letter keys used by TinyURL. So is it not possible, using the same method, to reduce the entire metafile (which is merely a textfile of less than 1kB) into a single-line URL? Then you can have the program retrieve the metafile from the URL and the actual file from the metafile. So instead of sending people a metafile, you can just copy and paste them one line of URL.
Or better yet, validate all entered URLs by attempting to establish a connection to the server. If the URL is invalid then kick it back.
You wouldn't even need to do this with every URL added to the system. Spot-checking every 1 in 10 URLs or so will go a long way to preventing any sort of abuse.
=Smidge=
Sure, well all know PHP is far from synonymous with security, but this seems to be a case of exploiting a web app using only the mechanics intentionally made available, just in a novel way. Seems like some unfounded (though not necessarily undeserved) PHP bashing.
It is a nifty hack, but let's not kid ourselves and pretend this is anything new, or that it's even a good thing.
At its core, Tinyurl is just a write-once database. You add data and get back a key/pointer to said data. As with typical databases, the size of the pointer is logarithmic in the size of the input (* number of keys stored, not bytes; however, the number of bytes/key is bounded under some constant, so it's effectively the number of bytes).
This gives us a logarithmic compression scheme, where our compression ratio (N-logN)/N approaches 100% as N gets large. This kind of "infinite compression" is what makes the method attractive: you put in say a kilobyte of data and get out a (currently) 5 byte key. All you have to do is keep an index of the keys.
TinyDisk doesn't seem to do this, but you could then turn around and store the index as a key. Take 1000/5 = 200 keys and get back one key. Lather. Rinse. Repeat. In the end, you have a single key that points to the backup of your mp3 collection, all in one TinyUrl! Not too shabby. After all, it's free storage, right? Wrong. Someone ends up paying for the infinite compression. In this case, it's Tinyurl. If this kid had stopped to think for a few minutes before publishing his hack, he would have realized that he's actually doing a malicious, antisocial thing. I suspect there will be a dozen copycats in the wild before the end of the day.
Farewell TinyUrl, we knew ye well.
Here is a video of Acidus's presentation. If you haven't seen him present before (At Hope, O'Reilly's E-Tech, Toorcon, Phreaknic, Interz0ne, etc, etc) he puts on a good show.
The presentation was called: Layer 7 Fun: Extending web applications in interesting ways. He discusses how traditional web applications work -vs- "new" web ppas that use AJAX. He talks about writing extensions to web apps using an API supplied (ala Housingmaps.com, or chicagocrime.org). Finally he talks about writing an extension to a web app where you don't have access to an API. TinyDisk was a case study for writes these so-called "non-sanctioned" extensions. He has a funny little slide he goes back to about how to properly implement a web app (which TinyRUL fails to do). Things like "don't wallow users to uploaded arbitrary amounts of data directly into your database."
Funny Stuff. His upcoming talk at Shmoocon seems pretty cool too.
Sorry to be Mr. Obvious this morning, but I take issue with submitter's conclusion that TinyDisk illustrates a security issue on the part of tinyurl.com. It rather illustrates the ease of creating a leachable web app that resource pirates can abuse. Yes, I have a negative opinion of those using such a creative hack against others who provide services to the general public in good faith.
-- @rjamestaylor on Ello
From the TinyDisk FAQ:
Q: This damn thing doesn't work on large files! #@%& You!
A: Did you not read the manual? Man I wish I could punch you in the face over TCP/IP! Change the config file's MaxSize line. By default the limit is 2 megs.