Level 8 of the Stripe CTF is a password server that returns success: true if and only if the password provided matches the password stored directly via
a RESTful API and optionally indirectly via a callback URI. The solution is side channel attack like a timing attack but with ports instead of time.
(I found this in my drafts folder and had intended to post a while ago.)
Code
def nextServerCallback(self, data): parsed_data = json.loads(data) # Chunk was wrong! if not parsed_data['success']: # Defend against timing attacks remaining_time = self.expectedRemainingTime() self.log_info('Going to wait %s seconds before responding' % remaining_time) reactor.callLater(remaining_time, self.sendResult, False) return
self.checkNext()
Issue
The password server breaks the target password into four pieces and stores each on a different server. When a password request is sent to the main server it makes requests to the sub-servers
for each part of the password request. It does this in series and if any part fails, then it stops midway through. Password requests may also be made with corresponding URI callbacks and after the
server decides on the password makes an HTTP request on the provided URI callbacks saying if the password was success: true or false.
A timing attack looks at how long it took for a password to be rejected and longer times could mean a longer prefix of the password was correct allowing for a directed brute force attack. Timing
attacks are prevented in this case by code on the password server that attempts to wait the same amount of time, even if the first sub-server responds with false. However, the server uses
sequential outgoing port numbers shared between the requests to the sub-servers and the callback URIs. Accordingly, we can examine the port numbers on our callback URIs to direct a brute force
attack.
If the password provided is totally incorrect then the password server will contact one sub-server and then your callback URI. So if you see the remote server's port number go up by two when
requesting your callback URI, you know the password is totally incorrect. If by three then you know the first fourth of the password is correct and the rest is incorrect. If by four then two
fourths of the password is correct. If by five then four sub-servers were contacted so you need to rely on the actual content of the callback URI request of 'success: true' or 'false' since you
can't tell from the port change if the password was totally correct or not.
The trick in the real world is false positives. The port numbers are sequential over the system, so if the password server is the only thing making outgoing requests then its port numbers will also
be sequential, however other things on the system can interrupt this. This means that the password server could contact three sub-servers and normally you'd see the port number increase by four,
but really it could increase by four or more because of other things running on the system. To counteract this I ran in cycles: brute forcing the first fourth of the password and removing any entry
that gets a two port increase and keeping all others. Eventually I could remove all but the correct first fourth of the password. And so on for the next parts of the password.
I wrote my app to brute force this in Python. This was my first time writing Python code so it is not pretty.
A Slower Speed of Light Official Trailer — MIT Game Lab (by Steven Schirra)
“A Slower Speed of Light is a first-person game in which players navigate a 3D space while picking up orbs that reduce the speed of light in increments. A custom-built, open-source relativistic
graphics engine allows the speed of light in the game to approach the player’s own maximum walking speed. Visual effects of special relativity gradually become apparent to the player, increasing
the challenge of gameplay. These effects, rendered in realtime to vertex accuracy, include the Doppler effect; the searchlight effect; time dilation; Lorentz transformation; and the runtime
effect.
“A particularly troublesome finding was that for some children, if they were told that sugar would make them hyper, then they actually would become hyper after thinking that they had eaten
sugar.”
“The disc itself is about 5 inches in diameter. It can record one hour of stereo music on one side — and it is only a one-sided disc, it’s not meant to be played on two sides…”
Sony demos the CD at TED in 1984 (by TEDBlogVideo)
Megabox is an ad-replacer - replacing ads on the web as you browse with its own. Ignoring security concerns, I hope this doesn’t result in over prescriptive laws that endanger things like
Greasemonkey.
To listen to songs through Megabox, users will have two options—purchasing the music through the service, or installing “Megakey” software onto their computer to listen for free. The Megakey
software, as Dotcom explained to Torrentfreak, acts like ad-blocking software—except that it isn’t. Megakey allows most advertisements to appear, but replaces about 15 percent of the ads served
up by websites with ads hosted by Megabox.
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