Bunny.py: A WiFi darknet that hides its traffic in the noise of 802.11

https://github.com/mothran/bunny

by mothran • 13 years ago

331 55 13 years ago

github.com

This is a project I have been working on for a while now and I would love some feedback.

danabramov• 13 years ago

I am a bit confused as to what this does.

Does it allow me to chat over someone's WiFi network with another client running this software?

Something else?

joshstrange• 13 years ago

I'm in the same boat, maybe I am just not familiar enough with this kind of software but I can't tell, do you have to have the SSID/Key to connect or does this piggy-back on it somehow?

shawabawa3• 13 years ago

It's not for hacking into other people's network, it's for communicating wirelessly invisibly. It hides in other people's wireless signals so that an eavesdropper doesn't even see it's there

mothran8• 13 years ago

Bunny basically sends raw packets are that build around a model of 802.11 packets that it has seen. It spoofs all the fields and then injects little bits of data into certain 802.11 fields that are rarely used or have someone random data when they are. So this means that bunny is essentially a ad-hoc style network that hides is traffic to look like whatever wifi networks are around.

friendcomputer• 13 years ago

From my reading of the included proposal.txt, it uses steganography to have side-channel communications that look like other wifi communication near you.

EvanAnderson• 13 years ago

Yes-- that's what it does. Nodes need to agree on a pre-shared AES key, a modulus, and a remainder, and with that information they can monitor the wifi network to locate Bunny frames.

I glanced over the "proposal.txt" file and I think a reasonable summary is as follows: Bunny monitors a wifi network to build a model of the types of common packets it "sees". Once it has built the model it can transmit data covertly by sending packets with a crafted length (based on a couple of pre-shared values) that are similar to the "average" traffic on the network. Bits of AES-encrypted data are stored in some of the various header and payload fields that are "sloppily" defined in the 802.11 standards. Other Bunny nodes are able to recognize these frames because their length modulus the pre-shared modulus value will equal the pre-shared remainder value.

mothran8• 13 years ago

Spot on.

lifeisstillgood2• 13 years ago

But

The packets sent wont be routed ? So this is a peer to peer / adhoc network between two clients who not only will encrypt their messages but will write it in invisible ink too.

It's a really cool hack, and mothran probably knows more about wifi packets now than anyone is legally allowed.

But if I am in a situation where the enemy is so sophisticated they can infer useful information from my non hidden encrypted traffic I am going back to filling in the Times crossword on a bench in st James park

pudquick• 13 years ago

To answer you directly - no, you technically don't chat "over someone's WiFi network". If you're thinking TCP/UDP, the ability to see other computers on a LAN segment, access to encrypted data over a WPA2 connection, etc. - that's too many layers up in the OSI model.

Bunny lives down at the layer 1 / layer 2 model - hardware to hardware communication. Negotiation of connections that eventually lead to joining a subnet, etc.

Since it's at this lower level, it still hasn't "signed on" to a WiFi network - it's just chattering like it would like to sign onto one. No traffic from a bunny client makes it any farther than devices that can directly hear the broadcast. For bunny to work correctly, your device would have to be within range of another device using bunny such that you could pick up the packets as they were broadcast directly from the device.

TL;DR: Nothing is routed.

bunny monitors the WiFi traffic, regardless of network, that it can see in the area. It then builds up a model of what packets it can see (the packets have identifying fields, bunny builds up a list of the common values it sees in those fields) and builds similar looking packets (with values from those lists). Here's the code for the 'fake packets' that it can make:

https://github.com/mothran/bunny/blob/master/libbunny/Templa...

The main difference between its fake packets and the real ones are that bunny repurposes part of the packets that normally don't contain any real data (vendor specific fields that are part of packets, but rarely used) and swaps them out with AES encrypted data that bunny understands (using an encryption key in config.py).

Any other bunny client with the same encryption key can see these broadcast fake packets, determine that they're fake (they're built in a very particular way), and then attempt to decrypt the data using the key it knows.

If it can decrypt the data into something meaningful, then data can be broadcast back and forth between the bunny clients.

The main packet types bunny clones are:

* Beacon: the packets that announce the presence of a WiFi network. These will be close clones of the existing beacons and are will contain the same core information the real beacons contain. A client looking for a WiFi network may end up using a bunny generated beacon to attempt signing in - but the actual connection negotiation won't be handled by bunny itself. bunny might be the source of the packet that causes WiFi network "Your Local Cafe" to appear in your available WiFi network menu, but it won't ever be involved in connecting you beyond that.

* Probe Response: This is the client counterpart to a beacon packet, basically. It's a client saying "Hey network <SSID name here> - are you there?" WiFi APs will likely respond to it with a "Yes, I'm here" but it won't go beyond that - bunny won't do anything with the responses.

* LLC QOS: This packet has the most potential to do something, in that it's a link level flow control quality of service packet. It's the kind of thing that one piece of the network would send to the other saying: 'Whoa, please slow down - too much data right now on <this stream>'. However, part of the data that's fudged in this packet is the sequence number. An invalid sequence number should cause any receiver of the packet to ignore it, making it safe for bunny to do this.

nlh• 13 years ago

This is an _extremely_ good and clear explanation. Thank you! Every time a new question popped into my head you answered it in the next sentence.

_b8r0• 13 years ago

Basically with a bit of work you should be able to implement something approximating a tty type interface over this, which means that you could (theoretically) sit in the car park running a metasploit session on an evil box hooked into the target network in a very difficult to detect manner.

It also provides all kinds of interesting potential capabilities for anonymous communication across crowded networks. This could be great for co-ordinating drug deals or suchlike but is probably better still for co-ordinating protests and exporting information when GSM's down.

tptacek2• 13 years ago

Anybody who made it through a couple levels of our crypto challenges want to take a run at evaluating this?

wulczer2• 13 years ago

Once this TODO is completed and real PKCS#5 is used, CBC padding oracle attack?

https://github.com/mothran/bunny/blob/master/libbunny/AEScry...

mothran8• 13 years ago

Yes, that is high on my list to fix.

mothran8• 13 years ago

The crypto is super simple currently. I have spent a long time trying to figure out a better solution but currently there is a single round of AES-256 in CBC mode, each message gets a random IV.

To answer the first questions from this, 1) yes I know there is no MAC I am working on that and could use some ideas 2) forward security is not built in, but if you can find a quicker way to renegotiable mpOTR we might be in business.

Any feedback would be great, I would really like to improve Bunny to be more solid in its use of crypto.

marshray5• 13 years ago

Suggestion: Forget the modulus and remainder trick and just use a cryptographically strong MAC to decide what to ignore and what to process. Even a truncated HMAC.

andrewcooke3• 13 years ago

you really need hmac or similar. someone else already said, but in more words: in a practical system (that has error handling etc) your current approach can allow someone to provide fake data. if they can trick you into repeating the same message (random iv doesn't help) then they can use padding to work out what bits of iv to flip to give any first block. and you including length in message only makes that easier (no second block error).

better: why not implement a lower level without crypto then layer a known good crypto on top? so just go for datagrams (udp), then add reliability (tcp), then add, say tls. I don't know much about this (sorry), but I bet once you have udp there are libraries to do almost all the rest.

KMag• 13 years ago

Others have rightly mentioned HMAC as being a good option, but being approximately equal to the work of the CBC encryption.

There are peer-reviewed standard cipher modes that provide a cryptographic checksum with a low overhead per block plus one extra block cipher operation per message. These are generally known as single-pass authenticated encryption modes. GCM mode is probably your best option. If you're willing to rekey every 64 GB, are releasing your code under an OSI-approved Open Source license, and you're okay using a mode that's patented, OCB mode is another option.

Really, you don't want to use a static key. Ideally you'd either use the shared master key just to provide confidentiality (in case ECDH is broken) and authentication for ECDH session key agreement. Failing that, you'd use the shared master key and the current time to generate the session encryption keys in order to limit the amount of traffic under a given session key that an attacker can use.

session_counter = (AES256_enc(master_key, 0) + time()) | 0x0FFF; session_key = AES256_enc(master_key, session_counter); will generate for you a 128-bit key that changes every 1.13 hours (2^12 seconds). If an attacker can notice some traffic pattern that gives away when the rekey happens, this will give away the lower 12 bits of AES256_enc(master_key, 0), but this is very little plain text to work with. Note that due to the | 0x0FFF, it's impossible to accidentally use the leaked bits in a session key by using AES256_enc(master, 0) as a session key. If you want a 256-bit session key, it's best to use a second 256-bit shared key to encrypt session_counter to generate the second 128-bit half of your session key. Of course, in practice you'd pre-calculate when the session_counter rolls over rather than recomputing the session key for every packet. You either live with data being lost a few seconds every hour, synchronize clocks very well using GPS or NTP, or else calculate two sets of session keys and use the MACs to figure out which key the sender is using. When using two sets of session keys, you'd throw away the "expired" key and calculate the "upcoming" key 2^11 seconds after session_counter rolls over. (That is, you actually roll your pair of session keys half out of phase of when you'd roll a single session key.)

Edit: Changed to use C's xor operator for exponentiation since Python's double-asterisk notation doesn't display properly on HN.

marshray5• 13 years ago

I haven't made it through your crypto challenges, so perhaps someone could explain this to me

https://github.com/mothran/bunny/blob/master/proposal.txt :

> To detect a bunny specific packet, each outbound packet is resized to match pre determined pack_len % mod = remainder values. Then when looking for packet bunny just tests each packets length against the modulus and remainder values.

https://github.com/mothran/bunny/blob/master/libbunny/SendRe... :

    if (round( (size - 4) % MODULUS, 2) == REMAINDER):
        print "pack num: %d, " % n

https://github.com/mothran/bunny/blob/master/libbunny/config... :

    MODULUS = 1.21
    REMAINDER = 0.85

What?!

mothran8• 13 years ago

Ok so the code is a bit weird in that section because of issues with different wifi chipsets (thus the -4). Sorry about the messy code, I would barely call Bunny alpha.

The mod/remainder values are agreed upon by the network operators, that is why they are in config.

The length % mod == remainder trick for detecting packets was inspired by the KIS rootkit in the later 90's. http://packetstormsecurity.com/files/25029/kis-0.9.tar.gz.ht...

cabacon• 13 years ago

You're sending the IV as part of the data, and the IV is not encrypted. The message being sent is time.time(), which is hugely predictable. The padding is easy to attack, and the inclusion of the IV means you'll get the first data block too.

tptacek2• 13 years ago

Exposing the IV is fine as long as an attacker can't predict it.

drippingwet• 13 years ago

Why not just be honest, and let everyone know that the fate of (2.4Ghz)802.11a/b/g/n/ac residential/commercial/enterprise/carrier grade rests on an unencrypted management packet framework(that some may argue is defective-by-design).

Until 802.11ad implements alternative methods of handling client/station management, it only takes one deauthentication packet to cause client(s)/AP interference, and possible interception/eavesdropping.

:-\

euroclydon• 13 years ago

No one is voting this up, but it's certainly interesting if true, or if I could actually understand it.

err_badprocrast• 13 years ago

Wifi authentication frames aren't encrypted, so you can craft bogus de-auth packets to disconnect clients. This has a lot of uses - you can DoS a client indefinitely, force them to reveal a hidden access point when reconnecting, or force them to disconnect and then reconnect to a rogue access point.

new standards encrypt management frames, though.

guelo• 13 years ago

Why did you specify 2.4Ghz? Is there something different about the 5Ghz protocols?

Repeaterbird• 13 years ago

Perhaps, 4.9Ghz public safety should be taken into high consideration.

jdthomas• 13 years ago

802.11w adds encrypted management frames, but in practice this tends not to be a huge issue and not many vendors implement it yet.

tlow• 13 years ago

"Bunny is intended to act as a layer 1/2 technology that attempts to hide its wireless mesh communication traffic."

I think there's a lot of interest in this article but also a lot of uncertainty.

There are some interesting comments on the theoretical basis of Bunny and Bunny packets, but as someone without a lot of technical knowledge of this area, I don't know: How effective Bunny is in practice? How visible is it...? If I were a network security professional, would I notice Bunny on my wireless network? Perhaps the author or a knowledgable person could speak to these questions?

jtchang• 13 years ago

So a possible use case for this covert channel:

You are trying to infiltrate a specific computer inside a large corporation. You have a wireless USB key that you sneak in and plug it into a target computer.

The problem is issuing commands to that USB dongle (which I assume is running some sort of OS).

If the dongle sets up a new wireless network it will be detected by rogue AP scanners (common feature in many enterprise access points). So instead you stick your data in a covert channel. You then sit in the parking lot and communicate with your device without it tripping any IDS systems. At least for now until the IDS systems start looking for weird packets with data stuffed in all the wrong places.

lifeisstillgood2• 13 years ago

I take back my previous pessimism - brilliance

jvictor118• 13 years ago

This is awesome.

skeletonjelly• 13 years ago

Can you elaborate on the OS on a USB thing? You mean you'd reboot the machine to the OS on the USB? Wouldn't that trigger things? Or that machine merely a conduit?

dublinben• 13 years ago

I think the USB key would have some logic so it could steal information from its host, and send these WiFi signals by itself.

Shish2k2• 13 years ago

If you can convince a machine to boot from USB, then one could make a liveUSB distro which automatically boots the first hard drive in a fullscreen VM (+ remote access), so it would appear to the user and network to be unchanged.

(Not sure how well that works for windows, which freaks out at the slightest hardware change, but it seems to work great for linux - I'm doing that at work to get modern hardware and software support of ubuntu while the software we use is only for centos; if I ever want to go back I just remove my extra hard drive and boot from the original again :) )

orangethirty2• 13 years ago

Cool, this is using pylorcon. I forked it to have fun with it. Let's see where can I manage to put this, and what kind of fun can be had. Hmm..., I can even send commands through this. Fun. Thanks for open sourcing this.

mothran8• 13 years ago

No problem man, if you get it working on your hardware that is not listed in the README, please tell me. I would love to keep a easy to find list of supported chips.

orangethirty2• 13 years ago

Will do, thanks. (:

zobzu• 13 years ago

I did something similar as in using the wifi chip for non-intended purposes (but not the same as you did with bunny) a few years ago.

Used same chipsets hehe. I found that lorcon and aircrack's libs were both lacking tho. It appears not much has changed :/ Made it in C as i eventually forked off aircrack's lib to fix stuff (lorcon is nicer yes, but the code is so abstracted that it makes it painful to modify)

silasdavis• 13 years ago

How about providing this as a transport layer for: http://briar.sourceforge.net/overview.html

informatimago• 13 years ago

How much hidden bandwidth can be piggy pegged on wifi with bunny?

alexkrycek• 13 years ago

Your README mentioned the following:

rtl8187 - Alfa AWUS036NH

Note: These are by far the WORST chipsets on the market, the RX sensitivity makes them almost worless for any kind of application besides cracking WEP passwords.

I have this model. Can you explain a bit more what the issue is with the RX sensitivity. Are there any workarounds?

punnerud• 13 years ago

This would not work on a lot of large enterprise networks that use RSSI (Received signal strength indication) to detect malicious devices. Unless you are close to one sender and are sending data at the same time as this sender is sending its data.

Bunny.py: A WiFi darknet that hides its traffic in the noise of 802.11

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