How does TI CC3000 wifi smart config work?

Question

The ti cc3000 wifi chip has a special smart config mode, this is to allow the initial configuration of the wifi access details.

The cc3000 wiki page gives some details on how the process works,

1. The chip enters a smart config "listen" mode
2. Application on smart phone sends a "UDP" packet with access point settings
3. The chip captures this data and configures itself

I am aware of packet capture and wifi sniffing, but how does the chip "decrypt" the raw packet to get any info out of it ? I use wpa2-personal with AES on my router.

Answer 1

As @Colin mentions the scheme that TI now use to communicate a network SSID and keyphrase from a setup application to a CC3000 enabled device is called Smart Config.

Smart Config has to communicate information (the network SSID and keyphrase) from a secure wifi network to a CC3000 enabled device that is not yet able to decrypt the traffic on that network.

Initially the CC3000 is not connected to the network (but can monitor the traffic), so the Smart Config application cannot send its information directly to the device. Instead it sends UDP packets to another existing machine on the network - the wifi access point (AP). That the AP isn't interested in receiving them is irrelevant, it's just important that the packets be visible on the network.

While the CC3000 can monitor the traffic it can't decrypt it, it can't even tell for certain that a given encrypted packet contains UDP data. So how can it pick out the UDP packets or do anything useful with them?

Basically Smart Config encodes its information not in the content of the packets it is sending but in their length. Wifi encryption affects the length of packets, but in a consistent way, i.e. it adds L additional bytes to the size of every packet, where L is a constant.

The Smart Config application encodes the SSID and keyphrase into the packet lengths of a sequence of UDP packets. The CC3000 can see the encrypted packets and their sizes.

In many environments the CC3000 will be able to see traffic from multiple nearby networks so how can it spot the relevant traffic? Even after encryption one can still see the MAC addresses of the source and destination of a packet so one can group traffic this way. In addition to the primary information that Smart Config is trying to send it also sends out regularly repeating patterns of packet lengths, so the CC3000 groups the traffic as described and then looks out for such patterns, when it finds them in the traffic of a given source and destination pair it then focuses in to recover the primary information.

There's obviously more to it than that, e.g. even once the CC3000 has found the source and destination pair, that correspond to the AP and the machine running the Smart Config application, how does it filter the Smart Config packets from other unrelated traffic going between the AP and the machine? I've written this all up in a series of blog posts.

The most technically detailed one covers the heart of Smart Config - how it encodes the SSID and keyphrase and transmits them such that a CC3000 can pick them up:

http://depletionregion.blogspot.ch/2013/10/cc3000-smart-config-transmitting-ssid.html

Then I have a post that's less technical, more an opinion piece about why you should always use an AES key with Smart Config:

http://depletionregion.blogspot.ch/2013/10/cc3000-smart-config-and-aes.html

There is a technical bit in the middle that does describe briefly how you'd configure a cipher in Java with the necessary AES transformation needed to work as the CC3000 expects.

And finally the proof of the pudding - I wrote an application to emulate the Smart Config related behavior of the CC3000, i.e. it can recover the SSID and keyphrase transmitted by any Smart Config application without needing to be able to decrypt the relevant network traffic. You can find where to download the source and all the details here:

http://depletionregion.blogspot.ch/2013/10/cc3000-smart-config-and-keyphrase.html

This should enable one to test the behavior of any Smart Config application one writes, i.e. one can see what a CC3000 would be able to reconstruct from the data transmitted by the application.

I also have a few more Smart Config / CC3000 related posts:

http://depletionregion.blogspot.ch/search/label/CC3000

For some background information it can also be interesting to read through these threads on the TI forum relevant to the CC3000.

First one covering Smart Config itself:

http://e2e.ti.com/support/low_power_rf/f/851/t/253463.aspx

And one on mDNS, the mechanism by which a Smart Config application detects that a CC3000 enabled device has joined the network:

http://e2e.ti.com/support/low_power_rf/f/851/p/290584/1020839.aspx

In both threads some initial messages may not seem so relevant but there's some interesting information mixed in too. But there's also a lot of inaccurate information as well so don't assume all of it is correct, even information from TI employees or from me (I learned a lot eventually but started with some incorrect assumptions/beliefs).

Patents have been mentioned a few times, however I can't find any evidence that there are patents pending or granted on this technology.

Answer 2

NB As noted in the comments to this answer, and in the other answers, the answer below does not reflect the current procedure. Leaving this for the historical record.

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It seems like the CC3000 is actually listening (in "promiscuous mode") on all wifi channels for an AP probe request, the probed (and fake) AP's SSID containing the information that the CC3000 requires to configures itself to connect to the "true" AP through which it will connect to the Internet.

After searching a bit, I found this description of the device's first time configuration which should make it clear:

http://processors.wiki.ti.com/index.php/CC3000_First_Time_Configuration

Most interesting bit:

A device such as a mobile phone or tablet used for performing a first time Configuration needs to be configured to connect to an AP with a specially crafted SSID. This SSID includes the name of the SSID to which we want the CC3000 to connect, as well as information about security options such as security type and key.

Answer 3

Look at this page for information.

The AP isn't involved in this process. The CC3000 is listening to the UDP packets from the mobile phone or other device. This communication is encrypted with AES, both devices having it. The mobile phone sends information about the router WPA2 key in these packets. The CC3000 knows the AES key used by the mobile phone, decodes the data and connects to thr router.

Answer 4

@Greg Sadetsky's answer (describing "First Time Configuration") summarizes the basic process well. But it was revealed in the discussion on the TI forum that the CC3000 has changed the process by which this automatic configuration is performed. The new process is called "smartconfig" instead of First Time Configuration, and TI is apparently preparing a patent application for the technology. It seems to use a similar scheme where special Wi-Fi "probe" requests are sent, which cleverly encode the network credentials for the CC3000.

If you choose not to use an AES encryption key for the automatic configuration, the smartconfig algorithm uses an undocumented method to obfuscate the access point SSID and security key. This is not inherently secure since if anyone learns the obfuscation algorithm, through reverse engineering or other means, the wireless network security is jeopardized. Once the patent application is filed, it is public domain knowledge and you must use an AES encryption key with the CC3000 automatic configuration mode in order to be secure.

As of September 2013 the patent application has not been filed, based on review of 2012-2013 patent applications by Texas Instruments (Google Patent Search Link: Texas Instruments, sorted by most recent filing date).

TI has acknowledged the insecurity of the non-AES configuration mode and has said they will recommend using AES and make it the default in the future.