The contemporary smartphone is a marvel of sensors, radios, inputs, outputs, as well as processing power. In particular, a few of those radios, such as WiFi as well as cellular, have grown fiendishly complex over the years. even when that complexity is compressed down for the individual into the one-dimensional area of the signal stamina bars at the top of your phone. So when [David Burgess] was asked to look at some cellphone records of text messages as well as figure out where a few of the a lot more mysterious messages were coming from, it led him down a rabbit hole into the dark arts behind the radiant phone screen.

The number in concern was 1111340002, sent by a phone linked to AT&T at the time, as well as was vital for a legal situation around distracted driving. [David’s] tools in his investigation were YateBTS (a cellular network simulator), SimTrace2 (pictured above), as well as old trustworthy Wireshark. considering that the number isn’t a certain phone number as well as is not reachable from the public phone network, it need to be a special number inside AT&T processed by one specific AT&T SMSC (Short Message service center). The SMSC in concern is in Atlanta as well as isn’t a normal texting center, so it need to have some specific purpose. The message’s payload is raw binary rather than text, as well as [David] has done a quite great task of decoding the majority of the format.

The a lot of interesting revelation in this journey is that the phone (in the standard sense) does not send this message. The processor on the phone does not understand this message as well as executes no code to send it. Instead, the SIM card itself sends it. The SIM card is linked directly to the baseband processor on the phone, as well as the baseband polls the sim every so often, asking for any type of commands. one of those commands is an SMS (though lots of other commands have fretting consequences).

The SMS that [David] was chasing is triggered whenever a SIM detects a new IMEI, as well as the message lets the network understand what about the previous as well as present IMEI. However, in the situation of this message, it was unlikely that the SIM altered phones, so what happened? After some extra lab work as well as the deposition of an AT&T employee, [David] showed that a baseband firmware update would likewise activate this SMS.

It’s a interesting journey into the fragmented world of a smartphone’s minds as well as [David] does a amazing task on the writeup. If you’re thinking about sniffing wireless accessories, you will take pleasure in this soundbar’s wireless protocol laid bare.