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Lecture: Apple's iPhone 15: Under the C

Hardware hacking tooling for the new iPhone generation

Hardware hacking tooling for the new iPhone generation

If you've followed the iPhone hacking scene you probably heard about cables such as the Kanzi Cable, Kong Cable, Bonobo Cable, and so on: Special cables that allow access to hardware debugging features on Lightning-based iPhones such as UART and JTAG. However with the iPhone 15, all of those tools became basically useless: USB-C is here, and with that we need new hardware and software tooling.

This talk gives you a brief history of iPhone hardware hacking through the Lightning port, and then looks at the new iPhone 15, and how - using vendor defined messages, modifying existing tooling like the Central Scrutinizer, and a bit of hardware hacking - we managed to get access to the (unfortunately locked on production devices) JTAG interface exposed on the USB-C port on the new iPhone 15.

And how you can do it using open-source tooling too.

The iPhone's Lightning connector was a proprietary beast with a lot of hidden features: By sending custom SDQ commands there, it was possible to get it to expose hardware debugging features such as JTAG and UART. For a long time, this was only easily possible using either gray and black-market cables such as the Kanzi-Cable, or proprietary tools such as the Bonobo Cable. Last year, we released an open-source tool to get access to the iPhone debugging features called the Tamarin Cable - finally allowing anyone to get JTAG and UART on the iPhone for just a couple of $ in parts.

But then the iPhone 15 came along, and with that USB-C: All previous hardware and software tooling basically became useless, but that did not stop us from trying: We knew from the Apple Silicon macs and the work of t8012-team and the AsahiLinux project that Apple uses USB-C's VDM feature - Vendor Defined Messages - to allow access to features such as the UART console, and so chances were high that we could use something similar to get access to the hardware debugging features on the iPhone 15.

So we pre-ordered the iPhone 15, a couple of PCBs, a case of Club Mate and got started: And less than 48 hours after the launch we got JTAG working on the iPhone 15.

In this talk we will start by looking at the history of iPhone and Lightning hardware hacking, and then look at how USB-C is used for debugging on Apple Silicon devices, and what we had to do to get JTAG on the iPhone 15.

We will also use this talk to release the new version of the open-source Tamarin Cable firmware: Tamarin-C. A fully integrated, open-source debugging probe for the iPhone 15 and other Apple Silicon devices. Tamarin-C is also able to give access to a DFU mode that you can't access without sending VDMs.

Note: This talk will not contain any 0days or previously unknown vulnerabilities. Production iPhones are locked, and so while we get access to some of the device's busses we can't for example access the CPU core.

This talk is about building tooling for future work.

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