Hacking the T-Mobile Sidekick, 20 Years Too Late

The T-Mobile Sidekick was an early cloud-dependent phone: its contacts, messages, photos, and settings lived on Danger’s servers, which shut down in 2011. To run original software on a Sidekick today, the author reverse-engineered Danger’s development tools and security system. Developer mode required a manufacturer-signed key tied to a phone’s IMEI, and no new keys had been available since Danger closed its developer program. Firmware images revealed that the operating system trusted a 512-bit RSA certificate for developers. By factoring its key across seven machines using 220 CPU cores, the author reconstructed Danger’s private signing key, verified it by reproducing an original developer key, and installed a new key on a Sidekick 3.

The unlocked phone ran a Java port of the visual novel Class of ’09, while a browser-based emulator now runs the original DangerOS using code from the archived SDK. The author is also rebuilding Danger’s backend as Re:Danger: so far it can set the phone’s clock, deliver messages through a Discord bridge, and serve simplified web pages. These services currently work only with the simulator; connecting real hardware remains the next challenge, potentially requiring a software-defined radio to create a private GSM network. Email, photo synchronization, revived AIM connections, and the download catalog are among the other planned features. The project shows how obsolete software and weak cryptography can be recovered to make a discontinued device useful again.