Is there some kind of IOTA C library just for signing transactions? The IOT device in question does not have Wifi and is too weak computationally to do POW.
I want the device itself sign the tx so that I can "prove" that the data in the transaction came from that specific device.
Yes, there is one: https://github.com/embedded-iota/iota-c-library You probably want to checkout the fork by francescolavra. He fixed a lot of issues and improved the library. If you want to use it within an RTOS, you might want to checkout the library implementation in RIOT.
