First I'd like to point out that "Decryptor" is an ill-chosen term: there's no encryption mechanism here, RDP is a software lock based on an internal flash state.
This dongle is very likely to be this original attack https://github.com/JohannesObermaier/f103-analysis/tree/mast... but now packaged. If you want to read more this repo has the best doc: https://github.com/CTXz/stm32f1-picopwner. It's a multi-step attack where a payload is executed from persisted SRAM (RDP1 means you can read/write to it) after a quick reset. The fact that they mention freezing the chip heavily weighs in that direction since it's needed for higher clock chips.
This dongle is very likely to be this original attack https://github.com/JohannesObermaier/f103-analysis/tree/mast... but now packaged. If you want to read more this repo has the best doc: https://github.com/CTXz/stm32f1-picopwner. It's a multi-step attack where a payload is executed from persisted SRAM (RDP1 means you can read/write to it) after a quick reset. The fact that they mention freezing the chip heavily weighs in that direction since it's needed for higher clock chips.