This is an implementation of RSA signing for MicroPython. It's writter in pure Python, and based on python-rsa version 4.0.
Originally, this port was supposed to be used for signing JWT claims on ESP8266. Since ESP8266 doesn't have too much memory, the original python-rsa library was truncated a lot. Nevertheless, it didn't work out. RSA signing worked very slow and threw exeptions due to low memory. In the end, the port successfully run only on ESP32.
PrivateKey class doesn't support loading keys in PKCS1 format (from PEM or DER files) because it would require porting pyasn1 library. It might be too much for a tiny ESP8266 board since it doesn't have too much memory. But maybe ESP32 boards can handle it.
Instead, PrivateKey class can load a private key from a JSON file which contains q, e, d, p and n:
{
"q": ... ,
"e": ... ,
"d": ... ,
"p": ... ,
"n": ...
}
Even though this library is based on a well-known python-rsa, there is no guarantee that the port has the same level of security as the original implementation. The library has been re-worked quite a lot. In particular, this port doesn't use blinding to preven side-channel attacks, and it uses a custom implementation of modular exponentiation since MicroPython doesn't support it (at least 1.10).
Additional security research is required to prove that this port doesn't contain vulnerabilities. Use with care.