ucrypto.generate_rsa_signature() gives ValueError: Invalid Private Key, error code: -4480

[BetterAutomations]

Please include the following information when submitting a bug report:

• The Pycom board you are using: WiPy 2.0

• The firmware version you are using.

  (sysname='WiPy', nodename='WiPy', release='1.20.0.rc13', version='94bb382c9 on 2021-05-06', machine='WiPy with ESP32')

• Exact steps to cause this issue

  1. First I installed firmware 1.20.2.r4.
  2. Then, I used genkey.sh from the Pycom GoogleIOT library to generate a private key
  3. Then, I uploaded my private key to /flash/cert
  4. Then, I ran this code:

     pk = open('cert/WiPy2-pk8.key').read()
     import ucrypto
     ucrypto.generate_rsa_signature("Hello world", pk)

• What you expected I expected a signed string

• What happened instead Instead, I got the following:

  Traceback (most recent call last):
  (..)
  ValueError: Invalid Private Key, error code: -4480

I then did some testing on various firmware. The ucrypto.generate_rsa_signature() function is failing on firmware greater than 1.20.0.rc13.

When I tried on that firmware, I see the correct output:

>>> pk = open('cert/WiPy2-pk8.key').read()
>>> import ucrypto
>>> ucrypto.generate_rsa_signature("Hello world", pk)
b'\x04\xac\xa6\xedo\xca\xc6\x88\xc9\x14h\xbd}\x10\x8dD%\x96E\xf6A.Y> \xf3\x18\x83\x99\x1c\xa4(..)\x05\x80\x04\x04|'
>>>

I did a diff and found that esp32/mods/moducrypto.c had indeed been changed in newer versions, specifically having to do with mod_pycom_generate_rsa_signature. But I don't know enough C to tell you why what had changed is having this effect.

Here is some forum discussion I've had on it: https://forum.pycom.io/topic/7022/mqtt-with-ssl-gives-error-oserror-4480?_=1620323774849

Thank you!