Trying to understand the following Python code:
signature = signing_key.sign(payload.decode('utf-8').encode('utf-16-le'), PKCS1v15(), SHA1())

This results in a signature digest that is 128 bytes long. SHA1 ordinarily results in 20 bytes long, so I presume it's then calling a PKCS1 function to (securely) convert that 20 bytes to 128 bytes.
Is there a nice simple tool / application that can do this PKCS function - either encode or decode?