How to identify my Private Key type

The Private Key must be of type PKCS1 in PEM format.

The easiest way to determine what type you have is to look at the certificate headers.

-----BEGIN RSA PRIVATE KEY-----
<YOUR PRIVATE KEY CONTENT>
-----END RSA PRIVATE KEY-----

-----BEGIN PRIVATE KEY-----
<YOUR PRIVATE KEY CONTENT>
-----END PRIVATE KEY-----

-----BEGIN ENCRYPTED PRIVATE KEY-----
<YOUR PRIVATE KEY CONTENT>
-----END ENCRYPTED PRIVATE KEY-----

Encrypted private keys are not supported

To convert an unencrypted private key from PKCS8 to PKCS1 use the openssl command below:

openssl rsa -in xxxxx-private-no-rsa.pem.key -out xxxxx-private-converted.pem.key

OpenSSL 3+ does not support PKCS1 by default and you will need use -traditional on the openssl rsa command.

openssl rsa -in xxxxx-private-no-rsa.pem.key -traditional -out xxxxx-private-converted.pem.key