Signing a pgp encrypted message in SAP PI

Hi Experts,

We have to PGP encrypt and sign the file and send it to 3rd party sftp server.

We are handling PGP encryption in S4 system and we are using 3rd party PGP public key.

They also expect want the sender file to be signed using our private key and algorithm to be used is SHA1, and for that I am using PGPEncryption module in PI and i am getting the below error.

Please check the PI module config for the same below -

I have tried placing the private key for signing as both .asc and .txt but none is working.

Can you please help me resolve this issue.

Regards,

Akash