NiFi ListSFTP connector cannot connect to sftp server - authentication

Question

I have problems getting ListSFTP processor to work.
First I have tested accessing the sftp server using the commandline on the NiFi server. This works but I have to provide the pass phrase of the private ssh key file.
Then I made sure that I configured the ListSFTP processor using the same settings as the sftp commandline:
Hostname: ip address of the server
Port: 22
Username: Username with access to the server and bound to the key
Private Key Path: set to the full path of the file containing
Private Key Phrase: password for the key file
Remote path: .
Strict Host Key Checking: false
Host Key File: File hat contains the output of ssh-keyscan for the
given server
With these settings I get an error in the logfile. Any idea why NiFi cannot access the key file and access the sftp server. Cheers
2020-03-19 15:43:19,736 ERROR [Timer-Driven Process Thread-2]
o.a.nifi.processors.standard.ListSFTP
ListSFTP[id=d343fa19-0170-1000-3352-999829a448cc] Failed to perform
listing on remote host due to java.io.IOException: Failed to obtain c
onnection to remote host due to com.jcraft.jsch.JSchException: invalid
privatekey: [B#6d9b662: {} java.io.IOException: Failed to obtain
connection to remote host due to com.jcraft.jsch.JSchException:
invalid privatekey: [B#6d9b662
at org.apache.nifi.processors.standard.util.SFTPTransfer.getChannel(SFTPTransfer.java:515)
at org.apache.nifi.processors.standard.util.SFTPTransfer.getListing(SFTPTransfer.java:212)
at org.apache.nifi.processors.standard.util.SFTPTransfer.getListing(SFTPTransfer.java:175)
at org.apache.nifi.processors.standard.ListFileTransfer.performListing(ListFileTransfer.java:106)
at org.apache.nifi.processors.standard.ListSFTP.performListing(ListSFTP.java:146)
at org.apache.nifi.processor.util.list.AbstractListProcessor.listByTrackingTimestamps(AbstractListProcessor.java:472)
at org.apache.nifi.processor.util.list.AbstractListProcessor.onTrigger(AbstractListProcessor.java:414)
at org.apache.nifi.processor.AbstractProcessor.onTrigger(AbstractProcessor.java:27)
at org.apache.nifi.controller.StandardProcessorNode.onTrigger(StandardProcessorNode.java:1162)
at org.apache.nifi.controller.tasks.ConnectableTask.invoke(ConnectableTask.java:209)
at org.apache.nifi.controller.scheduling.TimerDrivenSchedulingAgent$1.run(TimerDrivenSchedulingAgent.java:117)
at org.apache.nifi.engine.FlowEngine$2.run(FlowEngine.java:110)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748) Caused by: com.jcraft.jsch.JSchException: invalid privatekey: [B#6d9b662
at com.jcraft.jsch.KeyPair.load(KeyPair.java:664)
at com.jcraft.jsch.KeyPair.load(KeyPair.java:561)
at com.jcraft.jsch.IdentityFile.newInstance(IdentityFile.java:40)
at com.jcraft.jsch.JSch.addIdentity(JSch.java:407)
at com.jcraft.jsch.JSch.addIdentity(JSch.java:388)
at org.apache.nifi.processors.standard.util.SFTPTransfer.getChannel(SFTPTransfer.java:485)
... 18 common frames omitted