With the help of PuTTYgen tool, generate a public/private key pair as detailed in the link below :
Next, convert the private key(.ppk) to openSSH format supported by AtomSphere to configure the SFTP connector.
For 'Client SSH Key Path' under SSH options for the SFTP connection component, specify the path to the converted key.The path indicates the system path where the key is located on the server that the atom is running.
In short, All you need to do is to import the private key from the atom server and configure the path to the generated key in the SFTP connector.Please note that 'private key authentication' feature is not available on Dell Boomi Atom Cloud.
More details about the SSH authentication is available at the link below :