Sending an XML file to an FTP server using RSA key

Hello experts,

I need to send an XML file from SAP to an FTP server and i know how to do that using the server name or adress, the password (given as letters and numbers) and of course the username. The problem here is that the client gave me a RSA key instead of a password.

And i have no idea what it is or how does it work ? i tried to google it but it seems that i can't fully understand it, i read something about certificate..etc

PS : the way i generete and send the XML file is purely by using ABAP.

Any thoughts of how this works ?

Thanks in advance