I am little bit lost or confused. 

1. I have some secure server where inside `~/.ssh/authorized_keys` i have a key to remotely login those servers from my desktop (mac book )
2. Now that secure server need to SFTP/SCP to some third party servers

They provided me SSH ip, username, password, but i need to login with key. They asked me to share key.

Now confused which key i have to share to them? `id_rsa.pub` or the key from `~/.ssh/authorized_keys` 

NOTE: if i share my id\_rsa.pub key to third party can they use it to hack my secured servers in point 1?