ssh-add
carrega chaves privadas , e não chaves públicas . De man ssh-add
:
DESCRIPTION
ssh-add adds private key identities to the authentication agent, ssh-agent(1). When run without arguments, it adds
the files ~/.ssh/id_rsa, ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/identity. After loading a
private key, ssh-add will try to load corresponding certificate information from the filename obtained by appending
-cert.pub to the name of the private key file. Alternative file names can be given on the command line.
Tente executá-lo sem argumentos.